The US Department of Energy (DOE) "strongly supports" the Nuclear Regulatory Commission's (NRC) proposal to apply risk-based emergency preparedness requirements to small modular reactors (SMRs) and other new technologies. DOE said the NRC's proposed rule is "the next step in determining the appropriate Emergency Planning Zone size for SMRs and is crucial for the US nuclear industry and the overall development of the technology".The Clinch River site in Tennessee (Image: TVA)
The NRC's emergency preparedness programme for nuclear power plants has up to now focused on large, light-water reactors (LWRs). The proposed rule, together with a draft regulatory guide, considers advances in facility design and safety research, and their application to future operation of SMRs and other future technologies, including non-light water reactors and certain non-power production facilities, the regulator said.
The new rule would only apply to SMRs and so-called ONT (other nuclear technology) applications, not currently operating reactors or fuel cycle facilities. For existing plants, the plume exposure pathway emergency planning zone (EPZ) covers a radius of about 10 miles (16 km), with an ingestion pathway EPZ covering an area about 50 miles in radius. Future SMR and ONT applications are likely to reflect a "wide range of potential designs" that have smaller source terms and also incorporate emergency planning considerations as part of the design, with enhanced safety margins "and/or the use of simplified, inherent, passive, or other innovative means to accomplish their safety and security functions," the rule notes.
Following the publication of the proposed rule in the Federal Register in December 2019, the public and other interested parties were invited to comment on emergency preparedness issues, including the performance-based approach and the scalable EPZ approach. In a 22 May letter to NRC Chairman Kristine Svinicki, Assistant Secretary for Nuclear Energy Rita Baranwal highlighted the DOE's strong support for the proposed rule.
"The NRC's proposed rule, as described in SECY-18-0103, is a critical step in determining the appropriate EPZ size for SMRs using a risk-informed methodology as it will properly credit the advanced safety and performance characteristics of these new advanced reactor designs," the letter said. "The proposed rule allows determination of a plume exposure pathway (PEP) EPZ size that is commensurate with the potential radiological risk for a specific facility and the Department agrees that a risk-informed EPZ sizing approach, as applied to SMR designs and other new technologies, accurately reflects the technological advances in reactor design, gained nuclear industry experiences, and regulatory guidance updates while ensuring that there is no undue risk to public health and safety."
In her letter, Baranwal notes that advanced SMR developers are improving their designs and have incorporated inherent, passive safety features to improve plant resistance to design basis and beyond-design basis accidents, and to assure any potential off-site dose is minimised. Such features include design elements such as smaller reactor cores, lower reactor core power densities, below-ground siting, and redundant passive accident response capabilities.
"Due to these innovations, the probability of an accident involving a significant release of radioactive material in SMRs is expected to be considerably lower when compared to the large LWRs," she said. "Moreover, if such an event were to occur, the SMR design results in a significant time delay before any release to the environment can occur; thereby allowing for additional actions that could mitigate or preclude any release."
In partnership with DOE, Tennessee Valley Authority (TVA) developed an early site permit (ESP) application for the potential construction of SMRs at its Clinch River site near Oak Ridge, Tennessee. The application included a risk-informed, technology-neutral, dose-based, consequence-oriented EPZ sizing methodology. The NRC authorised the issuance of the Clinch River Site ESP in December 2019.
Researched and written by World Nuclear News