[2E10-13] Accident Progression

5:00 PM - 5:15 PM JST(8:00 AM - 8:15 AM UTC)

[2E11] Investigation into the cause of the dose rate increase near the main gate of Fukushima Daiichi NPP at 10:20 on March 12th, 2011

*Penghui Chai¹, Kenichiro Nozaki¹, Shouichi Suehiro¹, Masato Mizokami², Mutsumi Hirai², Akitoshi Hotta², Shinya Mizokami² (1. TEPCO SYSTEMS Corporation, 2. Tokyo Electric Power Company Holdings, Inc.)

Keywords:

Fukushima Daiichi Nuclear Power Plant Unit-1,Small S/C vent valve,Dose rate,GOTHIC code

The dose rate near the main gate raised up from 10:20 on March 12th, seemingly in response to the vent operation of 1F1 at 10:17. A series of numerical studies using GOTHIC v8.4(QA) code were performed to increase the resolution of this issue. The results suggested that the small vent valve was closed or opened very slightly to reproduce the D/W pressure. Based on these results, the main cause that triggered the rise in the dose rate near the main gate from 10:20 on March 12th will be discussed by estimating the amount of radioactive materials released through the vent line and the R/B, respectively.