The Nevada Nuclear Waste Storage Investigations Program of the Department of Energy is investigating Yucca Mountain in the Nevada Test Site as a possible repository location. As part of this investigation, the groundwater from all pumped wells in and near the site has been sampled and analyzed; the results are reported in this document. The speciation and solubility of nuclear waste elements in these groundwaters have been calculated using the EQ3/6 computer code. Estimates have also been made of the pH and Eh buffering capacity of the water/rock system of Yucca Mountain.

The most likely mechanism for release of radionuclides from a repository is transport in water from the repository to the accessible environment. The processes that can retard the movement of radionuclides in water are sorption, precipitation, and diffusion. These processes can occur anywhere along flow paths from the repository to the accessible environment.

This report summarizes the contribution of the Los Alamos National Laboratory to the Nevada Nuclear Waste Storage Investigations for the second quarter of FY 1983. The status of the following studies is reported: field experiments on nuclide migration in tuff; geochemistry of tuff; mineralogy-petrology of tuff; volcanism; rock physics; shaft and borehole sealing; exploratory shaft; and quality assurance.

Examples of data from International Atomic Energy Agency (IAEA) leach tests on spent fuel elements are shown that were displayed, not in the recommended manner in the IAEA leach test, but in the manner of the modifications of this leach test. The main difference in the display methods is in the plotting of incremental leach rates as a function of cumulative time of leaching rather than as a function of the mean time of leaching of each individual sample. This difference in display can lead to wrong conclusions if the display methods are not carefully considered.

Considerable information useful in nuclear waste storage can be gained by studying the conditions of uranium ore deposit formation. Further information can be gained by comparing the chemistry of uranium to nuclear fission products and other radionuclides of concern to nuclear waste disposal. Redox state appears to be the most important variable in controlling ura¬ nium solubility, especially at near neutral pH, which is characteristic of most ground water. This is proba¬ bly also true of neptunium, plutonium, and technetium. Further, redox conditions that immobilize uranium should immobilize these elements. The mechanisms that have produced uranium ore bodies in the Earth's crust are somewhat less clear. At the temperatures of hydrothermal uranium deposits, equilibrium models are probably adequate, aqueous ura¬ nium (VI) being reduced and precipitated by interaction with ferrous-iron-bearing oxides and silicates. In lower temperature roll-type uranium deposits, overall equilibrium may not have been achieved. The involve¬ ment of sulfate-reducing bacteria in ore-body formation has been postulated, but is uncertain. Reduced sulfur species do, however, appear to be involved in much of the low temperature uranium precipitation.

Work at the Los Alamos Scientific Laboratory on the fundamental solution chemistry of the actinides has thus far been confined to preliminary considerations of the problems involved in developing an understanding of the precipitation and dissolution behavior of actinide compounds under environmental conditions. Attempts have been made to calculate solubility as a function of Eh and pH using the appropriate thermodynamic data; results have been presented in terms of contour maps showing lines of constant solubility as a function of Eh and pH. Possible methods of control of the redox potential of rock-groundwater systems by the use of Eh buffers (redox couples) is presented.

In the early part of this decade, a research effort was initiated at the Los Alamos Scientific Laboratory (LASL) to investigate the feasibility of utilizing proton-induced spallation reactions as a means of preparing radionuclides of known or potential value in the health sciences. The irradiation source consists of the excess 800 MeV proton beam that reaches the main beam stop of the Clinton P. Anderson Meson Physics Facility (LAMPF). A description is given of the LAMPF accelerator and the Isotope Production Facility.

The Isotope Production Facility is an experimental area in which targets are irradiated with a proton beam to produce, by spallation reaction, a variety of radioisotopes for medical research. The method of operation and the equipment used to support the target experiments are discussed in this paper. The facility has been in operation for approximately two years, with irradiation exposures \u003e 200 mA/h on a molybdenum target.

Strontium-82, produced by spallation reaction with medium-energy proton beams, was used to evaluate Bio-Rex 70 and Chelex-100 ion-exchange resins for use in a compact Rb-82 generator. Adsorption of Sr-82 to the resin column, Rb-82 elution yields, Sr breakthrough, and 82Rb-Sr separation factors were determined for newly prepared columns and for longterm elution conditions. Separation factors of 10(7) to 10(8) were obtained with 2% NaCl elutions from Bio-Rex 70 resin columns while the separation factors was about 5 X 10(4) with the Chelex-100 resin column.