Nuclear Plants under Repair

Friday, November 30, 2012 @ 10:11 AM gHale

Two nuclear plants are either finishing work or starting repair work to get their plants back up and running.

U.S. power company Exelon Corp. completed repairs on a reactor vessel nozzle at the Oyster Creek nuclear power plant in New Jersey, federal nuclear regulators said.

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While they were working in New Jersety, Constellation Energy Group Inc. shut the 873-megawatt Calvert Cliffs 1 reactor in Maryland for unplanned work on control element assemblies.

“(Exelon’s) weld overlay repairs to a reactor vessel nozzle found recently to have two ‘indications’ (flaws or defects) are now completed,” said Neil Sheehan, a spokesman for the U.S. Nuclear Regulatory Commission (NRC).

“Our inspectors will review the final ultrasonic testing data to ensure we are satisfied with the repair work,” he said.

On Monday, Exelon said the 615-megawatt (MW) plant was in a safe shutdown mode and it would fix the nozzle before the reactor could exit a refuelling outage.

The company however did not say when the 43-year old unit – the oldest operating reactor in the United States – would exit the outage, which began on Oct. 22.

To fix the indication, which the NRC said was not a crack but could grow into a crack if left unaddressed; Exelon ground down the metal around the indication and welded a metal overlay on top of the site to keep it within engineering standards for thickness.

Separately, Exelon told the NRC in an event report early Tuesday it found a pinhole leak of about 2 to 3 drops per minute during testing of the reactor head spray line. The leak is through an earlier weld.

The NRC said the line was part of a reactor vessel head cooling system, which only sees use when the plant is shutting down. Its purpose is to assist in reactor vessel head cooling during shutdown.

The company said it was investigating the cause of the leak and developing a plan to fix the problem.

Meanwhile, Constellation Energy Group Inc. shut the 873-megawatt Calvert Cliffs 1 reactor in Maryland for unplanned work on control element assemblies.

Extensive monitoring at the unit, which slowed to 45 percent of capacity and then halted as of 8:37 a.m,, showed “traces of electrical noise” with one of the coils in the No. 37 assembly, said Kory Raftery, a plant spokesman. Crews are replacing the coils and conducting more tests on all assembly equipment, he said.

“We need to make sure our operators can control every piece of equipment at the plant,” Raftery said.

Constellation has been monitoring electrical coils at Unit 1 since the summer, when the equipment failed and caused a reduction in output, Raftery said. The coils hold up control rods and allow operators to insert those rods into the core to slow or boost output.

Calvert Cliffs Unit 2 continues to operate at full power. The plant is about 38 miles (61 kilometers) south of Annapolis, Maryland.

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