Dominion reviews Millstone glitches
Waterford - A recurring electrical problem at the Unit 2 reactor at Millstone Power Station will be fixed by installing a long-term uninterruptible power supply by the end of March.
In a quarterly report on Millstone operations, Donald Jackson, one of the Nuclear Regulatory Commission's Region 1 branch chiefs and a supervisor of Millstone's resident inspectors, noted four instances of technical problems that yielded "green" findings, which are considered "more than minor" but of low safety significance.
All four incidents were preventable, Jackson found, but Millstone owner Dominion Nuclear Connecticut took appropriate measures to address the problems. Two were labeled "non-cited" violations, meaning they are "very low" in safety significance and were entered into the company's corrective action program.
On Nov. 15, Dominion declared an "unusual event" when the Unit 2 reactor's control room annunciators lost power for 21 minutes. Annunciators are overhead panels that light up to warn when a system or component is removed from service or has a potential problem.
Other backup monitoring measures were working, but the power loss meant control room operators had to be that much more vigilant until the system was working properly again, said NRC spokesman Neil Sheehan.
An "unusual event" is declared when there is something atypical happening that has the potential to degrade safety. Jackson noted, however, that in this and the three other findings, there never was any threat to the public and safety was never compromised.
Upon review, Dominion acknowledged that two electrical buses were known to cycle on and off repeatedly whenever a disturbance on the electrical grid affects incoming power, and that minor fixes had not solved the problem.
Jackson and Dominion spokesman Ken Holt said a battery-backed-up power supply will be installed to prevent outside disturbances from interrupting power at the station by the end of March.
"Although these findings are of low safety significance," Holt said, referring to all four, "we take them all very seriously and we are working to correct them as quickly as we can, if we have not already implemented a fix."
The other problems and corrective actions included:
• On Nov. 15, a handful of temperature-measuring devices in a cooling monitoring system were not properly calibrated because of an inadequate procedure that had been in place since 1997. Other devices did operate properly, however, and Dominion has since revised its procedures.
• On Oct. 10, in preparation for defueling the reactor, a reactor vessel vent did not work properly because a manual valve had been positioned incorrectly, so water backed up instead of draining properly. As soon as operators discovered the mistake they corrected it, Jackson said.
• On Oct. 6, installation of a rain guard on a transformer accidentally led to a power surge that could have caused an automatic shutdown, so the Unit 2 reactor was shut down manually. Jackson determined that Dominion failed to conduct reviews that would have added precautions and led to postponement of the work until the reactor was offline for refueling.
Dominion is addressing the situation through its corrective action program.
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