Thursday April 7, 1994, began with both units at the Salem Generating Station in southern New Jersey operating at about 75 percent power. Operators had reduced power in case one of the circulating water (CW) pumps tripped. Five of the six CW pumps for each unit were running, with the sixth pump in standby. These pumps take water from the Delaware River, send it through the condenser to cool the steam leaving the turbine, then discharge it back to the river. Since the beginning of March, dead reeds and marsh grass floating on the tides had clogged the debris screens for the CW pumps several times each day. This was more than inconvenience--cooling water from the bay was needed to remove heat from the reactor core.

At 10:14 AM, debris began accumulating on the screens. Within ten minutes, two of the five operating CW pumps automatically tripped on high differential pressure across the debris screens (failures #1 and #2). An attempt to start the standby CW pump failed because its breaker had been improperly positioned after maintenance (failure #3).

By 10:30, operators were reducing power by injecting boric acid and inserting control rods. They rushed to get power down to the point where three circulating water pumps could handle the heat load.

At 10:36, an operator restarted one CW water pump. The pump's discharge valve, which had to be closed to restart the pump, began slowly re-opening.

At 10:39, two other CW pumps automatically tripped because of high differential pressure (failures #4 and #5). One other CW pump was restarted.

At 10:40, the plant's power level had been reduced to 57 percent. Although three CW pumps were running, only one was actually providing cooling water flow to the main condenser, since the discharge valves for the two other running CW pumps were still opening.

At 10:44, the power level was 24 percent. Three CW pumps were running, until another CW pump tripped because of high differential pressure (failure #6).

A minute later, with power down to 18 percent, an operator left the reactor controls to transfer electrical loads in the plant (failure #7).

At 10:46, power had dropped to 8 percent. The reactor coolant system temperature was too low, so a supervisor stepped to the reactor controls and withdrew control rods to bring it back up (failure #8). Another operator restarted a CW pump while another CW pump tripped again (failure #9).

At 10:47, reactor power was about 7 percent. The reactor coolant system temperature was below legal limits (failure #10). The supervisor stepped back from the reactor controls and directed an operator to restore the temperature to the legal range.

The operator withdrew control rods for 55 seconds to increase the plant's power level (failure #11). At 10:50, the reactor automatically scrammed because of high neutron flux at 25 percent power (failure #12).

By 11:19 AM, the pressurizer had completely filled with water, and its power-operated relief valve (PORV) was opening periodically to relieve the rising pressure (failure #13). The atmospheric dump valves (ADVs) should have opened to control pressure on the secondary side, but they failed due to a longstanding problem (failures #14 and #15).

At 11:26, all four main steam line safety relief valves opened to protect the secondary side from overpressurization. Operators tried but failed to reset the ADVs so they would automatically open (failure #16). The operators manually opened the ADVs to reclose the safety relief valves.

The open ADVs caused the pressure on the primary side to drop rapidly. The decreasing pressure resulted in another safety injection signal (failure #17). The safety injection flow increased primary side pressure until the PORV began cycling again (failure #18). The PORV discharged steam and water to the pressurizer relief tank until it overfilled (failure #19) and spilled contaminated water into containment.

Operators realized that primary side was water solid and secondary side pressure was being loosely controlled by the open ADVs. They were in a situation not even close to being covered by their procedures. They allowed the PORV to open and close for the next 20 minutes (failure #20).

At 3:11 PM, operators restored a steam bubble in the pressurizer. They were back in a condition covered by their procedures. A "routine" plant shutdown using normal procedures followed. [19]

The NRC was less than pleased by this event. They fined the plant's owners $600,000. [20] That's $30,000 per error. Since the NRC was allowed to assess penalties of $50,000 for each day of each violation, Salem's owners must have received the volume discount.

"Two wrongs don't make a right" is an old cliché. The folks at Salem tried to figure out just how many wrongs it does take to make a right.

Not So Slick

The Big Rock Point plant near Charlevoix, Michigan, shut down permanently in August 1997 after nearly 35 years of operation. A year later, as the plant was being decommissioned, workers couldn't empty the sodium pentaborate tank in the standby liquid control (SLC) system. They found the pipe that carried the sodium pentaborate solution to the reactor vessel was completely severed. They concluded that for at least the last 13 years of the plant's operation, this safety system would not have functioned had there been an accident. [21]

The acronym SLC is pronounced 'slick' within the industry. In this case, it was actually not so slick.

Wrong Place, Wrong Time

The following events demonstrate the value of the adage, "If it ain't broke, don't break it!"

On March 14, 1981, a worker de-energized five motor-operated valves on the safety injection system at the DC Cook Unit 1 plant in Michigan. Unfortunately, he had been told to de-energize the valves on Unit 2. The operator disabled a vital emergency system on an operating nuclear plant, instead of disabling an unneeded safety system on a shut down plant.

On April 22, 1982, an operator drained reactor water from Point Beach Unit 1 in Wisconsin. Problem was, he had been assigned to perform this activity on Unit 2, which was shut down at the time. Unit 1 was operating and had an urgent need for all of its reactor coolant.