Microbial Characterization for the Source-Term Waste Test Program (Sttp) at Los Alamos Page: 4 of 17
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MICROBIAL CHARACTERIZATION FOR THE SOURCE-TERM WASTE
TEST PROGRAM (STTP) AT LOS ALAMOS
Patricia A. Leonard', Betty A. Strietelmeierl, M. E. Pansoy-Hjelvik2, and Robert
Villarreal2
Chemical Science and Technology Division' and Nuclear Materials Technology
Division2
Los Alamos National Laboratory, Los Alamos, New Mexico 87545
ABSTRACT:
Microbes have been found to inhabit almost any subsurface environment,
including areas once thought to be too hostile for any life forms to exist. The effects of
microbial activity on the performance of the proposed underground nuclear waste
repository, the Waste Isolation Pilot Plant (WIPP) at Carlsbad, New Mexico are being
studied at Los Alamos National Laboratory (LANL) as part of an ex situ large-scale
experiment. Actual actinide-containing waste is being used to predict the effect of
potential brine inundation in the repository in the distant future. The study conditions are
meant to simulate what might exist should the underground repository be flooded
hundreds of years after closure as a result of inadvertent drilling into brine pockets below
the repository. The Department of Energy (DOE) selected LANL to conduct the Actinide
Source-Term Waste Test Program (STTP) to confirm the predictive capability of
computer models being developed at Sandia National Laboratory. The project consists of
15 drum-scale test vessels containing heterogeneous wastes, 33 liter-scale vessels with
homogeneous wastes, and six pressurized containers. Testing of the vessel contents has
included assays of the actinide elements and measurements of the headspace gases
generated by the transuranic waste immersed in brines that are chemically similar to
those found in the salt formation in which the WIPP repository is located. The waste is
representative of inventories that currently are stored temporarily at several DOE sites
nationwide. In addition, the test containers were inoculated with a microbial population
obtained from the hypersaline brine environment near the WIPP site. We have focused on
three major activities with regard to this microbial population: 1) viability of the
organisms in the liter-scale containers more than two years after inoculation, 2) microbial
contribution to gas generation, and 3) the toxic effects of magnesium oxide, a material
being considered for use as a backfilled barrier at the repository. Our studies of recent
brine samples revealed little or no growth under the conditions chosen, but the absence of
viable, but nonculturable cells could not be ruled out. Microbial cells are surmised to be
present as a biofilm coating the surface of the sludge material in the test containers,
which therefore were not sampled in the liquid column to any great extent. We utilized
fluorescent staining techniques that detect viable, respiring organisms. Low levels of
microbes were detected with these staining procedures in the liquid column of vessels
prepared with waste organics. Other experiments investigated the effect of radiolysis on
the generation of gases in the test containers. Large amounts of nitrous oxide detected in
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Leonard, P. A.; Strietelmeier, B. A.; Pansoy-Hjelvik, M. E. & Villarreal, R. Microbial Characterization for the Source-Term Waste Test Program (Sttp) at Los Alamos, report, April 1, 1999; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc678680/m1/4/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.