16.2 - Severe Accident Analysis (RRC-B) - EDF Hinkley Point

SUB-CHAPTER : 16.2PRE-CONSTRUCTION SAFETY REPORTCHAPTER 16: RISK REDUCTION AND SEVEREACCIDENT ANALYSESPAGE : 236 / 295Document ID.No.UKEPR-0002-162 Issue 043. RADIOLOGICAL CONSEQUENCES OF CORE-MELTSEQUENCES3.1. SAFETY REQUIREMENTS3.1.1. Safety objectivesThe safety approach for EPR reactors is deterministic, complemented by probabilisticanalyses, based on the concept of defence in depth. Within this framework, a number ofdesign provisions (depressurisation of the primary system, installation of re-combiner units,core catcher, EVU [CHRS]) are made to preserve the integrity of the containment in severeaccidents and hence reduce the accident consequences.The objective of the radiological consequence calculations for RRC-B core melt accidents isto show that, taking account of the above design provisions, the release of radioactivematerials outside the plant remains within the limits set out below.3.1.2. Radiological objectivesThe radiological objectives associated with RRC-B accidents are that only very limitedcountermeasures, that is countermeasures limited in area and in time, should be necessaryi.e.• limited sheltering duration for the public,• no need for emergency evacuation beyond the immediate vicinity of the plant,• no permanent relocation,• no long term restrictions on the consumption of foodstuffs.These countermeasures, which are those laid down in ICRP 63 (see [Ref] and Section 16.2.3- Table 3), relate to both the short term phase (sheltering and evacuation) and the mediumand long term phases, (absence of permanent relocation). The ICRP associates dose bandsor dose rates (averted doses or dose rates) with these protective measures, as follows:• sheltering: 5 – 50 mSv (effective dose),• evacuation; 50 – 500 mSv (effective dose),• issue of iodine tablets: 50 – 500 mSv (thyroid dose),• permanent relocation: 5 – 15 mSv/month for prolonged exposure (dose rate fromcontaminated ground). The value proposed by the ICRP is 10 mSv/month. TheICRP also recommends permanent relocation for an effective averted dose inexcess of 1 Sv (i.e. if an effective committed dose of > 1 Sv can be avertedthereby).