EDITORIAL: More work needed before declaring Fukushima plant safe

One important landmark in the process of dealing with the disastrous accident at the Fukushima No. 1 nuclear power plant has come into sight.

In the latest progress schedule for the work to bring the nuclear crisis under control, the government and Tokyo Electric Power Co., which operates the plant, clearly stated that the crippled reactors will be brought to a stable state known as "cold shutdown" by the end of the year.

The timeframe is in line with the deadline set in September by Goshi Hosono, the minister in charge of the nuclear accident, and Prime Minister Yoshihiko Noda. They promised the international community to make "flat-out efforts" to achieve the safe condition by the end of this year. The deadline represents moving up the previous target date for achieving the goal--"mid-January at the latest."

But what exactly does cold shutdown mean?

Unlike a bonfire, nuclear fuel in a reactor cannot be cooled immediately by splashing cold water on the rods. Even after the reactor is shut down, the fuel continues to emit heat due to radioactive decay. The heat could cause cooling water to boil, producing steam that may release huge amounts of radioactive materials into the atmosphere.

With this risk in mind, the government and TEPCO have decided that the temperature at the bottom of the reactor pressure vessel must be below 100 degrees, the boiling point of water, to declare that the reactor has been brought to the state of cold shutdown. Accordingly, the work at the Fukushima plant has been focused on pushing down the core temperature.

An additional condition they have set for declaring the reactors to be safe requires a sharp reduction in exposure of ordinary citizens to radiation newly released from the plant.

Preventing another massive discharge of radiation is crucial for ensuring there will be no additional damage and that members of the communities around the plant will be able to rebuild their lives in the areas.

That's why the government and TEPCO have been focusing on continuing to inject water into the reactors and restoring a cooling water recycling system over the past half year or so.

If the process of bringing an end to the nuclear emergency is compared to an underground stairway leading to the surface, the current situation means we are finally beginning to see the sunlight.

It must not be forgotten that the progress has been made possible by the valiant and prodigious efforts by workers who spent hours working in radiation protection suits during the summer heat on the premises of the plant, where radiation levels remained high.

There is, however, no room for optimism.

Before the March 11 earthquake and tsunami, cold shutdown generally referred to a stable condition that is realized by shutting down, cooling the reactor and containing radiation when a potentially dangerous situation arises.

But the reactors at the Fukushima plant are not in normal conditions.

It is likely that some of the fuel in the reactors has melted and their pressure vessels are damaged.

It is impossible to gain accurate information about the conditions of the reactors as in normal times.

The current emergency situation where exposed nuclear fuel is presumably lying in damaged reactors is likely to continue.

Another cause for worry is continued aftershocks that rock various parts of eastern Japan from time to time. There are concerns about what kind of effect a major earthquake would have on the fuel inside the reactors.

A careful assessment of the situation must be made to ascertain whether cold shutdown has actually been achieved.

It is also necessary to assess whether the response system to any sign of a massive radiation release is adequate.

Independent experts should be involved in making such assessments.

There are still high hurdles to overcome before the government can safely declare the reactors to be in cold shutdown.

--The Asahi Shimbun, Oct. 18