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 (γ 0.9 Gy h−1), inventory fraction leaching rates of fission-products (137Cs, 90Sr and 99Tc) and actinides (238U, 237Np) 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 238U, 90Sr, 99Tc and 237Np 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 μm per year, respectively. The observation of insignificant dissolution of spent fuel in the leaching solution equilibrated with 0.1 atm H2 is explained by the reducing effects of H2 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.
