Teleconference minutes, 18 December 1998 meeting
TELECONFERENCE - MINUTES, 18 DECEMBER 1998 MEETING
The following persons participated in the teleconference/meeting:
Mr Jeff Harris (convenor) - ISR
Dr Caroline Perkins - ISR
Mr Des Davy - MARTAC
Mr Bruce Church*
Mr John Morris - MARTAC
Dr Mike Costello - MARTAC
Dr Keith Lokan - MARTAC
Mr Terry Vaeth*
Mr Garth Chamberlain – GHD
Mr Tony Ryan – GHD
Mr Leo Thompson – Geosafe
Mr Jack McElroy*
Dr Pat Lowery*
Mr Craig Timmerman*
Mr Dale Timmons*
– consultant to Geosafe
Ms Sharon Burnell (minutes) - ISR
* - INDICATES PRESENT FOR TELECONFERENCE SEGMENT ONLY
Agenda item 1: Introductions
Mr Harris welcomed all participants to the meeting. Participants introduced
themselves and their respective roles in relation to the oversight, carrying out
or providing advice to the ISV process being carried out at Maralinga.
Agenda item 2: Purpose of the meeting
Mr Harris stated the purpose of the meeting as being to:
clarify areas of MARTAC concern with ISV to date;
identify issues in relation to the staging of the remaining inner pits so that
MARTAC’s concerns are addressed and operational limitations identified;
promote discussion on the specification of engineered pods.
At its MARTAC 13 meeting, MARTAC asked that MARTAC minutes be
annotated to include mention of the fact that the advice, explanations, and so
on, offered by Geosafe during the course of the meeting/teleconference reflect
Geosafe’s views and do not necessarily reflect those of MARTAC.
Agenda item 3: ISV to date
Dr Perkins asked the general question:
What does Geosafe believe it has achieved to date in its use of ISV in the inner
pits and in its ability to both learn from, and respond to, the difficulties
identified in earlier melts so as to improve the outcomes of the more recently
In response, Mr Thompson read Geosafe’s response from the paper included as
Attachment 1 (pages 1 to 4). In particular, Mr Thompson reiterated the point he
had made in his presentation to MARTAC on ISV at MARTAC 3, that the main
role of the vitrified mass was that of an intrusion barrier and suggested that:
in all of the pits treated date, the ISV process has resulted in converting
the friable mass of debris and soil into an intrusion resistant barrier which
has eliminated the potential for catastrophic subsidence and inadvertent
intrusion over the long term, with the overall result being that the process
has resulted in a substantial reduction, if not the virtual elimination, of the
long-term risks presented by the untreated pits;
experience with the operation of ISV in the pits has meant that Geosafe
has been able to make several improvements to the operations in the later
melts, with the result being that, for example, higher melt temperatures
have been achieved in the more recent melts;
Geosafe’s expectations for the melts were based on assumptions that were
found to be incorrect, with the resultant consequence that it had been
difficult assess the melts; and
in light of the problems in detecting previously anticipated indicators of
when a pit bottom was being reached, consideration should be given to
reviewing the pit probing records for the remaining inner pits.
Dr Lowery, Mr Timmerman, Mr Timmons and Mr McElroy voiced support for Mr
Thompson’s comments. Mr Timmons reinforced Mr Thompson’s statement that
the variability of the geology on site has meant that the subtle signs Geosafe
were originally expecting to see were missing.
Distance of refractory trenches from pit
In response to the question by Mr Davy as to why the refractory sand trenches
at the pits had been constructed 1m from the pit boundary compared to the
0.5m defined as the operational variable in the Geochemical Design Plan, Mr
agreed that the modelling which had been done for the melts had assumed
a distance of 0.5m; but
when the process had first been translated to site, it was considered that
the occupational health and safety risk of collapse of a 0.5m wide wall was
this, combined with Mr Thompson’s belief that he did not necessarily have
to melt steel, meant that Mr Thompson had made the decision to increase
the distance to 1m.
Mr Timmons advised that although he had designed the melts to minimise the
amount of calcium which goes into the melt, it was prudent for Geosafe to take
the safe course and move the trenches further out. The friable nature of the soil
is such that a real risk of collapsing walls exists and consequent worker risks.
Self-sweeping of contaminated material down by electrodes
In response to the question put by Mr Davy as to what thoughts Geosafe had to
deal with the apparent problem in the process of the downward, ‘self-sweeping’
of steel (in which the steel is, in effect, swept down past its true depth by the
advancing electrodes), Mr Thompson advised that he could possibly see such a
situation happening with respect to, for example, a bolt, but could not see bulk
waste or contaminated soil moving down. Mr Thompson advised that there is
not such sufficient strength in the system to push bulk waste down through the
10. Mr Timmerman stated that the ISV melt creates a sintered zone, or barrier or
skin to the melt in which the sand particles are transitioning from the soil into
the molten glass. Anything that is down below the melt, such as metal plate,
bolt etc would become incorporated into the sintered zone before it has even
had a chance to experience high enough temperatures to cause its deformation
or melting. Even if that occurred, it would be likely that the metals would be
within the sintered layer between the melt and electrode (and whatever other
penetrating device maybe forcing it downward), and it would simply ride on the
bottom due to gravity effects.
Movement and corrosion of electrodes
11. Mr Davy asked:
whether there is a better way of countering the ‘tooth effect’ (in which the
centre base of the melt is to a lesser depth than the depth of the melt at
the electrodes), than using the approach suggested by MARTAC of melting
down an extra 600mm and holding the electrodes steady for as long as
possible towards the end of a melt?; and
if collars have been used in the past to reduce corrosion of electrodes, why
are they not being used now?
12. Mr Thompson responded by saying in relation to the tooth effect at pit 3, that
was surprised at the bottom shape of the melt and that based on the
modelling results he had seen, he had not seen any heat distribution
pattern which would explain the significant arching at the 3.5m electrode
did not know the mechanism which caused the effect; and
could not say if the effect would be produced at the different melts in a
13. Mr Thompson suggested that:
MARTAC’s suggestion for melting an additional 600mm past the probed
base would seem appropriate; but
to address the problem of oxidation at the electrodes which would occur if
the electrodes were held stationary for a few days (as suggested by
MARTAC), Mr Thompson suggested a better approach was to move the
electrodes, inserting them a 100mm or so every shift after the base of the
pit had been reached.
14. Mr Thompson suggested that:
although melting an additional 600mm after the pit base does add calcium
(and possibly some silica to the melt), it was his impression that once you
have the melt to the bottom of the pit, if the temperatures were hot enough
at the pit base before the melt moved further down, then it is probably not
an issue if the melt temperature then begins to decline off when the
bedrock below the bottom of the pit begins to be processed; and
so long as temperatures of the order of 1600oC are wanted only up to the
point at which the base of the pit is starting to be incorporated into the
melt, such temperatures can be achieved. It is unrealistic however, to
expect to maintain melt temperatures of the order of 1600oC 600mm below
the base of the pit when large amounts of base bedrock have been
incorporated into it.
15. In relation to the use of collars, Mr Thompson advised that collars have never
been used in association with moving electrodes, only with static ones which
have the highest potential for failure. So long as electrodes can be continued to
be moved at some rate, Geosafe can minimise the potential for failures. Given
the fact that failure of electrodes does not affect the quality of the melts and the
collars have not been used before on moving electrodes, Mr Thompson
expressed the belief that it would not be cost effective to try and design for the
use of collars on moving electrodes.
16. Mr Thompson suggested that a simpler idea, if electrodes were to be held
stationary, would be to open up the hood and use the telescoping bucket to put
some soil around the electrodes (this would only be contemplated, however,
when the bottom of the pit is reached and dip sampling and temperature
measurements were completed).
17. Mr Timmerman advised that his only experience with non-movable electrodes
was back in the 1980s.
18. Mr Timmerman advised that the only times Geosafe had seen the tooth effect
was in the 1980s when stationary electrodes had been in use. In such
situations, he stated there was an opportunity with heat transfer of the
electrodes below the melt, to melt downwards around the electrodes and not
centrally. In the 50 plus melts Geosafe had since completed in the US, mostly
flat bases resulted with possibly only a ‘dimple’ of at most 15cm below the
bottom of the melt showing. Mr Timmerman expressed surprise at the bottom
formation at pit 3 and that given the lack of data available, he was not sure if it
was something particular to pit 3 or something potentially more widespread.
19. Mr Timmerman hypothesised that the possibly high metal content at pit 3 could
have be limiting the heat transfer if the metals had been piling up in the centre
of the melt and thus creating more melting around the hotter portion of the
melt near the electrodes.
20. Mr Timmerman stated that melting to the additional depth is one of the easiest
ways of achieving melting to the centre base of the pits and stated that one can
eliminate the problems associated with having additional calcium that would be
incorporated into the pits by going the extra depth.
21. Mr Timmerman advised that move to the use of engineered pods could
eliminate the incorporation of additional calcium by designing the pit chemistry
22. In relation to the collar issue, both Mr Timmons and Mr Timmerman suggested
that the alumima sleeves form a wetted surface with silicate melts and will
weld themselves to a cold cap that will also increase the chance of breaking
electrodes. With anything other than the graphite electrodes, any metal sleeve
will make an adherence with the glass and this will cause some sticking of the
electrodes and may cause other failure mechanisms.
23. In relation to the use of moving electrodes, Mr Timmerman advised that the
dynamic, downwards movement of the corrosion based area from primarily the
surface of the melt will minimise any oxidation problems. Typically, one only
might have a problem towards the end of the melt where the depth rate of
movement slightly slows down due to the fact that much of the mass growth is
in the lateral direction. Since the oxidation concern occurs only from about the
5m plus depth, this should not be a problem with the Maralinga pit melts.
24. Dr Lowery suggested that the high metal content in the centre of the melts
might be a contributing factor to the tooth effect and that by holding the
electrodes off the bottom of the pit towards the end of the melts and feeding
them down slowly, the tooth effect might be countered.
25. Dr Lowery advised that he had not seen such significant tooth effects elsewhere
in the Geosafe Corporation melts.
26. Mr Davy asked if Geosafe could quantify what it meant by ‘high metal content’
and what this meant for the setting of an objective for the concentration of
metal to be placed in an engineered pod?
27. Mr Timmerman stated that although important, it is not so much the overall
loading of metal that is at issue, but rather the concentration of metal in the
centre between the electrodes.
Engineered pod situation
28. Mr Thompson suggested that:
in an engineered pod, if one wanted to measure the contour at the base of
the melt, one could map it out using a range of type ‘C’ thermocouples a
couple of feet above and at the base of the melt (if one had a flat bottom to
the melt, then all the thermocouples would burn out at the same time. If,
however, a group of thermocouples in the centre region burnt out only after
the outer ones, then that would indicate there was type of ‘hump’ in the
if a layer of refractory sand is used at the bottom of the pit, this would
retard progress lower than the base at the electrodes and give the middle a
chance to catch up.
29. Mr Timmerman advised that what is being done now with respect to going the
additional 600mm below the probed depth is probably a reasonable approach
with respect to ensuring the entire pit contents are incorporated into the melt,
but it has a negative side in that it adds additional unwanted calcium to the
melt. Mr Timmerman was not able, however, to offer a better, easier to
30. Mr McElroy suggested, however, that the fact of going an additional 600mm
down means that melting of the high refractory sand at the side acts as a
counter by increasing the temperature.
31. Mr Timmons suggested that, assuming the target goals are known, it will be
relatively easy to design and stage a melt in an engineered pod.
32. Mr Harris asked Mr Timmons if Geosafe would be able to reach temperatures at
the base of the engineered pods that will melt steel. Mr Timmons, Timmerman,
McElroy answered yes, but reiterated that the expected outcomes of the
engineered melt must be defined first and the materials to be put into the pods
would need to be readily available at site (which it is expected to be the case).
33. Mr Thompson made the point that what is meant by the term ‘bottom of the pit’
must be defined and agreed to. Temperatures of the order of 1600oC could
readily be achieved within a few inches in the melt, up from the bottom of the
melt. However, in areas at, and just inside the fusion zone, where melting is
just starting to take place and soil is fusing, such high temperatures cannot be
34. Mr Thompson advised that achieving the desired temperature within the melt
primarily a matter of composition; and
the elimination of, as much as possible, such materials as limestone; and
getting high silica content in the melt.
35. Mr Thompson suggested that it might be useful for the last 300mm of an
engineered pod where one wants to melt down through, to be filled with clean,
minimal fluxed sand that will give clear indication to operators that the last of
the debris is being incorporated into the melt.
Reactive nature of Geosafe
36. Geosafe did not respond to the question put by Mr Davy as to why Geosafe has
not been seen to be the party to proactively offer solutions to problems and that
such a role has been left to MARTAC?
37. Mr Morris commented that both the initial Geochemical Design Analysis and
other Geosafe documents provided prior to work commencing in phase 4 were
pretty good and that MARTAC had expectations that have since appeared not to
have been met. This has led to a belief amongst some MARTAC members that
Geosafe has been slow to react to the problems and difficulties that have
developed during the melts, such as problems in ensuring the temperatures
achieved in the melts, the assessment of when to terminate a melt and
38. Mr Morris made the point that even though Mr Thompson believes the melts
are now progressing in a more conservative manner, the melt at pit 19a and
others since then, have been no less conservative than some of those of more
recent melts. The concern is that pit 19a does not now appear to have been as
conservative as it should have been, and that it was originally thought to have
been terminated in a very conservative manner..
Comparability of earlier and later melts and electrode penetration rate
39. Mr Morris expressed concern that:
one of the operational parameters has been changed, namely, electrodes
are now being held in suspension rather than being allowed to sit on the
because of electrode oxidation and breakage, we are currently not getting
probed depths at the base of each of the pits.
40. Mr Morris stated that, as a result, it will be difficult to compare the earlier with
the later melts. He further stated the belief that the electrode penetration rate
is likely to be an important factor in deciding whether or not there is significant
possibility and probability that the whole of pit contents have been inducted.
41. Mr Morris expressed caution in the use of pit probing information carried out by
Geosafe to both accurately define the pit base and in relation to decisions as to
when to terminate melts. The pit probing data should be seen as a valuable
indicator but should not be considered as absolute.
Ca/Si ratio – heat balance and temperature
42. Mr Morris questioned the use of the Ca and Si ratio as a guide to the melt
temperature that can be achieved. Mr Morris pointed out that Mr Timmons had
based his work on temperatures at100 poise, but excavation to date now
suggests that 100 poise was not being achieved and that temperatures were
neither high enough, nor sustained long enough, to melt steel.
43. Mr Morris asked what, quantitatively, will adding extra silica to the melt and/or
reducing the calcium in the melt do for the melt temperature, and why?
44. Dr Lowery pointed out that when you put power into a melt, energy is either
lost out through the top (if there is no overburden), or it results in an increase
melt rate out the side, or in an increase in melt temperature. Dr Lowery
for a given soil, the preference seems to be for an increase melt rate rather
than an increase in melt temperature; but
if the chemistry of the soil is adjusted so that the soil has a higher melting
point, then one effectively increases the viscosity so that at a given
temperature, a melt that has a more refractory composition:
will be more viscous (and, therefore, convective effects will be less
the melt temperature can be raised more efficiently; and
(iii) the melt rate is not raised as rapidly.
if the melt is high in calcium, increasing the power would cause flow
patterns in the melt to become more vigorous and increase the melt rate in
preference to just increasing the melt temperature; and
flow patterns set up in the melt are the dominant mechanism of energy
45. Mr Timmerman supported Dr Lowery’s comments and stated that the
composition of the melt is the primary driver in determining melt temperature.
The power input density into the melt is chosen so as to establish an effective
melt rate of the order of 1 – 3cm/hr and this is done by looking at the heat
transfer and heat flux parameters of the melt. Heat transfer and heat flux can
be varied by adjusting the composition, such as by adding Si.
46. Mr Timmons suggested that calcium in melts tends to promote crystallisation,
and that the calcium levels in the melts at Maralinga might be why
crystallisation is being seen in the Maralinga. Small bivalent cations (Mg, Ba,
Pb etc) in the melt are responsible for decreasing viscosity in silicate melts. If
you reduce these bivalent cations and increase the melt in Si, Al ions, then one
can get dramatic increases in viscosity.
47. Mr Timmons added that increasing the viscosity of a melt also increases its
resistivity, thereby increasing the ability, in some cases, to get higher power
factors and higher temperatures in a melt.
48. Mr Thompson advised that heat balance requires dealing with a delicate
balance of a lot of melt parameters, including:
thermal conductivity; and
density, and so on.
49. Mr Thompson advised that if more power is put into a melt, one effects certain
properties, which in turn, because of their interdependencies, affect other
properties. Ultimately, what is being looked at is a heat balance so that if more
power is put in to the melt, the melt moves faster, more heat is convected to the
sides, with the result being that the heat flux there is greater at the boundaries
and a possible increase in the melt rate.
50. Mr Thompson stated that in addition, heat losses through the top of a melt can
be significant. For example, heat losses out the top of a 4MW melt could be of
the order of 2MW at Maralinga. Operations, therefore, are aimed at putting the
highest amount of useable energy into the melt without wasting it.
51. Dr Lowery pointed out that the TEMPEST model they use addresses the
interdependency of the various factors and models all the phenomena
concurrently. If power input is increased, the increase in the rate of melt is
much more than the increase in temperature.
52. In response to a query from Dr Costello as to where a temperature of 2000oC
had been measured in a melt Dr Lowery had referred to, Dr Lowery responded
that such a temperature had been measured in an engineering scale melt that
Geosafe had done in the US. The temperature had been measured using a type
‘C’ thermocouple located beneath the melt and was inserted in the body of the
melt at the core between the electrodes. Dr Lowery advised that although he
was not advocating aiming for melts at Maralinga of the order of 2000oC, such
high temperatures can be reached using the ISV system if you have soils that
‘want to’ operate at such temperatures (namely, in high Si/Al, very viscous,
very high resistive melts).
53. Mr Thompson advised that during the phase 2 trials, temperatures of 1850 –
1900oC were often measured in the initial melts of the sandy cover soil and
suggested that one can expect to achieve such temperatures (at relatively low
power levels) in the first metre or so of soil at Maralinga.
54. Dr Costello commented that the temperatures in the middle or the top of the
melt were not as important as that at the bottom. To achieve at least
encasement or encapsulation of any unmelted steel, the melt temperature at the
bottom of the melt had to be high.
55. Mr Morris and Mr Thompson disagreed as to whether or not the temperatures
reported at MARTAC 12 for temperatures in the relatively high sodium content
fluxed sand, indicated high temperatures (of the order of even 1800oC) were
being reached there.
56. Mr Morris pointed out that the geology at Maralinga is variable and that at the
base of the pits calcium levels may actually be low and silica levels high.
Remaining inner pits
57. Dr Costello asked in relation to the four remaining melts in the inner pits, ‘how
confident is Geosafe that at encapsulation of the material at least will be
58. Mr Thompson stated that encapsulation is not so much a function of melt
temperature but of ensuring that the melt grows from a lateral perspective and
is deep enough. Mr Thompson advised that:
from a lateral perspective, Geosafe is highly confident that melting is done
far enough outwards; but that
from a depth perspective, pit depth and its probing are issues and, as a
result, Geosafe cannot be fully confident as to how much over melting is
needed to give a high level of confidence.
59. Dr Costello pointed out that at pit 3, investigation shows a couple of steel
plates at the edge of the melt that shows that the melt had not gone far enough
60. Dr Costello paraphrased MARTAC’s expectations that:
all the plutonium would be washed into the melt; and
any plutonium that had not been washed into the melt, namely that which
might be left on any unmelted steel, was at least encased or encapsulated
within the melt.
61. In response, Mr Thompson said he was not aware that there were any plates at
the lateral boundary of pit 3 but rather, that the metal being referred to had
been contained within the inner core which had only been exposed when the
edges of the vitrified block had been broken away. Mr Thompson then asked
from an encasement perspective “how good is good enough with respect to
encasement?” Does that mean the plate has to be, for example, 300mm from
the edge, or should it be at least 500mm?
62. Dr Costello volunteered a definition of ‘encasement’ as being that area in the
geology surrounding the steel, which fused and then crystallised again. Mr
Morris suggested that further investigation at pit 3 was warranted to determine
if encasement was or was not achieved on the unmelted steel.
63. Mr Thompson suggested that it should makes a difference whether the steel/
soil was un-encased at the sides or at the bottom of the melt. Taking a
pragmatic slant, Mr Thompson suggested that if unmelted and UN-encased
material is on the bottom, then MARTAC should go back to the fact that it
would be improbable to get to with respect to inadvertent intrusion, and with
respect to purposeful intrusion, it has been largely eliminated.
64. Mr Timmons stated although he could not visualise the piece of steel of concern
at pit 3, it was conceivable that a piece of metal could follow a melt down as a
melt progresses and be close to the edge of the melt yet still be encapsulated.
65. Mr McElroy stated he had seen pictures of the pit 3 and 19a reports done by Mr
Morris and pointed out that in melt 3 there is metal at the bottom of the melt.
66. Mr Timmerman offered the comment that metals become entrapped within the
sintered area and typically ride down as a molten slag. Mr Timmerman
suggested that because at Maralinga there are such large mass quantities, the
heat transfer mechanisms may not deform or totally melt the metals. He
ventured to say, however, that the metal would certainly be encased in the melt
and suggested that all the metal from the plates in the pit were contained in the
67. Mr Morris identified that he had been using the term ‘sintered’ differently to
that of Geosafe, and had in fact been referring to the ‘calcined’ layer (ie. to the
layer which has lost CO2) rather than the area of partially fused material which
Geosafe refers to as ‘sintered’.
Uniformity of mixing and melt sampling
68. Dr Lokan questioned the uniformity of mixing in the melts and asked if it was
possible to get a realistic estimate of plutonium content from almost any
sample of the ISV product.
69. In relation to the issue of uniformity of mixing, Mr Thompson responded by
expressing the views that:
apart from at the boundary edge of the melt, the melt, in particular, the
core, is very well mixed;
therefore, to ensure representative samples are taken, samples need to be
taken at an appropriate depth to avoid boundary effects; and
liquid dip samples should provide representative samples.
70. In relation to the issue of ability to determine Pu content of a pit from the
samples taken, Mr Thompson responded by saying that:
there is a greater chance that all the plutonium is transferred from the
steel into the melt if the steel has melted (and this is a function of
with appropriate residence time in the melt, temperatures in the melt can
be lower and still have the plutonium transferred into the melts. If there is
adequate residence time, the plutonium should be transferred into the melt
at temperatures of only 1400oC; and
if, however, the plutonium is embedded deep in cracks or on plates
sandwiched in layers in the melts, and so on, the plutonium won’t come off
into the melt from the inner layers.
71. Mr Timmons pointed out that one tends to have higher viscosities at the edge of
the melt, and that there is limited mixing within the first few centimetres of the
melt edge. Mr Timmons suggested that this is of real benefit when you look at
such things as the leach properties of the monolith because the monolith as
very low or no contamination at the edge, but rather, all the contamination is
thoroughly encased within the vitrified monolith.
72. Dr Lowery added that the ability of material which has been processed to come
out of the melt is hindered by:
the fluid mechanical properties of the glass itself; and
once the material has been melted, Geosafe have studies to show that the
partition co-efficient for the plutonium that gets out of the steel is of the
order of 10-7 of the plutonium which was there initially.
73. In response to Mr Church’s comment that Geosafe has yet to validate what was
said about the partition coefficient under the Maralinga conditions, Dr Lowery
advised that he has reports on samples which show very good mixing and which
supports Mr Thompson’s assertion that, assuming a fairly fluid melt, if the
plutonium is in the glass, it will be well dispersed throughout the glass.
74. Mr Timmerman said that excellent mixing is expected and Geosafe’s database
on prior melts shows that once plutonium is in the main melt body, it is well
Remodelling and validation
75. Mr Thompson further advised that, so as to maximise the likelihood that
Geosafe will be able to ensure achievement of a target temperature of 1600oC:
Mr Timmons will shortly:
remodel the remaining outer pits with respect to what is known about
the pits using the additional information now in on, for example,
geochemistry, pit size etc, model it; and
model some of the pit melts already done so as to try and validate his
Geosafe will look to moving the refractory trenches closer to the pit; and
Geosafe will remove the layer or “green” carbonate sand from the top of
76. Dr Lokan suggested that although it would be useful to carry out the
remodelling suggested that in the remodelling of some of the past pit melts and
model upcoming ones, he wondered ‘how useful it is given the continuing great
uncertainty in the pit contents?’ and ‘how vulnerable the gulf of that
remodelling is, particularly with respect to temperature, to uncertainties in the
77. Mr Thompson responded by saying they would look at a range of possible
compositions in the pits and try and identify a credible, worst case situation and
model on that basis.
78. Mr Timmons added that:
as far as he could recall, an assumption contained in his earlier report was
that the soil used to backfill the pits was the high silica sand that is
prevalent at site.
whether this assumption, and other assumptions, such as those of void
space, and the presence of barytes and lead bricks, are true, are still not
the surrounding pit soil is of primary importance as they make up the
dominant mass or volume incorporated into the melt.
79. Mr Timmons advised that to improve the predictability of what will be achieved
in the melts, a conservative approach can be taken in the remodelling and, for
assume the pits were actually backfilled with limestone rather than high
silica sand; and
where available, use surrounding soil geochemical data.
80. Mr Church said a critical concern of his rests in Geosafe’s ability to tie current
to past work so that MARTAC can feel confident that it can rely on the results
from the hundreds of Geosafe melts already carried out. Further, since the tooth
effect has been found to exist, with unencapsulated metal in evidence,
clarifying the link with past validation is important.
81. Mr Thompson suggested that, in relation to the inner pits being melted in-situ,
the excavation and breaking open of the vitrified product is a good means of
validating a number of MARTAC’s concerns, for example, in relation to the
presence or absence of the tooth effect. However, in terms of validating whether
all the Pu has been transferred into the melt, it is hard to do in a full scale melt
even if the product is excavated since one does not know the starting inventory.
82. Mr Timmerman suggested that core drilling, as opposed to excavation, if
feasible, would allow more absolute sampling that could address the question of
plutonium distribution in the glass.
83. Dr Lokan responded by saying that he had always thought core drilling was to
be carried out as part of the assessment of the total plutonium inventory.
84. Mr Davy added that what had been intended was that early sampling results
were intended to guide the amount of drilling that was to be required. Mr Davy
commented that we are at melt 11 before we are starting to get representative
samples being taken.
85. In response to Mr Vaeth’s query concerning intrusion resistance of the product,
long term stewardship and validation, Mr Thompson stated that:
he firmly believes that if there is contaminated soil or steel at the bottom
of the melt product, associated relative risks are not inconsistent with the
stewardship issue for any other parts of the site;
to validation, Geosafe is continually improving its actions and the
extent of lateral melting is okay;
to ‘deep enough’, Geosafe has limited ability to make that assessment
and the pit probing records need to be reviewed and their validity
considered more fully; and
(iii) Pu in steel, based on Mr Thompson’s experiences in phase 1 and 2 of
the Project, it is Geosafe’s belief that the vast majority of Pu on the
steel will have been transferred to the vitreous phase;
remodelling and improving pit chemistry should improve the melt
if MARTAC can accept relative risk at the melts in as pragmatic a way as it
took in, for example, defining soil removal boundaries, then some
uncertainty can be accepted. Nevertheless, what the level of uncertainty
that is acceptable is something for MARTAC to decide.
86. Dr Lokan asked for an explanation of a suggestion made to try to get a core
melt temperature profile using a sheathed tube.
87. Mr Thompson said he envisaged improvements could be made to the
thermocouple arrangements in relation to the yet to be staged pits and hybrid
pods. In relation to the in-situ pits, Mr Thompson suggested that probably the
best that could be done is to use a long probe and insert it to measure
temperature at various intervals (such as 300mm, 600mm and 900mm, and so
on intervals). The technique was used on the most recent melt with some
success until the thermocouple failed at the 900mm interval.
88. Mr Thompson advised that Mr Ombrellaro was meeting with the manufacturer
in Seattle so as to find out if the thermocouple life could be improved.
Treatment of remaining inner pits
89. Mr Church stated that:
because of the lack of characterisation of the pits prior to the melting made
every pit an experiment – assumptions not being met in relation to the
%steel, %silica, % limestone, and so on;
in-situ is a blind approach to making a good melt; and
confidence that steel is melted or encased is begging; then
one should not proceed with any more in-situ melts but go straight into
using the engineered pods.
90. Mr Thompson again questioned what level of confidence does MARTAC have
and thinks it needs with the process, and reiterated that, in relation to the
remaining inner pit melts:
with respect to the lateral melt, Mr Thompson is confident of
encompassing or encasing the steel;
with respect to the vertical melt depth, there is less certainty that there
won’t be any steel left on the bottom towards the lateral centre of the melt;
if a very high level of confidence is wanted in relation to the MARTAC
parameters, then exhumation and staging in engineered pods is warranted.
Characterisation of pits
91. Mr Chamberlain made the points that:
he was surprised that the lack of characterisation of the pits had not been
identified earlier on in the melts by Geosafe as a cause of significant
problem in the melts;
with respect to encapsulation and pit 3, the steel is not encapsulated and
therefore did not meet the MARTAC criteria;
the question has to be asked whether or not MARTAC accepts that the
criteria melt/encapsulation criteria does not have to be enforced; and
in order to really have 100% confidence then the only option is physical
92. In response, Mr Thompson stated that:
the actual size of the pits has been found to be an issue;
the ISV process can deal with a wide range of variation (as shown in many
other places) if a specific temperature at the base of the pit is not required;
if a minimum temperature is specified at the bottom of the pits is needed,
then characterisation data on the pits is essential.
93. Mr Thompson asked what MARTAC defines as ‘adequate’ in relation to
encapsulation of steel and melt depth and suggested that in relation to the
belief that the melt at pit 3 did not meet the MARTAC criteria for melting or
encapsulation, then if a pragmatic approach is not acceptable, then the melting
of the remaining inner pits in-situ should be stopped.
94. Dr Lokan pointed out that ARL will not countenance the digging up of all the
95. Mr Ryan made the points that:
in relation to the appraisal of progress to date, Mr Thompson had made no
mention of the MARTAC criteria and that since achievement of the
MARTAC criteria was what Geosafe had been contracted to meet, Mr
Thompson should make some comment on the matter; and
in relation to Mr Thompson’s view that the melting of steel did not have to
be achieved, file correspondence and reports put out prior to the phase 4
commencing, the ISV process seems to be predicated on having the steel
melted and asked when the view of not having to melt steel came about.
96. Mr Thompson stated in relation to the MARTAC criteria that they have been a
difficult subject, and that as late as 4 December, they were still being
‘tweaked’. In particular,:
Geosafe has always had the intention of melting steel, but not to 100%
level. The process does not melt steel for the sake of melting but rather so
as not impede electrode movement. From a lateral perspective, Geosafe
has virtually 100% confidence that the pit contents are treated and the
steel and other debris is melted. Questions remains though as to whether
or not there is vertical encapsulation;
everyone has struggled to determine if there is a minimum temperature
and what it should be? - 1600oC or as high above the melting point of steel
Geosafe is highly confident that most (90% or so) of the plutonium is in the
glass phase. This is a difficult thing to verify.
97. Mr Timmons stated that in his modelling report, the intention was stated as to
melt the steel for the purposes of preventing short circuits.
98. Mr Timmons defined ‘melting’ to include ‘truly melting ‘ the steel or softening
it enough so that it drops to the bottom so that it is removed from the vicinity of
Agenda item 4: ISV of remaining inner pits
99. Dr Perkins asked the general question:
How are Geosafe proposing to respond to the information and experience gained
in the existing melts for the staging, carrying out and analysing the remaining
100. In response, Mr Thompson read Geosafe’s response from the paper included as
Attachment 1 (pages 4 and 5). Mr Thompson highlighted, for example, the
recent action to minimise the amount of carbonates incorporated into the
melts (such as movement of refractory trench closer to the pit and removal
of the “green” carbonate sand from the top of the pits;
changes to the improve the geochemical and melt product sampling carried
out at the pits;
changes to improve the placement and reliability of thermocouples
measurements at the pits;
changes to the design of the cover soil and sand trenches to maximise the
likelihood of achieving melt temperatures of 1600oC; and
changes to electrode spacing and power inputs to ensure complete melting
or encasement of the steel.
101. Mr Thompson confirmed his intention to run a model for each of the remaining
inner pits before they are done.
102. In response to Mr Thompson’s comments, Mr Davy stated the view that:
for MARTAC to have reasonable confidence that steel is being melted at
various depths in the melt, then Geosafe must determine in at least one of
the pits, the temperature gradient in the melt; and
if MARTAC is to place any credibility on the figures for the amount of
plutonium determined to be in a melt, MARTAC needs certainty in at least
one pit that all plutonium has been transferred into the melt to start with
and this needs to be solved before the remaining inner pits are treated. Mr
Davy asked Mr Thompson to be prepared to discuss the matter further at
103. Mr Thompson responded to Mr Davy’s comments by stating that:
a temperature gradient can be determined in a future melt through the use
of a more elaborate array thermocouples than previously used (but that
MARTAC would first have to determine whether or not the gradient should
be measured when the melt first reaches the bottom of the pit or later on
when it is at the end of the melt); and
if MARTAC would nominate a pit that is characteristic of the others and
which might have steel at or near its bottom with the potential to have
plutonium on it, then Geosafe could investigate the melt with the intent of
trying to verify, as far as practicable, all the plutonium has been
transferred into the melt. Mr Thompson suggested using the most recent
melt at which there is the highest and best temperature for. No agreement
was reached at the teleconference as to which pit to use and how to
approach the task and whether or not ARL would accept/want an
additional inner pit being broken up.
104. In relation to the question about transients involving the drums in a melt, Mr
Thompson advised that it was a heat transfer problem and that the issue had
been addressed in detail in the written answers provided to MARTAC members
prior to the meeting.
105. In relation to Mr Thompson request for advice as to the best or preferred way to
approach the collection of temperature data, Mr Timmons commented that the
task is not easy and the melts appear to be very corrosive, complicating
Geosafe’s ability to get the measurements.
106. Dr Lowery stated in relation to the thermocouples that corrosivity and thermal
shock going through the cold cap makes it difficult to take temperature
measurements with thermocouples going in from the surface.
107. Mr Timmerman suggested that a possibility is to place type ‘C’ thermocouples
as done in the past in the lower portion of the excavated trenches and to come
in from the side of the melt.
108. Mr Morris echoed Mr Davy’s earlier statement by stating that MARTAC needed
to have a high level of confidence that the melt result is satisfactory and
suggested a need for improvements to the geochemical sampling program. Mr
Morris advised the meeting that although the samples he had received from
Geosafe for pits 19a and onwards provided useful background for MARTAC, the
samples were too small and too selective to be considered representative, and
hence would be of limited use in the geochemical modeling about to be done by
109. Mr Morris commented that assumptions in Dale Timmons’ report as to the pit
content and the nature of the soils in the pits had never been validated, and
that one way to do it would be to take a look at a melt block, surrounding
geochemistry, fluxed soil, and so on, but there is little information about the
melt chemistry back yet.
110. In response to Mr Morris’ comment that power input to the melts often ran at
quite high MW values compared to the average MW figure, the average power
input had fallen below the peak, Mr Thompson:
pointed out that earlier figures for average power which is reported
includes the first 24 hours period in which a melt is powering up, but that
reports now being developed will report the average power figure for the
last 5 or so days of a melt; and
agreed that increasing the on-line efficiency was a good idea.
111. Dr Costello asked Mr Thompson how he could say that a 40kW trial was
representative of a multi MW situation.
112. Mr Thompson referred to a graph included as Attachment 2 which shows heat
loss versus power input and highlighted the balance point on the graph where
the melt cannot deal with the extra amount of power in and the cold cap starts
to melt and the heat losses start to increase dramatically with little additional
power. In the region, just before the heat losses start to take off and go
exponential, is probably the ideal operating range for a melt. Mr Thompson
stated his belief that Geosafe have not been operating far from that ideal range.
113. Dumping say 10MW into the melt at that point will not yield more than
probably 2MW of useful power.
114. Dr Lowery stated that as one starts increasing the power into a melt, the
increase in power is first realised near the electrodes where the power density
is greatest and if the power is increased too dramatically, one might get
operational problems, such as making the melt too vigorous at the electrodes
when one is trying to increase the whole of the melt temperature.
115. Mr Timmerman reiterated the comments made earlier in the meeting that the
greatest effects of power input will be to the heat losses and to the heat rate.
He also stated that operational trade-offs have to be are applied to ensure, for
an adequate melt rate without transients; and the
maintenance of the cold cap (to minimise heat flux losses from the top)
whilst at the same time maintaining an adequate energy input to give an
approximate 2cm/hr melt rate.
116. Mr Morris commented that in terms of the melt volume calculations and energy
input, Mr Morris urged the validation of the assumption of the 0.7- 0.8 kWhr/kg
of pit content being melted and suggested an opportunity might exist for pit
117. Mr Thompson advised that Geosafe was currently working on validating the
energy-mass ratio kWhr/kg, and that based on existing samples (and with
deletion of those samples which Mr Thompson believed to not be
representative), values between 0.62 to about 0.9 had been determined for the
118. Mr Thompson and Mr Timmerman both described the energy-mass ratio number
as just one of the tools used to help validate mass which correspond with a
dimension and cautioned that it should be interpreted in that context.
119. Mr Timmons stated he was now in the process of planning for the modelling
which largely agreed with Mr Morris’ comments in relation to the geochemistry,
and so on.
120. Dr Costello stated that:
a lot of emphasis had been placed on the energy-mass ratio by Geosafe and
MARTAC members in the past;
that he had little confidence in the kWhr/kg as it is a differential
measurement (for example, how confident can one be that one is
measuring heat losses?; and
that it is not a realistic parameter on which to make judgements as to the
degree of pit contents melted.
121. Mr Thompson stated that although the kWhr/kg number has proven value as a
rule of thumb, it is not an exacting tool and that it can change depending upon
a number of factors (size of melt, heat loss factors etc).
122. For melts of a general size, Geosafe has found 0.7 – 0.8 to be a reasonable
123. Mr Timmerman commented that ISV was never designed to be steady state but
rather, is designed to melt the mass as quickly and safely as possible and move
onto the next melt.
124. In relation to electrode depth probing, Mr Thompson advised that:
although periodically probing the bottom is a good thing to do, when the
operators move the electrodes down at regular intervals, if they start to
see evidence of shorting before shorting occurs, they stop; and
insertion rates provide an indirect indication of where the bottom and
where the steel is.
125. In response to Mr Davy’s suggestion that a neutron detector/probe might prove
a useful tool in defining the bottom of a pit during pit staging, thereby providing
verification that probing is finding the true pit depth, Mr Thompson said he
would investigate the matter further.
126. Dr Costello asked that intrusion should be qualified as inadvertent intrusion,
and that a person with a backhoe would be attempting to deliberately intrude.
No-one should be expected to provide a guarantee against deliberate intrusion.
127. Dr Costello further stated that inadvertent intrusion cannot be considered a
possibility for plutonium under a block 200-300 tonnes in mass.
128. Dr Lokan asked if it was realistic to contemplate placing type ‘C’
thermocouples into the lateral central of the pit either at or below the level of
the bottom of the pit/probed depth.
129. Mr Thompson advised that
long type ‘C’ thermocouples were available;
a drill is available; and
providing there is no metal in the way to prevent the thermocouple from
reaching the centre, a means for taking a temperature data point at the
one elevation in the melt might be developed.
130. Mr Thompson pointed out that Geosafe could place thermocouples at 600mm
below the probed depth of the pits if requested to do so [thermocouples are now
being positioned at the probed depth of the pits].
131. Mr Timmerman pointed out, however, that there were practical difficulties in
getting useful temperature measurements at the centre base of the remaining
inner pits because of the potential tooth effect. In particular, when a
thermocouple is coming in laterally, the tip may not be the first part of the
thermocouple to come into contact with the melt. As a result, the thermocouple
might erode or melt off half-way between the tip of the electrode and the
refractory wall before the centre point is reached. Erroneous readings might be
132. In response to Mr Morris’ question as to the reasons why the type ‘K’ and type
‘C’ thermocouples have had such different failure rates, Mr Thompson stated
that although he did not fully understand the comparatively high rate of failure
amongst the type ‘C’ electrodes, he suggested the failures may relate to the fact
that the two types of thermocouples are used differently and the expectations
on each is different to start with and the:
rate of corrosion/melting of the part in the melt;
temperature gradient between the plastic head and the wire at the end;
their comparatively short length.
133. Mr Morris expressed disappointment that considerable effort and cost had been
spent on thermocouples to date for little data in return.
Advantages of continuing with inner pits in-situ?
134. In response to Mr Church’s question as to whether or not Geosafe saw a
technical advantage in completing the remaining inner pits in-situ compared to
exhuming and sorting into engineered pods, Mr Thompson offered the following
from a technical perspective, and in light of experience, if MARTAC wants
a very high level of confidence of treating the pit materials, then restaging
the remaining inner pit contents into engineered pods is a good approach
to take, but if, however, a lower level of confidence is required with respect
to the depth of treatment and the incorporation of all of the plutonium into
the melt, then continuing with the in-situ treatment of the inner pits is
his personal view (and not necessarily that of others in Geosafe) is that
wherever possible and wherever there is uncertainty as to pit depth, pit
contents and the possible existence of compressed gas cylinders in a pit,
then depending on the regulatory constraints which might be in place, his
first preference from a purely technical perspective is to try and exhume
the contents and restage it to eliminate uncertainties; and
there are no technical advantages in continuing to treat the inner pits in-
135. Mr Chamberlain and Dr Perkins advised there were significant practical
scheduling/cost disadvantages that would arise if the remaining inner pits are
not treated in-situ as previously agreed with the stakeholders.
136. Mr Vaeth suggested as an alternative, that before carrying out the last three
inner pit melts, it might be useful for the next inner pit to be treated to be
further investigated before melting commences so that some of the
uncertainties associated with it (such as in relation to pit volume, contents and
placement of thermocouples are resolved before the in-situ melting commences.
137. Mr Thompson voiced support for Mr Vaeth’s idea of treating the next pit as a
R&D exercise and suggested that it might be worthwhile to do some trenching
in towards the pit so that a couple of faces to the pit is exposed which could
then be investigated.
138. Dr Perkins asked that, in light of the limited time remaining available for the
teleconference, that MARTAC 13 should be used to fully discuss the technical
and other issues associated with the continued in-situ treatment of the inner
pits and alternative approaches.
Agenda item 5: Design of engineered pods
139. Dr Perkins asked the general question:
ISR requires that the contaminated metal and other debris from the outer pits be
treated in optimally constructed, configured and staged pits and Geosafe has the
responsibility for the specification of these requirements. What is Geosafe’s
thinking for the design of engineered pods?
140. In response, Mr Thompson read Geosafe’s response from the paper included as
Attachment 1 (pages 6 and 7). In particular, Mr Thompson highlighted the need
for MARTAC to clearly define the criteria to be met in treating the contaminated
contents of the outer pits in engineered pods, pointing out that:
although it is relatively easy to design large scale melts to ensure
achievement of temperatures of at least 1600 oC, the optimal design of the
pods will vary according to what is to go into the pods;
if it is acceptable to encase steel without melting it, then a lower level of
control is required on what goes into the pod with respect to limestone
material, concrete firing pads, bartytes brick wall sections, compared to
the situation if all the contaminated metal has to be melted; and
if full melting is required with a high degree of confidence, then minimal
amounts of limestone etc should be allowed into the pods, with instead,
predominantly high refractory materials being used to backfill the melts.
141. Mr Thompson highlighted the following additional matters as relevant to the
design of engineered pods and requiring of detailed discussion at MARTAC 13:
placement of steel in the pods;
potential for the generation of gases and the prevention of transient
the inner and outer bounds on what is to be put in the pods.
142. Mr Timmerman, Mr Timmons and Dr Lowery voiced support for Mr Thompson’s
143. In response to Mr Thompson’s comments on the matter, Mr Davy commented
that since MARTAC had yet to meet face-to-face to discuss the engineered pods,
he was only able to give his personal views on the matter at this time. Mr Davy
since the likely concentration of Pu in the engineered pod melts is likely to
be much higher than in the melts to date, it is essential that the
engineered pods be designed to ensure all the steel in the pods is melted
and not just encased;
inactive waste (such as barytes bricks) is not intended to go into the
engineered pods (thereby minimising both the volume of waste to treated
in engineered pods and the amount and types of gases which might be
generated in a melt); and
the engineered pods will need to be staged (such as through the use of an
appropriate depth of refractory sand at the base of the pods) to prevent the
‘tooth effect’ and any unmelted steel ‘riding’ the melt down below the
known bottom of the pods.
144. Mr Davy further suggested that although MARTAC will specify the overall
performance criteria to be met, it is for Geosafe to define how the performance
criteria will be met, and verified as having been met. It is up to Geosafe to
define such things as the:
nature of the backfill to be put into the pods;
means for constraining the lateral melt; and
shape and dimensions of the engineered pods.
Verification of melts
145. Mr Morris, Mr Church and Mr Davy variously suggested to Mr Thompson that,
in addition to staging the engineered pods with appropriate arrays of
thermocouples, he might like to investigate and consider staging the pods with
a volatile material or an appropriate alloy which, for example, generates gases
or puts a substance into the melt when heated to a suitably high temperature.
Such an arrangement, if technically feasible, could then be used to complement
the melt verification data to be gained from the use of the thermocouples.
146. Mr Timmerman advised that he had previously looked at the concept of using
volatile materials in melts and that there was some merit in considering their
use in the engineered pits. Mr Timmerman advised that several issues would
need to be considered, however, before any decision was made on the matter,
availability of suitable, real-time analytical equipment to register the gases
given off; and
potential decomposition of the generated gases in the Maralinga melt
147. Mr Thompson and Mr Timmerman suggested however, that, assuming improved
reliability, thermocouples should provide a more effective and responsive
indicator of the level of the melt.
148. In the course of discussions, Mr Thompson, supported by Mr Timmerman,
suggested it might be useful to investigate using fibre optic depth transmitters
to supplement the information to be gained from the use of staged
149. Mr Thompson made the point that although Geosafe “have been, and will
continue to do” the “best job possible”, Geosafe cannot guarantee the quality of
the remaining inner pit melts and that if a guarantee was wanted, then the
remaining inner pits should be exhumed and their contents treated in
Intrusion resistance of product produced in engineered pods
150. Dr Costello’s questioned how the intrusion resistance of the product produced
in engineered pods compared to that of the in-situ product. Mr Thompson
pointed out that although resistance against deliberate intrusion was a function
of melt depth and the engineered pod situation could allow for deeper melts,
less volume reduction and subsidence, Mr Thompson expressed the view that
the two situations would be roughly comparable.
Relationship between in-situ and engineered pod design
151. Dr Lokan made the point that it is desirable to stage the engineered pods in
such a way as to allow for verification of the interpretation of melt data
obtained in the course of the inner pit melts. As a result, the engineered pod
design should not be widely different to that of the pits already treated in-situ.
Preliminary design of engineered pod for discussion at MARTAC 13
152. Mr Thompson advised MARTAC members that with some guidance from
MARTAC members, he would be able to put forward a preliminary design for
the engineered pods, albeit with gaps in it for discussion at MARTAC 13.
153. Mr Chamberlain and Mr Ryan pointed out to participants to the meeting that:
the degree of debris sorting and the subsequent placement of steel in
engineered pods will be limited by the fact that such will be done using
construction plant and not with pick and shovel; and
the contents of the remaining inner pits cannot be controlled for but must
be dealt with.
154. Mr Thompson acknowledged the need to consider such practicalities in the
design of the engineered pods and what goes into them, but asked that every
reasonable effort be made to exclude uncontaminated debris and soil from the
original pits from going into the engineered pods.
155. Dr Perkins thanked everyone for their participation in the meeting and closed
the formal part of the meeting/teleconference. The formal meeting closed at
Agenda item 6: Other business
156. Discussions recommenced at 14.45 and continued without Mr Church, Mr
Vaeth, Mr McElroy, Dr Lowery, Mr Timmerman and Mr Timmons being on line.
MARTAC’s melt performance criteria
157. Mr Morris and Mr Davy made the point that the need to melt all the steel
virtually all the time (and not just encase it) had been clearly stated on
numerous occasions in discussions between various MARTAC members and Mr
Thompson in the period leading up to MARTAC recommending to DPIE that it
accept the use of ISV technology to treat the central Taranaki pits. Mr Morris
stated that allowance for encasement of steel in the melt was added to the first
MARTAC criteria to cover what were thought would be rare situations where
less than 100% of the steel had been melted.
158. Mr Ryan pointed out the fact that all the documents associated with the project
say things like ‘melt steel’. For example, the Remedial Design Plan refers to 4
models showing 1600oC as the target temperature.
159. Mr Thompson stated that although he had anticipated that most of the steel
would be melted most of the time, MARTAC’s first criteria does nevertheless
allow for encapsulation. Mr Thompson added that in hindsight, he had taken a
defensive position that encapsulation was fine.
Electrode spacing and the hitting of metal
160. In response to queries as to why Geosafe (Mr Obrellaro) had advised GHD that
the electrodes in the inner pit melts were never expected to encounter steel in
their progress through the melt, Mr Thompson advised that the original
assumption contained in the Geochemical Design Analysis was that since the
pits were expected to be small, the electrode spacing in the melts to be used
were such that they penetrated the area outside the pits, thereby, never directly
encountering the steel.
161. Mr Thompson advised the meeting that Geosafe could, if MARTAC thought it
necessary, increase the precision of their depth probing to more consistently
less than the 500 mm increments they had previously aimed for.
162. Mr Morris responded by stating his personal view that depth measurements to
the nearest 100mm (plus or minus 200mm) would be an appropriate target.
163. Mr Thompson explained how the rate and pattern of movement of the 3 tonne
probe through a pit was used to determine pit depth. In essence, the probe goes
in relatively easy until it hits something. However,:
if it hits a concrete firing pad, resistance against further movement is
registered, but the probe eventually breaks through and continues its
if it hits limestone, downward movement will be slow but incremental; and
if it hits steel, movement ceases.
164. When asked by Mr Thompson for their input on the matter, MARTAC members
were unable to suggest an alternative to the use of the 3 tonne probe to probe
Heat fin effect and power levels
165. Dr Costello and Mr Morris stated that MARTAC had recognised the ‘heat fin’
effect (where there is enhanced thermal conductivity below the melt because of
the presence of large metal plates and where the bulk thermal conductivity is at
least 10 times it would have been had the plates not been there) as possible.
166. Mr Morris stated that he would not have expected to see any heat fin effect in
pit 19a, as melting continued for longer.
167. Mr Thompson advised that Geosafe is using as much power input as is
necessary to achieve good melts without going overboard.
168. In relation to electrode spacing and power input, Mr Thompson advised they
are using the maximum sustainable power levels per unit volume (cf. the 3.5m
electrode spacing and power inputs of 2.5-2.7MW with 4.5m electrode spacing
and power inputs of 3.3 – 3.4 MW).
169. In response to Mr Davy’s question as to whether or not there is likely to be
some cavitation inside the melt with greater power loss, Mr Thompson said that
there would be certain contact resistance between melt and electrodes and that
resistance increases with increased power.
170. Dr Perkins asked Mr Thompson to explain what he meant by the term ‘over-
171. Mr Thompson explained that he used the term to relate to depth and not to the
lateral movement of the melts, and as a way of explanation, stated that if, for
example, the target depth was 4m, then over-melting has not occurred until the
electrodes have moved past the 4m mark.
172. Mr Davy pointed out that Geosafe needs to be very clear as to how their terms
are used in the final melt reports.
Quantity of barytes bricks
173. Mr Davy asked how convenient would it be for Geosafe to run data to give total
quantity of barytes bricks treated in the inner pits.
174. Mr Thompson advised that Geosafe is collecting data on this but have not been
175. Mr Thompson agreed to Mr Davy’s request to provide the data to MARTAC
before the specifications for the engineered pods are completed.
176. Using pit 6, melt 11data to illustrate his point, Dr Costello highlighted the fact
the thermocouple elevation views provided by Geosafe were not to scale
and did not include the datum from which depth was measured;
there were inconsistencies between the words and diagrams included in
the pit melt plans; and
that as a result, useful interpretation of the diagrams and pit melt plans
177. Mr Thompson undertook to review and improve the accuracy of all pit plans and
Engineered pod for contaminated soil
178. Mr Davy suggested that a pod be designed into which hot spots of contaminated
soil could be placed and that the specifications for this pod could be less
restrictive that those for the engineered pods used to melt steel in.
179. Mr Ryan stated that he expected:
larger debris to be put direct into the engineered pods; and
smaller debris to go into the trench where it is sieved and larger material
transported to the engineered pods. Finer material and soil ‘hot spots’
were intended to be spread in a thin layer, with early survey by CH2M
180. Mr Davy voiced general agreement but stated that:
he could not imagine the regulator setting criteria for hot spots different to
the category ‘C’ levels in the NH&MRC code [Code of practice for the near-
surface disposal of radioactive waste in Australia (1992
the only uncertainty is inspection of the bottom of the steel and looking to
see if it contains flaked off rust.
181. Mr Morris suggested that an alternative is to put contaminated soil hot spots
into the burial trench at depth.
182. Mr Ryan stated that GHD were now working with ARL to define the sorting
requirements to be applied in relation to the hybrid option
183. Mr Ryan asked Mr Thompson to:
provide advice as to his sorting requirements; and
his needs for layering of soil and debris in the engineered pods;
184. Mr Davy stated that it is intended to separate the steel from the
Geosafe input to MARTAC 13
185. Mr Davy asked Mr Thompson to prepare for discussion at MARTAC 13, a
proposal for the engineered pods which assumes/allows for:
the melting of steel (and not merely encasement);
temperatures of 1600oC at pit floor
excavation/sorting carried out to eliminate as much of the uncontaminated
bricks as possible;
all parts of the melt go past the known bottom location of the debris;
the holding of electrodes (as far as possible) static to ensure the steel is
melted, (duration and temperature to be factored in);
a power rating to be used which is towards the limit of the power density;
lateral extent of the melts to be confined;
an engineered pod which takes into account the practicalities required by
a melt which is well instrumented in terms of obtaining a temperature
gradient and limits the failure rate of the thermocouples as far as
if possible, allows for tracer release in accordance with melt progress.
186. Mr Davy added that it is up to Geosafe to define its needs in relation to the use
of overburden, whether or not to open the hood and its use of materials to
protect the electrodes when the electrodes are slowed to improve the
effectiveness of the melts.
187. In response to Mr Ryan’s comment that Theiss have been advised that they will
need to lay 0.5m of refractory sand at the bottom of the engineered pods, Mr
Thompson suggested that it might be more appropriate to place solid, high
temperature refractory panels there which will not fuse.
188. Mr Morris stated that as long as the metal is melted right at the bottom, then it
doesn’t have to be encapsulated as it will have had all the plutonium sloughed
Minutes of teleconference on status of bioassays
Maralinga bioassay (plutonium in urine) analytical status
4 November 1999
Bruce Coomer (CH2M Hill)
Bruce W Church (BWC Enterprises/MARTAC member)
Ernie Sanchez (ThermoNUtech)
Jeff Brown (ThermoNUtech)
Keith Baldry (GHD)
Garth Chamberlain (GHD)
The call began at 3 pm PST and ended at about 4:15 pm PST. Coomer and Sanchez
began the call by reconciling what sample results were outstanding and what
samples required reassessment to meet the sample analytical objective of 200 µBq as
the MDA. It was determined that 3 samples were completed, but had not been
reported to Coomer; 28 samples (since the establishment of the 200 µBq MDA was
set) had not met the MDA, and 48 samples [this number increases to ~66 with the
added QA samples that accompany the 48] (those analysed prior to the clarification
of the 200 µBq MDA) were still to be reassessed. Sanchez commented that if had to
recount all the 66 samples for 10 days, it would take until February 2000, to
complete the counting.
There was discussion concerning the problems with reaching the desired MDA, with
Sanchez affirming that sample volume, recovery of the tracer, and background at the
time of counting were controlling factors in reaching the MDA. It was determined
from this discussion that further solutions to the MDA question could not be
determined until Sanchez evaluated each outstanding sample and determined if
further analytical effort was merited. Sanchez noted that he would rather reanalyse
the samples rather than just recount for longer periods, as this tied up his counters
for long periods with little chance of improving the outcome (e.g. volume may not be
sufficient; background may be the limiting factor, etc). For those samples with
inadequate volume Coomer may be able to supply a new sample from archive, if
Sanchez accepted three action items:
send final results on the outstanding samples (3), completed but not received
review each sample not meeting the MDA (76) and advise what action he may
be able to take (e.g. reanalyse, request more volume, re-count, etc).
write a brief action plan
accommodating his recommended further Lab
activities. Sanchez indicated that this might be available next week.
A brief discussion was also entertained on what alternatives or options may be
available to the ‘client’ (DISR) if the Lab (Sanchez) could not meet the specified
MDA. These included evaluating the results from Harwell Scientific, sending those
samples not meeting the MDA to a Laboratory using a more sensitive procedure (e.g.
Fission Track Analysis), or developing a report by the joint project players explaining
the situation with pertinent documentation of what the samples’ results mean in the
way of possible exposure to Pu and resulting dose.
Chamberlain expressed concerned from the client’s point of view that with the
analytical situation dragging on so long, maybe there should be a report explaining
the situation. However, Church pointed out that until Sanchez performs the sample
by sample review it would be difficult to write such a report. It was left that in
approximately two weeks the MDA question would be revisited, with perhaps a
second conference call to revisit the results and options.
Observations and commentary by Bruce W Church
With a project as short as the Maralinga Remedial Action was planned to be, it was
natural for the HPRT team to expect fairly quick response to the team’s
recommendations. However, as the dates indicate in the letters to and from the
Department and the contractors, considerable time elapsed from the date of
completion of the audits until direction was given and a positive reply received.
There were some exceptions, specifically with the increased environmental air
monitoring in the operational area. The worst of these situations was the bioassay
program, which took nearly two years to begin receiving urine samples completed
with QA level three analyses recommended. The execution of the blind sampling
program took equally as long, and the results are still unknown as the project
concludes. Generally the Health Physics program was very conservative, probably
more than was needed. It is expected that the operational data collected during the
course of the cleanup will illustrate this point.
Health and safety issues addressed at MARTAC meetings
M-12, AUGUST 1998
Communication and skin contamination
Have just posted a ‘30 day snapshot’ for the site which mentions the surveys
carried out in the different areas and findings continuing to provide input at
tool box meetings
Waiting on Geosafe’s reply as to their and AMEC’s radiation monitoring
information needs as employers
Bioassay program (urine monitoring for plutonium)
Previously submitted samples have been located and can be recounted to the
200 level as a minimum
Level 3 QA reporting on the reanalysed and future urine samples has been
ThermoNUtech has been contracted to supply an ‘unknown’ for use as an
external QA tool
Expect to have data from the analyses by 20 October 1998
Mr Baldry/Mr Coomer will:
report on analysis results as soon as possible after receiving findings;
update the CH2M Hill implementing procedures for dealing with lost/
incomplete urine samples; and
organise the ‘leaked’ samples to be recounted if that can be done with
confidence, otherwise, they will ask for advice from DPIE.
Airborne activity monitoring
GHD recognises the need for the integration of data from the different
monitoring systems and have almost completed their review of the Geosafe
Two briefing sessions had been held for Geosafe/AMEC staff in which
explanations were given on HP, what the monitoring readings mean, how the
figures are combined and so on
Personal monitoring procedure has been updated
Use of lapel samplers will be addressed in a reissued environmental
Action continuing on the integration of the system data and documentation
Emergency response and evacuation
Geosafe have arranged for real time SO alarms to be installed at site
Geosafe had run training for all workers at site on the emergency response
and evacuation arrangements
Geosafe have yet to run a trial of their emergency response and evacuation
system but are expected to do so shortly
A mock emergency recovery situation at a hood is planned to occur
Final dose assessment
Had sought examples of dose reporting from Mr Church
Were waiting on the recounted sample results
Will develop a program for reporting results and clear it with ARL and DPIE
M-13, JANUARY 1999
Responding to a request from Mr Davy, Mr Coomer and Mr Baldry reported on the
status of the implementation of the recommendations of the 1998 Health Physics
Review, and also made some general comments about the general status of health
physics-related matters on site.
Mr Coomer commented that CH2M Hill was just keeping up with the demand for
their services in relation to pit preparations and the re-staging of the pits, and noted
(a) the off-gas filters were clogging up reasonably frequently (2-3 filters were
normally needed per melt), and that it had proved to be labour-intensive to
manually remove the contaminated particulate matter; and
(b) health physics support was needed when contaminated samples were
dispatched from site for analysis at ANSTO.
Mr Baldry reported that the bioassays were lagging behind because the first recount
of urine samples had been lost during a vacuum pump failure. The first batch of
results was expected before the end of January, with a second batch due in mid-
Mr Baldry commented that the quarterly refresher health physics course (initiated
because of the concerns of AMEC workers) was ongoing. Mr Coomer noted that
AMEC workers were now far more confident when dealing with radioactive material,
and seemed to stay cleaner during the operations. No instances of hand
contamination had been reported recently.
Mr Baldry reported that although Geosafe had yet to install a two-stage alarm, all
individuals carried radios on them at all times, and were in contact with a controller
who would alert them to any potential hazard
MARTAC asked Mr Chamberlain to follow-up with Geosafe and ensure the prompt
installation of the two-stage alarm system.
Mr Baldry briefed MARTAC on the status of the intended OHS audit at site, noting
that he would confirm the terms of reference for the audit with Ms Burnell.
With respect to the stack Eberline detector, Mr Baldry reported that testing had not
been completed, and that readings from the stack were not being used in dose
Dr Lokan suggested that ARPANSA needed a copy of the complete exposure records
of all Maralinga workers, and not just their lung monitoring results. Dr Perkins
undertook to discuss the matter with ARPANSA.
Mr Chamberlain noted that at the end of the project, GHD would hand over all the
data on CD-ROM to DISR.
Mr Baldry reported that there were some outstanding issues that needed to be
considered with respect to the dose and detection limits before an explanatory
paragraph on the dose records could be sent to workers. There was some discussion
as to whether a dose limit could be reported for the ‘standard Maralinga worker’,
with Mr Baldry commenting that the dose limit could vary considerably depending on
Dr Lokan suggested that a range of committed doses could be calculated using
ARPANSA’s minimum detection level and the ‘standard Maralinga worker’
parameters. It would need to be made clear that the committed dose was not an
Mr Burns suggested that although a lengthy report would need to be written by
ARPANSA outlining the relevant methodology, a short explanatory paragraph needed
to be released to workers as soon as possible. There was general agreement that the
summary paragraph and dose information should be released prior to the completion
of the ARPANSA report to MARTAC.
M-14, MAY 1999
Items related to the HPRT review and reported on at MARTAC 14 follow.
Mr Coomer advised that the spike sample had been received and that the final
recommendations of the 1998 Health Physics Review pertaining to urine
monitoring were being implemented.
In response to questioning by Mr Church, Dr Perkins advised that DISR had
yet to determine whether it would pursue the analysis of a selection of urine
samples using a technique with a more sensitive ‘minimum detection level’
than that generally used.
M-15, AUGUST 1999
The following items related to the HPRT were discussed at the conclusion of
Mr Baldry tabled a document titled Bioassay Update
at the meeting, and
discussed with MARTAC the approach to address the analysis delays
occurring at Thermo NUtech’s Albuquerque laboratories and to totally comply
with the recommendations of the 1998 Health Physics Review Team’s (HPRT)
audit in relation to urine analysis.
In relation to the HPRT recommendation that DISR give consideration to
sending a limited number of samples to a laboratory for analysis using ICP-
MS, Dr Perkins advised MARTAC that DISR had agreed to this being done and
that Mr Baldry was taking action for this to occur. Mr Church undertook to
provide contact details to Mr Baldry for the Brookhaven Laboratory that
carries out ICP-MS.
In response to a suggestion that the urine program was secondary to the lung
monitoring program carried out for the Project, Mr Burns noted that, because
of the variable plutonium ratios and solubility at Maralinga, urine monitoring
may, under some circumstances, be of more importance than lung monitoring.
Mr Burns advised that ARPANSA had received the quality control spike and
blanks and mock urine recommended by the HPRT, and that these would be
used, as appropriate, to QA the bioassay regime in the near future.
Mr Burns questioned whether it might be useful and possible for some of the
urine samples to be archived. Mr Baldry undertook to investigate the matter.
EXTRACTS FROM A MINUTE DATED NOVEMBER 28TH, 1991 ADDRESSED
Mr. Pat Davoren,
Mineral Industries and Nuclear Policy Branch
Department of Primary Industries and Energy,
GPO Box 858, Canberra.
I thought it might be useful to make a fast first pass through the Roller Coaster
information that has come to hand so far. As you know, it wasn’t looking too hopeful
as you left, but, in the end, it has proved to be quite illuminating, and I’m sure you’ll
want to know about it. Would you pass a copy to Des, please? ------
Roller Coaster comprised four trials
Double Tracks (15 May 63) looks like a re-run of a Vixen B but with less HE – the
cloud went to 220m rather than to – 760m.
Clean Slate I (25 May 63) had a different configuration from Vixen B, but, with nine-
times as much HE as Double Tracks, the cloud went to 710m, rather like a Vixen B.
Clean Slate II and III (31 May & 9 Jun 63) were in bunkers, and they were for
assessing the scavenging effects of different depths of soil overburden
Double Tracks in particular, and Clean Slate I as well, are of interest for our purpose.
The US knew before Roller Coaster – and further confirmed it then – that alpha-
survey monitoring of Pu fallout on soil underestimates the Pu surface density by an
order of magnitude, even when the survey is made in the day or so immediately
following deposition.They attributed this to what they termed “weathering effects”.
From the studies in “Project 2.5 – Alpha Survey” they concluded that
(a) for alpha-survey monitoring of Pu fallout on a clean, brushed-concrete surface
at ground level, the readings can be expected to fall by 1/6th to 1/10th or more
over ~7 days; their observations in Roller Coaster gave a typical reduction of
1/10th in the first 3 days, and similar results had been obtained in earlier trials;
(b) for alpha-survey monitoring over soil, a further reduction of ½ to 1/3 was
observed, and a total degradation of 1/12 to 1/30 can be expected; whereas
(c) for 17 keV & 60 keV photon monitoring of Pu fallout on the concrete surface,
the reduction to be expected is ½ to 1/3: and this monitoring method was
No operational use was made of alpha survey monitoring over soil in Roller Coaster.
The alpha-survey results came from measurements over 300x300 brush-finished
concrete surfaces, set flush with the ground for this purpose, in a network of –7500
monitoring points extending over the downwind grid to 15km – quite an effort!
The most valuable piece of information protruding from under the wraps is in
Appendix C of the Los Alamos National Laboratory report “Supplementary
documentation for an environmental impact statement regarding the Pantex plant –
dispersion analysis for postulated accidents” LA-9445-PNTX-D (December 1982).
The center-line Pu deposition data for Double Tracks and Clean Slate I are presented
and they are used there in demonstrating the validity of the Pu dispersion model
DIFOUT which was employed in the impact assessment.
Generation of DIFOUT was one of the original objectives of Roller Coaster. The
model rests heavily on the Roller Coaster observations for its concepts and input
perameters: for example, the concept that “Most of the plutonium mass in the
weapon-like assembly was aerosolized”, and the assumption that the size distribution
of the airborne particulate was as observed for the Double Tracks event.
The Pu deposition data in Appendix C are not expressed in absolute terms: they are
normalized to one kilogram of Pu in the explosion – life wasn’t meant to be easy!
“Although the actual plutonium amounts involved in the tests remain classified,
normalized airborne and deposited plutonium dosages have been presented as dosage
per kilogram dispersed under measured conditions. From these normalized dosages,
scaling to higher plutonium amounts in the postulated accident cases can be done with
reasonable accuracy if (1) the DIFOUT model can be shown to approximate the
Roller Coaster experimental results and (2) the dispersion conditions of the accident
cases are close enough to the Roller Coaster conditions to be considered applicable.”
I have used this normalization as the basis for comparing the Double Tracks and
Clean Slate I results with the post-firing alpha-survey measurements from the Vixen
B trials and the EC&G aerial survey data from Taranaki. On the Figure:
(a)I have transcribed the plotted data from Figures C-6 & C-8 as Ci/m2 per kg of Pu,
going from 100m. to about 40km down the plumes;
(b) I have added the values for the fallout plumes from VB1/2, VB1/3, VB2/2,VB2/5
& VB3/1 – which are all I can identify in the EG&G 241Am survey – converting
them from 241-Am to 239-Pu using the appropriate activity ratios. They are plotted
as the vertical bars, corresponding to the ranges of 241-Am surface density in which
the EG&G results were reported;
(c ) finally, I have included the post-firing alpha-survey results for VB1/1,2&3 and
VB3/1, 3& 4 for which the plumes are unambiguous and we have good plots; VB1/2
gave two plumes, and, unfortunately, we have only a poor set of plots for
The figure tells the story quite well. There are three points – which neatly close the
(a) The Roller Coaster data for Double Tracks and Clean Slate I, and the EG&G
data for the five identified plumes at Taranaki, agree very nicely – given the
differences in the firings, and the span of cloud heights and wind speeds.
(b) The values from the post-firing surveys beyond 100m. show a systematic 20-
fold underestimation of the Pu surface density when compared with the data
from either Roller Coaster or the EG&G work. The measurements were made
by 1320 alpha monitoring over soil and the deficient outcome is entirely
consistent with the US experience discussed in above.
(c) The values from the post-firing surveys within 100m. of the pads are
consistent with the Roller Coaster data. These close-in measurements were
made by 1320X 17 keV monitoring. The US experience at Roller Coaster was
that this type of measurement is reasonably reliable – to within a factor of two
(JOHN R MORONEY)
AUSTRALIAN RADIATION LABORATORY