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Switch problem causes unexpected reactor shutdown
Tuesday, March 20, 2001
The Associated Press
MONTPELIER, Vt. (AP) -- The Vermont Yankee nuclear plant shut down unexpectedly Monday after routine testing sent plant systems incorrect signals that there was a problem in the reactor core, officials said.
The incident occurred at about 12:30 p.m., as plant technicians were performing weekly tests on four monitors that track pressure levels in the reactor.
William Sherman, nuclear engineer with the state Department of Public Service, said there was no heightened risk to the public in the incident. "There is no safety issue associated with it," he said.
Sherman said the plant is designed to shut down automatically if two of the four pressure monitors indicate a problem in the reactor core.
The monitors are tested individually and in sequence; the test causes a trouble signal to be sent. Normally, there is no second monitor sending a trouble signal.
But on Monday, as one monitor was being tested, a second one also sent a trouble signal, triggering a scram -- nuclear jargon for the insertion of the plant's control rods into the reactor core. That shuts the reactor down.
Vermont Yankee spokesman Robert Williams said Monday evening that the cause of the second monitor's problem appeared to be faulty contacts in an electrical switch.
"The contacts didn't operate as expected, so during the test, that condition caused the plant to sense the need to shut down the reactor."
Sherman said plant safety systems reacted as they were designed to when sensing the trouble signals from the two monitors.
Aside from the monitors themselves, "All of the plant systems worked as they were supposed to. There weren't any abnormal things that happened," Sherman said.
Williams said Monday evening that plant personnel were still evaluating the shutdown and that he didn't know when the reactor would be back in service sending power to the New England electric grid.
Sherman said he expected Vermont Yankee to be back to full operation "within the next couple of days."
-- Doris (firstname.lastname@example.org), March 20, 2001