8 months into nuclear crisis, progress and uncertainties

November 14, 2011

By HIDENORI TSUBOYA / Staff Writer

Temperatures have cooled, the amount of radioactive substances released is lower and emergency equipment is working at the Fukushima No. 1 nuclear power plant, according to Tokyo Electric Power Co.

But eight months after the March 11 Great East Japan Earthquake and tsunami triggered the nuclear crisis, TEPCO still doesn't know exactly what is going on within the damaged reactor buildings.

The government and TEPCO plan to bring the plant to a stable state of "cold shutdown" within this year. The limited amount of information available indicates that progress has been made toward that goal, despite the use of temporary facilities to cool down the reactors.

The Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry is checking whether TEPCO is on track under its road map for a cold shutdown.

Two requirements in the road map to declare a state of cold shutdown are that temperatures at the bottom of the pressure vessels in the reactors must remain below 100 degrees and that the amount of radioactive materials discharged must be curbed.

On Nov. 12, Goshi Hosono, state minister in charge of the nuclear accident, said the government will add another requirement: The temperatures of melted fuel that leaked from the pressure vessels must also stay below 100 degrees.

But under the current circumstances, it will be difficult to measure such temperatures.

High radiation levels make it difficult for work to be done inside the reactor buildings. Instruments that could have provided a clearer picture of the internal situation at the reactors were rendered inoperable by the March 11 tsunami.

TEPCO officials will have to depend on other data to calculate the temperatures of the melted fuel.

The instruments that work showed that the temperatures at the bottom of the pressure vessels of the No. 1 to No. 3 reactors, which suffered meltdowns, were all below 100 degrees in late September.

On Nov. 12, the temperatures were between 30 and 70 degrees.

The systems in place to cool the reactors, including 4 kilometers of hoses, are temporary measures.

TEPCO says the current equipment can withstand another big earthquake or tsunami. But to be on the safe side, it has also constructed temporary sea walls and multiple water-supply systems to maintain the cooling capabilities.

TEPCO is also considering setting up smaller but more powerful cooling facilities.

The discharge of radioactive materials from the No. 1 to No. 3 reactors has decreased to 100 million becquerels per hour, or one-8-millionth the amount just after the accident started in March.

Under the road map, the annual amount of new exposure to radiation on the edge of the plant's compound will be reduced to 1 millisievert or lower. TEPCO released provisional figures showing that the level has already been cut to 0.2 millisievert.

TEPCO this year plans to complete the installment of air purification equipment in the No. 1 to No. 3 reactor buildings to further reduce the amount of radioactive materials that leak out.

Accumulated radioactive water is another problem that must be addressed at the Fukushima No. 1 nuclear power plant.

In late October, the utility started constructing shields to prevent contaminated water in the reactor buildings from leaking to the sea, even if it seeps into the ground first.

Water pumped into the No. 1 to No. 3 reactors becomes highly contaminated by radiation from the damaged fuel. In addition, underground water has flowed into the reactor buildings, increasing the amount of radioactive water that must be dealt with.

A total of 90,470 tons of water has accumulated in the reactor buildings, waste disposal facilities that store the water, and other facilities at the site.

The water is processed at purification facilities, and part of the purified water is used to cool the reactors. But the remaining water is stored in tanks, and totaled about 89,000 tons as of Nov. 8.

After about three years, the government and TEPCO plan to start decommissioning the reactors. After 10 years, they plan to remove the fuel from the reactors. The process is expected to continue for more than 30 years.

By HIDENORI TSUBOYA / Staff Writer
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