The Yomiuri Shimbun
Tokyo Electric Power Co.'s failure in its initial response to the crisis at the Fukushima No. 1 nuclear power plant in Fukushima Prefecture invited more trouble in a chain reaction, according to an analysis of events over the past three weeks since the March 11 great earthquake and tsunami.
At the crippled nuclear power plant, three reactors have been cooled by injecting water using temporarily set up pumps. However, there are fears the spent nuclear fuel rods stored in the reactors' temporary storage pools will overheat again.
TEPCO's sloppy way of publicly releasing information related to the accident also has drawn much criticism.
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Vent operation in trouble
The power plant lost all power on the afternoon of March 11 due to the gigantic tsunami that followed the great earthquake, causing an emergency halt to the operations of the Nos. 1 to 3 reactors. The Nos. 4 to 6 reactors already were not operating due to periodic inspections.
Temperatures and pressures inside the pressure vessels of the Nos. 1 to 3 reactors began rising sharply, complicating the injection of cooling water into the reactors. When the level of water in the reactors drops, nuclear fuel rods become exposed, overheat and may start melting, risking damage to the reactor as well as the emission of radioactive substances.
On the night of March 11, TEPCO planned a controlled release of vapor mixed with radioactive substances from the No. 1 reactor, in an operation to decrease pressure in the pressure vessel.
However, the operation was not carried out until 10:17 a.m. the following day, four hours after Prime Minister Naoto Kan left the Prime Minister's Office to travel to the Fukushima Prefecture plant for an inspection. Also, evacuation of residents in areas within 10 kilometers of the power plant had not been completed at that time.
Then, on the afternoon of March 12, a hydrogen explosion occurred at the No. 1 reactor, destroying the reactor building roof.
Kenzo Miya, professor emeritus at the University of Tokyo, an expert on nuclear engineering, said the prime minister's inspection delayed TEPCO's original plans to vent the pressure vessel.
"Because of the prime minister's [impending] inspection, the start of the 'vent' was delayed. The possibility that the subsequent actions all fell behind can't be denied," Miya said.
Haruki Madarame, chairman of the Cabinet Office's Nuclear Safety Commission, also noted the time-loss disadvantage.
"Work [to conduct the 'vent'] took time to get under way. As a result, several hours were lost before starting to inject seawater [to cool the reactor]. It was a painful incident," Madarame said, when recalling the situation on the night of March 23.
Meanwhile, TEPCO President Masataka Shimizu and Chairman Tsunehisa Katsumata were on separate business trips on March 11 when the tsunami hit the plant. They could not return to Tokyo until the following day. "As we communicated with cell phones and other measures, there were no chain of command problems," an official of TEPCO's public relations department said.
However, the absence of top management officials might have resulted in the delay in the initial response, some people involved in the handling of the accident said.
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Use of seawater
To cool the reactor core, TEPCO started injecting seawater in the No. 1 reactor shortly after 8 p.m. on March 12--a full 19 hours since the containment vessel's pressure began rising abnormally.
Since TEPCO began injecting seawater to cool the Nos. 2 and 3 reactors on March 13, the operation was believed to have only a limited effect.
On March 14 at the No. 2 reactor, cooling water ran out of supply due to loss of fuel for temporary pumps. On the morning of March 15, an explosion at the reactor was believed to have damaged its pressure suppression chamber, part of the containment vessel.
It is suspected that water contaminated with high concentration of radioactive substances leaked from the chamber to the reactor's turbine building. The water continues to hamper restoration work at the plant.
Since seawater contains impurities, and its use as a coolant damages the reactors, TEPCO had to consider possibly decomissioning the reactors.
"Crucial efforts to tame Japan's crippled nuclear plant were delayed by concerns over damaging valuable power assets," The Wall Street Journal reported in its electronic edition on March 19.
TEPCO was "reluctant to use seawater because it worried about hurting its long-term investment in the complex," the report added, quoting people familiar with the situation.
TEPCO Vice President Sakae Muto tried hard to refute the criticism in a press conference on the night of March 21.
"We've been exercising maximum effort to cool down the reactors," he said.
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Storage pool for spent fuel rods
Another factor complicating the handling of the nuclear crisis was the delay in TEPCO's response to cool the temporary storage pools for spent nuclear fuel rods.
Although the amount of heat generated by the fuel rods in the storage pools is less than the nuclear fuel within a reactor core, the central problem remains: If the fuel rods are exposed when water levels decrease, they will become damaged by overheating.
The storage pools are even more dangerous as they could easily discharge radioactivity as they are not stored in a tightly enclosed structure as a reactor.
The attention of the government and TEPCO initially only focused on the reactors themselves. However, both parties also began to consider the threat posed by the temporary storage pools on about March 13, around the time the temperatures of the pools were believed to have begun to rise due to the halt in the circulation of cooling water.
At the No. 4 reactor, the pool temperature rose to 84 C on the morning of March 14. In the early hours of the morning of March 15, an explosion and a fire took place at the reactor building, which also houses a temporary storage pool for spent nuclear fuel rods.
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TEPCO updates late, unreliable
Tokyo Electric Power Co. has been criticized for its delays in disclosing information and repeatedly making inconsistent announcements about the problems at Fukushima No. 1 nuclear power plant.
For example, when explosions at buildings housing reactors at the plant were aired live on TV, TEPCO made no prompt statement about the facts behind the incidents.
TEPCO's failure to obtain and distribute information about important developments at the plant in a proper manner has been partly due to the fragile state of its internal telecommunications network, which has hampered the transfer of information within the company.
(Apr. 2, 2011)
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