The Nuclear Regulatory Commission said yesterday that it is fining Virginia Electric and Power Co. $15,000 for an April incident in which a shift supervisor at the utility's Surry nuclear plant deliberately overexposed himself to radiation to check what he feared was a serious safety problem.

Larry Wagner, 36, dashed into an instrument room under the Surry Two reactor shortly after 11 p.m. last April 14. In 15 minutes, he received more than three times the maximum amount of radiation that federal standards allow nuclear workers to receive in three months, according to an agency report on the incident.

NRC officials said Wagner told them he entered the highly radioactive area because he saw water leaking and feared the reactor's main cooling system had ruptured.While the reactor was not in operation at the time, officials said the core still had to be cooled.

Wagner was not sickened by the unusually high radiation dose he received, but the long-term health effects are not clear. Radiation can cause cancer, birth defects and other illnesses.

The nuclear agency, which over the years has fined Vepco more than any other utility, said it was particularly upset because Wagner, a senior Vepco employe, had ignored NRC safety rules.

"We are seriously concerned that the actions of this senior member of your staff might serve as an example to your employes," wrote Victor Stello, director of the NRC's office of inspection and enforcement, to Vepco president Stanley Ragone. "The significance of this event cannot be overstated."

Vepco, which has 20 days to pay or contest the fine, refused to identify the employe involved, say why or how long he was in the instrument room or reveal the time of day the incident occurred at the plant 120 miles south of Washington.

"We choose not to answer those questions right now because our review is continuing and since the incident is potentially subject to litigation," said Vepco spokesman August Wallmeyer.

Wallmeyer said disciplinary action had been taken against the employe, but would not be specific.

Wagner, a Smithfield resident who was named by sources within both Vepco and NRC as the supervisor involved in the incident, could not be reached for comment. His wife said in a brief phone interview that her husband still is working at the Surry plant, leaving open the possibility that the company is still in violation of NRC radiation standards.

Besides proposing the fine against Vepco, the NRC took the unusual step of sending a separate letter to Wagner.

"Your April 14, 1979, entry into a potentially high radiation area in violation of the facility's technical specifications, Vepco procedures and the commission's regulations, demonstrated a failure to follow basic radiation protection requirements and a serious lack of good judgment," Stello wrote Wagner.

He also told Wagner that future recurrences of "such flagrant violations of requirements or demonstration of poor judgment may result in stringent NRC action."

"This kind of thing has happened three or four times in the last couple of years," said Dudley Thompson, the agency's acting deputy director for inspection and enforcement. "We are putting the country's reactor operators on notice that it has to stop and they have to take responsibility for it, or we'll pull their tickets."

An NRC investigative report said Wagner decided to enter the instrument room under the reactor vessel after workers reported that water was leaking into the area.

"He didn't know where the water was coming from, but he was looking at what he perceived to be a serious problem," said Thompson.

The reactor has been shut down since February for replacement of its clogged steam generator system. But Thompson said heat and radioactivity in the reactor was still high enough to require cooling by the plant's water systems.

The report said Wagner wore a film badge that recorded radiation and carried a small pocket dose meter, but lacked a larger meter required by regulations. He also did not obtain required clearnace from the plant's health personnel that the area was safe.

To enter the instrument room, the report said, Wagner passed through a doorway clearly marked: "Caution: high radiation area; prior health physics notification required for entry."

Wagner took 15 minutes to determine that the leak was not serious, at which point he noticed that his pocket dose meter was off the scale.

According to the report, Wagner immediately left the room and reported to the plant's health physics section, where an analysis of his film badge showed he had absorbed 10.093 rems of radiation. NRC standards allow workers to receive up to three rems, a standard measure of radiation absorption, in a three-month period.

Both Vepco and the NRC denied that the reactor was ever in serious danger during the incident.

"As it turned out, there really wasn't any serious problem," said Thompson of the NRC. "To be candid, what he [Wagner] did was a dumb thing to do."

In the past, Vepco has been fined a total of $112,400 for various safety violations at its two nuclear plants. The most recent of these was a $31,900 fine paid in 1977 for 30 violations during construction of the utility's North Anna nuclear plant in Louisa County, 65 miles southwest of Washington.