TRACE ELEMENT AND ISOTOPIC ANALYSIS OF URANIUM ORE AND ORE CONCENTRATES: IMPLICATIONS FOR FRACTIONATION OF FORENSIC SIGNATURES IN THE NUCLEAR FUEL CYCLE

Yellowcake, or uranium ore concentrate (UOC) represents an important intermediate material in the nuclear fuel cycle. The importance of extracting chemical and isotopic information regarding provenance from UOCs and other U-oxide materials for the purpose of source attribution has been well established in the field of nuclear forensics. Several samples of UOC and uraninite (UO_2+x) have been analyzed for trace element and isotopic signatures. Materials under investigation originate from sandstone hosted roll-front U deposits of the Powder River Basin (PRB) U province in Wyoming, USA. Trace element analyses conducted using ICP-MS reveal that no significant fractionation of rare earth elements (REEs) occurs during the extraction and separations processes. Identical REE signatures are observed regardless of the sample introduction method (laser ablation vs. solution mode) or ICP-MS instrument (Thermo Fisher Scientific Element 2 vs. Nu Instruments Attom) employed. In addition to trace element signatures, U isotope systematics are important indicators of deposition and alteration environments. ²³⁸U/²³⁵U ratios indicate the degree to which redox chemistry is responsible for U ore deposits and ²³⁵U/²³⁴U ratios represent the extent of post-depositional aqueous alteration. ²³⁸U/²³⁵U and ²³⁵U/²³⁴U ratios for UOCs from the PRB have been investigated with MC-ICP-MS and these indicate relatively unaltered, low temperature redox deposits.