The off-site emergency planning measures provide a necessary protection at Level 5 of the defence-in depth “Mitigation of radiological consequences of significant releases of radioactive materials” [9.8, 9.9] and generally include the designation of a zone (or several zones) around the plant with certain restrictions on residence and activities, as well as planning of the evacuation and relocation and other measures for the emergency cases. Rated necessary from the viewpoint of protection of the population and environment from radiological consequences of beyond design basis accidents, the off-site emergency planning generally narrows the siting possibilities for NPPs and may add certain economic burdens on a new NPP project [9.6].

For SMRs, location in closer proximity to the users is rated important for the following reasons [9.10, 9.11, 9.12 and 9.13]:

• Some of the niche markets targeted by SMRs offer no space for a large off-site emergency planning zone.

• Many advanced SMRs provide for non-electrical applications, such as district heating or desalinated water production, that benefit economically from plant location in the proximity to the users.

• Some advanced SMRs (e. g., HTGRs) foresee the collocation of chemical or other process heat application plants on the site.

• SMRs do not benefit from the economy of scale and, therefore, reduction of the costs associated with the off-site emergency planning is viewed as one of the factors to combat the negative economic impacts of a smaller plant size.

The basis for justifying the reduced off-site emergency planning for SMRs is provided by a smaller source term offered by some of the SMR designs, rather than by low CDFs and LERFs which are often matched by state-of-the-art NPPs with large water cooled reactors [9.14]. Smaller source terms for advanced SMRs may result from [9.6, 9.14]:

• smaller fissile inventory;

• smaller stored non-nuclear energy (pressure, temperature, chemical energy);

• the provision of a higher margin to fuel failure and the elimination of certain initiating events by design.

Some SMR designers examine options to reduce the emergency planning zone radius for their plants, as indicated by the summary data given in Table 9.2.

Off-site emergency planning has legal and institutional aspects varying from country to country.

In all countries with an ongoing nuclear power programme there are some more or less strictly prescribed values of the emergency planning zone radius for nuclear power plants. For example, in the United States the radius is 16 km around the plant, in Japan — 10 km, in France — 5 km, in the Russian Federation — 3 km (but with a 30 km monitoring zone) [9.6], all for NPPs of essentially the same type and independent on the number of units on the site.

In some countries, e. g., the Russian Federation, there are provisions for the redefinition of the off-site emergency planning zone radius on a plant specific basis. For example, the smaller radius for a floating NPP with the two KLT-40S reactors (see in Table 9.2) has been justified using such provisions as adopted in the Russian Federation. The justification was based on a deterministic analysis with the supplementary probabilistic analysis to determine the CDF and LERF.

In other countries, e. g., the United States, the regulations could be more prescriptive. In such circumstances the progress in justifying the reduced off-site emergency planning is associated with the introduction of risk-informed safety regulations which would allow account to be taken of smaller source terms offered by some SMRs on a more realistic basis [9.6]. Reference [9.6] provides an example of the risk-informed methodology that might be used for the justification of a reduced emergency planning zone radius.

More details about the current maturity status of the risk-informed approaches are provided in the following section.

9.2 New regulatory approaches

This section provides a short summary of the emerging regulatory approaches and highlights the potential benefits to advanced SMRs that could result from the future implementation of these approaches.