OSAKA – Mitsubishi Heavy Industries Ltd. kept track of nuclear inspections in notebooks — rather than in a computerized database — when it was first assigned to inspect the nuclear power plant in Mihama, Fukui Prefecture, in 1989, informed sources said Saturday.
The coolant water pipe of Mihama’s No. 3 reactor — the cause of Japan’s deadliest nuclear accident earlier this month — was missing from the list of inspection items, the sources said.
Mitsubishi Heavy says it is looking into why the pipe was missing from the list, although some experts suspect human error when the list was made.
On Aug. 9, four workers were killed and seven others injured when superheated steam burst from a corroded water pipe for the reactor operated by Kansai Electric Power Co.
According to Mitsubishi Heavy and other sources, the company kept track of about 6,000 inspection items using notebooks for about six years through 1994, when it computerized the record-keeping system.
Mitsubishi Heavy created the notebook-based inspection system in 1989 at the request of Kepco, three years after an accident at the Surrey nuclear power plant in the United States which also involved a ruptured pipe.
In 1996, Mitsubishi Heavy handed the notebooks over to Osaka-based Nihon Arm Co., which took over the inspection work, the sources said.
Nihon Arm said it computerized the information in the notebooks on its own so it could easily collate drawings of pipes and other parts of the reactors with the list of inspection items.
Nihon Arm said one of its veteran engineers discovered that the part of the coolant water pipe involved in the accident was missing from the inspection items while inspecting the power plant in April 2003.
Nihon Arm said it notified Kepco of the finding, but the utility said that until the accident it was unaware of the omission.
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