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UCS: NRC's contradictory safety decisions

As posted by Dave Lochbaum of UCS (reposted here with permission):

Good Day:

Federal regulations require that nuclear power plants be designed to experience a loss of coolant accident (LOCA, where a pipe connected to the reactor vessel ruptures and drains cooling water) and a loss of offsite power (LOOP, where electricity from the offsite power grid is unavailable) should they occur separately or concurrently. All but one US nuclear power plant has two or more emergency diesel generators (EDGs) to comply with these regulations.

In 2008, the NRC received a petition for rulemaking seeking to decouple LOCA from LOOP. Plants would still have to be capable of mitigating a LOCA and of mitigating a LOOP, but would no longer be required to mitigate the LOCA/LOOP combo, if the petition was granted.

On January 26, 2017, the NRC staff recommended to its Commission that the petition for rulemaking be terminated. The staff cited numerous unanswered safety questions that would have to be resolved before they could justify decoupling LOCA from LOOP. The Commission voted unanimously to terminate the rulemaking.

But 22 days earlier, on January 4, 2017, the NRC staff decoupled LOCA from LOOP in reaching its decision to let Palo Verde Unit 3 operate for up to 62 days with one of two EDGs broken.

UCS's research also uncovered that the NRC sanctioned Palo Verde Unit 3 a decade earlier (February 2007)  for operating for 18 days with one of two EDGs broken. In imposing that sanction, the NRC staff coupled LOCA with LOOP, as federal regulations require.

The NRC's contradictory answers to the same nuclear safety questions are troubling, at least some of the time. UCS wrote a letter to the NRC's Inspector General outlining this checkered past and requesting that his office formally investigate the goings on to see whether different answers to the same questions comply with the agency's regulations, policies, and practices.

A link to the UCS letter and additional background about this matter was posted to our All Things Nuclear blog at


Dave Lochbaum