ECCS meaning

Emergency Core Cooling System (ECCS): In nuclear law and practice, ECCS refers to the suite of engineered safety systems on a power reactor that automatically injects coolant to keep the reactor core covered and remove decay heat during accident conditions (e.g. loss‑of‑coolant accident), preventing fuel damage and core melt. The term is not defined in UK primary legislation; it is an engineering expression used in nuclear safety regulation. It appears in ONR Safety Assessment Principles and in licensees’ safety cases under nuclear site licence conditions (e.g. LCs 14, 23, 27, 28). It is central to design basis and beyond design basis analyses, regulatory assessment, and maintenance and testing. In BWRs, ECCS typically includes high‑ and low‑pressure injection and core spray; in PWRs, high‑ and low‑pressure safety injection, accumulators and residual heat removal. In normal operation, heat is removed by the turbine steam cycle: in BWRs, condensed steam returns as feedwater to the reactor vessel; in PWRs, condensate/feedwater returns to steam generators, with a separate primary circuit. Usage is consistent across England & Wales and Scotland. Northern Ireland and Ireland have no civil power reactors, but the term appears in transboundary and emergency planning.