Undetected crack at Hamaoka 2

3 July 2002

Japanese utilities may have to undertake a potentially expensive overhaul of their method of conducting outage inspections, in the wake of a problem that arose at Hamaoka 2.

Reforms in inspection routines have significantly contributed to reductions in outage length in Japanese LWRs. Anticipated pressure on outage management comes just after Tepco learned that the financial benefits from a decade of fuel efficiency improvements may be eliminated by taxes raised by local governments who complain of lost revenues.

Hamaoka 2, owned by Chubu Electric, was shut last year after Hamaoka 1 suffered a hydrogen explosion in piping associated with the high pressure injection system (HPIS). After auxiliary HPIS piping similar to that at Hamaoka 1 was removed and capped off, Hamaoka 2 was subject to routine inspections and returned to service on 24 May. During start up tests on 25 May, it was found that coolant was leaking from a weld in a valve on piping associated with the low pressure injection system (LPIS). Start up was immediately aborted, and the reactor shut down manually.

An official at Chubu Electric described the event as a small leak, and said that the coolant had escaped at about 600cm3/minute, and leaked a total of 20 litres. The radioactivity of the leaked water was measured at 103 becquerel/cm3, producing a dose of 0.08 mSv/h.

Japan's government and industry are already concerned about public acceptance of the nuclear programme, and are tying to ease public concerns to allow introduction of plutonium fuels in Japanese LWRs, which has already been delayed for three years. As a result, industry sources said it will take longer than normal for Hamaoka 2 to be returned to service, and that the impact of the finding will be felt at all 52 Japanese reactors.

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