Canisters lifetime

Duijvestijn 1994) are extremely conservative and a more realistic estimate of the canister lifetime (which is well supported by extensive natural analogue studies, discussed below) would be about 10 years. 

These are now considered in turn, emphasising the effects of selecting more conservative values. The canister lifetime (in terms of loss of containment) of 10 years is considered to be very conservative with respect to the assumed corrosion rate which is, in itself very conservative in the light of natural analogue data... 

Zielinska et al. (1996) and Kelly and Holdren (1995) have summarized the stability in canisters of organics, some of which are U.S. EPA designated HAPs (hazardous air pollutants). Kelly and Holdren propose that for compounds whose stability in canisters is not known, estimates can be made based on species of similar physical and chemical characteristics. These characteristics include their vapor pressure, polarizability, water solubility, Henry s law coefficient in water, and estimated lifetimes with respect to reactions in air and in the aqueous phase. 

Under the conditions to be expected in deep granitic ground-water copper is thermodynamically stable. Considering possible oxidation mechanisms and the concentrations of potential oxidants in the ground the lifetime of the copper canister around the SUF would be at least several hundred thousand years before penetration occurs, probably more than a million years (13). 

The basic design and operation of the MDI has changed little over its lifetime. Aerosols are generated from a formulation of drug (0.1-1% w/w) either suspended or in solution in the liquefied propellant. The formulation is held under pressure in a canister. 

For long term storage ( 10 y) the fuel elements must be recanned. For this purpose single fuel elements or bundles are placed in cylindrical containers, and the void is filled with some suitable material like lead, which has good heat conductivity and also provides some radiation protection. Depending on the external condition at the final storing place (humidity, temperature, etc.) the canisters are surrounded by an additional container to improve the lifetime of the fuel elements, which — preferably — should not be exposed to the biosphere until all radioactivity has disappeared. 

Water reaches the disposal drifts via small fractures, and saturates bentonite in a few decades. Minimum container lifetime due to anaerobic general corrosion is 20,000 years, although in the evaluation it is assumed that a few (up to 10) canisters fail much earlier due to a fabrication defect. After canister failure, and since no credit is given to the cladding as a barrier, there is an instantaneous release of some volatile radionuclides, such as C1 and Cs. When the water reaches the waste, the gradual release of the radionuclides in the UO2 matrix starts. 

In this chapter, the point defect model (PDM), describing the formation and breakdown of passive films, is reviewed and developed. It is shown how important model parameters can be extracted from experimental impedance data and used to calculate the steady-state barrier layer thickness and passive current density as a function of voltage. In particular, the model is used to define the mechanism of the formation of CU2S on Cu in sulfide-containing brine. The present studies were conducted to provide a scientific basis for estimating the lifetimes of copper canisters in crystalline rock repositories in Sweden for the disposal of high level nuclear waste (HLNW). 

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