When an earthquake hit Virginia Tuesday afternoon, nuclear power plants up and down the East Coast — including Exelon Nuclear’s Limerick Generating Station — began assessing if damage had occurred.
Part of the problem, however, may be that the place an earthquake is most likely to cause damage is also the place the hardest to inspect — underground.
Making that scenario more worrisome is a June investigative report by the Associated Press which found that as the nation’s nuclear fleet ages, much of its underground infrastructure, exposed to corrosion – and is constantly exposed to moist conditions, may be deteriorating even faster.
Assessing earthquake damage is not a simple operation given that “each plant has unique design specifications for seismic resistance,” according to Nuclear Regulatory Commission spokesman Neil Sheehan.
Called its “design basis,” each plant is “built to withstand the largest historical earthquake in the area, with additional margin on top of that,” Sheehan wrote in an email answering questions from Journal Register News Service.
Sheehan noted that in the wake of the Mineral, Va. tremblor, “walk down” or visual inspections “of key infrastructure at each facility” at all nuclear plants were conducted both by plant personnel and independently by the resident NRC inspectors at each plant.
“No structural damage has been identified at any of the affected plants,” he wrote.
But while visual inspections may have found no damage, any underground damage not evident to the naked eye could only be identified by a change in readings for pipes, gauges or underground valves, according to Sheehan.
“Any significant impacts on buried piping would be readily noticeable via changes in flows. Also, plant owners are required to perform flow tests on safety- and non-safety-related piping at regular intervals,” Sheehan wrote in his email.
“Whether those checks would need to be accelerated in light of yesterday’s earthquake will have to be determined,” he added.
Perhaps that determination will be influenced by the AP report which found underground leaks “sometimes go undiscovered for years, the AP found.”
The AP found that leaks of water laced with traces of tritium, a radioactive form of hydrogen, have been found at 48 of 65 nuclear sites “repeatedly at many of them.”
Although some of those leaks occurred at plants owned by Exelon, no such leak has ever been reported at the Limerick Generating Station.
However, “slightly elevated levels of tritium” were found in six water samples taken from on-site wells at Limerick as well as in one surface water sample according to a study released in 2006. However, the company statement issued at the time said those higher levels are the result of “historic releases.”
In other words: surface spills, not underground leaks.
The “historic releases” were described by a company spokesperson as four “unplanned liquid releases” of tritium that took place “over the past 20 years.”
The tritium was the result of spills, not underground leaks, that had all occurred “in isolated areas on the plant property where you don’t normally find tritium” and had all been reported to the NRC and to the Pennsylvania Department of Environmental Protection.
All the spills were “within our permitted discharge levels” and there were no fines or violations associated with them and the spokesperson said the tests showed none of Limerick’s underground systems were leaking in 2006.
But there were leaks at three Illinois nuclear plants owned by Exelon, one of them from an underground source that went on for four years.
The AP reported that “nuclear operators have failed to stop an epidemic of leaks in pipes and other underground equipment in damp settings. The country’s nuclear sites have suffered more than 400 accidental radioactive leaks during their history, the activist Union of Concerned Scientists reported in September.
“Plant operators have been drilling monitoring wells and patching hidden or buried piping and other equipment for several years to control an escalating outbreak.
“Here, too, they have failed. Between 2000 and 2009, the annual number of leaks from underground piping shot up fivefold, according to an internal industry document obtained and analyzed by the AP.”
The AP investigation also reported “many of the pipes or tanks have been patched, and contaminated soil and water have been removed in some places. But leaks are often discovered later from other nearby piping, tanks or vaults. Mistakes and defective material have contributed to some leaks. However, corrosion — from decades of use and deterioration — is the main cause. And, safety engineers say, the rash of leaks suggest nuclear operators are hard put to maintain the decades-old systems.”
All of which occurred, presumably, without the added stress of an earthquake on aging materials exposed to corrosion.
In addition to publishing an assessment of NRC investigation and enforcement following incidents at plants in 2010, The Union of Concerned Scientists recently issued a set of recommendations for ways NRC could improve safety at the nations 104 nuclear reactors.
Among those recommendations:
• “The NRC should require plant owners to use multiple inspection techniques to ensure detection of any degradation in aging, high-risk equipment.
• “The NRC should require plant owners to periodically inspect equipment outside the scope of normal inspections, both to determine whether that scope is appropriate and to detect problems before safety margins are compromised.”