Provision of Support on External Hazards Safety Assessment for Step 3 of the GDA of the UK ABWR

BACKGROUND TO THE PROJECT 1) In January 2014 ONR formally started Step 2 of the Generic Design Assessment (GDA) of Hitachi General Electric’s (Hitachi-GE) UK Advanced Boiling Water Reactor (UK ABWR). Hitachi-GE is the Requesting Party for the UK ABWR GDA (referred to as “the RP” in this specification). 2) Step 2 of GDA is an overview of the acceptability, in accordance with the regulatory regime of Great Britain, of the design fundamentals, including review of key nuclear safety and nuclear security claims with the aim of identifying any fundamental safety or security shortfalls that could prevent the issue of a Design Acceptance Confirmation (DAC) (see http://www.onr.org.uk/new-reactors/ngn03.pdf for details). 3) During Step 2, ONR has reviewed the key safety claims put forward by RP in the area of external hazards Preliminary Safety Report (PSR).

ONR completed Step 2 at the end of August 2014. ONR’s technical assessment reports covering the assessment work undertaken during Step 2 and key conclusions were also published in August 2014. 4) During Step 3, ONR will assess the “safety arguments” of the external hazards safety case submissions which support the safety claims made. 5) For external hazards “safety argument” is interpreted as the structured robust justification to underpin the claims made by the RP (see also scope of the services required).

The safety arguments should be coherent, sufficient and commensurate with the potential risks. They should provide the entry points and clear links to the safety case documentation as a whole. 6) ONR’s Step 3 assessment plan in the area of external hazards acknowledged that the key claims on external hazards by the RP during Step 2 were incomplete.

As a result, ONR’s Step 3 assessment will also consider whether the key claims relating to external hazards that underpin the safety of the UK ABWR are complete and reasonable. 7) For External hazards “safety claims” are interpreted as specific statements about the design features which prevent, limit the severity and limit the consequences of the external hazards on Structures, Systems and Components (SSCs) important in the delivery of the fundamental safety functions, which when implemented will demonstrate that the threats from External Hazards are either removed, withstood or minimised. 8) ONR commenced its Step 3 assessment of GDA on 1st September 2014 and expects to be completed at the end of August 2015. 9) During Step 4, ONR will assess the evidence by conducting in-depth assessment, on a sampling basis, of the external hazards safety case submissions to confirm that the claims and arguments are underpinned by robust evidence. ONR expects to start Step 4 of GDA on 1st September 2015 and complete it at the end of 2017. 10) A key part of Step 2 was for ONR inspectors responsible for assessing the ABWR design to identify areas where timely input from Technical Support Contactors (TSCs) is required to enable GDA to progress to programme,