Beyond EPZs: nuclear emergency management frameworks when using site boundary emergency planning zones, with a case study on high temperature gas reactors

Adapting emergency management programs to the risk profile of small modular reactors, while ensuring that they still meet necessary defence in depth safety objectives, is a key pillar in the responsible deployment of the technologies. Predicated on the assumption that urgent protective actions would not be required even following a bounding emergency, a site boundary EPZ approach allows for a measurement-driven framework for implementing protective actions. It is a reactive approach that uses dose measurements and operational intervention levels (OILs) to trigger the early (non-urgent) protective actions aimed at averting doses over the longer term, and confirm assumptions about urgent protective actions. A case study based on a high temperature gas reactor (HTGR) safety analysis is performed to show the potential source term and off-site consequences, develop HTGR-specific OILs, and show how different non-urgent protective actions can be triggered with measurements exceeding OIL values.