Provision of Support on Probabilistic Safety Assessment (PSA) for the Generic Design Assessment (GDA) of the UK AP1000

1 BACKGROUND TO THE PROJECT 1.1 In December of 2011 ONR formally completed Step 4 of the Generic Design Assessment (GDA) of Westinghouse Electric Company’s (WEC) UK AP1000 reactor design. WEC is the Requesting Party for the UK AP1000 GDA (referred to as “the RP” in this specification). 1.2 Step 4 of the GDA was an in‐depth ONR assessment of the safety case evidence for a generic site envelope undertaken in accordance with the regulatory regime of Great Britain.

The general intention of Step 4 was to move from the safety arguments and system level assessment of Step 3 to a fully detailed examination of the available evidence, on a sampling basis. The aim of Step 4 was to identify any fundamental safety or security shortfalls and allow ONR to come to a judgment of whether (or not) a Design Acceptance Confirmation (DAC) or Interim Design Acceptance Confirmation (iDAC) can be issued (see http://www.onr.org.uk/new-reactors/ngn03.pdf). 1.3 On completion of Step 4 ONR’s assessment was largely complete and the generic design was found to be generally acceptable but some nuclear safety, security or environmental issues remained.

These outstanding issues were identified as GDA Issues, for which the Requesting Party will be required to provide credible resolution plans. ONR was satisfied with the resolution plans and was therefore able to issue an iDAC for the AP1000 generic design. 1.4 These GDA Issues are considered by ONR as significant, but resolvable, and require resolution before nuclear island safety-related construction of such a reactor could be considered.

ONR’s Step 4 PSA assessment can be found at http://www.onr.org.uk/new-reactors/ap1000/reports.htm. 1.5 Following the issue of the iDAC in 2011, WEC paused their GDA related activities. In August 2014, WEC recommenced GDA in order to close-out the outstanding GDA Issues.

During this close-out stage, which is the subject of this statement of service requirements, the Requesting Party will submit additional information in response to all the GDA Issues; and the regulators will undertake sufficient assessment to be able to judge whether this additional information adequately addresses all the GDA Issues. Following the satisfactory completion of the GDA Issue close-out stage, the regulators may then be able to issue a final DAC. 1.6 During the close-out phase ONR will assess the information supporting the GDA Issues by conducting reviews of an appropriate depth, on a sampling basis, of the PSA model, data and supporting analyses, to confirm that the claims and arguments are underpinned by robust evidence. 1.7 ONR expects to start the close-out stage GDA on 1st April 2015 and complete it at the end of 2016.