Meltdown occurred at Fukushima No. 1 reactor 16 hrs after March 11 quake
May 16, 2011
A nuclear fuel meltdown at the No. 1 reactor of the crisis-hit Fukushima Daiichi power plant is believed to have occurred around 16 hours after the March 11 quake and tsunami crippled the complex in northeastern Japan, Tokyo Electric Power Co. said Sunday.
The reactor, the fuel of which was found Thursday to have largely melted, was already in a critical state at 6:50 a.m. on March 12 with most of its fuel having melted and fallen to the bottom of the reactor pressure vessel, the plant operator said based on its provisional assessment.
The reactor automatically halted shortly after the 2:46 p.m. earthquake, but its water level dropped to the upper part of the fuel rods and the temperature began to rise around 6 p.m. The damage to the fuel had begun by 7:30 p.m. with most of it having melted by 6:50 a.m. the following day, the utility said.
While the utility is aiming to bring the worst nuclear accident in Japan under control in around six to nine months from mid-April, it has no choice but to abandon a plan to flood and cool the No. 1 reactor's containment vessel as holes have been created in the pressure vessel by the melted fuel, an adviser to Prime Minister Naoto Kan indicated earlier Sunday.
But the government will keep intact the firm's timetable for stabilizing the crisis, Goshi Hosono, tasked with handling the nuclear crisis, told TV programs.
On the original plan to completely submerge the 4-meter-tall fuel rods by filling the vessel with water, Hosono said, ''We should not cause the (radioactive) water to flow into the sea by taking such a measure,'' alluding to the holes.
Hosono said that the government will instead consider ways to decontaminate water used to cool fuel in the reactor so that the water can be reused.
The remarks were made after TEPCO found a pool of water over 4 meters deep, which could be highly contaminated and total 3,000 tons, in the basement of the No. 1 reactor building, suggesting water poured into the reactor core may be seeping through holes created by melted fuel. The water is then suspected to have leaked from the containment vessel or suppression pools, which form the vessel, into piping.
In a related revelation concerning one of the major mix-ups after the natural disaster knocked out power at the six-reactor complex, TEPCO and other sources said the same day that the utility had assembled 69 power supply vehicles by March 12 at the plant but to no avail.
The inability to use the vehicles caused a delay in the damage control work at the plant, significantly worsening the emergency.
TEPCO earlier said it had tried to connect the vehicles to power-receiving equipment, a procedure necessary to operate pumps that would pour water into the reactors to cool them. But workers failed to carry out the task because the equipment was submerged in seawater from the tsunami, creating the risk of shorting out.
TEPCO's account is at variance with the one given by the government's Nuclear and Industrial Safety Agency, which mentioned the first arrival of such a vehicle on the evening of March 11 but stopped mentioning it the following day as the focus of attention had shifted to how to let out radioactive steam to relieve pressure that had built up inside the containment vessel of the No. 1 reactor.
The different versions of the story given by TEPCO and the agency might come to a head as investigations progress to determine why efforts to immediately contain the crisis failed.
(Distributed by Kyodo News on May 15, 2011)
The reactor, the fuel of which was found Thursday to have largely melted, was already in a critical state at 6:50 a.m. on March 12 with most of its fuel having melted and fallen to the bottom of the reactor pressure vessel, the plant operator said based on its provisional assessment.
The reactor automatically halted shortly after the 2:46 p.m. earthquake, but its water level dropped to the upper part of the fuel rods and the temperature began to rise around 6 p.m. The damage to the fuel had begun by 7:30 p.m. with most of it having melted by 6:50 a.m. the following day, the utility said.
While the utility is aiming to bring the worst nuclear accident in Japan under control in around six to nine months from mid-April, it has no choice but to abandon a plan to flood and cool the No. 1 reactor's containment vessel as holes have been created in the pressure vessel by the melted fuel, an adviser to Prime Minister Naoto Kan indicated earlier Sunday.
But the government will keep intact the firm's timetable for stabilizing the crisis, Goshi Hosono, tasked with handling the nuclear crisis, told TV programs.
On the original plan to completely submerge the 4-meter-tall fuel rods by filling the vessel with water, Hosono said, ''We should not cause the (radioactive) water to flow into the sea by taking such a measure,'' alluding to the holes.
Hosono said that the government will instead consider ways to decontaminate water used to cool fuel in the reactor so that the water can be reused.
The remarks were made after TEPCO found a pool of water over 4 meters deep, which could be highly contaminated and total 3,000 tons, in the basement of the No. 1 reactor building, suggesting water poured into the reactor core may be seeping through holes created by melted fuel. The water is then suspected to have leaked from the containment vessel or suppression pools, which form the vessel, into piping.
In a related revelation concerning one of the major mix-ups after the natural disaster knocked out power at the six-reactor complex, TEPCO and other sources said the same day that the utility had assembled 69 power supply vehicles by March 12 at the plant but to no avail.
The inability to use the vehicles caused a delay in the damage control work at the plant, significantly worsening the emergency.
TEPCO earlier said it had tried to connect the vehicles to power-receiving equipment, a procedure necessary to operate pumps that would pour water into the reactors to cool them. But workers failed to carry out the task because the equipment was submerged in seawater from the tsunami, creating the risk of shorting out.
TEPCO's account is at variance with the one given by the government's Nuclear and Industrial Safety Agency, which mentioned the first arrival of such a vehicle on the evening of March 11 but stopped mentioning it the following day as the focus of attention had shifted to how to let out radioactive steam to relieve pressure that had built up inside the containment vessel of the No. 1 reactor.
The different versions of the story given by TEPCO and the agency might come to a head as investigations progress to determine why efforts to immediately contain the crisis failed.
(Distributed by Kyodo News on May 15, 2011)
