An attempt to confirm the origin of Xe135 detected in the Fukushima Daiichi II Nuclear Power Plant in November 2011

Abstract

► The 135 Xe production due to fission processes in the Fukushima Unit 2 was calculated. ► The uncertainties in the isotopic concentration and xenon activity were calculated. ► A indicator for evaluation of the neutronic condition of the damaged fuel was defined. ► The spontaneous fission process was the unique responsible for xenon production. ► There is no evidence of recriticality in the damaged nuclear reactor. The recent detection of 135 Xe activity opens doubts about the evidence of nuclear recriticality in Fukushima Daiichi Nuclear Power Plant – Unit 2. The nuclear plant operator, after some investigation, reported that the measured concentration would be consequence from spontaneous fission process from damaged fuel. This work aims to perform an independent calculation to confirm the origin of 135 Xe activity measured. The 135 Xe activity calculated was compared to the experimental measurements accomplished by TEPCO. The comparison between the value obtained experimentally and the value calculated in this work, for 135 Xe activity, shows that the spontaneous fission process of actinides, presents in the nuclear fuel, was the unique responsible for the production of xenon, since the value of the xenon activity is within the range of uncertainties calculated in this work. It was also defined in this work a complementary indicator for the assessment of the neutronic condition of the nuclear fuel, based on the ratio between the activities of 135I and 135 Xe. From this result, one can conclude that there is no evidence of recriticality in the damaged reactor.