Support for assessment of Hitachi-GE Human Based Safety

1.1 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). 1.2 Step 2 involved 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). 1.3 During Step 2, ONR reviewed the key human-based safety claims (HBSC) or assertions put forward by the RP in the area of human factors (HF).

These claims require modern standards substantiation in the RP’s safety case in a logical structure of claims, arguments and evidence and in a manner that is proportionate to their risk. ONR’s technical assessment report for the HF assessment work done during Step 2 and key conclusions are published on ONR’s website (http://www.onr.org.uk/new-reactors/uk-abwr/reports.htm). 1.4 ONR commenced Step 3 of GDA on 1st September 2014 and expects to complete this stage at the end of August 2015.

GDA Step 4 is therefore intended to start on 1st September 2015 with completion scheduled for the end of 2017. 1.5 Substantiation of HBSC and the associated human reliability analysis is a key activity in the design of the new plant. It provides input and is informed by a number of cross-cutting areas such as: fault studies regarding the identification of claims and feasibility of any operator actions, verification of function allocation and input to the Probabilistic Safety Analysis (PSA) to enable a best-estimate risk to be evaluated, demonstrate whether a balanced design has been achieved, and to identify areas where the human-contribution to plant risk may be dominant and further reasonably practicable design improvements and re-allocation of function may be needed. 1.6 Hitachi-GE’s submissions to ONR that seek to provide the HBSC substantiation will be phased during Steps 3 and 4 of GDA and will provide increasing detail and evidence as the design and safety case develops and is finalised.

During Steps 3 and 4 of GDA, ONR will undertake assessments of increasing detail, to confirm that the claims are supported by an adequate body of arguments (reasoning) and evidence. During Step 4 in particular, ONR will continue its assessment but with increased focus on the evidence, conducting in-depth reviews, on a sampling basis, of the RP’s HF substantiation and reliability analysis for the UK ABWR HBSC. The outcome of this is to confirm and have sufficient confidence that the HBSC are supported by cogent arguments that are underpinned by robust evidence.