The Weakest Link --
Emergency Diesel Generatorsby Scott D. Portzline - Three Mile Island Alert
During a "station blackout" (loss of offsite power) emergency diesel generators (EDGs) supply the electricity needed to bring a nuclear plant to a safe shutdown. If they fail, the chance of an accident approaches certainty. Former NRC Chairman Dr. Shirley Jackson said, "NRC reviews in recent years have left no doubt that a station blackout at a nuclear power station is a major contributor to reactor core damage frequency." The NRC claims a 97.5 reliability rate but watchdogs say it is lower. Nearly every month, the EDGs fail at a nuclear plant; fortunately not during a station blackout.
When a tornado struck the Davis Besse plant (same design as TMI) in Ohio in June 1998, for 41 nervous hours an array of equipment problems complicated efforts to keep the reactor under control. One of the two EDGs overheated and the other failed briefly due to a faulty relay switch. It was a close call which caused the plant's emergency director to say, "For a few minutes your heart goes up into your throat.'' This station blackout also caused the temperature of the spent fuel pool to increase to the point where water would be lost. Nuclear plants currently don't have an emergency power supply for these pools. A petition has been filed by the Nuclear Information and Resource Services (NIRS) to add this safety feature.
Fires have temporarily knocked out the EDGs at the Limerick and Crystal River nuclear plants in recent years. Six years ago, TMI's EDGs were inoperable for one month before the problem was discovered. Last year, TMI's EDGs were labeled a "fire hazard" by an NRC administrator who said they were as "ugly as I have ever seen" because of leaking oil. TMI has since "cleaned up" that situation.
At a June 15, 1999 Y2K meeting between the NRC and the Nuclear Energy Institute (NEI), I recounted what the administrator said about TMI. The vice-president of NEI answered, "So what? As long as they are up to regulations." This is the same kind of arrogance that led to the TMI accident.
The NRC does not draw a clear line for safety. The General Accounting Office (GAO) stated that despite six major reviews over two decades of NRC regulatory oversight, the NRC still does not adequately define safety. For example: the very same valve which caused the loss-of-coolant accident at TMI 20 years ago is still not rated as a safety component.
Emergency Diesel Generator Defects at US Nuclear Plants
as reported by the US Nuclear Regulatory Commission
This database includes incidents and reports from January, 1999 to December, 1999. It shows that defects and problems occur on a weekly basis. There are 32 reports affecting virtually half (49.5%) of all US commercial nuclear plants so far this year.
The Nuclear Regulatory Commission denied a petition for rule-making regarding additional backup power supplies on August 12,1999. The NRC was three months late on making its decision and claims a 98% reliabilty rate for emergency diesel generators.
South Texas, Texas: August 12, 1999
Emergency diesel generator inoperable for 3 days in July 1999.Cooper, Nebraska: August 12, 1999
Degraded backup power supply batteries.Millstone, Connecticut: August 11, 1999
Diesel generator degraded for 32 days. Company was aware of suspected low voltage problem but mistakenly believed it was acceptable.Nine Mile Point, New York: August 11, 1999
During troubleshooting of a speed control problem the diesel generator experienced an inadvertent start-up.Nine Nuclear Plants: August 5, 1999
Manufacturer reports a premature overvoltage protection actuation during diesel generator loading which could affect 9 plants.Cook, Michigan: July 27, 1999
All four diesel generators are declared inoperable but still functional. Discovery of condition which could leave EGDs inoperable following a tornado.Beaver Valley, Pennsylvania: July 16 - 17, 1999
Diesel Generator fails during test due to voltage and current problems. Battery chargers become inoperable. Generator restart faulty. Batteries are inoperable. Plant shutting down. Pumps inoperable briefly.Pilgrim, Massachusetts: July 16, 1999
An existing modification of the circuit logic would prevent bus from energizing properly from diesel generators.Idaho National Engineering and Environmental Laboratory, Idaho: July 12, 1999 (not a commercial power reactor) Two diesel generators fail following a fire at substation. No fuel from Three Mile Island remains onsite.
Pilgrim, Massachusetts: July 5, 1999
Both diesel generators for Unit 1 outside design basis due to high room temperature..Cook, Michigan: June 25, 1999
Diesel generator oil lubrication valve installed backwards. Uncertainty about the ability to operate for 7 days has caused the EDG to be declared inoperableKewaunee Wisconsin: June 14, 1999
Diesel generator declared inoperable due to misadjusted speed sensor. This event report was later retracted.Ginna, New York: June 10, 1999
Both diesel generators inoperable. There would have been an inability to automatically respond to an event coincident with a loss of offsite power.Summer, South Carolina: May 5, 1999
Faulty circuit breaker identified as substantial safety hazard used with diesel generators.Six Nuclear Plants: April 28, 1999
Manufacturer reports a potential defect in connecting rod assemblies, which are components of diesel generator systems.Nine Mile Point, New York: April 24, 1999
Reactor scram. Diesel Generator starts but fails to load. Partial loss of lighting in the control room. Loss of lighting in turbine building. Loss of site perimeter lighting. Natural circulation of coolant.Arkansas Nuclear, Arkansas: April 23, 1999
During Y2K testing, would not properly load. Only 500 Kw, instead of its expected load of 4400 Kw.Point Beach, Michigan: April 20, 1999
Design defect could have disabled diesel generators.Susquehanna, Pennsylvania: April 17, 1999
Operator switching error causes diesel generator to be inoperable.Beaver Valley, Pennsylvania: April 9, 1999
Following instructions in operator's manual could have caused diesel generators to fail.Ginna, New York: April 9, 1999
Missing oil drain port could have caused serious diesel generator damage.Cook, Michigan: April 7, 1999
Design defect could cause long-term operational failure of diesel generator following a seismic event.Seabrook, New Hampshire: March 31, 1999
Defective relay might not have allowed bus to load to diesel generator.Grand Gulf, Mississippi: March 25, 1999
Diesel Generator declared inoperable due to leaking oil. The event was later retracted when it was discovered that it was not necessary to declare it inoperable.South Texas, Texas: March 12, 1999
Diesel Generator output circuit breaker failed to close.Pilgrim, Massachusetts: February 25, 1999
Temperature of diesel generator building fell below design due to winter storm.Wolf Creek, Kansas: February 18,1999
Improper switching could have caused fire and loss of diesel generators.River Bend, Louisiana: February 2, 1999
The NRC proposes a $55,000 fine for the company's failure to correct deficiencies in the compressed air system that controls the emergency diesel generators.San Onofre, California: February 1, 1999
Diesel generator started but did not complete circuit due to relay lockout.Fitzpatrick, New York: January 21,1999
Emergency diesel generators may have failed to energize emergency buses.Hope Creek, New Jersey: January 20, 1999
Incorrect resistor could effect speed switch on diesel generators. This manufacturer defects also could effect 8 other US nuclear plants at Hatch, Fermi, Millstone, Beaver Valley, Limerick, Callaway and Wolf Creek which might have the same defect.Duane Arnold, Iowa: January, 20 1999
Forced reactor shutdown after both standby diesel generators failed test to reach required voltage and frequency within the required time.Grand Gulf, Mississippi: January 13, 1999
Diesel generator degradred due to output transformer leaking.North Anna, Virginia: January 5,1999
Spillway emergency diesel generator declared inoperable during test. This was done in error as it was not necessary to declare it inoperable. The event notification was retracted.