Virginia's two nuclear power plants, Surry I and II, will be shut down for $60 million worth of major repairs next year because of a problem that has the nuclear energy industry worried nationwide.

Virginia consumers, who may be asked to underwrite the repairs, may also have to pay for the more than $54 million in coal or oil tha tmust be burned to provide power while the nuclear plants are closed, according to a spokesman for the Virginia Electric Power Co. (VEPCO).

The plants could be closed for as long as three months each, for a total six-month period of reduced production.

The problem, called "denting," is the subject of a $40 million research effort by the nuclear industry.

So far, over the last years the problem has shown up in 14 of the 38 plants that are technologically susceptible to it, according to Vic Stello, director of the operating reactors division of the Nuclear Regulatory Commission (NRC). In four of those cases, including the two in Virginia. Stello described the damage as "extensive."

Denting is the term used to describe a buildup of a substance around pipes containing the water that is superheated by the nuclear reactor. The substance buildup eventually strangles the pipes, causing cracks and leaks.

VEPCO has already ordered six new Westinghouse steam generators - at $10 million each - to replace the ones damaged by denting. The complex replacement operation, the first such one ever conducted in a U.S. utility, will involve cutting holes into the protective containment walls of the nuclear reactors, removing portions of the steam generations, and cutting the pipes that cool the heart of THE REACTORS.

"Installing the (steam) generators in the first place was a whole lot easier than this will be, because now we have to go through the containment . . . wall to get to them," said James Wittine, electrical engineer of the Virginia State Corporation Commission, which oversees VEPCO.

He said the commission would decide how much of the cost of labor and materials would be borne by consumers when VEPCO makes some sort of proposal on it. "I expect they're not going to just ask their stockholders to pick up the tab," he said.

Some industry sources ridiculed VEPCO's repair estimate of $60 million as too low and said it could cost five times that amount since labor costs will be substantial.

Costs of the coal and oil needed as replacement fuels cannot be estimated now for next year because of the unpredictable world energy situation, Wittine said. However, he said it would cost between $215,000 and $300,000 a day if the repair work began now, he said. Energy costs are expected to rise in the next year.

The two Surry plants produce 22 to 23 per cent of all power in the VEPCO system. Company spokesman Doug Cochran said the utilitp hopes to have the North Anna plant in Louisa county operational by the time the Surry repairs begin, although North Anna faces strong opposition from citizens' groups.

Spokesmen for each of four nuclear power companies contacted agreed that their plants remained reliable and had already paid for themselves, often twice over, in fuel savings costs to consumers.

"If these were coal-fired plants, such a conversation (about costs) wouldn't go going on," said Stello of the NRC. "Nuclear power gets a lot more publicity and it's a lot more spectacular, but I'm not so sure that the economics of a coal plant are so different. They also shut down for major maintenance. The most economic fuel source is still nuclear," he said.

The denting problem is complex, involving all three of the water systems that make up a nuclear power generator. The first water system flows around the nuclear reactor itself, carrying the heat produced away. This water is superheated to more than 650 degrees Fahrenheit but is kept under tremendous pressure so that it does not boil.

Pipes carrying the superheated water are in turn surrounded within the steam generator by water from the secons system, which is heated and allowed to boil to make steam. The steam is then carried away to drive, the turbines that produce the electric power.

After passing through the turbines, the steam flows over the pipes that make up the third system. The third system's pipes contain cold water from the outside and, after passing over the cool pipes, the steam is condensed back to water and returned to the steam generator for another round of heating.

Denting occurs on the outside of the primary system pipes where they pass through support plates inside the steam generator, like spaghetti through a sleve.

For reasons that are still debated, a substance called magnetite or "green grunge" builds up around the holes in the plates, pinching and denting the primary system tubes. Eventually they crack and leak and have to be plugged as useless.

"The question becomes an economic one very quickly," said Stello of the NRC."When 20 per cent of the tubes are plugged, the plant might have to operate at less than 100 per cent of capacity. The Surry plants are at a point where further plugging could cause that." A VEPCO spokesman said 18.5 per cent of the primary system tubes were already plugged in Surry I and 16.8 per cent in Surry II.

Florida Power & Light Co. has the next most severe denting problem after the Surry plants. Its Turkey Point III and IV units have 5.5 per cent and 7.5 per cent of their primary sustem tubes plugged. Florida Power & Light has ordered six replacement steam generator "tube bundle assemblies" for $10 million each from Westinghouse for delivery beginning in 1979. The company estimates total cost of the units and replacement fuel and labor at $380 million.

A spokesman for Florida Power & Light said repairs there could take nine to 11 months for each unit. "We still hope the problem could be solved and the process arrested so that we won't have to replace the units," said Charlie Scheer, the spokesman. He called the $60 million order for new units "a ledge" because of the 21-month delivery time.

Denting has also occurred in California's San Onofre nuclear power plant and New York's Indian Point, which use salt or brackish water - as do the Surry and the Florida plants - for the third cooling water (condenser) system. That was at first though to be significant, but ZStello of the NRC said denting has also been found at fresh water coolant plants: Palisades on Lake Michigan, Point Beach in Wisconsin and the Ginna plant on Lake Ontario.

Denting is much less in some plants than in others and just why perplexes officials. "The industry is kind of tied up in knots trying to answer that question right now," said Ron Britt of the San Onofre, Cal., plant headquarters.

There is general agreement that the culprit is bad chemicals in the second water system, the one that flows in and out of the steam generator and turns to steam to drive the turbines. The "green grunge" builds up on metals exposed to this water.

Efforts to stop denting have been complicated by the chemicals used to combat the corrosion that constantly eats away at all pipes that carry hot water. Westinghouse, manufacturer of the Surry, Indian Point, Turkey Point and San Onefre-reactor plants, among others, has experimented with different types of water treatment, various pipe metals and different support plate hole-sizes and shapes.

"We now believe the villain is chlorides which get into the (secondary) system as a result of condenser tube leaks," said nuclear division spokesman Paul Jones of Westinghouse. "The way you fix that is by operating the plant so as to maintain the (leak-free) integrity of the condenser."

The notion that the basic problem lies in the condensers, the third-water cooling system that cools steam back into water for re-use, is currently not widely accepted within the industry. "It becomes more acceptable every day," said John Randazza, superintendent of the Maine Yankee atomic power plant in Augusta, Me.

His plant has one of the highest overall performance ratings in the industry. A major factor in that, he said, was "watching for the smallest kind of (condenser) leaks and repairing them right away." That prevents buildup of chlorides in the second water system and "green grunge" doesn't form, he said.

The $40 million research effort on denting by 19 utilities will be conducted by the Electric Power Research Institute (EPRI) of Palo Alto, Cal. It will investigate the water chemistry problem as well as the kinds of metals involved, and will check design factors while trying to find a way to reverse the buildup of the "green grunge," according to company head Chauncey Starr.