Environmental behaviors of spent nuclear fuel and canister materials

The world's first spent nuclear fuel repository concept (Swedish KBS-3) is illustrated and the results of experiments on environmental behaviors of spent fuel and canister materials under a potential canister breaching at early stage of disposal are reported. In a deoxygenated synthetic groundwater (2 mM NaHCO3) under radiation (gamma 0.9 Gy h(-1)), inventory fraction leaching rates of fission-products (Cs-137, Sr-90 and Tc-99) and actinides (U-238, Np-237) from a spent fuel segment were found to be around 10(-6) and 10(-7) per day, respectively. A cast-iron canister surface was found to be able to immobilize U-238, Sr-90, Tc-99 and Np-237 dissolved from spent fuel, but a copper surface could not. In the presence of the oxidative species generated from water radiolysis, the corrosion rates of waste canister materials, copper and cast-iron were found to be 1 and 30 mm per year, respectively. The observation of insignificant dissolution of spent fuel in the leaching solution equilibrated with 0.1 atm H-2 is explained by the reducing effects of H-2 in the presence of fission-product alloy particles (Mo-Tc-Ru-Rh-Pd) as catalysts and dissolved Fe(II) in groundwater. The coating effect of ferric precipitates on spent nuclear fuel dissolution is also discussed.