Memorial Day was a busy one for the 104 nuclear reactors in the United States. In addition to a pair of emergency diesel generator problems, two unscheduled activations of emergency cooling systems and a sulfuric acid spill, there were three scrams over the weekend:
1. On Friday afternoon, the Unit 1 reactor at the Summer nuclear power plant in South Carolina reported an unexpected activation of the Emergency Core Cooling System. The reactor had been shut down for refueling, and operators were attempting to bring the reactor back online when the unanticipated activation of the cooling system happened. The plant reported that a differential in steam pressure caused the system to trip. Cause of the steam pressure differential is under investigation.
2. Also on Friday afternoon, an undercurrent signal in a transformer caused the startup of all diesel generators serving the Unit 1 reactor at the Diablo Canyon nuclear station in California. Plant operators say that the incident was the result of “human performance error” during testing. The EDGs have now been secured and normal power restored.
3. Early Sunday morning, the Unit 1 reactor at Watts Barr in Tennessee experienced an automatic reactor trip following a turbine trip. During the shutdown, the Pressurizer Backup Heaters failed to energize. Cause of the turbine trip is still being investigated.
4. Also Sunday morning, the Unit 2 reactor at the Limerick nuclear power plant in Pennsylvania scrammed from 75 per cent power due to low pressure in the Electro Hydraulic Control system, which was undergoing maintenance at the time. Reactor is currently in Hot Shutdown.
5. Later that morning, the San Onofre nuclear power plant in California suffered a sulfuric acid leak. The amount of acid spilled was not specified, and the spill was contained and remediated.
6. On Monday morning, the Unit 2 reactor at Surry in Virginia experienced an Auxiliary Feedwater System initiation when one of the two main feedwater pumps developed a loss of pressure. (The second main pump was out of service for maintenance at the time.) The activation was the result of action taken by maintenance: “The operating team took the deliberate action to secure the running main feed pump to prevent bearing damage with the knowledge that an Auxiliary Feedwater actuation signal would be generated.”
7. And on Monday morning, operators at Limerick Unit 2 were forced to scram the reactor for a second time following the failure of both Recirculation Pumps.
You can see NRC Event Reports at www.nrc.gov.