Analysis of Savannah Survey Sediment Collections of 30 Sep 04

Wimer, N ; Hutcheon, I ; Esser, B ; Ramon, E

Lawrence Livermore National Laboratory

关键词: Uranium Isotopes;    Lawrence Livermore National Laboratory;    Uranium;    Gamma Spectroscopy;    Sediments;   

DOI  :  10.2172/15015143
RP-ID  :  UCRL-TR-208419
RP-ID  :  W-7405-ENG-48
RP-ID  :  15015143

美国|英语

来源: UNT Digital Library

【 摘 要 】

This report summarizes laboratory radiochemical analyses of sediment samples collected by the Defense Threat Reduction Agency during the DoD Savannah Survey operations of Sep 04. The analytic goal was to determine if Wassaw Sound sediment collections of 30 Sep 04 display evidence for local anthropogenic uranium, as distinct from the recognized regional background stemming from the Savannah River Site (SRS). Radiochemical methods were selected to maximize detection sensitivity for such anthropogenic uranium. Within the suite of twelve collections, there would be evidence for a localized source if individual collections were to differ from the population as a whole. If in fact non-natural uranium were observed, definitive determination of whether the source was SRS effluent or a localized release would likely involve additional field sampling. These collections were logged by the LLNL Forensics Science Center, photographed, and laboratory chain-of-custody was begun. The inventory received at LLNL is reported in Table 1. The separate collections were not assigned any relative priority among them. LLNL has separately reviewed detailed records of the item in question, and determined what materials are involved and what radiochemical assays are of value. Attempting quantitative estimates of source-item material release, transport, and collection levels would be quite uncertain. Rather, present assays examine for departure from natural background isotopic compositions. To summarize the findings, analyses for all collections displayed natural uranium isotopic composition--considering the {sup 238}U/{sup 235}U and {sup 236}U/{sup 235}U ratios--within measurement uncertainties, which were quite low. No one collection or set of collections stood apart from the others in its uranium isotopes. These {sup 238}U/{sup 235}U data uncertainty levels also determined with 99.5% confidence (a three-standard-deviation determination) that no more than 0.46% of the total uranium present in the Savannah Survey collections could be depleted uranium. Based on gamma spectroscopy assays of {sup 137}Cs specific activity (Becquerels per kilogram), no collection displayed {sup 137}Cs content levels above background levels present in the natural marine/riverine environment. Therefore, there is no measurable detection of Savannah River Site effluent in these collections based on {sup 137}Cs assay.