The shutdown of a nuclear power plant in Virginia because of possible weaknesses in its colling system pipes could make electricity 6 percent more costly, according to Virginia Electric and Power Co. data.

Vepco officials said today they are unable to calculate the costs to consumers of shutting down its Surry I nuclear unit, but the company has estimated that replacement of a nuclear plant with coal and oil generators costs customers an average of $250,000 a day.

This would translate to a 15 percent increase in the average daily fuel costs reported by the company last year and a 6 percent increase in average daily charges to customers.

The 6 percent figure is a measure of the overall increase; when applied to Vepco's 1.3 million residential customers only, the cost of the shutdown apparently would be less than 5 percent -- about $2 added to monthly bills that averaged $41.26 last year. Fuel costs account for a smaller portion of bills to small residential users than they do for other commercial and industrial customers.

It was unclear today how long the nuclear plant shutdown will last.

The shutdown of Surry and four other nuclear units on the East Coast, was ordered yesterday by the staff of the Nuclear Regulatory Commission after it was discovered that a design error may have resulted in cooling pipes too weak to withstand earthquakes.Pipe failure could cause a reactor to lose its coolant and melt, releasing readiation into the environment, according to Harold R. Denton, director of the NRC's office of nuclear reactor regulation.

Vepco spokesman Doug Cochran said the overall economic impact of the shutdown is impossible to assess immediately because it depends on unknown factors, such as the length of the shutdown, weather-related demand for electricity and the availability of power from other units with widely varying generating costs.

Vepco Chairman T. Justin Moore said during a speech to the Greenville, N.C., Chamber of Commerce that he expects the Surry shutdown to last only about three weeks. Other Vepco officials said they believe inspections at the Surry plant will show that the cooling systems are built to withstand tremor stresses.

But Denton of the NRC said it could be "some months" before any piping deficiencies at the five units are determined and corrected.

The five, including Surry, were all designed by the Stone and Webster Engineering Co. of Boston. Another Vepco nuclear unit, Surry II, was included in the order but already was out of service for eplacement of generator tubing.

The potential price impact on consumers posed by the shutdown produced immediate calls for Stone and Webster to bear any costs resulting from the design error.

Tayler Cousins, a director of Consumers in electric rate cases, also said press conference that fuel cost increases caused by the shutdown should not be passed on to the consumer. "If Vepco has been sold a bill of goods in faulty design, it should go after the designer and contractor, not the consumer," he said.

Virginia Attorney General J. Marshall Coleman, who represents consumers in electric rate cases, also said in an interview that he would expect Vepco to look to Stone and Webster for payment of costs resulting from the shutdown.

"We will be trying to determine through the State Corporation Commission (SSC) what Vepco's plan is for recovering from Stone and Webster," he said. "However, it's nothing we could do anything about instantly. We will have to wait until the smoke clears a little."

Fuel costs account for about 40 percent of Vepco charges and are passed on to customers through a fuel adjustment charge. Fuel cost changes were passed on automatically through monthly fluctuations in bills until this year. Now the SCC must approve any fuel charge change in advance after quarterly hearings. The next fuel hearing is expected to be held next month.

The SCC staff said today that it has asked Vepco "to advise it of any financial impact" from the Surry I shutdown as soon as possible. The statement noted there would be no immediate change in rates.

Despite the rarity of earthquakes in Tidewater Virginia, where the Surry plant is located, state officials were eluctant to challenge the NRC shutdown order. "I think we have to defer to their judgment," Coleman said.