On October 11, 2005, units 2 and 3 of the Palo Verde Nuclear Generating Station (PVNGS) were shutdown because the plant operators could not prove the validity of a calculation made in the 1970s when the plants were designed. The Nuclear Regulatory Commission (NRC) challenged the plant engineers to prove that the Emergency Core Cooling System (ECCS) would function as designed during all postulated accident conditions.
The concern was that a coolant leak of just the right size – not too big and not too small – would allow the Safety Injection pumps to empty their primary source of borated water and not properly switch their suction to the alternate source. The NRC thought that there was a possibility that a vortex would develop in that primary source – known as the Refueling Water Tank – and that vortex could cause the Safety Injection pumps to become air bound if operators did not take manual action to isolate the tank.
The plant operators could not prove that the NRC’s scenario would not happen, so they were forced to shutdown two operating power plants, each with a net generating capacity of 1325 MW of electricity, while they recalculated the plant’s design basis. The third plant at PVNGS was already shutdown for refueling and other maintenance, but if it had been operating, it would have also been required to shut down.
According to recent reports, the operators are now satisfied that they can prove that the plant is safe, so they have begun the lengthy process of reheating and restarting the plant from its cold shutdown condition. The operators expect that the plants will return to full power by the October 21, ten days after the initial shutdown. The NRC, however, is not completely satisfied and will review the calculations with a three member team before allowing the plants to actually return to full power. (Ref: Palo Verde faces more tests)
Of course, there are plenty of people that cheer this kind of conservative response – the NRC discovered a situation that might complicate the response to a postulated accident and the plant owners could not immediately disprove the theoretical scenario, so they put their plant into a shutdown and cooled down condition where the Emergency Core Cooling System was not required to be operational. With a responsibility that is focused purely on “nuclear” safety, the NRC’s action could be considered to be entirely appropriate.
However, the action to shut down PVNGS, under slightly different circumstances, could have had a serious effect on people in the areas served by the plant. Without any consideration of effects outside of its narrow arena of responsibility, “conservative” decisions directed by the NRC to shut down nuclear plants can have significant unintended consequences.
It is fortunate that the situation was discovered at a time when the overall electrical power demands in the area are relatively low because of mild temperatures; there was enough spare generating capacity available and enough available fuel supply for that capacity so that there was not a need to curtail the supply to any customers.
Even with the low demand, however, there were at least two days during the shutdown when California declared a stage 1 power emergency and urged consumers to conserve electricity in order to avoid power outages. In our society, loss of electrical power often has dangerous effects, vulnerable people experience health problems, traffic accidents increase, and people lose hours of work.
There is also a very real cost to the decision to shut down a large production facility. While operating normally, each reactor at Palo Verde produces about 31,800 MW-hours of electricity per day. Though the price of electricity in the market is variable, Bloomberg.com’s commodity price page has pegged the value of MW-hours at the Palo Verde hub at about $80.00-120.00 during the past week or so. By that measure, each lost day of production costs the owners of the 2 plants affected about $6 Million, plus or minus 20%. Palo Verde is a large facility with ownership shared among seven different entities, so the losses are distributed but still significant.
Remember, this shutdown was not due to any operational problem, equipment malfunction, or gross violation of license rules. (Ref: Event Notification 42050 – TECH SPEC REQUIRED SHUTDOWN OF BOTH UNIT 2 AND 3) Here is a quote from the NRC document about the hazard of the event:
“There were no RPS/ESF actuations, and none were required.
“There were no structures, systems or components that were inoperable at the start of event that contributed to the event.
“This condition did not result in any challenges to the fission product barrier or result in any releases of radioactive materials. There were no adverse safety consequences or implications as a result of this event. This condition did not adversely affect the safe operation of the plant or health and safety of the public.
The action to shut down two large electrical production facilities was initiated because an NRC inspector questioned a calculation about the automatic performance of a piece of emergency equipment in a postulated plant malfunction under very specific and unlikely circumstances. Based on the information about the issue published on the NRC ADAMS document center, it appears that reasonably timely operator action could have been directed to ensure complete plant safety if the unlikely event actually occurred. (Ref: TECHNICAL SPECIFICATION REQUIRED SHUTDOWN OF PALO VERDE UNITS 2 AND 3)
Without sacrificing any public safety at all, plant operation could have been allowed to continue while the calculations were performed to determine if the components in question would perform properly. It might have been necessary to station a special watch or to institute special procedures, but surely that could have been done at a far lower cost than $6 Million per day.
There are a number of very good reasons to believe that an aggressive program to develop new nuclear power plants would help make the world a safer and cleaner place. The Energy Policy Act of 2005 contained a number of rather expensive incentive programs designed to encourage investment in those necessary new nuclear power plants. NRC actions like the one described above, where there is tiny to no risk, may render the effort to design and implement the incentives a moot point. Investors hate it when their investments can be idled for capricious reasons.