The nation's nuclear watchdog said five safety violations occurred during this year's maintenance shutdown of the Columbia Generating Station near Richland.
Federal safety inspectors classified in a Nov. 2 report three of the events as "more than minor" and called them "violations."
All events were determined to be in the "green" category, the lowest on a four-color scale.
Because of the low risk factor and the corrective actions that already had been taken, plant operator Energy Northwest will not be cited by the Nuclear Regulatory Commission, according to a letter sent to the company last week.
Backup safety systems remained intact during each event and operators never were at risk of losing control, according to the report.
Energy Northwest welcomes the agency's inspections, said spokesman Michael Paoli. The plant near Richland still is in the highest category on every safety measure regulated by the NRC, he said.
The plant produces about 1,150 megawatts, or enough electricity for about 1 million homes.
The safety violations happened during the power plant's refueling outage, which took it off-line from April to September.
Outages typically are planned every two years to replace a share of the reactor's fuel. This outage also was used to replace the plant's 26-year-old condenser, which turns steam that has flowed through the turbine back into water for re-use in the reactor.
The special inspection started at the end of the outage. NRC inspectors reviewed records and spoke to personnel.
One of the events was an equipment failure unrelated to operator error. An electrical safety circuit tripped without being triggered by any reactor malfunction. The logic card containing that circuit had been found to be faulty in some General Electric reactors in 1990, but never had caused a problem at the Columbia Generating Station.
It was replaced with a differently designed logic card after the Aug. 27 failure.
But the other four events were based on poorly executed procedures or poor supervision, inspectors found.
Operators performed work that was not approved and continued with procedures after they encountered "unexpected plant conditions," according to the letter.
On some occasions, operators "suspected something was wrong but didn't speak up," inspectors found. They said supervisors failed to "aggressively enforce" mandatory procedures. This was particularly evident during the refueling outage, but "the willingness to work around substandard procedures was a long-standing operator behavior," according to the report.
"Conservative decision making was not evident," the inspectors said.
Operators did not follow procedures or did not monitor equipment properly on four occasions, according to the report:
w On April 11, operators inadvertently drained about 4,000 gallons of coolant water from the reactor to a drain sump, because they did not close two main steam valves.
w On July 28-30, operators allowed 4,300 gallons of water to escape from the reactor into the drain sump, because water level indicators in the reactor vessel were left uncalibrated by maintenance personnel because of an inadequately designed procedure.
Operators did not stop the activity that caused the water to drain after being told that the levels might not be as indicated.
w On Sept. 10, a control room operator realigned a heat removal system without proper authorization and asked another control room operator to peer-review his actions.
The second operator later told inspectors he silently questioned the procedure, but did not want to speak up against the more-experienced employee. Almost 300 gallons of reactor coolant drained into a suppression pool, triggering alarms.
The primary operator was "permanently disqualified," the report said.
w On Sept. 15, operators performed a test of the control rods -- which determine the intensity of nuclear reaction during normal operation of the plant -- without first checking that the system driving the rods' movement had been restored to its normal settings after maintenance. The rods moved faster than expected and two rods lowered when they were given the command to raise.
The NRC inspectors said that each single event did not pose significant risk, but that the number and type of events taken together could "represent a larger concern."
They did note, however, that Energy Northwest's corrective measures "should be effective at preventing recurrence."
-- Jacques Von Lunen: 582-1402; email@example.com