The Virginia Electric and Power Co.'s North Anna 1 nuclear generating plant was shut down late Thursday night after a valve malfunctioned during a routine test, utility officials said yesterday.

No radiation was released during the incident, according to Vepco and Nuclear Regulatory Commissioin officials. An NRC spokesman termed it "a rather routine shutdown."

The incident occurred shortly after 11 p.m. Thursday as workers were checking a valve in the generating plant's steam pipes, Vepco and NRC officials said. The valve was supposedto move slightly during the test. Instead, officials said, it closed, causing the generating unit to shut itself down automatically.

The North Anna unit, about 80 milessouthwest of Washington, was expected to be back in operation last night, the Vepco spokesman said. The spokesman said the cost of the shutdown could not immediately be determined, although similar incidents have increased Vepco's fuel costs by about $200,000 to $300,000 a day.

The planned startup of Vepco's North Anna unit 2 has been delayed because of an NRC slowdown in issuingnew licenses for nuclear plants.

Vepco's two other nuclear generating units -- Surry 1 and 2 -- have been out of operation since last year for repairs and tests. The Vepco spokesman said Surry 1 is expected to go back into service later this month, with Surry 2 scheduled to follow in early summer.

After the North Anna 1 shutdown Thursday night, officials said, a second malfunction occurred in a diesel-poweredemergency backup engine. The engine started running too rapidly and was shutoff. A second diesel backup engine operated normally, officials said.

The North Anna shutdown was described by Vepco and NRC officials as an automatic safety precaution. The plant's emergency cooling system "functioned properly," the NRC spokesmand said.