Estimated nuclide activity of nuclear fuel in the core of the Fukushima Daiichi Unit 1

Activity of nuclides in the nuclear fuel at the time of an event initiating the transition from normal reactor operation to an accident is seen as important input data supporting the modeling of subsequent nuclide behavior in the reactor and radioactive releases. This study calculates the activity of the main dose contributing actinides and fission products in the nuclear fuel from the core of the Fukushima Daiichi NPP Unit 1 based on the SOCRAT/V3 code designed to model severe NPP accidents. The paper compares SOCRAT/V3 calculations with those based on ORIGEN2 and SWAT. The paper shows that qualitatively SOCRAT/V3 correctly reproduces the changes in the activity of the considered nuclides and the error for most of them does not exceed 20%.