BRATTLEBORO — The Vermont Yankee power plant has been at reduced power for the past two days because of a problematic valve in a turbine in the non-nuclear side of the plant.

Entergy Nuclear spokesman Laurence Smith said late Wednesday afternoon that Yankee was at 43 percent power, but was increasing power production. On Tuesday, the Vernon reactor was at 20 percent, and earlier Wednesday, it was at 34 percent, according to the morning report posted by the Nuclear Regulatory Commission on its website.

Smith said that plant personnel were performing scheduled maintenance surveillance of the turbine valves when the problem occurred. He said the valve closed properly, but would not “respond as expected” and reopen.

He said that engineers from Vermont Yankee and General Electric performed repairs on the 640 megawatt reactor.

He said the problem was with a pilot valve on the main valve on the B turbine.

Neil Sheehan, a spokesman for the Nuclear Regulatory Commission, said that the problem was traced to a lack of lubrication.

“They identified a lack of lubrication on the pilot (control) valve for the stop valve,” Sheehan wrote in an email.

Turbine stop valves are swing disc-type valves on the lines carrying steam from the reactor to the turbine, he said, and they are designed to abruptly close when the reactor trips, or shuts down, causing the turbine to slow down and eventually stop.

Sheehan stressed that the valve problem occurred in what the NRC considered was the “non-nuclear” side of the plant, meaning the power-generating side of the plant.

“Problems involving the turbine can force a shutdown, which can challenge plant operators,” he added.

Sheehan said that Entergy employees used the reduced power time to clean the water box of the plant’s condenser. He said the water box, at the base of the condenser, is cleaned out periodically.

@Tagline:susan.smallheer @rutlandherald.com