K West Basin Sand Filter Backwash Sample Analysis

Fiskum, Sandra K.¹  Smoot, Margaret R.¹  Coffey, Deborah S.¹  Pool, Karl N.¹ 

[1] Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

关键词: CESIUM 137;    STRONTIUM 90;    AMERICIUM 241;    EUROPIUM 154;    EUROPIUM 155;    PLUTONIUM 238;    PLUTONIUM 239;    PLUTONIUM 240;    N;   

DOI  :  10.2172/1244800
RP-ID  :  PNNL--25241
PID  :  OSTI ID: 1244800
Others  :  Other: 830403000
Others  :  TRN: US1601170

美国|英语

来源: SciTech Connect

【 摘 要 】

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 samples (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 (??Ci/g dry) relative to ⁹⁰Sr and to ¹³⁷Cs concentrations (??Ci/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.