Increasing access to electricity and powering economies while minimizing greenhouse gas emissions are central goals of many governments, and advanced nuclear power reactor designs, including small modular reactors (SMRs), can play a crucial role in meeting these goals. However, novel approaches to their design and deployment pose challenges to the existing regulatory framework.
Although the IAEA safety standards – which serve as a global reference for protecting people and the environment from the harmful effects of ionizing radiation – can generally be applied to SMRs, experts from the SMR Regulators’ Forum are working on a tailor-made solution to help national authorities regulate this new class of nuclear power reactors.
Their new safety recommendations for SMRs are now available online, following a meeting of experts working on the development of national standards specific to SMRs. This new generation of nuclear power reactors, with output of no more than 300 MW(e) per unit, offers the possibility of flexible supply, including in combination with renewables, while being deployable either as single or multi-module plant.
“The SMR Regulators’ Forum considers that deployment of SMRs requires a flexible regulatory framework to address the specific safety challenges related to novel aspects of proposed designs,” said Camille Scotto De Cesar, Associate Nuclear Safety Officer at the IAEA, who works with Forum members. “It has published new recommendations on safety implications that arise from the use of modularity and compactness of SMRs and on the SMR lifecycle licensing framework.”
Hosted by the IAEA, the SMR Regulators’ Forum is an international group of regulators working on the challenges of regulating the novel designs of SMRs. Founded in March 2015, the Forum gathers nine countries and other stakeholders sharing SMR regulatory knowledge and experience. Together, they identify and propose solutions to common safety issues that may challenge regulatory reviews associated with SMRs.
“The work of the SMR Regulators’ Forum allows us to better understand the current state of practice and challenges in licensing of SMRs,” said Greg Rzentkowski, Director of Nuclear Installation Safety Division at the IAEA. “Although currently we have no plans to develop specific safety standards for SMRs, we will use these insights in the establishment of our holistic, technology neutral, framework for safety of nuclear installations, which also applies to novel designs, to help harmonize international approaches by using the IAEA safety standards.” To be effective, the regulators must be prepared to recalibrate the current model of regulations by increasing reliance on risk and performance insights, he added.
We have asked Karine Herviou, Director at the Institute for Radiological Protection and Nuclear Safety (IRSN, France) and member of the Forum, to present these latest recommendations.
What kind of SMR design specificities may impact safety?
Karine Herviou: The modularity and compactness inherent to SMRs may have safety implications and introduce new challenges to the SMR lifecycle, associated with design, construction, commissioning, operation and decommissioning stages.
What does the term “modular” refer to?
Karine Herviou: It refers to the way SMRs are built (“modular construction approaches”) or to the capability to allow additional power units on the same site or in the same infrastructure (so-called “modular design approaches”). The SMR Regulators’ forum is considering both definitions of modularity as both may have safety implications.
What are the safety implications that could arise from the use of modularity in SMRs?
Karine Herviou: Multi-module SMR designs may have certain operational and safety benefits, such as interconnections between modules to strengthen the availability and reliability of support services (electric power, compressed air, water) or qualified personnel. On the other hand, the current operational experience with multi-unit nuclear power plants indicates that they may require specific consideration for nuclear safety, emphasized by the lessons learned from the multi-unit Fukushima-Daiichi nuclear power plant accident. The use of shared systems may for instance introduce risk of vulnerabilities in the design, along with dependencies among the facilities. In other words, when one module faces a safety problem, it should not have any bearing on the other modules [see Interim report on Multi-unit/Multi-module aspects specific to SMRs].
How can SMR designers improve safety?
Karine Herviou: The SMR Regulators’ Forum considers that it would be beneficial for both designers and regulators to think beyond the single unit mindset. This might involve extending their considerations to whole site risk including developing methods of aggregating risk from differing on site sources. For instance, for maintenance of modules, consideration should be given to ensure that a hazard in a module under construction, in maintenance or in operation would not have any safety consequences for neighbouring operating unit or the safety consequences are properly considered by designing provisions to mitigate such hazard (for example a protective shell or constraints on the operation of neighbouring modules during introduction of a new module or during sensitive activities).
What are the safety implications related to the compactness of SMRs?
Karine Herviou: Most SMRs are designed to be compact in order to enable their manufacture at a factory and to facilitate their transportation to the plant site. However, the compact nature of SMRs may prove challenging when it comes to performing the necessary inspections, operations and maintenance, not only during the manufacturing stage, but for the entire life cycle of the SMR. For instance, inspection and non-destructive examination of the welds of components are necessary to check the quality of the manufactured items.
Who could contribute to address this situation?
Karine Herviou: Manufacturing processes would need to be properly coordinated to allow accessibility for the necessary inspections and examinations. Vendors should also need to consider up-front, how inspections would be performed during the operation of the reactor and discuss accessibility with potential licensees and regulators prior to finalizing such designs. Moreover, the development of specific control devices may be requested [see Interim report on manufacturability, supply chain management and commissioning of Small Modular Reactors].
What are the safety challenges faced within the SMR lifecycle licensing framework?
Karine Herviou: New challenges to the SMR lifecycle regulatory framework are mainly associated with the construction, commissioning and decommissioning stages, especially for multi-module SMRs. In addition to novel design features and approaches, SMR projects may indeed introduce several differences to a new-build projects, ranging from factory manufacturing and testing, to new construction and commissioning methods. These may impact potential stages for SMR licensing and pose challenges to the traditional view of the licensing approach that considers subsequently the following high-level stages of activities: siting and site evaluation, design, construction, commissioning, operation, decommissioning and release from regulatory control. For instance, all activities associated with the project, including the impact of construction and operation of multiple modules (or units) on a single site, should be considered in the licence application.
What are the implications of shifting more of the manufacturing and construction from site to factories, as it is the case for SMRs?
Karine Herviou: This may change how and where initial plant tests are conducted, as compared to conventional nuclear power plants. Many tests that were previously initial plant tests conducted at the site may now be factory tests, conducted by the supplier. Since the Licensee remains responsible for the design and construction of the SMR, the Licensee would have to provide enough oversight of any factory tests performed as part of initial plant testing.
