Release behavior of Cs and its chemical form during late phase of fukushima daiichi nuclear power plant accident
In order to understand what happened in reality during the Fukushima Daiichi nuclear power plant accident,the phenomena within reactor pressure vessel(RPV)and their discussion with the data of environmental radiation are very important.However,there are few studies with these points of view even six years has passed since the accident.It should be also pointed out that the release behavior of cesium(Cs)has not been examined so far from an aspect of its chemical forms.For this reason,the present study focused on the release mechanisms and chemical forms of 137Cs after March 17-the day when the core state became relatively more stable than before,using the data and information published until now.Concerning the Cs behavior in the RPV,we estimated it based on thermo-hydraulic data in the RPV during the accident,referring to the information of the PHEBUS/FPT3 test on the core degradation with the B4C absorbers.As for the source terms,we referred to the previously-published reports,which evaluated them reversely by the atmospheric dispersion code,WSPEEDI,with the monitoring data at Tokai.It was found that the excess release of 137Cs over 131I,i.e.decrease in the 131I/137Cs ratio,occurred several times for a certain duration after March 17.In addition,a report on the environmental monitoring showed that gaseous 137Cs was measured before March 29 but not after March 30 while the concentration of particulate 137Cs increased drastically after March 30.Based on these findings,it can be inferred that the chemical form of CsBO2 was produced in the RPV by a reaction with the B4C absorbers and that the release of CsBO2 occurred during the Fukushima accident as that had happened in the PHEBUS/FPT3 test.
Fukushima Daiichi nuclear power plant accident source terms 131I/137Cs ratio CsBO2 B4C absorbers PHEBUS/FPT3 test environmental radiation monitoring
Akihide HIDAKA Hiroya YOKOYAMA
Nuclear Human Resource Development Center,Japan Atomic Energy Agency,2-4 Shirakata,Tokai-mura,Naka-gun,Ibaraki 319-1195,Japan
国际会议
沈阳
英文
29-42
2017-09-26（万方平台首次上网日期，不代表论文的发表时间）