A Radiochemical Analyses of Metastudtite and Leachates from Spent Fuel
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A Radiochemical Analyses of Metastudtite and Leachates from Spent Fuel Bruce McNamara, Brady Hanson, Edgar Buck, Chuck Soderquist Radiochemical Processing Laboratory, Pacific Northwest National Laboratory 902 Battelle Blvd., Richland, WA 99352, USA [email protected] ABSTRACT We have characterized considerable amounts of the two known uranyl peroxide phases that formed under static immersion conditions on commercial spent nuclear fuel (CSNF) samples. Milligrams of corroded fuel aggregates were observed at the air-water interface in each sample. The bulk fuel and the interfacial solids were examined by SEM, EDX, and XRD and were found to contain studtite and metastudtite, respectively. The reason for the partitioning of the two phases is not clear at this time. The unique occurrence of the floating phase prompted a radiochemical analysis of these solids. The analysis indicated that 90Sr, 137Cs, 99Tc, and to a lesser extent of 238,239Pu and 237Np, had partitioned with the air-water interface aggregates. The concentration of 241Am in the interfacial solids was two orders of magnitude lower than the inventory in the fuel prior to contact with water. The radiochemical analyses of two fuel leachate samples are compared to reported leaching data of a similar fuel which did not result in the formation of studtite. INTRODUCTION The structure of studtite [(UO2)(O2)•(H2O)2](H2O) 2 has recently been characterized by Burns and by that author’s account, studtite and metastudtite (UO4•2H2O) are the only known peroxide-containing minerals [1]. Experimental conditions that gave rise to formation of studtite and metastudtite on commercial spent fuel have been reported by McNamara [2]. An apparent phase separation of studtite and metastudtite in several samples held at 25-28°C, was also described. Studtite was found as mats of brittle, tightly packed, single crystals on the particles of fuel, while metastudtite was found at the air-water interface as an intertwined mat of fibrous crystals. This paper describes the results of radiochemical analyses of the metastudtite aggregates that were collected from the air-water interface and also reports the analyses of the sample leachates. The starting CSNF powders had previously been characterized by Wilson [3] and a more recent partial analysis of the radionuclide inventory was carried out. In all cases, the measured concentrations validated calculated inventory values [4]. EXPERIMENTAL The starting material was a low burn-up fuel (27.7 MWd/kgM ) that had been discharged from the H.B. Robinson pressurized water reactor, located in Hartsville, South Carolina, approximately 30 years ago. The fuel was cut, sectioned, crushed and sieved in 1983 [4]. The particle size range retained for these experiments ranged from 100 to 500 um. The CSNF used was the same used in static dissolution tests reported by Wilson in 1985 [3]. The radiochemical inventory for the fuel has been updated in Table I to reflect the full period of discharge as of 2004. Additionally, a newly measured radionuclide i
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