In December, Prime Minister Yoshihiko Noda announced the “conclusion” of the meltdown crisis at the Fukushima No. 1 nuclear plant, saying Tokyo Electric Power Co. was managing to keep the three crippled reactors cool, as well as the facility’s spent fuel pools.
But a former special adviser to Naoto Kan, who was prime minister when the crisis started, warned that the situation is far from resolved and said Fukushima has exposed a raft of serious nuclear problems that Japan will have to confront for years.
“I would say (the crisis) just opened Pandora’s box,” Hiroshi Tasaka, who has a doctorate in nuclear engineering and is now a professor at Tama University, said in a recent interview with The Japan Times.
He was one of a select group who glimpsed the secret worst-case scenario document written up by the Japan Atomic Energy Commission on March 25 that was later reportedly quashed by the government.
According to the scenario, the biggest risk during the meltdown crisis wasn’t the reactors themselves but the spent fuel pools sitting atop them, particularly the one above reactor 4, which still contains about 1,500 nuclear fuel assemblies, Tasaka said.
Unlike reactors 1, 2 and 3, the No. 4 unit was offline for regular checks when disaster struck on March 11 and thus didn’t suffer a meltdown. But its fuel rods were in the pool outside the reactor, and its coolant water fell dangerously low.
Adding to the danger is that the fuel pool is now directly exposed to the outside environment after a hydrogen explosion blew off the upper part of the reactor building on March 15, Tasaka noted.
The potential heat from the pool was also much higher than other pools because 204 of the 1,535 assemblies were still “new ones” that had been temporarily removed from reactor 4 for regular checks.
The Fukushima crisis has highlighted the dangers of spent fuel pools, which are outside the robust primary containment vessels of the reactors themselves, Tasaka said.
Under the current circumstances, the nation has no prospect of starting up the experimental high-level nuclear waste processing facility in Rokkasho, Aomori Prefecture, because of both technical difficulties and the sentiments of antinuclear activists.
This means utilities must store their spent fuel assemblies in cooling pools at their respective reactor sites as a “temporary measure.” This situation greatly increased the danger at Fukushima No. 1 on March 11.
“The storage capacities of the spent fuel pools at the nation’s nuclear power plants are reaching their limits,” Tasaka wrote in a new book, “Kantei Kara Mita Genpatsu Jiko No Shinjitu” (“The Truth About the Nuclear Accident as Viewed From the Prime Minister’s Office”).
According to Tasaka, the utilities’ fuel pools were about 70 percent full on average in 2010, but the figure was 80 percent at Fukushima No. 1.
The makeshift cooling systems set up at Fukushima No. 1 to stabilize the stricken reactors and fuel pools have greatly reduced the possibility of another catastrophe, Tasaka said, but the ad hoc system for decontaminating the coolant water is nevertheless generating large amounts of highly contaminated waste every day.
Making matters worse, the government doesn’t have any place to permanently store it, he wrote.
Tasaka is also deeply concerned about the “groundless optimism” displayed by bureaucrats and business leaders as they rush to restart dozens of reactors that remain halted for safety checks since March 11.
“I understand quite well the intentions of the government, which now wants to send out a message of hope. But at this stage, all the risks should be put on the table,” he said.
The nation’s nuclear regulators must carry out drastic reforms to regain the people’s trust. This is an imperative for the government if it wants to keep pushing nuclear power, Tasaka said.
He recalled viewing the government’s worst-case scenario in late March. He was officially appointed special adviser to the prime minister on March 29.
The document detailed a hypothetical Fukushima crisis worst case: Eventual contamination from the plant would require the government to assist residents in the Tokyo area to evacuate if they wanted to voluntarily “migrate,” based on the same evacuation protocols adopted for the 1986 Chernobyl accident.
The scenario assumed another hydrogen explosion would occur in the reactor 1 building and radiation would force all of the workers at the plant to evacuate.
All of the pools storing hundreds of nuclear fuel assemblies would eventually lose their cooling ability and the assemblies would melt down and breach the pools.
According to Kyodo News, the simulation was “so shocking” that top government officials decided to keep the paper secret by treating it as a mere personal document of Japan Atomic Energy Commission Chairman Shunsuke Kondo, who compiled the simulation. The government only gave it official recognition at the end of December, according to Kyodo.
More than 10 months after he saw the worst-case scenario paper, Tasaka is still not sure if such scary information should immediately be made public during a nuclear plant crisis.
The assumed worst case was extreme and people did not need to immediately flee the Tokyo area even in March or April, Tasaka said. Disclosing the simulation could have caused panic in the capital, he said.
Tasaka was obliged to keep secret what he learned through his work at the prime minister’s office and was not in a position to decide what information was to be made public during the crisis.
He said he decided to start talking about the worse-case scenario only after Kan mentioned some of its highlights during an interview with the media in September.
Tasaka believes the media and government should lay some ground rules in advance on what sensitive information should be made clear in a nuclear crisis.