Reportable Radionuclides in DWPF Sludge Batch 7a (Macrobatch 8)

Abstract

Extensive radionuclide analyses were performed on a Sludge Batch 7a (SB7a) sample collected from Tank 40. Results of these analyses were used to project the radionuclide content of the SB7a waste over the 1100 year time period from calendar year 2015 to 3115. This was done to determine which radionuclides were reportable per the requirements of the Waste Acceptance Product Specifications (WAPS) and the Defense Waste Processing Facility (DWPF).Twenty-five radionuclides in SB7a waste were identified as being reportable based on the criterion of contributing ≥ 0.01 percent of the total curie content from 2015 to 3115 and having half-lives ≥ 10 years. These twenty-five radionuclides are: Ni-59Ni Three of these radionuclides -Th-229, Cm-246, and Cf-251 -are ones that are absent from the list of radionuclides projected to be reportable in the DWPF glass design basis. In contrast, three of the nuclides identified in the DWPF glass design basis -Pd-107, Cs-135, and Th-230 -are ones not found to be reportable based on the SB7a characterization. These deviations should not be considered unique, as they also occurred in several of the previous sludge batches. However, they demonstrate the importance of utilizing laboratory data to test process expectations.In addition to the twenty-five radionuclides identified above, U-235 and U-236 are also considered reportable -not because of the curie content/half-life criterion -but because of their identification as being always reportable per the requirements of Section 1.6 of the WAPS.Based on the 2015 to 3115 radionuclides projections, the total curie content of the SB7a waste will decrease three orders of magnitude over the upcoming 1100 year time period. Most of this decrease will occur over the first 400 years, due to the dominance of radionuclides with half-lives of 100 years or less. Specifically, Sr-90 (and its short-lived daughter Y-90), Sm-151, and Pu-238 are the primary radionuclides driving the curie content over the first 400 years (2015 to 2415), and each of these radionuclides has a half-life of 100 years or less. In contrast, Pu-239 (and its short-lived daughter U-235m) and Am-241 will dominate the curie content after 2415, once the majority of the Sr-90, Sm-151, and Pu-238 have decayed away. This should not be considered surprising, given the significantly longer half-lives of Pu-239 and Am-241 (24,000 and 430 years, respectively).Three of the reportable radionuclides in SB7a (Sn-126, Pu-242, and Cf-251) were identified based upon minimum detection limits, rather than true detectable concentrations. Methodologies for reducing the minimum detection limits of these particular analytes could be pursued in the future, if more accurate projections are needed. This would improve the ability for making a clear determination of whether or not these radionuclides are reportable.

Preliminary analysis of species partitioning in the DWPF melter. Sludge batch 7A

“…Calculated elemental compositions of MFT576 to MFT580 in weight percent (wt%) calcined solids (CS) are compared in Table 4 to the elemental compositions of Tank 40 in wt% total solids (TS) and the PS glass sample in wt% (note the slurry composition in wt% CS is the same as wt% in glass). 6,8,9 As stated above, these MFT batch compositions represent in Eqs. (3) to (6).…”

Potential Application Of Radionuclide Scaling Factors To High Level Waste Characterization

“…5 In cases where an alternate reference was utilized, the reference was specifically cited. The relative radionuclide solubilities and distributions were taken from a series of references: reports addressing characterization of DWPF sludge batches, [6][7][8][9][10][11][12][13] reports addressing characterization of Tank Farm saltcake and supernatant, [14][15][16] and miscellaneous reports focusing on concentrations and distributions of specific radionuclides. [17][18][19] Since the primary sources of fission products in SRS waste are from fission of U-235 used to generate neutrons and fission of U-235 in uranium irradiated to generate Pu-239, all of the fission yields identified in this report are those applicable to U-235, as opposed to those applicable to U-233 or Pu-239.…”

Determination Of Reportable Radionuclides For DWPF Sludge Batch 7B (Macrobatch 9)

“…All radioactive U-235 fission products and all radioactive activation products that could be in the SRS HLW were considered. No new isotopes have been added to the list in Table 1-1 since the SB7a report 7 . In addition, all U and Pu isotopes identified in WAPS 1.6 have been included in this list.…”