Police in Fukui prefecture searched Kansai Electric Power Co (Kepco) offices on 3 September as part of their investigation into the 9 August pipe rupture at Mihama that resulted in five deaths.
Police were hunting for documents that may help to determine official responsibility for the company’s failure in inspections. The ruptured pipe, which carried water and steam at 150°C, had never been tested for thickness since installation in 1976 and over the years had been eroded from its initial thickness of 10mm to 0.6mm in places.
About 150 officers took part in a three-day search of the offices of Kepco and Nihon Arm, a contractor overseeing maintenance operations at Kepco’s plants. Kepco’s head office in Osaka will also be searched.
Following the 1986 steam generator tube rupture at the Surry plant’s second unit in the USA, Kepco drew up guidelines for the inspection of similar pipes at its own plants. A year later, Mitsubishi Heavy Industries was contracted by Kepco to perform maintenance operations and compiled an inspection checklist – omitting the Mihama condensate pipe that was to rupture on 9 August 2004.
In 1996 Nihon Arm took over the maintenance contract from Mitsubishi but did not realise the pipe was missing from the inspection list until April 2003. Six months later Nihon Arm notified Kepco that some pipes were not on the lists and should be examined at the next scheduled inspection, 14 August. The pipe failed five days before that date.
If Kepco’s original guidelines had been followed, the pipe would have been replaced in 1991. Mitsubishi admitted that a similar pipe at Hokkaido Electric Company’s Tomari plant was similarly omitted from inspection lists. That mistake was discovered in 1996.
No charges have been brought in connection with the Mihama accident, which killed four workers at the scene and hospitalised seven more, one of whom died of his injuries two weeks later.
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