Accident spurs Japanese anti-nuclear movement

March 27, 1991

By Norm Dixon

Japan's most serious nuclear power accident has given the anti-nuclear movement a powerful impetus. Japan barely escaped a nuclear accident of Chernobyl or Three Mile Island proportions on February 9, when a pipe broke inside the 19-year-old Mihama reactor.

In pressurised light-water reactors like Mihama, water is super-heated by the nuclear reaction and then pumped through thin tubes into a second vessel. Heat from these tubes turns water in the second vessel into steam, which then powers turbines. Radioactivity in the second vessel's water system is warning of a leak.

In this case, radioactive water leaked out of the thin tubes and contaminated the steam generator. According to the daily Asahi Shimbun, as much as 20 tonnes of water leaked before the plant was shut down. The leak caused a major drop in the pressure of cooling water around the core while the 500-megawatt reactor was running at full capacity.

Technicians, believing that the gauge was faulty, ignored a 10-fold rise in radioactivity in the power station's secondary cooling system for almost two hours. False readings and inaccurate gauges have plagued nuclear power plants, encouraging such dangerous complacency.

By the time the workers were convinced something was really wrong, radiation levels inside the steam generator had rocketed to 1250 times the normal level. As they began to reduce power, the computerised emergency cooling system dumped millions of litres into the core. Had that system failed, an uncontrollable meltdown would have been under way.

Workers then tried to release the pressure inside the generator, but two safety valves failed. Radiation was released into the atmosphere and the sea.

Just two weeks after the Mihama accident, a nuclear power plant at Niigata, 260 kilometres northwest of Tokyo, was shut down after a drop in pressure in the pump that feeds lubricating oil to the generator.

The Mihama "phenomenon" (as officials of MITI — theMinistry of International Trade and Industry — described it) has added momentum to Japan's growing anti-nuclear movement at a time when the government is trying to boost the use of atomic power. "This could be a major setback", conceded a MITI official. Nationwide demonstrations were held demanding that the Kansai Electric Power Company, Mihama's owner, close its eight other plants.

MITI planners have been trying to convince people that oil-poor Japan must double its number of nuclear power stations from the present 40. These generate over 25% of the country's electricity; the ar power to produce 36% by 1995.

Even before the latest accidents, the anti-nuclear movement had become quite powerful. At least a dozen projects have been delayed. The movement surged after the Chernobyl disaster in the Soviet Union and was further spurred by the disclosure that several potential accidents occurred in 1987-88. In 1989 a plant in Fukushima ground to a halt when chunks of metal broke off and jammed a vital pump.

A government poll in 1984 showed that 70% of Japanese felt nuclear power to be safe and reliable. By 1987, the figure had dropped to 52%.

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