Exelon Nuclear’s Limerick Generating Station is seeing white via an “apparent violation” of Nuclear Regulatory Commission rules, according to an inspection report issued earlier this month.
The inspection was the result of the month-long failure of two safety components involved with the cooling and containment of a nuclear reactor core. The NRC issued a preliminary “white finding” in connection with the problem.
Two other less serious “green findings” indicated the cause of two reactor “scrams” or unscheduled shut-downs, this spring.
All three issues were the result of inadequate guidance or instructions on the part of Exelon personnel, based on inspections completed Sept. 30, according to the report.
April Schilpp, senior manager of Mid-Atlantic Nuclear Communications, said the company had not yet decided whether to request a hearing on the findings.
NRC spokesman Neil Sheehan wrote if the more serious finding “is finalized, the plant will receive increased scrutiny from the NRC until we’re satisfied the root causes of the problem are fully understood and corrective actions sufficient to prevent a recurrence have been implemented.”
The color-coded findings indicate the level of seriousness with green being the lowest and red the highest.
A “white finding” is of “low to moderate safety significance.” The “green findings,” which Exelon discovered and reported to the NRC, are of “very low safety significance,” according to the NRC ranking systems.
At issue for the more serious problem was a valve failure which “resulted in the Reactor Core Isolation Cooling system and a Primary Containment Isolation Valve being inoperable from April 23 to May 23 due to” the valve “failing to fully shut,” the inspection report found.
The problem, according to the NRC report, was “operations procedures did not contain adequate technical guidance to ensure that operations personnel operated” the valves “ in proper sequence to remain within valve design limitations.
The result was that valves “failed to fully close on April 22, 2011, although they indicated closed in the main control room.”
Once they identified the problem, Exelon workers closed the valves and they revised the operating procedure, the report indicated.
“Additionally, preventive maintenance activities which could potentially have prevented this issue were deferred without an appropriate evaluation,” the report’s authors wrote.
The first “green finding” had to do with the May 29 shut-down of Limerick’s Unit 2 nuclear reactor at the end of the spring maintenance “outage.”
“Exelon did not provide adequate instructions for restoration of the Limerick Unit 2 number three turbine control valve following maintenance,” the report said.
The second “green finding” was the result of another “scram,” this one on June 3, which apparently occurred when a piece of test equipment accidentally grounded and closed the loop on “turbine trip circuitry,” according to the NRC.