The design-basis, defense-related, transuranic (TRU) waste to be emplaced in the Waste Isolation Pilot Plant (WIPP) could, if sufficient H2O and nutrients were present, produce as much as 1,500 moles of gas per drum of waste. Gas production could pressurize the repository to lithostatic pressure (150 atm) and perhaps higher.Anoxic corrosion of Fe and Fe-base alloys and microbial degradation of cellulosics are the processes of greatest concern, but radiolysis of brine could also be important. The proposed backfill additives CaC03, CaO, CuSO4, KOH, and NaOH may remove or prevent the production of some of the expected gases. We describe these processes and present preliminary results of laboratory studies of anoxic corrosion and microbial activity.

Zirconium and Zircaloy-2 were found to gain more weight in oxygen than in water vapor at low pressures. The pretransition oxidation kinetics of Zircaloy-2 are comparable with those of pure zirconium, both following a cubic rate law. The pretransition oxidation kinetics of Zircaloy-2 are sensitive to water vapor pressure in the range of 5-25 mm, but are not sensitive to oxygen pressure. The post-transition oxidation kinetics of Zircaloy-2 are notably dependent on the pressure of either gas, indicating a gaseous diffusion rate control. Zirconium exhibited no transition in rate from the cubic over the duration of the exposure. It is shown that the rate-controlling mechanism which results in the cubic rate law is not directly dependent on the total thickness of the oxide layer. Activation energies for the rate-controlling mechanism of the cubic rate law lie in the range 50-63 kcal/mole, indicating that similar mechanisms are operative, regardless of material or atmosphere.

An effort to develop licensable engineered barrier systems for the longterm (~l,OOO yr) containment of nuclear wastes under conditions of deep continental geologic disposal has been underway at Pacific Northwest Laboratory since January 1979, under the auspices of the High-Level Waste Immobilization Program (HLWIP). This program is funded by the Division of Waste Products, U.S. Department of Energy. In the present work, the barrier system comprises the "hard" or structural elements of the package: the canister, the overpack(s), and the hole sleeve. A number of candidate metallic, ceramic, and polymeric materials are undergoing mechanical and corrosion screening tests to determine their potential usefulness in barrier-system applications. Materials demonstrating adequate properties in the screening tests will be subjected to more detailed property tests, and, eventually, cost/benefit analyses, to determine their ultimate applicability to barrier-system design concepts. Two titanium alloys were investigated in the mechanical property portion of the studies: Grade 2 (commercial purity) and Grade 12 (a titanium-nickelmolybdenum alloy). These alloys are considered prime candidates for barriersystem applications because of their already-demonstrated corrosion resistance in elevated-temperature corrosive environments. Tensile, impact, fracture toughness, and corrosion fatigue properties have been determined on both sheet and plate stock of these two alloys. It has been found that the mechanical properties of Grade 2 are superior to those of the Grade 12 alloy, except in the case of tensile and yield strengths. The comparisons include fatiguecrack-growth rate, fatigue-crack-growth rate in a simulated Hanford groundwater, fracture toughness, impact toughness, and dynamic fracture toughness. There is a significant difference in the fracture toughness behavior of the two a 11 oys. So far there is no evidence that presence of a simulated Hanford ground water at ~940C promotes the rate of crack growth in either material iii under fatigue conditions over conditions found in an air environment. The effect of other groundwater environments on corrosion fatigue-crack-growth rates has not yet been determined. Stressed specimen corrosion tests were used to evaluate the reaction of a number of candidate metallic barrier materials with two potential repository environments, i.e., a simulated Hanford ground water and a Waste Isolation Pilot Plant (WIPP) intrusion brine (NaCl-MgC1 2) at 250 0 C. The Hanford groundwater system involves a partially equilibrating slow flow of simulated ground water through crushed basalt at 250 0 C before the water is brought in contact with the corrosion specimens. Several oxygen levels have been examined. The brine studies utilize an essentially static autoclave system with occasional sampling. Corrosion samples of 300 and 400 series stainless steels, Inconels, Hastel loy C-276, titanium, Zircaloy, copper-nickel alloys and cast irons were prepared as U-bend specimens with simulated welds. These electric...

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Spent l i g h t water r e a c t o r f u e l contains radioisotopes t h a t present w i d e l y v a r y i n g degrees o f p o t e n t i a l hazard t o t h e biosphere. The f i s s i o n products, n o t a b l y and 13'cs, a r e responsible f o r t h e major p a r t o f the r a d i a t i o n and decay heat e v o l u t i o n f o r time periods ( a ) The "packageUordinarily comprises the spent fuel and those elements of the engineered barrier that are emplaced as a unit in the repository. I t ..includes the spent fuel, the stabilizer material (the medium lying between the inner canister wall and the spent fuel ) , the canister (the primary container), and the overpack (a canister container attached to the canister). The barrier system consists of the package, the hole sleeve(s), and the backfi 11 (embedment) medium.