[en] ⁹⁹Tc and ¹²⁹I are important contributors to risk assessment due to their long half-lives and high mobility as aqueous anionic species. We analyzed ⁹⁹Tc and ¹²⁹I in groundwater samples in and near 11 underground nuclear tests and in melt glass and rock samples retrieved from the Chancellor test cavity, Nevada Test Site. The ¹²⁹I/¹²⁷I ratio ranges from 10^-3 to 10^-6 in cavity water and 10^-4 to 10^-9 in satellite wells. The ⁹⁹Tc concentration ranges from 3 to 10^-4 Bq/L in cavity waters and from 0.3 to 10^-4 Bq/L in satellite wells. Downstream migration is apparent for both radionuclides. However, it is affected by both retardation and initial distribution. In-situ ⁹⁹Tc and ¹²⁹I K_ds calculated using rubble and water concentrations are 3 to 22 mL/g and 0 to 0.12 mL/g, respectively and are suggestive of mildly reducing conditions. ¹²⁹I distribution in the melt glass, rubble and groundwater of the Chancellor test cavity is 28%, 24% and 48%, respectively; for ⁹⁹Tc, it is 65%, 35% and 0.3%, respectively. Our partitioning estimates differ from those of underground tests in French Polynesia, implying that fission product distribution may vary from test to test. Factors that may influence this distribution include geologic conditions (e.g. lithology, water and CO₂ content) and the cooling history of the test cavity

[en] The application of ultra-sensitive heavy isotope measurements continues to expand in a variety of fields relevant to the management of nuclear materials, including nuclear isotope forensics and radiobioassay. We have developed a heavy isotope accelerator mass spectrometry (AMS) system at Lawrence Livermore National Laboratory's (LLNL) Center for Accelerator Mass Spectrometry (CAMS). The system was designed particularly for the measurement of actinide concentrations and isotopic ratios, but also allows the measurement of other heavy isotopes such as ¹²⁹I. The system includes a fast isotope switching capability that allows flexibility in isotope selection and for the quasi-continuous normalization to a reference isotope spike. Current background levels for ²³⁹Pu and ²⁴⁰Pu are equivalent to <10⁶ atoms and measurements of known materials indicate that our ²³⁹Pu and ²⁴⁰Pu measurements are accurate and precise for samples containing from ∼10¹² atoms down to the Bq level (∼10⁶ atoms). Recent exploitation of the fast isotope switching capability has allowed the quasi-simultaneous measurement of several Pu isotopes in individual samples. Our AMS measurement capability has been extended to U isotopes, with particular emphasis on ²³⁶U. Our current ²³⁶U background level is equivalent to ∼10⁶ atoms and the linear measurement range is 5-6 orders of magnitude. We have also utilized our Heavy Isotope AMS system for the measurement of ¹²⁹I. Initial measurements of available low level samples show that background contributions for 1 mg I samples are below ¹²⁹I/¹²⁷I levels of ∼10^-14, and measurements of prepared standard samples demonstrates linear measurement response to ¹²⁹I/¹²⁷I levels greater than 10^-10. The AMS technique provides high rejection of interferences, including molecular interferences, and low susceptibility to matrix components, both of which are of particular relevance to the measurement of complex sample matrices. The attendant significant reductions of demands on sample preparation chemistry allow relatively simple, cost-effective procedures to be employed. When such sample preparation improvements are combined with the high sample throughput capabilities of our AMS system, the result is a rapid and cost-effective measurement technique for heavy isotopes in a wide range of studies

[en] This report describes FY 2005 technical studies conducted by the Chemical Biology and Nuclear Science Division (CBND) at Lawrence Livermore National Laboratory (LLNL) in support of the Hydrologic Resources Management Program (HRMP) and the Underground Test Area Project (UGTA). These programs are administered by the U.S. Department of Energy, National Nuclear Security Administration, Nevada Site Office (NNSA/NSO) through the Defense Programs and Environmental Restoration Divisions, respectively. HRMP-sponsored work is directed toward the responsible management of the natural resources at the Nevada Test Site (NTS), enabling its continued use as a staging area for strategic operations in support of national security. UGTA-funded work emphasizes the development of an integrated set of groundwater flow and contaminant transport models to predict the extent of radionuclide migration from underground nuclear testing areas at the NTS. The report is organized on a topical basis and contains five chapters that highlight technical work products produced by CBND. However, it is important to recognize that most of this work involves collaborative partnerships with the other HRMP and UGTA contract organizations. These groups include the Energy and Environment Directorate at LLNL (LLNL-E and E), Los Alamos National Laboratory (LANL), the Desert Research Institute (DRI), the U.S. Geological Survey (USGS), Stoller-Navarro Joint Venture (SNJV), and Bechtel Nevada (BN)