Engine Systems, Inc. (ESI) of Rocky Mount, North Carlina issued a followup to an earlier Event Report about the failure of a thermostatic valve element in the Emergency Diesel Generator (EDG) in a reactor at the Palo Verde nuclear power plant in 2009. The incident revealed that an element of the assembly was difficult to remove, showed evidence of gouging and exhibited brass machining chip debris.
ESI addressed the effect of the valve element defect: “This defect could affect operability of the thermostatic valve within the diesel engine cooling water and/or lube oil system, resulting in elevated fluid system temperatures during engine operation. Engine performance and/or load carrying capability could be impacted with the possibility of eventual engine failure, thereby preventing the emergency diesel generator from performing its safety related function.”
Subsequent updates showed similar brass debris at other units, and indicated that ESI would not be able to complete its analysis of the problem within the 60-day statutory requirement. The first update also said that examination of other ESI valve elements showed similar brass debris, although the update did not say what emergency diesel generators were checked, only that the analysis was done by Exelon, a corporation that owns 17 nuclear reactors at 10 plants.
Another update reported that the valve elements were actually manufactured by and supplied to ESI by Amot. ESI reported on the way in which the elements were manufactured: “The pills used in the 9760X elements are made by converting another part number pill. This conversion consists of removing the stem from the pill and performing some machining. Amot believes the brass debris may have entered the pill as a result of this conversion process.”
Yesterday’s update included a list of US nuclear plants that used Amot thermostatic valve elements in their EDGs:
Braidwood and Byron in Illinois
Nine Mile Point in New York
Oconee in Florida
Palo Verde in Arizona
South Texas Project
Susquehanna in Pennsylvania
Waterford in Connecticut
The latest update added two nuclear power plants in foreign countries that use the Amot part:
Laguna Madre in Mexico
Ergytech/Iberdroia in Spain