Editor's Note: John Boyd is an IEEE Spectrum contributor reporting from Kawasaki, Japan. This is part of IEEE Spectrum's ongoing coverage of Japan's earthquake and nuclear emergency. For more details on how Fukushima Dai-1's nuclear reactors work and what has gone wrong so far, see our explainer and our timeline.
As government agencies were reporting the highest levels of radiation so far measured in the ocean near Japan’s troubled Fukushima Dai-1 nuclear power plant, the Tokyo Electric Power Company (TEPCO) said it has decided to scrap four of the plant’s reactors. Tsunehisa Katsumata, chairman of TEPCO, said Wednesday afternoon that TEPCO would, in a years-long process, decommission the reactors, which crews have struggled to keep under control since the 11 March earthquake and tsunami.
Katsumata also apologized for causing citizens “anxiety, worry and trouble because of the explosions in the reactor buildings and the radiation released.”
Hidehiko Nishiyama, the deputy director general of Japan's Nuclear and Industrial Safety Agency (NISA) said that once the reactors had been brought to a cold shutdown, work would begin on dismantling equipment first on the periphery of the complex; gradually workers would move in toward the reactor buildings. He added that, as a rough estimate, decommissioning could take as long as 10 years.
NISA reported some progress toward the goal of getting the reactors cold enough. In particular it reported some success at pumping out the radioactive water discovered in the basement of the turbine building next to reactor No. 1. The process of getting the reactors' automatic cooling systems up and running again has been delayed while workers scrambled to deal with the radioactive water.
The discovery of the water indicated that TEPCO's emergency cooling procedure--repeatedly spraying the reactor buildings with water--may have had dangerous side effects. It seems likely that the sprayed water came into contact with radiation from a still unknown source within the reactor buildings.
TEPCO reported during the morning that it has succeed in reducing the radiated water pooled in the basement of the No. 1 turbine building by half: The water was 40 centimeters deep several days ago, and is now 20 centimeters deep. By reducing the radiated water levels in the turbine basements, TEPCO hopes to also reduce the radiated water in the connected trenches which house cables and pipes for the turbines. However, TEPCO said it still had not discovered from where the water was leaking.
Nishiyama clarified the procedure being used to pump the radioactive water that has pooled in the turbine buildings for reactors No. 1, 2, and 3. Because the water storage tanks outside the turbine buildings are full, he said there were three alternative tanks that could be used: the condenser tank located in each turbine building, the hotwell located in the condenser tank and which is used to cool the steam used to turn the turbines, and the surge tank normally used to remove water from the reactor’s suppression pool or torus.
The procedure being used for turbine buildings No. 2 and 3 is to move the water in the condenser tank to the suppression pool tank, then pump the water from the hotwell into the condenser tank. With the hotwell emptied, TEPCO then intends to pump the radioactive water into the hotwell. This work is only now getting started. In the case of turbine basement No. 1, Nishiyama said that the hotwell there was now full, so TEPCO has begun following the same procedure being employed for No. 2 and 3 turbine buildings.
In a morning press conference, Nishiyama said that radioactive iodine-131 some 3350 times greater than the government safety limit had been found in seawater roughly 300 meters south of the Fukushima plant’s drainage outlets. The measurement, the highest so far, was taken Tuesday afternoon after higher and higher levels were measured in the morning. Nishiyama said the iodine would dilute greatly before it reached the outer boundary of the 20-kilometer evacuation zone. He said he did not believe there was an immediate danger to human life or marine products, as no fishing or gathering was going on in the zone.
A British newspaper yesterday quoted a U.S. nuclear engineer saying he thought the core of one the reactors had melted through the bottom of the pressure vessel; IEEE Spectrum got a more detailed analysis from the engineer, Richard Lahey, today. But the story didn’t gain momentum in Japan. One Japanese expert, Kazuaki Matsui, executive director of the Institute of Applied Energy, said, “Where’s the evidence?” He agreed there had been “a chance of a meltdown” earlier when water was lost in the No. 1 reactor, but given there is a pressure difference between the reactor pressure vessel and the containment vessel, he said this indicated “there was no big hole. So I don’t see the evidence for a meltdown,” he said, stressing that this was his own view of the situation.
NISA’s Nishiyama had a similar view when IEEE Spectrum asked him about the report during an evening press conference for foreign journalists. “We consider without doubt that part of the fuel (in the No. 1 reactor) was not submerged in water for a time and probably suffered some damage. But after that we have made efforts to continuously inject water into the reactor, and since then we do not have any data that shows there has been any further damage to the fuel. Also, when we look at the release of radioactive material up to now, while we do not believe there is any major breach either to the pressure vessel or the containment vessel, we are pretty sure there is some leakage. So we are working to bring the reactor to a cold shutdown.”
Separately, a group of experts advising the government is mulling over the idea of setting up some kind of fabric covering over the damaged reactor buildings with the aim of preventing more radiation from escaping into the atmosphere. They offered no additional information on what would be an unprecedented move.
PHOTO: Haruyoshi Yamaguchi/Bloomberg/Getty Images