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Nearly one in six nuclear reactors faced safety breaches last year, according to a report released by the Union of Concerned Scientists on Thursday, March 7.

The organization says lax oversight by federal authorities is at least partly to blame, and includes the emergency shutdown of San Onofre Nuclear Generating Station due to a small radiation leak that led to the discovery of abnormal tube wear in the twin reactors’ steam generator units among the 16 plants reporting problems. The Nuclear Regulatory Commission says 14 “near miss” incidents occurred including the one at San Onofre, in which the risk of meltdown was raised to at least ten times the normal expectancy during operation.

“The NRC must not allow these reactors to restart until the cause of the steam generator degradation has a robust explanation rather than the flimsy, unsubstantiated one offered by the plant’s owner to date,” the report’s section on San Onofre concludes.

Meanwhile, a report direct from the NRC indicates that San Onofre will be one of 14 plants receiving increased inspection scrutiny in the coming year to resolve what are described as minor compliance issues. Plant operator Southern California Edison greeted the report, noting that despite the issues (and the fact that the reactors have been offline for more than a year) that the NRC expected to return San Onofre to “column one,” signifying the highest of five available performance ratings.

In further news, heavily redacted reports from Mitsubishi Heavy Industries, manufacturer of the faulty steam generators, were released to the public on Friday. They seem to back up the claims made by environmentalists and championed by Senator Barbara Boxer that both Mitsubishi and Edison knew about a possible defect in the generators that could lead to a condition known as void fraction, causing the tubes to thin from the inside, which is precisely what investigators determined had occurred and led to the leak.

Further, it indicates that Edison considered making corrections but balked due to the fact that such changes would have led to the need to apply for a NRC license amendment, apparently contradicting statements from the utility that it would never install equipment that it did not believe would perform safely.

Edison, however, contradicted the claims again in a release shortly after reporters began to pick up the story.

“[Edison]'s own oversight of MHI's design review complied with industry standards and best practices. [Edison] would never, and did not, install steam generators that it believed would impact public safety or impair reliability,” said Pete Dietrich, SCE senior vice president and chief nuclear officer, in the release.

“At no time was SCE informed that the maximum void fraction or flow velocities estimated by MHI could contribute to the failure of steam generator tubes,” Dietrich continues. “At the time, the design was considered sound.”

The company further continues to deny rejecting any proposed design changes to address the void fraction issue due to concerns over NRC licensing.

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