Vermont Yankee Condenser Woes

Monday, April 16, 2012 @ 05:04 PM gHale

Power output at Vermont Yankee nuclear power plant reduced last week to allow for repairs to the plant’s steam condenser.

By Wednesday afternoon, the plant was running at 34 percent but on its way back up to full power, said Larry Smith, director of communications for Yankee, owned and operated by Entergy.

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He said at no time was the public in any danger.

The condenser consists of thousands of tubes through which water runs in from the Connecticut River. After steam generated by the plant’s reactor goes through the turbine, it circulates around the tubes, where it cools and then goes back to the reactor to repeat the process.

In the past few years, the condenser developed small leaks, in which water from the tubes leaked into the system.

Officials sealed holes in the condenser with Plasticor, an epoxy-like material, said Arnie Gundersen, a member of the Public Oversight Panel, which reviewed a reliability assessment commissioned by the state.

The oversight panel identified the condenser as a significant challenge to the continued reliability of the plant, said Gundersen, partially as a result of the increased flow due to a power uprate in 2006.

“Entergy Nuclear Vermont Yankee (ENVY) has budgeted for future condenser improvements; however, the current condition of the condenser, coupled with the increased flow from (the power uprate), is posing both a reliability challenge and affecting plant chemistry,” the reliability report said.

The condenser consists of Admiralty brass, a metal alloy that includes elemental copper, affected by the chemistry of the steam produced by the reactor.

“Entergy VY uses extensive monitoring using industry-standard predictive maintenance to ascertain condenser health,” the reliability report said. “Condenser tube wall thinning is a known power plant phenomenon; wear rates are predictable based on these measurements. Tubes that show advanced wear can be plugged or monitored more frequently.”

While adequate margins exist to allow for tube plugging to prevent leaks through the current license period, modifications to the condenser need to be done to guarantee its reliability during extended operation, the report said.

The plant just received a new 20-year license and Entergy will eventually need to replace the condenser, at a cost of about $150 million, if it wants to continue to operate the plant for the full 20 years.

Repairing or replacing the condenser was not one of 54 commitments Entergy agreed to prior to receiving its license renewal from the Nuclear Regulatory Commission (NRC), said Neil Sheehan, spokesman for the NRC.

“The condenser is on the non-nuclear side of the plant,” he said. “Though we care about it from the perspective that problems affecting it can challenge the operators, especially when those issues result in plant scrams.”

During a refueling outage in 2010, they resleeved the condenser, a temporary fix that cost between $10 and $15 million and consists of the insertion of short pieces of tubing into the ends of the approximately 30,000 condenser tubes.

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