The last week at the severely damaged Fukushima Daiichi nuclear plant in Japan saw the departure of the plant’s leader and new estimates of fuel damage that suggest unit 1’s core may have melted through more than two feet of concrete.
Recent developments at the Tokyo Electric Power Co. plant blacked out by the March earthquake and tsunami include:
Fuel Damage Estimates Updated
TEPCO modeling released Wednesday indicates the core of unit 1 melted completely but did not escape its containment. The report estimates corium from the unit ablated 65 centimeters of the concrete below the reactor pressure vessel, Japan Today reported. An additional 37 centimeters of concrete, a layer of steel and another concrete floor below the reactor are believed to separate the material from the environment.
Damage is not believed to be as bad in the other two reactors in operation the day of the earthquake. The estimates assumed 57 percent of unit 2’s fuel escaped the RPV and penetrated 12 centimeters of concrete below it. In unit 3, the analysis assumes 63 percent of the fuel escaped the RPV, penetrating 20 centimeters of concrete. The estimates were based on the Modular Accident Analysis Program developed by Westinghouse subsidiary Fauske & Associates. Data used for the analysis, such as gas and heat measurements, indicate the fuel is no longer melting the concrete.
Fukushima Chief Hospitalized
The leader of the Fukushima Daiichi plant was relieved of that position Thursday. Masao Yoshida, who led a group that has come to be known as the Fukushima 50 through the early days of the crisis and who has directed onsite operations there since, checked into a hospital Monday. TEPCO did not release further details or his accumulated dose at the plant. The utility did say, though, that physicians did not link his illness to radiation.
New data on unit 4 spent fuel tank
Another TEPCO study summarized by Kyodo News Thursday indicated the water level in unit 4’s spent fuel tank fell to 1.5 meters above the top of the fuel. Water remained at that low level for more than a month early in the crisis, and the report said the fuel would have become exposed if crews hadn’t sprayed tons of water into the tank. Following explosions and fires in the area initially blamed on hydrogen from exposed fuel, the head of the US Nuclear Regulatory Commission said in March the tank had likely boiled dry. But in late April, a remote controlled camera showed no significant damage to fuel assemblies in the tank.