In addition to their potential safety advantages, iPWR SMRs also pose specific safety-related challenges. The main ones are briefly summarized below:

• While in principle the reliability of passive systems and components should be higher, the actual experience-based reliability data are generally scarce. Thus, a large uncertainty may need to be included in PRA/PSA.

• In particular, natural circulation plays a prominent role in the safety approach and safety systems of many iPWR SMRs, but all related relevant phenomena are not as well understood or quantified as for traditional systems.

• Smaller-power, multiple-unit sites will likely require a common control room to achieve economic competitiveness. Not all the implications for safety performance and safety analyses are well known at this time.

• Multiple SMR units at the same site will each have a smaller source term than a large unit, but a similar total source term for a similar total power. While not likely, common mode failure cannot be completely excluded. There is no clear consensus how to treat and evaluate this situation in technical or regulatory space.

• SMRs are more conducive for co-generation applications. Their market niche will likely include desalination, district heating and other industrial processes where the PWR temperature is sufficient. Conceivably, there may be coupling and feedback between the nuclear and non-nuclear portion with an impact on safety performance. However, this has not been analyzed in detail, and actual experience is lacking.