Containment vessels also damaged : National : DAILY YOMIURI ONLINE (The Daily Yomiuri) - 0 views
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Energy Net on 30 May 11"Not only the pressure vessels, but the containment vessels of the Nos. 1 to 3 reactors at the Fukushima No. 1 nuclear power plant were probably damaged within 24 hours of the March 11 earthquake and tsunami, according to Tokyo Electric Power Co.'s analysis of the nuclear crisis. In a report on the analysis, the utility said it carried out minute calculations on internal pressure and other measurements in the nuclear reactors after the earthquake. The report was submitted to the Economy, Trade and Industry Ministry's Nuclear and Industrial Safety Agency on Monday night. TEPCO said it found that an isolation condenser, a type of emergency cooling device, did not work properly at the No. 1 reactor. This caused the core meltdown to progress until it damaged the bottom of the pressure vessel about 15 hours after the earthquake. Along with the meltdown, the temperature inside the steel containment vessel, which contains the pressure vessel, rose until it reached 300 C in 18 hours after the quake, much higher than 138 C the vessel was designed for. It is believed the internal temperature continued to rise after that. Containment vessels are designed for a much lower temperature and pressure than pressure vessels, which can be exposed to temperatures close to 300 C and pressure reaching 70 bars when a reactor is in operation."