Release of Radioactive Materials and the Evacuation of Residents

Abstract

This chapter discusses with the relation between the release of the radioactivity and the resident evacuation. The first half devoted to a precise, comparative analysis of the time evolution of the released background radiation level measured at the site boundary which reflects the behavior of the core melts, hydrogen explosions or containment vessel vents in the Unit 1 to Unit 3. The most significant finding is the effect of the SC vent, suggesting a decontamination coefficient of as much as 750.

The second part of this chapter discusses with the necessity of resident evacuation. I checked the radiation level and the timing of the release of the radioactivity and found that if Fukushima had followed ICRP recommendation of 20 mSv, the emergency evacuation order by the government at the midnight of the first day was not necessary. This is because the level at the residential area was far below this level. The highest background was resulted from Unit 2 direct release, and necessitated residence evacuation. It leads to a conclusion that should the SC vent of the Unit 2 be successful, no evacuation of the residents would have been needed.

Appendices

Appendices

1.1 Appendix 4.1

On December 13, 2013, I was finalizing this book, when TEPCO newly reported on the seawater injection situation. It said that the pipe that had been used to inject seawater into the reactor from the fire engine had several branch pipes, some of which had outlets at the turbine building. If so, the sealing of hose-connecting joints is no longer an issue. Radioactive materials must have leaked from the reactor into the turbine building through the branch pipes of the pipe used to inject seawater into the reactor. Although related parties, including myself, had vehemently insisted on either of the two views, both proved correct. This report by TEPCO was very helpful for me in writing this book. Therefore, TEPCO’s announcement did not affect my study results, but rather corroborates them.

1.2 Appendix 4.2 Radiation Level and Annual Exposure Dose

One day is 24 h and 1 year is 365 days. When converting the radiation level to an annual exposure dose, the former is multiplied by 365, assuming ① a person spends 8 h a day outdoors and the remaining 16 h indoors and ② the indoor radiation level is four tenths of the outdoor radiation level.

For example, if the radiation level is 1 μSv/h, the annual exposure dose is 5 mSv.