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J Environ Radioact. 2014 Nov;137:163-172. doi: 10.1016/j.jenvrad.2014.07.011. Epub 2014 Jul 28.

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

Author information

1
G. T. Seaborg Institute and Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550, USA. Electronic address: zhao1@llnl.gov.
2
Earth Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.
3
G. T. Seaborg Institute and Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550, USA.

Abstract

A high sensitivity analytical method for (237)Np analysis was developed and applied to groundwater samples from the Nevada National Security Site (NNSS) using short-lived (239)Np as a yield tracer and HR magnetic sector ICP-MS. The (237)Np 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 (237)Np concentrations are well below the drinking water maximum contaminant level for alpha emitters identified by the U.S. EPA (560 mBq/L). Nevertheless, (237)Np remains an important indicator for radionuclide transport rates at the NNSS. Retardation factor ratios were used to compare the mobility of (237)Np to that of other radionuclides. The results suggest that (237)Np is less mobile than tritium and other non-sorbing radionuclides ((14)C, (36)Cl, (99)Tc and (129)I) as expected. Surprisingly, (237)Np and plutonium ((239,240)Pu) 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, (237)Np is migrating downgradient from NNSS underground nuclear tests at very low but measureable concentrations.

KEYWORDS:

Environment; Neptunium analysis; Nevada National Security Site; Retardation; Ultra-low level

PMID:
25078472
DOI:
10.1016/j.jenvrad.2014.07.011
[Indexed for MEDLINE]
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