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In October, Harris Plant management visited NRC Region II headquarters in Atlanta to address a possible NRC "white" finding regarding an inoperable chiller. The NRC issued a decision on Tuesday to categorize that finding as "green," indicating a very low safety issue. The NRC had previously issued a preliminary determination that the finding was "white," indicating a low to moderate safety issue.
The NRC uses a color-coded system to categorize inspection findings. It ranges from "green," for a very low safety issue, to "red," for a high safety issue. In this case, the finding was determined by the NRC staff to be "green," or of very low safety significance.
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Why is the NRC issuing a finding?
On June 1, Harris Plant personnel discovered that one of the two water chillers used to cool certain emergency components was inoperable. Personnel reported this problem and took immediate actions to restore the chiller to service within 36 hours. The chiller had been inoperable since May 25, longer than the 72 hours allowed under the plants technical specifications. The NRC decided this week to categorize the finding as "green," based on information Harris personnel was able to provide regarding the assumed risk of the chiller being out of service more than 72 hours.
What is the functionality of a chiller?
The Essential Services Chilled Water System (ESCWS) is designed to provide chilled water to the cooling coils of air handling units. The air handling units serve ventilation systems in the Main Control Room, Fuel Handling Building, and in the RAB.
The NRC's primary concern is that if the air conditioning or ventilation is not operational, the ambient temperature of the rooms/buildings will rise. Since sensitive equipment is housed in these rooms/buildings, the NRC requires the plant to ensure a safe temperature for operation. At the October meeting, plant personnel provided test data that determines the equipment in those areas would have been safe to operate, even at temperatures over 130 degrees. The ESCWS chills the water to approximately 44 degrees.
Was the plant safe while the chiller was out of service?
Yes. The backup chiller was functional and in-service the entire time. Nuclear plants are designed with two sets of every piece of safety equipment for the purpose of having an operable backup if something doesn't work. Redundant safety systems are in place to ensure that the plant operates safely and so that we can protect the health and safety of the public.
Contingency plans are in place to address a condition where neither chiller is available. These contingency actions were evaluated by the NRC for its final decision.
Even if both chillers failed, that would not eliminate the many ways we can get cooling water into the reactor in the event of an emergency.
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