Beyond Nuclear and Sierra Club have intervened in the Nuclear Regulatory Commission’s (NRC) review of Duke Energy’s application requesting a second twenty-year license extension (60- to 80-years) for the three-unit Oconee nuclear generating station near Seneca, South Carolina. The groups have requested a public hearing before an Atomic Safety Licensing Board based largely on an expert declaration and safety concerns of retired NRC nuclear engineer and Senior Risk Analyst, Jeff Mitman. Mr. Mitman is professionally familiar with Duke Energy’s inadequate flood preparations for the reactor site. He was a Senior Risk Analyst for the federal agency starting in 2008 and worked on the safety risk review of Oconee nuclear power station’s flood preparations downstream of the Jocassee Dam and the Keowee Dam.
The three Oconee units initially received their operating license in 1973 and 1974. Duke Energy had convinced the federal nuclear regulator, then the Atomic Energy Commission, the NRC’s predecessor, that Oconee’s design and construction did not need any flood protection from a catastrophic failure of the Jocasse Dam, a 385-foot earth and stone filled hydroelectric facility built by Duke simultaneously to the nuclear power station.
Subsequent to the ongoing reactor operations, in 1983 Duke performed a hydrological study for the Oconee site that recognized a “sunny day” failure of the Jocassee Dam was possible and could result in inundating the safety-critical power block for all three units under more than four feet incapacitating the reactors’ Emergency Core Cooling System. To reduce that flood-caused accident risk, Duke constructed a five-foot wall around the reactors’ Safe Shutdown Facility, another late added compensatory structure that was not part of the Oconee’s design basis.
In the early 1980’s, Duke would also perform one of the nuclear industry’s first site-specific Probabilistic Risk Analysis (PRA) report looking at core damage frequency, containment failure and radiological impacts on the surrounding population and economy from a severe accident. The Duke analysis also included the Jocassee Dam failure. However, the analysis of dam failure-related cause of a nuclear accident did not consider dam failures due to an earthquake or overtopping of the earthen-rockfilled dam by extreme rainfall.
By 1988, the NRC issued a Generic Letter to all licensees to “identify any plant-specific vulnerabilities to severe accidents and report the results to the Commission.” Initially focused on internal reactor events, the NRC request proceeded through five revisions eventually asking licensees to expand the scope to include external events such as tornados, seismic events and external floods. At first, Duke considered the risk of a “probable maximum precipitation” event directly over Oconee site but dismissed it based on the large capacity of the reservoirs behind the Keowee and Jocassee Dams.
Duke later considered three more risks to Oconee reactors from seismic-induced dam failure, a random “sunny day” dam failure, and a dam failure caused by extreme rainfall above the Jocassee Dam that overtopped the dam. In that evaluation, Duke would dismiss the overtopping of Jocassee Dam as not credible. However, a later analysis submitted to the Federal Energy Regulatory Commission (FERC) identified that a dam failure could result in 16.5 feet of water inundating the reactor site and the Safe Shutdown Facility rendering all of Oconee’s safety and shutdown systems “inoperable.” While the FERC document was non-public, the details of the vulnerability would laterbe described in a 2011 NRC Safety Evaluation Letter.
During Oconee’s first 20-year license extension, Duke would consider raising the flood protection around Oconee’s Safe Shutdown Facility but dismissed it as not cost-beneficial. Further NRC evaluations, starting in 2006, identified a Oconee performance deficiency involving discovery of a missing flood barrier around the Safe Shutdown Facility and characterized it as a safety violation. Duke’s repeated appeals of the safety violation resulted in NRC re-evaluating Oconee’s flood protection and the Jocassee Dam failure rate as characterized by Duke and determined it was too low.
By 2009, the NRC issued Duke a letter stating that a Jocassee Dam failure was a credible event with accident consequences that needed to be addressed by “deterministic” actions other than dismissing a catastrophic dam failure as highly unlikely. In response, Duke raised the flood barrier around the Safe Shutdown Facility by 2.5 feet to 7.5 feet which was completed in 2009. Duke additionally responded to the increased attention of the NRC with additionally analysis of a Jocasse Dam failure. But instead of finding lower projected flood levels at Oconee, Duke’s new methodology using conservative but not worst-case scenarios found an increase in teh Jocassee flood water to 18.5 feet onsite. In 2011, a subsequent NRC Safety Evaluation required Duke to increase its flood barrier protection around safe shutdown systems to 19.5 feet. The NRC would also finalize its own generic dam failure rates for large earthen stone-filled dams like Jocasse by significantly raising the risk of dam failure rate (2.8×10-4 per year).
According to Mitman’s expert opinion which accompanies the groups’ legal filing, “Ten years later, the 2011 Safety Evaluation and the safety requirements it imposed remain in effect. Duke has not appealed the 2011 Safety Evaluation, nor has the NRC retracted or repudiated it. Yet, there is no record that Duke has completed the required modifications to protect the plant to a flood depth of 19 feet. Nor has the NRC sought to ensure its completion.”
“Oconee’s current operation, and proposed operation under an additional twenty-year subsequent license renewal term [60- to 80-years], pose an unacceptable risk to public health and safety, due to Duke’s failure to fully implement flood-protective measures required by the NRC in a 2011 Safety Evaluation,” Mr. Mitman asserts. “The NRC deemed those flood protection measures necessary to protect against a core melt accident in the event the Oconee site becomes inundated by failure of the Jocassee Dam,” Mitman declares. Just as Japan’s 2011 unpredictable and disastrous impact of a severe earthquake and a 48-foot tsunami’s that caused three nuclear accidents at Fukushima, the overtopping of the Jocasse and Keowee Dams due to severe storms and unanticipated precipitation could reasonably cause the catastrophic failure of the dams and similarly a triple meltdown. Such a wall of water would inundate the downstream Oconee units by as much as 18 to19 feet of water and according to NRC and Duke Energy's own analysis and documents publicly released under the Freedom of Information Act (FOIA) a multiple nuclear accident would ensue.
Duke Energy is seeking to extend the operating licenses of the Oconee nuclear power station out to 2053 and 2054 in a time of an accelerating climate crisis including unprecedented and strengthening storms, rainfall and flooding. Beyond Nuclear and the Sierra Club firmly believe that a public hearing and review of the public record under the National Environmental Policy Act’s “hard look” must be required.
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