N-reactor decommissioning a long, arduous task

N-reactor decommissioning a long, arduous task

The second phase of the reactor decommissioning process, which will begin as early as 2015 and which will follow the first phase of removing nuclear fuel assemblies from the No. 4 reactor building of the Tokyo Electric Power Co.'s Fukushima No. 1 nuclear power plant, is to recover a total of 1,573 assemblies from storage pools in Nos. 1 to 3 reactors.

Each assembly contains multiple fuel rods.

As the radiation level is higher inside those reactor buildings than in the No. 4 reactor building, workers will first face the challenge of removing debris and decontaminating the area before they can begin work. It also could take some time to set a crane to lift up nuclear fuel assemblies at Nos. 1 and 3 reactors, where hydrogen explosions occurred, depending on the reactor buildings' strength.

In addition, 70 fuel assemblies, most of which were used in the early days of the plant, are damaged among 392 stored at the oldest No. 1 reactor.

The most difficult part of the decommissioning process, which could last as long as 40 years, will be recovering melted fuel debris inside Nos. 1 to 3 reactors. The work will be conducted in the third phase from fiscal 2020.

Using examples from the partial nuclear meltdown at Three Mile Island in Pennsylvania in 1979, melted fuel debris will be recovered while the reactor buildings are filled with water to shield workers from strong radiation. For this, the leakage of radioactive water must first be halted at the three reactor buildings.

However, TEPCO found last week the first clue that could point to the locations of water leaks at the No. 1 reactor after a series of failures.

It is necessary to develop a new method to recover melted fuel debris. The International Research Institute for Nuclear Decommissioning will publicly solicit measures from home and abroad to find a prospective method.

Basing its cost estimates on the Three Mile Island accident, TEPCO expects to spend ¥172 billion (S$2 billion) to recover nuclear fuel assemblies stored in fuel pools at Nos. 1 to 4 reactors, while it estimated ¥263 billion would be needed recover melted nuclear fuel debris at the Nos. 1 to 3 reactors. However, as the number of workers necessary for the decommissioning work is not known, the cost will probably soar.

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