Leaching of actinide elements from simulated fuel debris into seawater

For the prediction of the leaching behavior of actinide elements contained in the fuel debris that has arisen from the severe accident in Fukushima Daiichi Nuclear Power Station (NPS), a simulated fuel debris consisting of UO₂-ZrO₂ solid solution doped with ¹³⁷Cs, ²³⁷Np, ²³⁶Pu and ²⁴¹Am tracers was synthesized, and agitated leaching tests were conducted for the simulated fuel debris in seawater. The synthesized simulated fuel debris was immersed and shaken in natural seawater collected at a coast 11 km away from Fukushima Daiichi NPS. The brief leaching test conditions were T = 25 °C and solid-liquid ratio = 4 g/l, and the test duration was up to 31 days. The ratio of tracers leached into seawater from the simulated fuel debris by the agitated leaching test for 4 days was evaluated to be 0.09% for U, 0.01% for Np, 0.01% for Pu, 0.01% for Am and 35.39% for Cs by the or γ spectrometry of the soluble fraction. The leaching of actinides from the real fuel debris in reactor units 1-3 in Fukushima Daiichi NPS is expected to be suppressed in comparison with that from normal light water reactor spent fuel.