TEPCO has made two major admissions on the Fukushima nuclear disaster. The Japanese press has documented these two out of a large data dump of accident review reports.
The new admission for unit 2 was that the pneumatic air controls for the steam relief valves failed early in the disaster. These air lines are used to open and close steam relief valves (SRV) to relieve pressure on the reactor vessel. Our extended report on unit 2 showed the SRV valves were a serious failure point due to the valve components failing when containment temperatures reached over 526 celsius. The pneumatic lines fail at 200 celsius according to the NHK article. This admission hints that the SRV valves may have failed earlier than previously assumed and could have hastened over pressurization of the reactor vessel. These valves are considered critical safety components of a reactor. TEPCO claims all other BWR reactors in the world may have this identical design flaw. This new understanding as serious implications for reactor safety. Asahi Shimbun pointed out that this failure prevented water injected by fire trucks to try to cool the reactor failed to reach the reactor vessel. The water would then have all run back into the turbine building condensers as has been known for about the last year.
A radiation release during the disaster is now being blamed on unit 3 having a containment failure. The report from NHK is quite vague but states that between March 14-16 containment failed and began to leak directly to the environment. They cite the heat from the nuclear fuel as the cause rather than solely based on pressure. Sealing gaskets for BWR containment systems are known to have heat resistance limits below the expected temperatures of a meltdown.
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