The U.S. nuclear industry last year scored its worst safety record since the Three Mile Island accident of 1979, with about 10 percent of atomic plants experiencing "significant" mishaps or management problems, according to a Nuclear Regulatory Commission member and a congressional critic.

While none of the problems resulted in radiation leaks, there were "near-miss" accidents at facilities near Toledo, Ohio, and Sacramento, Calif., a "serious incident" at a plant near San Clemente, Calif., and a "complete collapse of management" at two Tennessee Valley Authority plants in the South, NRC Commissioner James K. Asselstine said.

Safety problems at 10 of the 97 U.S. facilities were detailed in the NRC's annual report to Congress on "abnormal occurrences," which are considered potential threats to public health and safety. The report was released by Rep. Edward J. Markey (D-Mass.), a longtime critic of the nuclear industry.

Although the significance of last year's safety lapses is subject to varying interpretations, the study attracted special attention because of the meltdown of a Soviet nuclear reactor in the Ukraine.

Asselstine said that while U.S. and Soviet plants differ in design and safety features, the Soviet accident shows that nuclear reactors are "still an immature technology." He said last year's mishaps at the Davis-Besse plant near Toledo and the Rancho Seco facility near Sacramento came dangerously close to the breakdown in safety systems experienced by the Ukraine reactor last weekend.

Asselstine and Markey said the number and severity of incidents last year mark the industry's worst safety record since the partial reactor meltdown at the Three Mile Island plant in Pennsylvania.

"The list of close calls strongly suggests that a major U.S. nuclear accident could be lurking around the corner," said Markey, chairman of the House Energy and Commerce subcommittee on energy conservation and power, who called last year's safety lapses "too close for comfort."

Ellen Werther, spokesman for the Atomic Industrial Forum, said last year's problems represent "small glitches" that were easily ironed out. The fact that no radiation was released shows the "system works well," she said.

"Ed Markey loves to grandstand," said Werther, whose group represents nuclear utilities. "If he is suggesting that we need to look at the problems to further ensure safety operations, the nuclear industry could not agree more."

Among 1985's most serious safety problems cited by the NRC was loss of the feedwater systems at the Davis-Besse plant on June 9, which threatened to overheat the core reactor. The feedwater systems remove heat from the core.

Plant operators restarted the auxiliary pump in time to prevent "any abnormal releases of radioactivity and any major damage," the report said, but the two steam generators "had essentially boiled dry before feedwater from any source became available to them." NRC officials blamed Toledo Edison Co. for "lack of attention to detail in the care of plant equipment."

At Rancho Seco, a 26-minute loss of power Dec. 26 led to overcooling of the reactor vessel, and could have ruptured or weakened it, the report said. A number of such mishaps have occurred at the plant, raising the possibility of "more serious consequences," it added.

A loss of power Nov. 21 at the San Onofre plant near San Clemente caused a buildup of pressure in the pipes, which damaged equipment and caused the feedwater system to leak, according to the NRC. Five key valves at San Onofre "degraded to the point of inoperability" in less than a year, jeopardizing a safety system's integrity, it said.

Safety problems at TVA's Brown's Ferry plant near Decatur, Ala., and Sequoyah plant near Chattanooga, Tenn., reflected "ineffective management," the report said.