NRC CONDUCTING SPECIAL INSPECTION AT DIABLO CANYON NUCLEAR PLANT

The U.S. Nuclear Regulatory Commission is conducting a special inspection at the Diablo Canyon nuclear plant in order to determine how two switches were misaligned, potentially impairing operators’ ability to respond in the event of a severe accident.

On October 23, during a maintenance procedure, workers discovered that a set of switches that are intended to allow control room operators to remotely open cooling water valves were misaligned. The valves are part of a system that would collect water from the floor of the containment building for recirculation to cool the reactor during some severe accidents. If the valves could not be opened remotely, operators would be required to manually open them or use a different system to provide cooling water for the reactor.

“This problem did not endanger public health or safety because operators would have been able to take compensatory actions in the event of a severe accident,” said Region IV Administrator Elmo E. Collins. “But we want a better understanding of why this occurred and the potential impact of this problem.”

A four-person team of NRC specialists will review the circumstances related to the problem, the licensee’s root cause evaluation and the effect it had on the availability and reliability of plant safety systems. The team consists of the Diablo Canyon senior resident inspector, two reactor specialists and a senior emergency preparedness inspector from the NRC’s Region IV office in Arlington, Texas.

The inspection will begin today and is expected to take several days. The team will issue a report about 45 days after completion of the inspection. The report will be available on the agency’s online document library at: http://www.nrc.gov/reading-rm/adams/web-based.html.