Radionuclides release behaviors unique to the Fukushima Daiichi Nuclear Power Plants accident

Hidaka, Akihide   

During the Fukushima Daiichi NPP accident, I-131 release could have occurred from a large amount of contaminated water in the basements of Units 2 and 3 reactor buildings because of the gas-liquid partition of I-131 and steam generation from the accumulated water by decay heat. The chemical form of certain fraction of released Cs could have been CsBO, which was formed by reaction of CsOH with the boron originated from the BC absorbers. The chemical form could affect not only the Cs-137 source term but also the environmental transport behavior. Te-129m release behavior showed that the release from the containment vessel could be affected by the difference in failure location between the top or middle height of drywell without pool and the bottom of suppression pool where the pool scrubbing is expected. These findings have never been considered in most of the existing severe accident codes such as MELCOR that have been developed based on the findings of the TMI-2 accident.