This morning, Minnesota’s Monticello nuclear power plant informed the Nuclear Regulatory Commission (NRC) that it had determined that a number of relays in the facility’s sole reactor had exceeded their analyzed shelf life and as a result had been declared inoperable. The relays are part of the primary containment isolation valves on the Hydrogen-Oxygen Analyzing System.
According to the Event Report: “This affected both primary containment isolation valves for a containment penetration on multiple flow paths.” The incident was reported as “an event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material and mitigate the consequences of an accident.”
The relays at Monticello have been in service for 11 years, despite the manufacturer’s estimate that the parts had an operational life of 10 years. One assumes that the next step will be to remove and replace the old parts, although there is no indication that Monticello plans to do this, or that the NRC is taking steps to require their replacement. The reactor is currently operating at 69 per cent power.
The situation at Monticello could have been mitigated if the NRC had allowed the facility’s license to expire as scheduled in 2010. instead, the NRC approved an application to extend Monticello’s license through 2030.
There are tens of thousands of parts in the typical nuclear power plant, most of them of direct safety significance. In the current case, we got lucky, and plant operators identified the potential problem before the relays failed, even if there is no current plan to replace them. Of greater concern is the fact that the Nuclear Regulatory Commission has routinely rubber-stamped dozens of license extensions for plants as old or older than Monticello.