NRC Releases Oyster Creek Inspection Report Detailing Shutdown Causes

by Patricia A. Miller

The federal Nuclear Regulatory Commission has released the results of a four-day inspection at the Oyster Creek Nuclear Plant, after the plant had four unplanned shutdowns within a 10-month period.

Oyster Creek had four unplanned shutdowns - also known as scrams - between Oct. 3, 2013 and July 11, 2014, including two in October 2013. The four shutdowns triggered the inspection when Oyster Creek “crossed the “Green/White threshold” performance indicator rating system during the fourth scram, the NRC said.

“Based on the results of this inspection, the NRC concluded that, overall, the supplemental inspection objectives were met and no significant weaknesses were identified, “according to a Jan. 20 letter from Silas R. Kennedy, NRC Chief Reactor Projects Branch 6, to Bryan Hanson, Senior Vice President, Exelon Generation Company. ”The NRC determined that your staff’s evaluation identified a collective root cause of the four reactor scrams which was decision makers do not always understand the likelihood or consequence of the malfunction of degraded equipment...”.

The NRC rates performance indicators by color. Green is of very low safety significance. White is of low to moderate safety significance. Plants with multiple shutdowns for each 7,000 hours of operation must have a supplemental NRC inspection.

Oyster Creek had unplanned shutdowns on Oct. 3, 2013, Oct. 6, 2013, Dec. 14, 2013 and July 11, 2014, according to the NRC.

The Oct. 3, 2013 scram - occurred during a plant start-up after a maintenance outage. The scram was caused by problems with reactor protection system channels, which began receiving erratic signals, the report states.

The Oct. 6, 2013 scram - occurred during a plant start-up after a maintenance outage when the main condenser vacuum began to “significantly degrade.” The cause was a one-inch hole in a steam inlet expansion joint.

“Inadequate protection of the bellows led to fracture by fatigue cracking or stress corrosion cracking,” the report states.

The Dec. 14, 2013 scram - occurred due to an uncontrolled reactor pressure rise, which happened when brackets holding turbine control valves loosened, then detached from their supports.

“The original equipment manufacturer did not follow their assembly drawings during manufacturing and installed inappropriate locking mechanisms instead of instead of the assembly drawing required parts,” the NRC said.

The July 11, 2014 scram - occurred due to a ”rapidly degrading” condenser vacuum and reactor power was lowed to stabilize plant conditions. An expansion joint downstream bellows failed due to fatigue cracking caused by high stress from from repeated temporary leak repairs, the report states.

“This finding was more than minor, because it was associated with the Design Control attribute of the Initiating Events cornerstone and adversely affected the cornerstone objective to limit the likelihood of events that upset plant stability and challenge critical safety functions during shutdown as well as power operations,” the NRC said.

Nevertheless, inspectors determined that the finding was of ”very low significance” because the problem did not cause a reactor trip and the loss of mitigation equipment to take the plant to a stable shutdown,” the report states.

Oyster Creek is the oldest nuclear plant in the United States. It went online on Dec. 23, 1969.