ML20217B689

Provides Paper Summarizing Knowledge of Radioactive Source Term for West Valley Facility Disposal Area.Paper Addresses Only NFS Burials in Facility Disposal Area

ML20217B689
Person / Time
Site:	Erwin
Issue date:	09/07/1983
From:	Hurt D NRC
To:	Theresa Clark NRC
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REF-PROJ-M-32 NUDOCS 9709300133
Download: ML20217B689 (10)

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' f Note for Tom Clark

SUBJECT:

SOURCE TERM FOR WEST VALLEY FACILITY DISPOSAL AREA The attached paper summarizes our knowledge of the radioactive source term 4 for the West Valley f acility disposal area. As discussed in the paper, there are still some significant gaps in our information about the disposal area, particularly as relates to the chemical characteristics of the buried i

materials, in fact, we know so little at present about waste chemistry that I have not included the subject.

This paper addresses only the Nuclear Fuel Services (NFS) burials in the facility di5posal area. It does not- cddress the adjacent state-licensed disposal site or the recent burials by West Valley Nuclear Services.

The subjects covered are (1) volumes of waste buried by NFS,. (2) fission product activities of the wastes, (3) cctivation products, (4) plutonium content, and (5) location of the wattes within the disposal area.

hl Davis Hurt

Enclosure:

As stated cc: LCRouse WBurkhardt PHLohaus TCJohnson TJNicholson ,

I 9709300133 970912 ' Enclosure PDR PROJ M-32 PDR;

L A'. Major Sources of~Information , j i

l This synopsis is primarily based on information derived .from the following a -sources. There are many additional documents in our possession thas i contain information on West Valley waste disposal, but they do not 6dd substantially to the sources listed below, in the text that follows, I ,

i -have indicated in- parentheses which of the sources I used for the various '

I topics.

! 1. _" Compilation of West Valley Solid Radioactive Waste Burial Operations,"

j James P. Duckworth.(NFS), February 16, 1981, unpublished.

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! 2 " Safety Evaluation of NPR Fuel in Hull Burial," no author cited 4 (presumed _ prepared by NFS staff), no date cited (presumed sometime after August 1969), unpublished.

3. Personal communication with Donald R. Joy, Division of Safeguards, USNRC.

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i 4 Personal communication with James Clark, Nuclear Fuel Services.

5. West Valley burial logs

6. " Final Report on Analysis of 80-2 Supernatant," John L. Knabenschuh, West Valley Nuclear Services, Jan. 12, 1983.

B. Waste Volumes Between 1966, when the first buria}s were madgjn the facility disposal agea, and-1980, NFS buried 4,300 m of waste. Approximately 185

-m- (4.3_ percent) consisted of 30-gallon cans of leached hulls and other spent fuel hardware. Three of the 30-gallon cans buried along with the leached hulls contain irradiated New Production Reactor (NPR) fuel. The cladding on this fuel was too badly damaged to permit processing, and it was buried at the bottom of one ~of the 50-foot deep shaft normally used for disposing of the leached hulls. The other 96 percent of the waste was composed of.a wide variety of wastes from the reprocessing plant, most of them much lower in act4 *ity than the leiched hulls. The prominent categories of- other wastes were f ailed ecuipment, used filters, laboratory wastes, and degraded solvent absorbed in solid media. Many of the buried containers were described in the burial records ly as " general plant waste," with

.no further identification of contents lhe-last leached hull burial was in 1973, after the reprocessing plant cl osed . Between 1973 and 1980, the period during which the plant was closed but still. ender -NFS's. jurisdiction, about 1,900 m3 (43 percent of the-total of 4,300 m#) of waste was interred. Most of this was apparently sludge from the low-level liquid waste treatment facility or wastes from decontamination activities in the plant.

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-l C. Fission Product Radioactivity The._ fission' products in the facility disposal area can be thought of -

as divided between the leached hulls, the NPR fuel, and the miscellaneous plant wastes. From the general characteristics of these materials, we can be fairly confident that the great majority (at least 90 percent) of the

. fission product activity is in the first two categories, and we can be quite confident that nearly all of the remaining fission product activity.

is in the-form of Sr-90 and Cs-137.

Duckworth estimated the quantities of several major isotopes at time of burial, ass

- for two years.gng By thatmy the' average fuel interpretation, had been figures Duckworth's out of the reactor show a total fission product activity of about 144,000 Ci at time of burial, with about 125,000 Ci in th.e hulls area and.19,000 Ci elsewhere. . (See Section F and Figu a 1 for more detailed discussion of the exact location

- of_ the wastes within the disposal area.) Duckworth does not discuss the spent fuel in his paper, and it is not clear if the 125,000 Ci includes the spent fuel activity. ' As discussed further below, the spent fuel safety evaluation report gives an activity at the time of burial of about 105,000 Ci, so it seems unlikely that Duckworth meant to include the spent fuel in his value of 125,000 C1.

Duckworth's activity estimates weregparently obtained by summing the activity values in the burial logs. He does not state this in his paper, but his figures agree with the burial log sums to within-less than-1 percent. The burial logs were records kept at the disposal area of the activities of each batch of- buried containers. When two contractors and I visited the site in April 1983, we were tald that the activities were obtained by measuring the gamma dose rate at the surface of each container

-with a_ hand-held counter and converting the dos? ' ate to an activity value with an empirically-derived chart. Duckworth appears to have then partitioned the total activity value into its major fission product and activation product constituents. The selected fission products were Sr-90, Cs-137, and

-Ru-106, and their contributions to the total fission product activigwere assumed to be 45 percent, 45 percent, and 10 percent,respectively.

Based on these percentages, che total disposal area activity in 1983 would be about 93,000 Ci, with 78,500 Ci in the hulls area and 13,500 Ci elsewhere.

As discussed above, it is not clear if these values include the NPR fuel.

It-is not a very good assumption that 90 percent of the activity in two-year old spent fuel is due to Sr-90 and Cs-137. Even for high burnup-(33,000 MWD /MTU) PWR fuel, ORIGEN calculations show that less than 40 percent of the activity in 2-year old spent fuel is due to these two isotopes.

The fuel processed at West Valley was of much lower burnup, averaging about 13,000 MWD /MTU for the 228 MTU of power reactor fuel and about 2,000 MWD /MTV for the 380 MTU of NPR fuel. The West Valley wastes would be expected to have relatively less of tile long-lived fission products like Sr-90 and Cs-47, and more of the shorter-lived isotopes like Ru-106, Ce-144, and Pm-147. The data on the buried NPR fuel shows that at years only 21 percent of its activity was due to Sr-90 and Cs-137.go Back-calculating from the results of the chemical analysis of the 80-2 high-level waste _(HLW) tank provides another check on the relative isotopic

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abundances.(6) 12.4 years before the chemical anlaysis was performed, which would correspond to an average out-of-reactor time of two years, the Sr-90 and Cs-137 accounted for about 20 percent of the combined activity of the Sr-90, Cs-137, Ru-106, Ce-144, and Pm-147. (ORIGEN calculations for 33,000 MWD /MTV PWR fuel show that these five isotopes provide 87 percent of the activity at one year out of the r 2 actor.) Due to preferential deconta-mination or dissolution of sonie elements, the isotopic ratios in the HLW may not be identical to those in the leached hulls, but these comparisons give some idea of the extreme conservatism of the assumption that 90 percent of the activity at two years was due to Sr-90 and Cs-137. The various comparisons of isotopic ratios are summarized-in Table 1.

l Table 1 COMPARIS0N OF ISOTOPIC RATIO ESTIMATES l IN TWO-YEAR OLD SPENT FUEL (Expressed in Percent of Total Activity) l l Sr-90 Cs-137 Ru-106 Ce-144 Pm-147 i Duckworth Pacer 45 45 10 0 0 l

HLW Analysis 10 10 9 57 14

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BurieG NPR Fuel 10 11 4 59 15 ORIGEN PWR 17 24 30 22 7 (33,000 MWD /MTU)

A more detailed examination of the HLW analysis can provide another estimate of total fission product activity in the hulls. The activities of five major fission products at two years out of the reactor can be obtained by using HLW ac. clysis values and :orrecting for 12.4 years of decay. These activities are listed in Table 2.

Table 2 FISSION PRODUCT ACTIVITIES OF HIGH LEVEL WASTE AT TWO YEARS OUT OF REACTOR (Based on HLW Analysis)

Isotope Curies x 10-6  % of Total Sr-90/Y-90 20.8 10 Cs-137/Ba-137m 20.8 10 Ru-106/Rd-106 18.9 9 Ce-14'4/Pr-144 116.7 57 Pm-147 29.2 14 l Total 206.4 100 I have assumed that other isotopes were of negligible activity at two  ;

years. The activity value in Table 2 is the total for the HLW. It remains i to relate the fission product contents of the HLW ta the fission product contents of the leached hulls. As mentioned earlier, there may be some difference between relative elemental abundances in the HLW and the leached hull s . The hulls are contaminated by fission products that did not dissolve, the HLW by fission products that dissolved but were separated from the product stream by solvent extraction. While there is data showing that some elements are preferentially dissolved or extracted, I will assume that this is a second order effect and that the two types of waste have the same relative abundances of radioisotopes.

As discussed in Section E, 6he average .neasurad fractiggjl loss of plutonium in the hulls was 0.17 percent of plutonium throughput. This percentage could easily be in' error by 25-50 percent (See Section E), and the question remains of whether the fractional loss for plutonium is the same as the fractional loss for fission products. Nevertheless, this is probably the best estimate available for fractional spent fuel loss in the hulls. Using 0.17 percent as the average fractional spent fuel loss yields a time-of-burial leached hull fission product activity of 351,000 Ci. If the isotopic distribution of Table 2 is correct, the 1983 activity is 53,600 Ci, of which 97 percent is due to Sr-90 and Cs-137 and the remainder due to Pm-147.

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reported to check this NPR the buried valuefuel.

is tognsider the fission product activity At two years out of the reactor the j buried fuel would have had the following isotopic activities, i

Table 3 i

FISSION PRODUCT ACTIVITIES OF BURIED NPR FUEL AT TWO YEARS OUT OF REACTOR

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!' Isotope Curies x 10-3 .% of Total i

Sr-90/Y-90 6.08 10

Cs-137/Ba-137m 6.42 11 l Ru-106/Rh-106 2.56 4 Ce-144/Pr-144 34.04 59

Pm-147 8.43 15 Other 0.56 1 Total 58.09 100 The burnup of the buried fuel was 2,600 MWD /MTU, about 30 percent highei -

than average for _the NPR fuel processed at West- Valley, So it would yield conservative results to assume that all of the NPR fuel. had the same isotopic activities as the buried fuel. The quantity of fuel buried was 458 kg, compared to the NPR fuel throughput of 380,00g kg. The total NPR activity at two years would thus be 48.2 x 10 C1. Assuming as before that 0.17 percent of the' fuel rema!ns in the hulls, the fission product activity of the NPR' hulls would have been about 82,000 Ci et time of burial.

The consistency of this value with the total activity estimate obtained-from the HLW analysis can be checked by comparing the megawatt-days of energy generated by the NPR-fuel to the energy generated by all of the fuel processed at West Valley. The energy produced by the NPR portion of th?

throughputwas-773,000gWD. The energy produced by all of the fuel processed was 2.97 x 10 MWD or about 3.84 times the NPR energy.

.Multiplyi_ng 82,000 Ci by 3.84 should yield the approximate total fission product activity-in= the hulls, This approach gives a value of 315,000 C1, about-10 percent less than HLW analysis estimate of 351,000 Ci. Such close agreement seems-to indicate that either of these values is a better estimate than the earlier estimate of 125,000 Ci.

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.,  ! To summarize, it would apprear from our present information- that the beit i estimate of time-of-burial fis; ion product activity.in the hulls is between l

300:,000 Ci- and 350,000 Ci, 'with about 20 percent of this due to Sr-90 and

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Cs-137. The best estimate of 1983 activity would thus be between 48,000 Ci and 54,000 C1, about 97 percent due to Sr-90 and Cs-137. This is about 35

, percent lower than the 1983 estimates based on Duckworth's paper.

The 1983 fission product activity in the buried NPR fuel is about 9,500 C1.(2)

Duckworth estimates that the activity ighe miscellaneous wastes is about 4 percent of the activity in the hulls. -This would add about 2,500 Ci l of. fission products to the-disposal area inventory, for a total of about j 63,000 Ci of fission products overall.

, D. . Activation Products

At time of burial, activation product activity was substantial. Most of

_ the activity was due to Zr-95 (T 1/2 = 6a days) and Co-60 (T 1/2 = 5.3 years). The combined activity of these isotopes was estimated by Duckworth to have been about 385,000 Ci at time of. burial, with 55 percent of this j due to Zr-95. In 1983 the Zr-95 is essentially gone, and the Co-60 has

! decayed to about 24,000 Ci . Considering the relatively short half-life of

. Co-60, plus the fact that the activation products are bound into the j metallic structure of t he hulls, this contribution to the source term would j' seem to be of minimal- concern.

1 l E. Plutonium i

j The quantities of- plutonium buried by NFS in the facility disposal area i are estimated to be 3.7 kg in the hulls, 0.8 kg in the NPR fuel distributed among th2 remaining burials, for a total of 4.9 kg.g 0.4 kg The NPR fuel figure is probably the most accurate of the three estimates.

All of the plutonium created in the fuel was buried with it, and DOE routinely uses computer codes to predict the amount cf plutonium in NPR

( fuel. It seems unlikely that the 0.8 kg estimate could be in error by more

than a few percent, and the relative uncertainty.it contributes to the

! estimatt.d total ^' 4.9 kg ould be even smaller.

The 3.7 kg in the leached hulls is less certain. Duckworth obtained the 3.7-kg value by summing the plutonium losses of the individual campaigns.0)

In the first few NPR campaigns, NFS sampled and analyzed the leached hulls at the AEC's request. The results were consistent enough that- NFS was given permission to forego such analysis"in future NPR campaigns and insteag3) assume that 0.1 percent of the weight of the. leached hulls was heavy metal'.

The. hulls were also sampled and measured for most of the power reactor campaigns. There was no regulatory requirement to do so, but the contractual O

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agreements between NFS and its customers usually stipulated that such a measurement be performed to determine how much plutonium remained in the f

. hulls. This being the purpose of the measurements, the figures may to some extent represent plutonium figcial compromise as much as objective estmation of the contents. As a percentage of plutonium throughput, the hull-losses reported by Duckworth range from a low of 0.06 percent to a high of 0.94 percent, with the average being 0.17 percent. Thesafeguardsrecogry of plutonium losses in the hulls agree closely with Duckworth's figures and appear to be based on the same source data.

, The information we have now does not provide much of a basis for judging the accuracy of the 3.7 kg estimate. Most of the plutontum in the hulls was probably in a minority of the pieces, particularly the ends of the fuel rods, which may have-been exposed to acid through only one opening, and crimped pieces of fuel rodg,43hich likewise may not have had their fuel l contents completely exposed. \ It would have been difficult to take a representative sample of the hulls. There was also substantial uncertainty in the chemical analysis. The sampled hulls were not themselves dissolve but were subjected to hydrofluoric acid leaching to remove residual fuel.{3)

Plutonium that had migrated into the metallic structure of the hulls may not have been detected. To the extent that a weight percent factor was used in some campaigns instead of a measurement, the question arises as to I whether the unmeasured batches were dissolved as completely as the batches l' on which the factor was based. These considerations justify some conservatism in assigning an uncertainty to the 3.7 kg estimate. On the other hand, there is no special reason to believe that any of the batches of fuel were dissolved less thoroughly than others, and it was certainly in everyone's economic interest to recover as much of the plutonium as possible. It seems reasonable to conclude'that the estimate could be inaccurate by-a factor of 50 percent of so, but I see no reason why it is likely to be off by more than that.

Duckworth estimates that there is about 0.4 kg of plutoniuin distrged among all of the NFS burials other than the hulls and spent fuel. His paper (in Table yl) implies that this valu.e may have been obtained by adding the estimatM plutonium contents of buried birdcages and resins. It does not appear that his vaiue includes tne plutonium that might be present as a minor contcminant in general wastes from the plutonium load-out areas or laboratory. The waste packaging procedures used by NF

- keep the average plutonium level below 1 g per container.{3}ere The burialintended to logs and records in our possession do not indicate how many individual containers from plutonium-contaminated areas were buried; if they did, we could use the 1 g per container limit to establish a reasonable upper bound. There must have been hundreds of packages of plutonium-contaminated solid waste generated during the life of the plant'. In addition, there must be some plutonium in the absorbed decontamination solutions and spent solvent. Even with generally low levels of plutonium contamination among 4 these wastes, the total quantity could easily exceed the 0;4 kg estimate.

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d The safeguards' records show-a cumulative inventory difference of 10.2 kg of -

plutonium over the plant's lifetime. This is the difference between input at the accountability include measured losses tank and to the measured high-levelproduct wasteoutput, ar(g)does not or huils. There are, <

of course, many 'possible explanations for the inventory difference, principally

- - .the errors that could occur-in measuring.its components. But it should be 4

noted that a plutonium loss in raiscellaneous trash going to the burial i ground significantly higher than Duckworth's estimate of 0.4 kg is not i inconsistent with the safeguards records. Considering all of these issues, l, it would seem that a conservative estimate of plutonium inventory in the j: miscellaneous might -be about one kilogram, i

l Considering all three constituents together--hulls, spent fuel, and miscellaneous--

the information we have at present indicates that a censervative estimate of

[ total plutonium inventory would be about 5,5 kg, with an uncertainty of about l 2.0-2.5 kg.

2 b 'F. Distribution in Burial Ground

Figure 'l ilkustrates the general location in the burial ground of the j major source term components. The small dark spot indicates the location

< of the NPR fuel. This single hole probably contains close to 20 percent

{ of the fission product activity and about 15 percent of the plutonium

remaining from the NFS burials. The dashed line surrounding the spent fuel 1 indicates the approximate boundaries of the leached hull burials. Over-l' 95 percent of the fission products and around 80 percent of the plutonium

{ are believed to lie inside the dashed box. The shaded areas indicate the i- location of the-remaining NFS burials; the unshaded areas were not used.

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