Slightly more than 3,800 mishaps at nuclear plants occurred last year, more than 100 of them "especially significant," according to Critical Mass, an anti-nuclear group affiliated with Ralph Nader.

The figures were drawn from reports to the Nuclear Regulatory Commission by the utilities operating nuclear plants. The number of incidents support "our long-held position that nuclear power is a dangerous and deeply flawed technology," the group said.

The NRC requires utilities to report any events, even minor ones, that involve a violation of safety specifications or rules. The reports are called Licensee Event REPORT (LERs).

NRC staff members yesterday called the study "seriously flawed by an inconsistent use of data."

"Simply counting LERs is not at all indicative of the safety of operations. You have got to lookat the nature of the experience," said Carl Michelson, head of the NRC office that reviews the reports.

The NRC said it will soon release its own report card for each reactor that will give a truer picture of performance because it will take into account not only the number of incidents reported but also many other factors.

The Critical Mass report showed a 20 percent increase in the number of LERs over the previous year, with the greatest number of Sequoyah in Tennessee, which had 238 incidents even though it was in operation only 11 percent of the year.

Paul Turner, vice president of the Atomic Industrial Forum, a nuclear, a nuclear trade group, said the event reporting simply meant that the system designed to catch problems was working. "What would be worrisome is if you were not finding these things; that would mean your scrutiny system was not working."

He said the nuclear industry's safety record was "perfect" last year -- there were no injuries to employes or the public involving nuclear technology, although there were some of the common accidental injuries.

Also released in the Critical Mass report was the NRC's own rating code used to screen events by degree of seriousness on a letter scale from A to E.

The NRC placed none of the events in the A, or most serious category, and placed "less than five" in the B category, said Richard Udell of Critical Mass. He reported that NRC's definition of a B event as one involving "a moderate actual or potential impact on public health or safety . . . a major reduction in degree of safety."

Categories C and D are listed as "moderate" and "minor" reductions in the degree of protection against accidents. Category E is events involving "only high public interest."

The year's worst accidents, Udell said, were at the Crystal River plant in Red Level, Fla., and at the Brown's Ferry plant in Decatur, Ga.

At Crystal River, the report said, "A control room loss of instrumentation dumped tens of thousands of gallons of contaminated water in the reactor containment building." The lightly radioactive water was pumped out of the room without further incident.

At Brown's Ferry, "76 out of 185 control rods failed to fully insert" and thus failed to do their job in tamping the nuclear reaction. If the accident had occurred when the plant was a full power, the report said, it might have caused a more worrisome accident in which a burst of activity in the core might have caused an explosion within the system containing the nuclear fuel.