IT WAS the worst-ever accident at a nuclear power plant in Japan. On 9 August a pipe carrying superheated water exploded in the turbine building of the Unit 3 reactor, one of the three at the Mihama nuclear power facility, 80 kilometres north of Kyoto. At the time, there were 104 people in the building. The superheated water flashed into steam, killing four people and injuring seven others, two of them seriously.
The regulatory authorities immediately swooped on Mihama to inspect the damage and reassure the public that things were under control. But why did it happen, and could it have been prevented? The evidence that is emerging makes uncomfortable reading for those responsible for the plant. It throws into question the safety culture of the entire industry and deals yet another blow to the Japanese government鈥檚 plan to build 11 more reactors by 2010.
Japan relies heavily on nuclear power because it has no fossil fuel resources of its own. Nuclear plants supply just under a third of the country鈥檚 electricity. In the early 1970s Japan took a strategic decision to reduce its reliance on imported oil and gas. Mihama was one of the reactors built in that period of rapid investment, and Unit 3 began operating commercially in December 1976.
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A decade on, alarm bells began to ring. In 1986 there was an accident in the US at a reactor of similar design to Mihama that would have important implications for the Japanese. At the Surry nuclear power plant in Virginia a pipe carrying superheated water exploded, killing four workers. The US Nuclear Regulatory Commission (NRC) found that turbulence in the superheated water had led to the carbon-steel pipe corroding faster than had been expected.
Then in 1989 the NRC recommended urgent examinations of similar sections of piping in similar reactors after two more corroding pipes were found in US reactors in 1987 and 1988.
But the reaction from Kansai Electric Power Company (KEPCO), which operates Mihama, was extraordinary. In a statement the day after the accident, the company said that the bend sections close to the length of pipe that burst were inspected after the NRC recommendation, but admitted that the ill-fated pipe itself was not.
Amazingly, it wasn鈥檛 until April 2003 that KEPCO鈥檚 maintenance subcontractor realised this. Yet an inspection was not scheduled until 14 August this year, during a routine close-down. It was during preparations for this inspection that the pipe burst. In the 28 years the reactor had been operating, the pipe that burst had never been inspected. According to the Citizens鈥� Nuclear Information Center, a Tokyo pressure group that gathers data on nuclear accidents in Japan, KEPCO has since found 17 pipes at three other nuclear power plants that have never been inspected.
Had this been an isolated incident, the Japanese nuclear industry might have been able to study the accident, learn from its mistakes and move on. But it is not. In 1999, sloppy handling of uranium at the Tokaimura nuclear plant north-east of Tokyo triggered a chain reaction that killed two people and irradiated hundreds of others in the world鈥檚 worst nuclear accident since Chernobyl. Then last year, the Tokyo Electric Power Company was forced to shut down its 17 nuclear power plants after revelations that it had consistently covered up accidents and falsified safety inspections at the plants.
The Mihama accident is bringing matters to a head. Japan has some big problems to solve, perhaps the most serious is the Japanese government鈥檚 failure to control the nuclear industry. The country has nowhere else to turn to for the energy it needs. But unless the industry changes dramatically, Mihama will not be the last serious accident at a Japanese nuclear power plant.