Rancho Seco Nuclear Leak Raises Questions

When the lights suddenly began flashing in the control room of the Rancho Seco nuclear power plant at 4:14 a.m. on Dec. 26, they touched off a 4 1/2-hour scare that not only left the Sacramento-area plant crippled but also raised questions about possible design flaws at seven other nuclear plants around the country.

The alarm at Rancho Seco sounded after an inexplicable power failure caused its reactor to over-cool, triggering a small radiation leak into the atmosphere that officials now say was harmless.

By the time frantic workers brought the pre-dawn emergency under control, an employee in his early 30s--considered the most experienced worker in the control room at the time--collapsed under the stress and had to be taken to a hospital.

Federal investigators now say that Rancho Seco’s electrical problem may be due to a design flaw that could endanger other nuclear power plants manufactured by Babcock & Wilcox Co. And the U.S. Nuclear Regulatory Commission has asked operators of the other Babcock & Wilcox plants, none of which are in California, to inspect their facilities for similar potential problems.

For the Sacramento Municipal Utility District, Rancho Seco’s owner and operator, the emergency capped a difficult year in which assorted mechanical problems have caused the plant to be out of action for 240 days.

The incident occurred at a time when California’s two other nuclear generating plants--San Onofre and Diablo Canyon--also have experienced operational difficulties, although no radiation leaks have been reported.

None of the problems caused an interruption of service. “These problems at San Onofre and Rancho Seco are solvable, technical problems that in no way endanger the public,” said Ron Weinberg, a spokesman for Pacific Gas & Electric Co., owner of Diablo Canyon nuclear power plant.

Still, the incidents could renew debate over the safety of nuclear power plants.

NRC officials plan to meet with Babcock & Wilcox representatives in Washington this week. The NRC is expected to issue a report in mid-February.

The Rancho Seco plant was generating at 75% of capacity when, for reasons unknown, two circuit breakers opened and cut the power to the integrated control system, which automatically operates much of the plant’s equipment. Within moments, cooling water to the nuclear reactor was first reduced by half and then increased too much as crippled automatic systems tried to cope.

Temperatures in the atomic reactor vessel plunged faster than safety standards specify, which raised the possibility of serious damage to its eight-inch thick steel walls. But, according to a preliminary Babcock & Wilcox analysis, the incident “did not challenge the integrity of the reactor vessel. . . .”

Forced to manually operate valves, the workers had difficulty in bringing the water flow into balance. By the time the plant was brought under control at 8:41 a.m., 450 gallons of radioactive water had spewed out of a damaged pump and some of the water had vented into the atmosphere as radioactive steam.

The amount of radioactivity released was not a health threat, the NRC said. It later described the incident as an “unusual event,” the least severe of four emergency action levels.

“The incident is complex and has potentially significant implications for other nuclear power plants,” NRC spokesman Greg Cook told The Times.

“Rancho Seco is a plant that’s had more than its share of problems, especially in the past couple of years,” Cook said. The Sacramento Municipal Utility District has moved to correct many of the problems, Cook said, and a new management team is in place.

“We can see some very visible effects of their effort to improve their operation. Yet, they are continuing to have trouble, and it’s a plant we have watched very closely and will continue to watch very closely,” Cook added.

At the San Onofre nuclear power plant in northern San Diego County, a major water leak and power outage two months ago forced the shutdown of the oldest of three reactors--17-year-old Unit I.

And earlier this week, Southern California Edison Co., which operates the San Onofre plant, announced that it had found leaks in 105 of 57,505 nuclear fuel rods in Unit III, which caused radiation levels in the reactor’s cooling water to be 10 times higher than the cooling water in Unit II, which was operating at normal temperatures. The higher levels, however, were still within federal safety standards, Edison spokesman Dave Barron said.

Minor Problems Cited

Several minor problems also have been reported at the Diablo Canyon nuclear power plant near San Luis Obispo, operated by Pacific Gas & Electric Co. Unit 2, which is not in commercial service, recently shut down unexpectedly during a test.

But despite the problems at Rancho Seco, San Onofre and Diablo Canyon, Weinberg said California’s nuclear plants have more than proven their value to customers.

He noted, for example, that Diablo Canyon’s Unit I has been at full power 85% of the time since it went into commercial operation last May 7.

Barron also said San Onofre’s three reactors last year produced electricity at 71.6%, 78% and 56% of capacity, excluding times when the reactors were shut down for scheduled refueling. Problems caused four unscheduled shutdowns of Unit I, seven of Unit II and six of Unit III.

“We’ve had a good year,” Barron said.