The government and Tokyo Electric Power Co. are boasting success in achieving the first stage in the road map to stabilize the reactors at the Fukushima No. 1 power plant, but experts said big challenges remain as the utility moves to the second phase, the goal of which is to achieve a cold shutdown in three to six months.
In the newly updated plan, released Tuesday, the two sides defined cold shutdown as bringing the temperature at the bottom of the pressure vessels in the stricken reactors to below 100 degrees. They also plan to reduce the amount of radioactive materials being released from the containment vessels and keep the radiation level around the plant to less than 1 millisievert per year by mid-January, which may enable some evacuees to return home.
When the second phase is over, "it will depend on radiation levels in the various areas, but I think we can achieve some specific results even for the evacuation area (within 20 km of the plant)," said Goshi Hosono, state minister in charge of the crisis, stressing that the government will make every effort to decontaminate areas around the plant.
To substantially reduce the amount of radioactive materials released from the plant, Tepco needs to get to the bottom of the problem: plugging holes or cracks in the reactors' containment vessels that are allowing contaminated water to flood on-site facilities, including the reactor buildings and turbine buildings, experts said.
The updated road map, however, includes no reference to this critical work in the second stage, even though it was mentioned in past plans. And without fixing this problem, it is difficult to say that the release of radioactive materials is under control.
"In terms of managing the leakage of radioactive materials, I think plugging the holes will be the most important point," said Tsuyoshi Misawa, a professor of reactor physics at Kyoto University's Research Reactor Institute, adding he was perplexed it wasn't included in the new plan.
Hisashi Ninokata, a professor of reactor engineering at Tokyo Institute of Technology, also stressed the importance of plugging the leaks in the containment vessels.
"It seems unclear what kind of plans they are considering," Ninokata said.
Tepco said it wants to focus on the circulation cooling system, in which contaminated water leaking from the reactors is processed and pumped back into the reactors. Even though the radioactive water will keep leaking from the reactor buildings, it will be monitored and controlled, the utility claimed.
"As for containing the radioactive materials, considerable progress is expected by lowering the temperature inside the reactors to below 100 degrees through the current circulation cooling system," said Zengo Aizawa, Tepco's vice president.
Meanwhile, it will consider how to seal the containment vessels, Aizawa said.
While plugging the holes is vital, Misawa and Ninokata acknowledged it will be difficult because the radiation level is dangerously high near the reactors, making it hard to work at the site.
Six employees at the plant have been exposed to radiation levels above the emergency limit equivalent of 250 millisierverts per year.
A cold shutdown is usually defined as bringing the temperature of the reactor-core coolants to below 100 degrees. But this has been redefined as bringing the temperature at the bottom of the pressure vessels to below 100 degrees and reducing the release of radioactive materials from the reactors because the cores in units 1, 2 and 3 are believed to have melted down to the bottom of the pressure vessels.
The cooling system has experienced numerous problems from the 4-km-long series of hoses and the water treatment system and has been halted several times.
"The problem is that this system has to work without trouble" for the circulation cooling system to function properly and maintain the temperature at the bottom of the pressure vessels below 100 degrees, Ninokata said.
He added it is risky to use the current circulation cooling system, saying a more compact version should be set up in the future.
Tepco said it plans to build and start operating a full-scale circulation cooling system within three years.
Misawa also pointed out that while the government and Tepco said the system has achieved stable cooling, it is still too early to describe the crippled reactors as "stable."
Kyushu resignation offer
Kyushu Electric Power Co. President Toshio Manabe offered to resign Wednesday over a scandal involving the utility's attempt to promote the restart of reactors by sending emails favoring nuclear power to an industry ministry-sponsored TV program.
Appearing before the Lower House Budget Committee, Manabe voiced his willingness to resign a day after the utility's chairman, Shingo Matsuo, said Manabe was ready to step down.
Manabe indicated he may resign after Kyushu Electric works out measures to prevent such scandals.
Senior company officials orchestrated the email campaign in June to manipulate public opinion regarding whether two reactors at the utility's Genkai power plant in Saga Prefecture, shut down for regular maintenance, should be allowed to resume operating.
Public concern over nuclear safety had surged since the crisis began at the Fukushima No. 1 power plant.
Kyushu Electric said 141 people who were its employees or employed by affiliated companies sent comments in favor of nuclear power to the program, aired June 26, via email and fax.
"The campaign runs counter to common sense or ethics in society," Manabe told the committee.