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Title: K West Basin Sand Filter Backwash Sample Analysis

A sand filter is used to help maintain water clarity at the K West Basin where highly radioactive sludge is stored. Eventually that sand filter will require disposal. The radionuclide content of the solids trapped in the sand filter will affect the selection of the sand filter disposal pathway. The Pacific Northwest National Laboratory (PNNL) was contracted by the K Basin Operations & Plateau Remediation Project (operations contractor CH2M Hill) to analyze the radionuclide content of the solids collected from the backwash of the K West Basin sand filter. The radionuclide composition in the sand filter backwash solids will be used by CH2M Hill to determine if the sand filter media and retained sludge solids will be designated as transuranic waste for disposal purposes or can be processed through less expensive means. On October 19, 2015, K Basin Operations & Plateau Remediation Project staff backwashed the sand filter into the North Load-Out Pit (NLOP) and immediately collected sample slurry from a sampling tube positioned 24 in. above the NLOP floor. The 764 g sand filter backwash slurry sample, KW-105 SFBW-001, was submitted to PNNL for analysis on October 20, 2015. Solids from the slurry sample were consolidated into two samplesmore » (i.e., a primary and a duplicate sample) by centrifuging and measured for mass (0.82 g combined – wet centrifuged solids basis) and volume (0.80 mL combined). The solids were a dark brown/orange color, consistent with iron oxide/hydroxide. The solids were dried; the combined dry solids mass was 0.1113 g, corresponding to 0.0146 weight percent (wt%) solids in the original submitted sample slurry. The solids were acid-digested using nitric and hydrochloric acids. Insoluble solids developed upon dilution with 0.5 M HNO3, corresponding to an average 6.5 wt% of the initial dry solids content. The acid digestate and insoluble solids were analyzed separately by gamma spectrometry. Nominally, 7.7% of the 60Co was present in the insoluble solids; less than 1% of other gamma-emitters (i.e., 137Cs, 154/155Eu, and 241Am) were present in the insoluble solids. Aliquots of the acid digestate were analyzed directly using gamma energy analysis (GEA) and after separations for 238Pu, 239+240Pu, 237Np, and 241Am radioisotopes using alpha energy analysis (AEA). The 90Sr was measured by liquid scintillation counting (LSC) on the Sr-separated fraction. The plutonium isotopic distribution of the acid digestate was analyzed following Pu separations by thermal ionization mass spectrometry (TIMS). A table summarizes the results for the primary and duplicate samples. The 239+240Pu concentration (µCi/g dry) relative to 90Sr and to 137Cs concentrations (µCi/g dry) was examined. The K West Basin sludge has a 239+240Pu/90Sr ranging from 0.1 to 1.2 and the 239+240Pu/137Cs ratio ranging from 0.10 to 0.47. In contrast, the sand filter backwash solids 239+240Pu/90Sr ratio was 10.6 and the 239+240Pu/137Cs ratio was 2.0. The ratio differences indicate a relative enhancement of the Pu concentration in the sand filter solids relative to the 137Cs and 90Sr sludge concentrations currently in the K West Basin. A dose-to-curie radioisotope evaluation of the sand filter waste form may need to consider this dissimilarity.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
OSTI Identifier:
1244800
Report Number(s):
PNNL--25241
830403000; TRN: US1601170
DOE Contract Number:
AC05-76RL01830
Resource Type:
Technical Report
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; CESIUM 137; STRONTIUM 90; AMERICIUM 241; EUROPIUM 154; EUROPIUM 155; PLUTONIUM 238; PLUTONIUM 239; PLUTONIUM 240; NEPTUNIUM 237; SLURRIES; CONCENTRATION RATIO; SOLIDS; FILTERS; MASS SPECTROSCOPY; SAND; GAMMA SPECTROSCOPY; ABUNDANCE; PLUTONIUM; SLUDGES; HYDROCHLORIC ACID; NITRIC ACID; SCINTILLATION COUNTING; MASS; WEIGHT; RADIOACTIVE WASTE DISPOSAL; BATTELLE PACIFIC NORTHWEST LABORATORIES; RADIOACTIVE MATERIALS; QUANTITATIVE CHEMICAL ANALYSIS K Basin; sand filter; north load-out pit; backwash