Or none, as was result of a natural disaster?
The government was aware of the possibility that the reactor cores of nuclear plants could partially melt down if all power supply equipment was crippled, making it impossible to cool down the cores' nuclear fuel, even before the March 11 accident at the Fukushima Daiichi nuclear plant, according to last May's lower house minutes.
Nobuaki Terasaka, who heads the government's Nuclear and Industrial Safety Agency, said on May 26, ''It is logically possible for a reactor core to melt down if all outer electricity sources were lost, leading the plant's cooling functions to be lost for many hours,'' according to the minutes of a House of Representatives committee.
Terasaka also said the operators of Japanese nuclear plants ''have ensured safety'' by fitting the plants with multiple backup electricity sources. He was responding to a question from Japanese Communist Party legislator Hidekatsu Yoshii.
Although the Nos. 1, 2 and 3 reactors of the Fukushima plant automatically shut down after the March 11 massive quake, the subsequent tsunami paralyzed backup power sources, leading the plant to lose the ability to cool down nuclear fuel with water.
As a result, the water boiled away due to heat stemming from the nuclear fuel, causing water levels inside the reactors to go down and leading the reactor cores to be exposed.
Fuel temperatures are estimated to have reached 1,200 C.
Plant operator Tokyo Electric Power Co. said 70 percent of nuclear fuel at the No. 1 reactor and 33 percent of nuclear fuel at the No. 2 reactor appears to have been damaged, with fuel at the No. 3 reactor partially damaged.
The agency said it had expected the functions of power supply sources to return to normal due to the presence of multiple safety-ensuring mechanisms in a few hours, even if they were crippled for some factors.
An agency official said, ''It is clear that this quake went beyond our expectations, so we have to take some countermeasures.''
Jun Tateno, former researcher at the predecessor of the government's Japan Atomic Energy Agency, said, ''The accident would not have occurred if Japan had had a philosophy of protecting backup power generators even if a quake of a magnitude of once in a thousand years or a tsunami twice as high as expectations may strike.''
Kyodo news agency
Nobuaki Terasaka, who heads the government's Nuclear and Industrial Safety Agency, said on May 26, ''It is logically possible for a reactor core to melt down if all outer electricity sources were lost, leading the plant's cooling functions to be lost for many hours,'' according to the minutes of a House of Representatives committee.
Terasaka also said the operators of Japanese nuclear plants ''have ensured safety'' by fitting the plants with multiple backup electricity sources. He was responding to a question from Japanese Communist Party legislator Hidekatsu Yoshii.
Although the Nos. 1, 2 and 3 reactors of the Fukushima plant automatically shut down after the March 11 massive quake, the subsequent tsunami paralyzed backup power sources, leading the plant to lose the ability to cool down nuclear fuel with water.
As a result, the water boiled away due to heat stemming from the nuclear fuel, causing water levels inside the reactors to go down and leading the reactor cores to be exposed.
Fuel temperatures are estimated to have reached 1,200 C.
Plant operator Tokyo Electric Power Co. said 70 percent of nuclear fuel at the No. 1 reactor and 33 percent of nuclear fuel at the No. 2 reactor appears to have been damaged, with fuel at the No. 3 reactor partially damaged.
The agency said it had expected the functions of power supply sources to return to normal due to the presence of multiple safety-ensuring mechanisms in a few hours, even if they were crippled for some factors.
An agency official said, ''It is clear that this quake went beyond our expectations, so we have to take some countermeasures.''
Jun Tateno, former researcher at the predecessor of the government's Japan Atomic Energy Agency, said, ''The accident would not have occurred if Japan had had a philosophy of protecting backup power generators even if a quake of a magnitude of once in a thousand years or a tsunami twice as high as expectations may strike.''
Kyodo news agency
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