Fukushima Daiichi Nuclear Plant Weekly Review

The last several days at the damaged Fukushima Daiichi nuclear plant included a video-recorded tour of unit 4 by a deputy cabinet minister and further debate over the manuals that guided reactor operators during the crisis.

Developments at the Tokyo Electric Power Co. plant blacked out by last year’s earthquake and tsunami include:

Emergency Procedures Questioned

Manuals that drove reactor operators’ decision making during the crisis have drawn further scrutiny from a Japanese government researcher and a panel investigating the accident. On Tuesday, the Asahi Shimbun quoted Toyoshi Fuketa of the Japan Atomic Energy Agency’s Nuclear Safety Research Center as saying the manuals’ instruction to vent steam before using isolation condensers worsened conditions at the plant. While TEPCO described the manuals’ wording differently, Fuketa contended they instructed operators at unit 1 not to use the condensers first in an emergency. The steam safety release valves, though, could cause coolant to boil because of the corresponding reduction in pressure, Fuketa argued. A government investigation committee will address the manual’s emergency procedures in a coming report. At unit 1, the first reactor to sustain core damage, the relief valves could not be opened as prescribed. The isolation condensers tripped automatically but were manually turned off, per the manual, after they began cooling the reactor too quickly. Operators turned a condenser on again later but were eventually stymied when valves stopped working.

TEPCO Prepares Worker Dose Report

TEPCO continues to send regular reports on its workers’ radiation exposure to the Japanese government. The most recent figures made publicly available indicate that in March the number of “newly engaged” workers was 483. The maximum worker external dose was measured at just over 19 millisieverts, with no significant internal exposure reported.