WENRA Reactor Safety Reference Levels January 2007

Western European Nuclear Regulators’ AssociationREACTOR HARMONIZATION WORKING GROUPAppendix EDocument status: FinalIssue: Design Basis Envelope for ExistingReactorsSafety area: DesignReference levels:1. Objective1.1 The design basis 13 shall have as an objective the prevention or, if this fails, the mitigationof consequences resulting from anticipated operational occurrences and design basisaccident conditions. Design provisions shall be made to ensure that potential radiationdoses to the public and the site personnel do not exceed prescribed limits and are as lowas reasonably achievable.2. Safety strategy2.1 Defence-in-depth 14 shall be applied in order to prevent, or if prevention fails, to mitigateharmful radioactive releases. The design shall therefore provide multiple physical barriersto the uncontrolled release of radioactive materials to the environment, and an adequateprotection of the barriers.2.2 The design shall prevent as far as practicable:- challenges to the integrity of the barriers;- failure of a barrier when challenged;- failure of a barrier as consequence of failure of another barrier.3. Safety functions3.1 The plant shall be able to fulfil the following fundamental safety functions 15 :- control of reactivity,- removal of heat from the core and- confinement of radioactive material,13 The design basis shall be reviewed and updated during the lifetime of the plant (see ref level 11.1).14 Defined in the IAEA Safety Requirements NS-R-1, 2.9- 2.11. Further information is provided in INSAG-10.15 Under the conditions specified in the following paras.9