TY - JOUR
T1 - Analysis of reactor water level measurements during the Fukushima unit 2 accident
AU - Sevón, Tuomo
N1 - Funding Information:
The water level measurement system of Fukushima unit 2 was analyzed with the MELCOR code. The analysis results support the hypothesis of the Japanese accident investigation committee ( ICANPS, 2012 ): there was probably a leak of superheated steam from the reactor to the drywell, starting 78.5 h after the earthquake (March 14, 21:18). The leaking gas heated up the drywell, causing the water to evaporate in the reference leg and in the variable leg of the measurement system. This, in turn, distorted the measurements so that the indicated water level was much higher than the actual level. The leak hypothesis is supported by the dose rate measurements in the drywell.
Publisher Copyright:
© 2020 Elsevier B.V.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2020/9
Y1 - 2020/9
N2 - The reactor water level measurement system in Fukushima was based on measuring the pressure difference between two water-filled pipes that were connected to the reactor at different elevations. A Japanese accident investigation committee has presented a hypothesis that a leak of superheated steam from the unit 2 reactor to the drywell caused evaporation of the water in the measurement system, causing the indicated water level to be much higher than the actual level. This article presents an analysis of the measurement system with the MELCOR code. The results support the hypothesis of a small leak, starting 78.5 h after the earthquake. The best agreement with the measurements was obtained with 8 cm2 leak area. The leak was probably located close to the water level measurement system, so that it caused localized heating in the drywell. The leak increased the fission product release to the environment because it bypassed the suppression pool. The calculated cesium release from unit 2 to the environment was 2.1% of the core inventory. Combined with the author's earlier MELCOR calculations of units 1 and 3, the current estimate of the total Cs-137 release from all three accident units at Fukushima is 14.3 PBq.
AB - The reactor water level measurement system in Fukushima was based on measuring the pressure difference between two water-filled pipes that were connected to the reactor at different elevations. A Japanese accident investigation committee has presented a hypothesis that a leak of superheated steam from the unit 2 reactor to the drywell caused evaporation of the water in the measurement system, causing the indicated water level to be much higher than the actual level. This article presents an analysis of the measurement system with the MELCOR code. The results support the hypothesis of a small leak, starting 78.5 h after the earthquake. The best agreement with the measurements was obtained with 8 cm2 leak area. The leak was probably located close to the water level measurement system, so that it caused localized heating in the drywell. The leak increased the fission product release to the environment because it bypassed the suppression pool. The calculated cesium release from unit 2 to the environment was 2.1% of the core inventory. Combined with the author's earlier MELCOR calculations of units 1 and 3, the current estimate of the total Cs-137 release from all three accident units at Fukushima is 14.3 PBq.
KW - BWR
KW - Fukushima accident
KW - MELCOR
KW - Water level measurement
UR - http://www.scopus.com/inward/record.url?scp=85087886532&partnerID=8YFLogxK
U2 - 10.1016/j.nucengdes.2020.110760
DO - 10.1016/j.nucengdes.2020.110760
M3 - Article
AN - SCOPUS:85087886532
VL - 366
JO - Nuclear Engineering and Design
JF - Nuclear Engineering and Design
SN - 0029-5493
M1 - 110760
ER -
