Determination of Emergency Planning Zones distances and scaling-based comparison criteria for downsized Nuclear Power Plants

Highlights: • SMRs require plant-specific methods for EPZ distances. • SMR lower radioactive releases do not necessarily mean higher offsite safety levels. • Site proliferation by SMR deployment needs be addressed through scaling criteria. • Deterministic and probabilistic criteria for offsite hazard comparison are provided. • Two plant-specific methods for the determination of EPZ distance are developed. Nuclear Small Modular Reactors (SMR) present innovative features in design and safety compared to existing Nuclear Power Plants (NPP). Some of these features may turn into a reduction in radioactive releases –both in magnitude and frequency. It seems reasonable to think that smaller plants, i.e. featuring lower power levels, should present lower radioactive releases and offsite consequences. However, how small is small enough cannot be addressed through direct comparison. Furthermore, since multiple nuclear sites to compensate for the same amount of power provided by a single, large nuclear site, might be needed, such direct comparison is ill-conceived. Scaling-based criteria to facilitate comparison of radioactive releases between plants of different size –i.e. power– are proposed. Such criteria set limits to radioactive releases and offsite radioactive risk for SMRs so that offsite consequences of replacing large NPPs by a wider set of SMR sites are not exceeded when assessed globally, i.e. in terms of power generation. The first, deterministic-oriented criterion looks at the radioactive source strength of the SMR based on the maximum size of the SMR Emergency Planning Zone (EPZ) in order not to exceed the EPZ of another NPP when normalizing the EPZ to the power generating unit. The second, risk-informed criterion, looks at the sum of the radioactive harm caused by any event considered under probabilistic analysis application weighted by its frequency, i.e. standard definition of risk. Aside from these two scaling-based criteria for offsite nuclear hazard comparison between nuclear sites of different size, this paper presents two different methods for the determination of EPZ distances. The first method is straightforward based on plant-specific data for dose-consequence calculation, whereas the second, inverse method, builds on extrapolating the EPZ distance of a reference, large NPP down to the SMR. The scaling-based criteria and the methods for the determination of the EPZ distance are put into practice in an application exercise for an integral Pressurized Water Reactor (PWR) SMR.