The following news article originally appeared in NEI’s Nuclear Energy Overview.
NEI has reiterated its position that the key to minimizing radioactive releases during an accident is to avoid core damage. In a letter to the NRC, NEI is also urging the agency to consolidate several issues it is analyzing separately.
NEI’s letter says the best approach to reduce the potential for land contamination is fundamentally by the numerous actions to prevent core damage already promulgated under the high-priority (Tier 1) recommendations issued by the NRC’s post-Fukushima task force.
“Having stated this, it is important to also state that the industry is fully committed to continuing our scientific research and technical analysis to provide the most effective means to further improve our mitigation capabilities,” NEI says.
If a severe accident progresses to the point where nuclear fuel is damaged and fuel debris goes outside the reactor vessel, the need to employ an appropriate filtering strategy would arise. NEI says that a performance-based analysis should be used to select the best strategy.
“The approach to developing these [filtering] strategies or enhancing existing strategies should be founded on scientific and factual analysis and should be performance-based to achieve the desired outcome,” the NEI letter said.
NEI makes clear that in order to address this issue, plant modifications may be needed that could include:
• ensuring reliable containment spray or immersion during a severe accident
• enhancing FLEX capability
• adding filters on a plant-specific basis.
No matter what solution is selected, the actions of reactor operators remain the key component of any filtering strategy, NEI’s letter says.
“First and foremost, all effective filtering strategies—with or without external filters—must rely on operator action and active systems to provide water to cool the fuel debris that is outside the reactor vessel.”
Situations that involve the prolonged loss of electricity to a site would rely on the industry’s FLEX strategy to maintain the flow of water and cooling to the reactor core.
“Substantial decontamination factors for radioactive releases can be achieved by a comprehensive strategy that includes installed equipment, operator actions and capabilities that are largely consistent with the diverse and flexible coping strategy (FLEX).”
Operator actions would include cooling fuel debris, water injection and controlled containment venting (periodic opening and closing of the vent). Taken together these actions could dramatically reduce the release of radioactive particles, NEI said.
“A combination of these actions would result in 99.9 percent removal of radionuclides that have the potential to contaminate the environment. (They provide for a containment system decontamination factor of greater than 1,000, which is a common international requirement.)”
The addition of external wet filters would offer only marginal benefits.
“Low specific-decontamination factor filters used in combination with the other strategies may further reduce radionuclide releases. However, the aerosols remaining after using the other required strategies would be composed of much smaller particles. The efficiency of the removal of these very small particles has not been demonstrated with current filter designs and additional research would be needed.”
NEI’s letter also references a study released last month by the Electric Power Research Institute, which analyzed various filtering strategies. Based on the findings of the report, deciding the correct strategy for each reactor or reactor design would take a considerable amount of time.
“Applying the findings of the EPRI study to individual plants will take significant effort and time. At a minimum, each plant (or class of plants) will have to perform a specific evaluation based on the EPRI methodology to determine the appropriate strategy to implement,” the letter said.
NEI also urged the NRC to take a holistic approach and resist the temptation to analyze each issue in isolation. Instead, the agency should focus on combining its analysis of filtered vents, economic consequences of land contamination, review of beyond-design-basis regulation (Fukushima task force recommendation 1) and the work of its risk-management task force.
“Each of these four major efforts has the potential to alter in a significant manner all or important parts of the way NRC regulates nuclear power plants. The NRC should consider these matters as one and develop a consistent direction,” the letter said. “This would allow for synergistic decision making that would benefit each matter by avoiding overlap and the potential for conflicting decisions.”