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Title: Analysis of trace neptunium in the vicinity of underground nuclear tests at the Nevada National Security Site

A high sensitivity analytical method for 237Np analysis was developed and applied to groundwater samples from the Nevada National Security Site (NNSS) using short-lived 239Np as a yield tracer and HR magnetic sector ICP-MS. The 237Np concentrations in the vicinity of the Almendro, Cambric, Dalhart, Cheshire, and Chancellor underground nuclear test locations range from <4 × 10-4 to 2.6 mBq/L (6 × 10-17–4.2 × 10-13 mol/L). All measured 237Np concentrations are well below the drinking water maximum contaminant level for alpha emitters identified by the U.S. EPA (560 mBq/L). Nevertheless, 237Np remains an important indicator for radionuclide transport rates at the NNSS. Retardation factor ratios were used to compare the mobility of 237Np to that of other radionuclides. The results suggest that 237Np is less mobile than tritium and other non-sorbing radionuclides (14C, 36Cl, 99Tc and 129I) as expected. Surprisingly, 237Np and plutonium (239,240Pu) retardation factors are very similar. It is possible that Np(IV) exists under mildly reducing groundwater conditions and exhibits a retardation behavior that is comparable to Pu(IV). Independent of the underlying process, 237Np is migrating downgradient from NNSS underground nuclear tests at very low but measureable concentrations.
Authors:
 [1] ;  [2] ;  [1] ;  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Grant/Contract Number:
AC52-07NA27344
Type:
Published Article
Journal Name:
Journal of Environmental Radioactivity
Additional Journal Information:
Journal Volume: 137; Journal Issue: C; Journal ID: ISSN 0265-931X
Publisher:
Elsevier
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; ultra-low level; Neptunium analysis; environment; Nevada National Security Site; retardation
OSTI Identifier:
1197796
Alternate Identifier(s):
OSTI ID: 1201503