Operating problems continue to mount at the Palo Verde Nuclear Generating Station.

It seems Arizona Public Service Company engineers have had a difficult time keeping a diesel electric generator running, let alone all three nuclear reactors at the power plant. APS manages the plant for a consortium of utilities.

The failure of the diesel generator and the sudden shutdown of Unit 2 last week underscore the serious management problems gripping the huge industrial complex 50 miles west of Phoenix.

Diesel generators provide power in case of a power failure at the plant, which could threaten its safe operation.

Last July, an emergency diesel generator for Unit 3 broke down during a routine monitoring test. Yet APS failed to fix it until April, when Unit 3 was shut down for refueling.

The Nuclear Regulatory Commission conducted a special investigation into the failure of the diesel generator and APS' less-than-expeditious response to the problem. The NRC has found four apparent violations of federal nuclear power plant regulations. The agency has scheduled a June 10 enforcement conference with Palo Verde managers to discuss penalties, which may include a fine.

The NRC's investigation discovered a familiar litany of management problems found in past years at Palo Verde by the NRC and an industry watchdog group that closely monitors nuclear power plants.

Those problems include poor inspection of damaged equipment, inadequate engineering and overall weak management. Rather than repairing the diesel generator within 72 hours of its July 1993 failure or shutting down Unit 3 as required by NRC regulations, APS let the problem slide until the April 1994 refueling.

In its investigative report, the NRC wrote that "inspectors concluded that the licensee had missed several opportunities to identify and correct the damage" to the generator.

Given the problems with running a diesel generator--technology that has been around for more than 70 years--it's not too surprising that APS repairmen last week fouled up a separate routine maintenance job, resulting in the sudden shutdown of Unit 2.

On May 28, repairmen were supposed to work on one of two sets of electrical relays that control the sprinkler system inside the Unit 2 containment building.

Basically, according to NRC inspector Ken Johnston, the workers opened up the wrong electrical box. "It's like going to your stove and you've got a couple of burners," Johnston says. "They turned on the wrong burner."

When they began working on the wiring, the workers caused a valve on the sprinkler system to open and water was sprayed into part of the containment building.

The water got inside a supposedly waterproof junction box and caused an electrical short, stopping one of the pumps that provides cooling water for the reactor.

When the pump shut down, the reactor immediately shut down. "It was a normal shutdown and there were no complications," says Palo Verde spokesman Mark Fallon.

It took almost a week to repair the damage, and Unit 2 was not brought back on line until Friday. Four NRC inspectors were dispatched to investigate the incident, and are expected to issue a report on the mishap in about a month.