A malfunctioning valve has forced the shutdown of Virginia Electric and Power Co.'s North Anna I nuclear unit, leaving all three of the company's nuclear stations out of service at the same time.

Vepco spokesman August Wallmeyer said the valve requiring repairs at North Anna I controls the flow of steam to the generating turbine and is not related to the nuclear components of the plant.

Plant operators detected a problem with the valve last Friday and shut the plant down immediately, he said. He added that the company will use the shutdown to perform routine maintenance and inspections that were scheduled to take place later this month and will take less than two weeks to complete.

North Anna I, located on the North Anna River in Louisa County about 40 miles northwest of Richmond, has been in service since last June 6.

Vepco has two other nuclear stations on the James River in Surry County about 60 miles southeast of Richmond. Surry II has been out of service for about three months for replacement of leaking tubes in its generating unit. Surry I was shut down on March 13 when the Nuclear Regulatory Commission (NRC) learned that pipes in its cooling system might not be strong enough to withstand earthquakes.

Surry I already was scheduled for tube replacements in the last half of this year and the cooling systems of Surry II also must be reanalyzed to determine their ability to withstand earthquakes before it can be returned to service.

Nuclear power accounts for about 25 percent of Vepco's generating capacity. Wallmeyer said, however, the company does not expect a brief shutdown of North Anna I to affect the utility's ability to serve its 1.3 million customers because of the relatively low power demand during the spring.

Vepco officials have said that prolonged outages at Surry I and II to analyze and revise cooling systems could force summer power curtailments and add $11.5 million to customer-paid fuel costs for each month each unit is out of service.

Vepco earlier estimated that the tubing replacement at Surry I and II would add only $5.5 million a month to fuel bills for each month each unit is out of service.

Wallmeyer said Vepco was able to secure coal-generated electricity to make up for the planned shutdowns of Surry I and II to replace the tubes. To place power capacity lost through the unplanned shutdowns ordered by the NRC, the company will have to use generators that burn oil costing $15 to $18 a barrel, Wallmeyer said. This is expected to double the costs of the planned shutdowns.

Consumer representatives already have called on Vepco to seek damage payments from Stone and Webster Engineering Co., designer of Surry I and II,to recover any additional fuel costs caused by design errors in the cooling systems. Vepco previously recovered $9 million from Stone and Webster and Sun Shipbuilding and Drydock Co. for defective pump supports fabricated for its North Anna station.