Researchers from the Japan Atomic Energy Agency have conducted simulations that show that Fukushima Daiichi Reactor 2 may have sustained damage immediately after the earthquake. The simulations showed that a hole possibly 6 or 7 inches in diameter may have occurred in the containment vessel.
This is the first estimate of damage to the concrete containment vessels, and was presented in a forum held in Kitakyushu City. The report said that the heat from the melting fuel should have caused pressures to exceed the design basis for the containment within 48 hours, but at Reactor 2 it took over 72 hours before the reactor reached the critical pressure levels.
TEPCO has been working to calm fears after a flurry of failed thermometers in the Unit 2 reactor in recent months, 25 of 42 gauges have failed to date. According to a report to the Nuclear and Industrial Safety Agency, the utility is considering putting a thermometer down to a depth of 15 to 20 meters through an existing pipe to gauge the temperature of water at the bottom of the No. 2 reactor in late July at the earliest. After the government declared that the plant had been brought to cold shutdown in December, contaminated water leaked from 44 locations at the plant.
“One of the important lessons from this accident is that we have to care very much about the temperature of the containment vessel; that means some cooling of the containment vessel is needed” following a disaster, Akira Omoto, a member of the five-person Atomic Energy Commission (AEC) of Japan said.