New safety recommendations for small modular reactors (SMRs) are now available online, following a meeting of senior national nuclear regulators in Vienna on 25-28 March.  

They discussed challenges and shared experiences in developing regulations for SMRs, which are defined by the International Atomic Energy Agency (IAEA) as advanced reactors that produce electricity of up to 300 MW(e) per module. With advanced engineered features, SMRs can be deployed either as a single or multi-module plant. They are designed to be built in factories and shipped to utilities for installation as demand arises.

Many IAEA member states are now focusing on their development, and there are some 50 SMR designs and concepts globally. Some are believed to be near-term deployable, including four SMRs in advanced stages of construction in Argentina, China and Russia (one now deployed).  However, IAEA said novel approaches to SMR design and deployment pose challenges to the existing regulatory framework.

The SMR Regulators’ Forum, hosted by the IAEA, is an international group of regulators working on the challenges of regulating the novel designs of SMRs. The forum was founded in March 2015, bringing together nine countries and other stakeholders sharing SMR regulatory knowledge and experience.

“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.

“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.”

“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 harmonise international approaches by using the IAEA safety standards.”

Karine Herviou, director at France's Institute for Radiological Protection and Nuclear Safety noted that the modularity and compactness inherent to SMRs "may have safety implications and introduce new challenges".  This could impact all stages of the lifecycle from design, construction, commissioning, operation and decommissioning.

“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,” she said.

However, Herviou stressed that current operational experience with multi-unit nuclear power plants indicates that they may require specific consideration for nuclear safety, as emphasised by the lessons learned from the multi-unit Fukushima-Daiichi accident. "The use of shared systems may for instance introduce risk of vulnerabilities in the design, along with dependencies among the facilities,” Herviou said.   

She added:  “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.”

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 units.

New challenges to the SMR lifecycle regulatory framework are mainly associated with the construction, commissioning and decommissioning, Herviou said. SMR projects may 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.”

Shifting more of the manufacturing and construction from site to factories,  may change how and where initial plant tests are conducted, compared with conventional facliities. “Many tests that were previously initial plant tests conducted at the site may now be factory tests, conducted by the supplier,” she said. “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. “