TEPCO: Recovery Roadmap Could Put Units into Cold Shutdown within Six Months
The Tokyo Electric Power Co. (TEPCO) unveiled a two-stage plan to put units at its quake and tsunami–crippled Fukushima Daiichi nuclear plant into cold shutdown within six to nine months, and the International Atomic Energy Agency (IAEA) said that if efforts go as planned, the amount of radiation may not increase.
According to TEPCO’s so-called “Roadmap towards Restoration,” the first step will entail ensuring radiation doses are in steady decline. To achieve this, first the utility will try to prevent additional hydrogen explosions inside the primary containment vessels of Daiichi 1, 2, and 3 through injection of nitrogen gas to keep the concentration of hydrogen and oxygen below flammability limits. The risk of a hydrogen explosion was exacerbated by pumping freshwater into the reactor to cool it, TEPCO said, because it increased the chance of steam condensation. The first step is expected to take around three months.
The second step, which could span three to six months, entails ensuring that the release of radioactive materials is under control and radiations doses are held down. TEPCO said it would endeavor to prevent the release of contaminated water with high radiation levels outside the plant boundary. One problem TEPCO has so far encountered is that while cooling Daiichi 2 with freshwater injection, highly contaminated water in the turbine building is increasing, which increases the possibility that the water could leak outside the contained area. TEPCO plans to secure several ways to store this water as well as install facilities to process the contaminated water and reduce radioactivity.
Denis Flory, IAEA deputy director general and head of the agency’s department for nuclear safety and security, on Tuesday said at a news conference that "if things go as foreseen and taking into account all the measures in this road map, the new amount of release will be decreasing and decreasing and the total amount would not be much different from what it is today."
At the Daiichi site, meanwhile, the situation remains “very serious,” the IAEA said, though there are signs of recovery in some functions, such as electrical power and instrumentation. Unmanned robots were used to conduct inspections of Units 1, 2, and 3 on April 17 and 18.
On Tuesday, workers completed efforts to strengthen the electrical power system between Units 1 and 2, and Units 3 and 4. White smoke continues to be emitted from Units 2, 3, as well as Unit 4 (a new development that started on April 16), however. Freshwater injections continue at Units 1, 2, and 3, and at Unit 4, TEPCO has been spraying water onto the spent fuel pool using a concrete pump truck.
Nitrogen injections also continue at Unit 1. TEPCO reported that while the pressure in the unit’s containment vessel has stabilized, the pressure in the reactor pressure vessel is increasing.
Temperatures today at the feedwater nozzle of the reactor pressure vessel at Unit 1 read 164C; at Unit 2, 133C; and at Unit 3, 110C.
Sources: POWERnews, TEPCO, IAEA