The government certified as “appropriate” a 2000 report by Kansai Electric Power Co. on pipe safety measures at its Mihama Nuclear Power Plant in Fukui Prefecture, sources said Thursday.
On Monday, superheated steam exploded from a ruptured coolant water pipe at the plant, killing four employees and injuring seven others, in the nation’s worst nuclear plant accident. The pipe was reportedly corroded and never checked in 27 years.
In the 2000 report, Kepco said: “Tests on the thickness (of the pipes for the secondary loop) have been conducted at a large number of spots for a few years. Now that we understand the corrosive tendency of the pipes, we have set a more economical inspection standard.”
In its appraisal of the report, the then Ministry of International Trade and Industry said, “Improvements are made appropriately by reflecting operational experiences at home and abroad.” The ministry has been renamed the Ministry of Economy, Trade and Industry.
It was revealed after the accident that Kepco — despite being warned by a subcontractor last year that the pipe in question needed to be inspected — did not address the problem, waiting instead for this year’s checks, which were scheduled to begin Friday.
Kepco had not inspected the pipe since the reactor began service in December 1976.
The damaged pipe was found to have been corroded by coolant water to a thickness of 1.4 mm. Its original thickness was 10 mm.
The Nuclear and Industrial Safety Agency, which is under the METI, said it did not know why the ministry approved the 2000 safety review report.
The review report system was introduced in 1992 to ensure safe operations of nuclear plants at the same levels as new facilities.
The importance of managing corroded pipes of the so-called secondary loop, which carries water through the steam generator, was highlighted after a 1986 accident at a U.S. pressurized light-water reactor killed four people.
It was also learned Thursday that a Kepco official who was told the ill-fated pipe had missed inspection, not thinking the matter to be serious, did not assess the durability of the pipe.
Based on calculations done by the utility with fragments of the pipe, the pipe wall was thinner than the acceptable thickness 15 years ago.
The government safety agency said this latest admission by Kepco indicates “a serious breach of safety regulations.”
METI Minister Shoichi Nakagawa told a news conference Thursday that the Mihama accident was a “man-made disaster.”
He said METI will call for executives of Kepco to accept responsibility for the accident after conducting a thorough investigation to determine its cause.
Japan notifies IAEA
NEW YORK (Kyodo) Japan has notified the International Atomic Energy Agency of Monday’s deadly accident at the Mihama nuclear plant in Fukui Prefecture, according to the U.N. nuclear watchdog agency.
The Vienna-based IAEA said in a statement that it received information from Japanese nuclear regulatory authorities Tuesday “about an accident in the steam generator turbine circuit of the Mihama Nuclear Power Plant” unit 3.
“The IAEA continues to be in contact with Japanese authorities and expects to receive updates on a continuous basis. No request for IAEA assistance has been received at this time,” the statement said.