Small modular reactors (SMRs) may be smaller and use innovative technologies with many inherent safety features, but the ultimate goal when it comes to regulation remains the same: ensuring the protection of people and the environment and minimizing the risks of accidents and any radioactive release.

The novel approaches in the design and deployment of SMRs can pose challenges to the existing regulatory framework. In comparison to existing reactors, proposed SMR designs are generally simpler and the safety concept for SMRs relies more on passive systems and inherent safety characteristics of the reactor, such as low power and operating pressure. These increase safety margins and, in some cases, practically eliminate the risk of severe damage to the reactor core and thus the potential for large releases of radioactivity in case of an accident. Consequently, the reliance on robust containment and emergency response measures is reduced.

“SMRs are in general less dependent on safety systems, operational measures and human intervention than existing reactors. Therefore, the usual regulatory approach, which is based on overlapping safety provisions to compensate for potential mechanical and human failures, may not be appropriate and new ideas should be considered,” said Greg Rzentkowski, Director of the Nuclear Installation Safety Division at the IAEA. However, the main concepts underpinning the current safety approach – such as, for example, defence-in-depth, which assures prevention and mitigation of accidents at several engineering and procedural levels – are relevant for SMRs if implemented using risk and performance information, he added.

To demonstrate the safety of the design of a nuclear power plant of any kind, a comprehensive safety assessment of all plant states – normal operation, anticipated operational occurrences and accident conditions – is required. On that basis, the capability of the design to withstand internal and external events can be established and the performance criteria for safety features, including emergency planning, can be defined.

“The proof of concept for SMRs requires the demonstration of the effectiveness of the fundamental safety functions – reactor control, core cooling and confinement of reactivity – based on the optimization of the defence-in-depth strategies to minimize the risks of accidents and, should an accident occur, practically eliminate its consequences,” Rzentkowski said. Given new design and safety concepts, specific consideration should be given to the validation of the safety case, interfaces between units, material properties and human factors. Furthermore, no matter how low the risk of accidents is, scalable arrangements for confinement and emergency response are essential to cover the unexpected, he added.