EDITORIAL: Water leaks raise concerns about pressure vessels

Highly radioactive water is leaking out of reactor pressure vessels and containment vessels at the Fukushima No. 1 nuclear power plant, which was severely damaged by the March 11 earthquake and tsunami. These vessels are apparently failing to perform their core function of acting as a radiation shield.

The government and the plant operator, Tokyo Electric Power Co., must face up to the possibility that these vessels were breached and develop a plan to deal with the problem.

The reason for suspecting that these vessels may not be completely sealed off is that high levels of radioactivity have been detected in water trapped in the basements of the buildings adjacent to the reactor buildings and in an underground tunnel outside the buildings.

Especially high levels of radioactivity were discovered in water in the basement of the turbine building next to the No. 2 reactor.

The radiation levels were 100,000 times greater than those normally detected in cooling water circulating within a reactor in operation.

The only plausible explanation for such high levels of radiation is that the nuclear fuel in a pressure vessel, the main body of the reactor, has melted due to high temperature and flowed into the cooling water.

A reactor pressure vessel is made of thick steel. It is the most important structure of a reactor designed to contain radioactive substances in the reactor core.

A pressure vessel is enclosed in a container vessel that is linked to the adjacent building with coolant and other pipework.

The Nuclear Safety Commission of Japan believes that water within vessels that had come into contact with melted nuclear fuel somehow found its way into the adjacent buildings.

Are the pressure vessels in sound condition?

TEPCO has acknowledged the possibility that water is leaking from a pressure vessel to its container vessel. But the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry assumes that the likelihood of a breach in a pressure vessel is low.

There is no way to look at a pressure vessel directly. Its condition can only be assessed from measurements of the temperature and pressure.

It is important to analyze such data carefully, confront the implications of the information, even if it is alarming, and communicate what could happen clearly to the public.

The discoveries of highly contaminated water are bound to have a significant impact on the fundamental component of the efforts to put the stricken nuclear power plant under control.

The central task is to restore power supply to the plant in order to bring the water-circulation cooling system back into operation.

The mission of fixing the system involves checking whether the electric wirings and pumps struck by the quake and tsunami can still work and replacing dysfunctional wirings and equipment, if any.

Areas of high radiation levels scattered around the facilities, however, make it necessary to replace workers at short intervals, causing delays in the work. It is also necessary to increase the total number of workers engaged in the dangerous tasks.

Even more worrisome is the possibility that a major breach in a pressure vessel could hinder efficient circulation of water even after the pumps start functioning again.

The only reliable way to get a destabilized nuclear reactor back in order is to cool it sufficiently.

The existence of highly contaminated water is likely to pose a raft of obstacles to the efforts to contain the nuclear crisis.

We hope the government and TEPCO will be able to develop effective plans to deal with various possible situations and make quick progress toward stabilizing the crippled nuclear power plant.

--The Asahi Shimbun, March 29