PLYMOUTH — Electrical relays at Pilgrim Nuclear Power Station, relied on to shut safety valves in the reactor building should an accident occur, had long exceeded their shelf life when checked by federal inspectors last week.

• The role of the relays is to close so-called containment isolation valves to prevent a release of radioactivity into the environment.

  Federal inspectors found the relays were 22 years old. According to the product vendors, those relays are supposed to be switched out every 10 years.

  After the discovery, plant owner Entergy Corp. declared the relays inoperable because their age did not "provide reasonable assurance" that they would work if called upon, said Neil Sheehan, spokesman for the Nuclear Regulatory Commission.

  “Based upon an NRC inspection sample, it was identified that scheduled replacements of the six safety-related components (relays) were not occurring,” Sheehan said.

  As a precaution, the valves have been closed and deactivated while the electrical relays are replaced, Sheehan wrote in an email. “Our resident inspectors at Pilgrim will be following up on the repair work.”

  The reactor was operating at 100 percent power when the outdated relays were found, and it continues to operate while relays are changed. Sheehan said there is no reason to shut down since leaving the valves in the closed position eliminates the possibility of a radioactive leak if an accident happened.

  Pilgrim management is now reviewing how the replacement of the relays was overlooked.