Japan nuclear power plant accident results from pipe

The escaped steam that killed four at the Mihama nuclear plant was the result of not replacing a 27-year-old pipe.

TOKYO, Aug. 17 (Xinhuanet) — Last week’s disaster at west Japan’s Mihama nuclear power plant was likely caused by Kansai Electric Power Co. (KEPCO)’s failure to check on a well-known phenomenon in which steam pipes wear thin under the stress of erosion and corrosion.

The accident occurred when super-hot steam erupted from a pipe at KEPCO’s No. 3 nuclear reactor in Mihama, Fukui Prefecture, killing four workers and injuring seven. The pipe had not been changed in 27 years.

According to a Kyodo News report, the accident was most likely caused when pressure was applied to the thin carbon steel pipe, tearing the metal. Metal becomes compromised by erosion from physical stress and chemical corrosion.

The damaged pipe part is a complex structure used to regulate the flow of steam for volume measurement, the report said. The pipe was originally 10 millimeters thick, but had thinned to only 0.6 mm.

“Even an amateur would be surprised to see the pipe problem,” Kyodo quoted Shoichi Nakagawa, minister of economy, industry and trade, as saying after inspecting the accident site.

After the disaster, the ministry’s Nuclear and Industrial Safety Agency asked operators of boiling water reactors, differentfrom Mihama’s pressurized water reactor, and even entities runningthermal power plants to check their reactors because pipe-thinningis a well-known phenomenon.

In 1986 in the United States, a similar accident occurred at the Surry nuclear plant, killing four workers. It prompted Japanese plant operators to devise pipe-checking plans, and carbonsteel pipes liable to erode were replaced with stronger steel ducts.

A KEPCO subsidiary checked the Mihama plant last year and told the parent company the burst pipe was not covered by its inspection, but KEPCO took no immediate action to check pipe thickness.

In secondary coolant pipes at the Mihama No. 3 reactor, there are about 60 pipes with the same structure as the damaged part, according to Kyodo.

Local industry analysts said the fatal accident occurred because KEPCO failed to pay proper attention to a facility important for operation, but related less to radioactive substances.

ChinaView.net