Passively safe meaning

Passively safe describes plant, equipment or a facility designed to achieve and maintain a safe state through inherent physical processes (such as gravity, natural circulation or pressure relief) without operator intervention and without reliance on off-site power or backup generators, typically for a defined period after an incident or shutdown. In UK and Irish legal practice, the term is used descriptively rather than being defined in primary legislation or case law. It commonly appears in nuclear safety cases, planning and environmental permitting materials, technical schedules to EPC and O&M contracts, insurance disclosures and transactional due diligence. UK regulatory guidance (including the ONR’s Safety Assessment Principles) and international standards use the concept to assess design resilience. Usage is broadly consistent across England & Wales, Scotland, Northern Ireland and Ireland, though Ireland has no nuclear power stations; in Ireland the concept is more often applied to Seveso/COMAH major hazard installations and radiological protection planning. Key legal significance includes demonstrating robustness to station blackout and loss of external power, informing emergency planning assumptions, evidencing ALARP/so far as is reasonably practicable measures, and allocating design and performance risk in procurement. Following the Fukushima Daiichi accident in 2011, scrutiny of passive safety and loss-of-power tolerance has increased.