The Yomiuri Shimbun
The chief of a key government nuclear safety panel has denied telling Prime Minister Naoto Kan on March 12 that pouring seawater into a reactor at the Fukushima No. 1 nuclear power plant might trigger a dangerous re-criticality event.
The injection of seawater was being considered because of the urgent need to cool the reactor, with supplies of fresh water having been exhausted after the March 11 earthquake and tsunami knocked out the reactor's cooling system.
Haruki Madarame, chairman of the Cabinet Office's Nuclear Safety Commission, on Saturday night adamantly refuted an account of events provided earlier that day by the joint crisis-response headquarters set up by the government and Tokyo Electric Power Co.
Madarame told The Yomiuri Shimbun, "I didn't give a warning about seawater causing re-criticality. I'm insulted by the claim."
Criticality refers to the self-sustaining, energy-producing chain reaction of nuclear fission in uranium atoms. Re-criticality is when a system achieves criticality even though mechanisms intended to prevent this have been activated.
At a press conference Saturday, the headquarters said Madarame had told Kan on March 12, the day after the massive earthquake and tsunami, that injecting seawater into the No. 1 reactor could trigger re-criticality.
According to the headquarters, the injection of seawater into the No. 1 reactor was suspended for nearly an hour while Madarame's warning was being discussed by government officials.
The disparities between the headquarters' and Madarame's accounts will likely become a hot issue in Diet deliberations from Monday.
According to the headquarters' account of events, the supply of fresh water for injection into the No. 1 reactor ran out on March 12.
Around 6 p.m. on the day, the prime minister instructed Madarame's commission and the Economy, Trade and Industry Ministry's Nuclear and Industrial Safety Agency to discuss whether seawater should be injected, according to the headquarters.
The headquarters claims Madarame warned that injecting seawater risked causing re-criticality in the reactor, and that the prime minister then asked for additional measures to prevent re-criticality to be considered, such as injecting a boric-acid solution into the reactor.
TEPCO started injecting seawater into the reactor at 7:04 p.m., basing the decision on assessments by engineers at the plant.
TEPCO believed the operation would be effective in cooling the reactor, and intended to continue, according to the headquarters.
But a TEPCO official working in the Prime Minister's Office notified plant engineers and TEPCO's head office that government officials were still discussing the risk of re-criticality.
TEPCO therefore halted the seawater injection at 7:25 p.m.
The headquarters said neither the start nor subsequent halt of the seawater injection were reported to Kan and the other government officials.
TEPCO officials said they told the nuclear safety agency orally about both actions, but the agency claims there is no record of such reports, indicating communication problems between the various officials.
At 7:40 p.m., the nuclear safety agency and other government bodies presented to Kan a plan to inject seawater containing boric acid.
At 7:55 p.m., Kan ordered the commencement of seawater injection operations, but they did not start until 8:20 p.m.--almost one hour after the initial seawater injection had been stopped.
Madarame said to The Yomiuri Shimbun: "I never said there was a risk [of seawater triggering re-criticality]. It's impossible for switching from fresh water to seawater to cause re-criticality. This is elementary knowledge about nuclear power."
He continued: "My commission might recommend the risk of re-criticality be monitored, but it would never say water injection should be stopped for checks to be done. [On March 12] I was insisting that water of any kind should be injected into the reactor."
(May. 23, 2011)