The summary of this report is: (1) biogenic flux increases as hydrologic residence time decreases; (2) reaction-based reactive transport modeling can capture this effect; (3) solid-phase Fe(III) bioreduction can be sustained at long residence times in natural sediments; and (4) long-term coupled Fe(III)/U(VI) bioreduction can be sustained in natural sediments.

Analysis of the Genetic Potential and Gene Expression of Microbial Communities Involved in the In Situ Bioremediation of Uranium and Harvesting Electrical Energy from Organic Matter The primary goal of this research is to develop conceptual and computational models that can describe the functioning of complex microbial communities involved in microbial processes of interest to the Department of Energy. Microbial Communities to be Investigated: (1) Microbial community associated with the in situ bioremediation of uranium-contaminated groundwater; and (2) Microbial community that is capable of harvesting energy from waste organic matter in the form of electricity.

The objective of this report is to understand fundamental biogeochemical processes that would allow for the use of bioremediation approaches for cleaning up, managing, or understanding fate and transport at DOE's contaminated legacy waste sites.

The hypothesis of this report is Mobile radionuclides in low-permeability porous matrix regions of fractured saprolite can be effectively isolated and immobilized by stimulating localized in-situ biological activity in highly-permeable fractured and microfractured zones within the saprolite.

None

The primary objective of this report is to evaluate the rates and mechanisms of U(VI) reduction by microbial populations.

The purposes of this report are to: (1) to determine how flow and transport influence the distribution of U(VI) under field-relevant conditions and the transfer of reductive equivalents to the aqueous and solid phases by DMRB; and (2) to examine the solid-phase stability of bioreduced uranium phases--effects of mass transfer on reoxidation of U(IV) by O{sub 2} and other oxidants (e.g., NO{sub 3}{sup -}, denitrification products).

Cr alloys containing 0-30 weight % W were investigated for their high temperature strength and oxidation resistance. These experimental alloys are intended for use in elevated temperature applications. Alloys were melted in a water-cooled, copper-hearth arc furnace. Microstructure of the alloys was studied using X-ray diffraction, scanning electron microscopy, and light microscopy. Meyer and Vickers hardness tests were utilized for measuring room temperature strength. A hot hardness tester with a spherical ruby indenter was used to study the strength of these materials between 800ºC and 1200ºC. A parabolic relationship was observed between load and indent size at all temperatures. On the other hand, decrease in hardness of the alloys with temperature was linear up to 1200ºC.

This research hypotheses is: (1) Indigenous microorganisms in the shallow aquifer at the FRC have the capability to reduce U(VI) and Tc(VII) but rates are limited by--Scarce electron donor, Low pH and potentially toxic metals, and High nitrate. (2) U(VI) and Tc(VII) reduction rates can be increased by--Successive donor additions, Raising pH to precipitate toxic metals, and Adding humics to complex toxic metals and serve as electron shuttles.

Past studies demonstrate that complexation will limit abiotic and biotic U(VI) reduction rates and the overall extent of reduction. However, the underlying basis for this behavior is not understood and presently unpredictable across species and ligand structure. The central tenets of these investigations are: (1) reduction of U(VI) follows the electron-transfer (ET) mechanism developed by Marcus; (2) the ET rate is the rate-limiting step in U(VI) reduction and is the step that is most affected by complexation; and (3) Marcus theory can be used to unify the apparently disparate U(VI) reduction rate data and as a computational tool to construct a predictive relationship.