The review of the applicability of submitted UK AP1000 design basis fault modelling to the GDA reference design

.1 ONR has already undertaken a comprehensive assessment of the adequacy of WEC’s extant UK transient analysis of design basis faults (Ref 1) against the 2006 ONR Safety Assessment Principles (SAPs). It is for WEC to propose a new design reference point, identify analysis appropriate for that design reference point (either new or existing analysis), justify why the analysis is appropriate for UK AP1000 design reference point, and comment on whether the “delta” is small enough such that ONR’s conclusions on the previous fault studies safety case submissions remain valid. 2.2 For this work package, a technical support contractor (TSC) is required to assist ONR by:  On a sampling basis, review the new [US] transient analysis and form an independent view on its appropriateness for the revised UK AP1000 design reference point.  On a sampling basis, review the differences between equivalent analyses submitted as part of EDCD Rev 0/Rev 1 and the latest [US] transient analysis, to form an independent view on the size of the “delta” between the two sets of analyses and the continuing applicability of ONR’s regulatory conclusions made from its assessment of the EDCD analyses.  Informed by the work on items 1) and 2) above, form an independent view on any justification provided by WEC for the continuing appropriateness of UK-specific analysis undertaken during GDA Steps 3 and 4 for the revised design reference point.

2.3 The size and choice of sample will be a matter of judgement. However, there will be advantages in looking at the faults considered by ONR in Steps 3 and 4 (see Ref 1). The majority of the faults sampled are expected to be documented in Chapter 15 of the EDCD. However, containment analysis in Chapter 9 and shutdown faults in Chapter 19E will require consideration.

2.4 Additional information (for example, calculation notes) can be requested from WEC using the Regulatory Query process established between ONR and WEC. The task is expected to be largely a review of references undertaken by fault studies specialists with demonstrable experience in running reactor transient analyses, as well as knowledge of UK and US reactor design basis safety cases. It is likely that the size of the delta between the predicted results of different generations of analyses can be determined from the high level documentation provided at the start of the contract. Changes in assumptions in computer code input decks will likely on become apparent through the examination of lower level documentation received via Regulatory Queries.

2.5 It is not anticipated that any independent transient analysis will be required as part of this contract. One outcome may be a recommendation (to ONR) for additional analyses to be undertaken, either by ONR or by WEC (the latter being more likely). The ultimate deliverable will be a report to ONR detailing the review undertaken and the conclusions reached, with recommendations (to ONR) made.