Activity and weight ratios of cesium, uranium, plutonium, and curium isotopes based on elaborate inventory calculations of Fukushima Dai-ichi NPP units 1 to 3

Abstract

ABSTRACT For the reactor cores just before the accident of Fukushima Dai-ichi NPP (FDNPP) units 1 to 3, the core average activity ratios of 134Cs/137Cs, 238Pu/(239Pu+240Pu), and 242Cm/(243Cm+244Cm) and the weight ratios of 235U/238U, 240Pu/239Pu, and 241Pu/239Pu were evaluated applying the nuclide inventories calculated with CASMO5 based on the detailed assembly specifications and the assembly-axial burnup histories and correcting the calculated inventories with the biases of the inventory calculations. The obtained activity and weight ratios were compared with those evaluated with the preceding inventory calculations with ORIGEN2.2. The present 134Cs/137Cs activity ratios were smaller by 3% to 5% than those with ORIGEN2.2. The measured results of the activity and weight ratios in the samples taken from the contaminated water in the plant facilities and the soil, dust, and others inside and outside of FDNPP were distributed around the calculated core average values, while some of them were deviated from them. The 240Pu/239Pu weight ratios can be used to distinguish the radioactive materials originating from unit 2 from those from unit 3 assuming that the measured results represent the core average values.