Level 3 PSA - EDF Hinkley Point

HPC-NNBOSL-U0-000-RES-000028 Version 1.0
Level 3 PSA
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The Level 2 PSA considers sequences that lead to core damage. As the containment
function is considered as part of the Level 2 PSA, the results contain sufficient detail to
allow this Level 3 risk assessment to be performed.
The methodology for the individual risk assessment is summarised in Figure 1.
The Safety Design Objectives (SDOs), as set out in the Nuclear Safety Design
Assessment principles (NSDAPs) [Ref. 1], for individual risk are as follows.
SDO-6: The risk of fatality of any person off-site (public) due to exposure to
radiation from on-site accidents will be below 1x10 -6 per year and/or demonstrated
as ALARP.
Effective Dose (mSv)
Total Predicted Frequency (per year)
BSO
BSL
0.1 – 1.0 1 x 10-2 y-1 1
1.0 – 10 1 x 10-3 y-1 1 x 10-1 y-1
10 – 100 1 x 10-4 y-1 1 x 10-2 y-1
100-1000 1 x 10-5 y-1 1 x 10-3 y-1
>1000 1 x 10-6 y-1 1 x 10-4 y-1
.SDO-7: The design of an NNB GenCo NPP will ensure that the total frequency of
accidents in each of the different dose categories (dose bands) in the above table
is below the BSL. However, the design objective will be to achieve an accident
frequency in each dose category (dose band) that is below the BSO.
3.1 Identification of Initiating Events for Assessment
The list of initiating events has been drawn from three sources:
Those considered in the Design Basis Analysis (see Chapter 14). These events are
listed in Table 8.
Initiating events modelled in the Level 1 PSA (see Sub-chapter 15.1 [Ref. 7]). These
events are listed in Table 9.
An expert review [Ref. 8] of the design and operating practices to identify additional
initiating events whose consequences would be within the design basis. These
events are listed in Table 10.
The main purpose of the expert review was to identify those initiating events not already
modelled in the Level 1 PSA which have the potential to result in off-site radiological
consequences within the dose band range considered for the assessment of individual
risk. These include reactor based faults and non-reactor faults. The panel of experts
have knowledge of both the EPR design and safety assessment, with experience of
safety cases for facilities licensed in the UK.
The result of the expert review process is a combined list of initiating events not included
in the Level 1 PSA. These are listed in Table 11. Note that not all the events listed in
Tables 8 and 10 appear in Table 11. This is because some of the design basis events
(Table 8) are considered in the Level 1 PSA, and some of the ‘additional’ events
identified in the expert review had also been identified in the Level 1 PSA. (The expert
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