The Nuclear and Industrial Safety Agency has decided not to file a criminal complaint against Tokyo Electric Power Co. for allegedly running nuclear reactors it knew were cracked, government sources said Saturday.

The agency also decided not to impose an administrative punishment on Tepco for six incidents involving five reactors in Fukushima Prefecture. It said there was no clear evidence the utility had violated the law.

It was difficult for the agency to investigate the cases because the equipment in question had already been repaired or replaced, the sources said.

According to agency inspections, Tepco is suspected of violating the Electric Utility Law by failing to replace core shrouds at five reactors in the 1990s at its two plants in Fukushima Prefecture, despite having discovered cracks in them between two and five years earlier.

Tepco is also suspected of violating the Nuclear Reactor Regulation Law in connection with cracks in the steam dryer of the No. 1 reactor at the Fukushima No. 1 plant.

More violations found

Three more reported defects at Tokyo Electric Power Co. reactors may have violated the law, sources close to the case said Saturday. Six other such cases were revealed earlier.

Tepco is suspected of keeping the three reactors at three plants on line without fully inspecting whether their shrouds had cracks — just as they had in the six other cases, the sources said.

Keeping the possibly damaged reactors in operation may be a violation of the technical requirements of the Electric Utility Law.

The three were identified as the No. 4 reactor of the Fukushima No. 1 plant, the No. 2 reactor of the Fukushima No. 2 plant — both in Fukushima Prefecture — and the No. 1 reactor of the Kashiwazaki-Kariwa plant in Niigata Prefecture.

All the facilities are now scheduled to undergo emergency checks. If cracks are found, the Nuclear and Industrial Safety Agency, which oversees Tepco, may face more criticism for laxness, according to the sources.

The agency, affiliated with the Ministry of Economy, Trade and Industry, said Friday the preliminary results of its investigation found that five reactors at two plants in Fukushima Prefecture continued running with cracks in shrouds for several years in the six earlier cases.

Tepco also found signs of cracks in the three reactors as well as the No. 4 reactor of the Fukushima No. 2 plant from 1993 through 1997.

In these four cases, the agency only noted that the firm neglected its obligations to report their findings to the government, saying the investigation could not detect any cracks.

Tepco reported to the government that it found nothing wrong at some of the reactors during inspections conducted on the agency’s orders between last October and May this year. But the firm did not actually carry out full inspections of the weld lines in question, the sources said.

Tepco admitted in August that it may have falsified facility inspection reports. It later finalized a list of 29 inspection reports from the late 1980s to the 1990s that may have been falsified.

The reports cover 13 of the 17 reactors at the firm’s Fukushima No. 1 and No. 2 plants and its Kashiwazaki-Kariwa plant.

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