Level 3 PSA - EDF Hinkley Point

HPC-NNBOSL-U0-000-RES-000028 Version 1.0
Level 3 PSA
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Screen out initiating events which are assessed as low frequency (less than
1E-06/ry) and hence are unlikely to affect the outcome of the assessment
significantly.
Group the remaining initiating events into broad consequence bins based on the
available design basis analysis. In a process comparable to that used for the Level 1
PSA success sequences, each consequence bin characterises the potential for
off-site impact.
Screen out initiating events which result in a deterministic off-site effective dose of
less than 0.1 mSv, as this magnitude of release is sufficiently low to be discounted
from this assessment. This may be done directly for DBA initiating events where
detailed plant analysis is available. For those initiating events not considered in the
DBA, the screening process is on the basis of similarity to DBA events and / or the
Low Consequence Release Categories of Table 12.
Allocate the remaining initiating events to off-site dose bands according to the
release categories of Table 12. At this stage some consideration of the off-site
consequences and conditional probabilities of partial failure of barriers to release is
made.
Two sequences remain after the frequency and consequence screening steps: fuel
handling accident in the spent fuel pool and fuel assembly drop occurring in the reactor
building.
These sequences have been assessed individually, so they can be assigned to an
appropriate dose band. This initial assessment uses the analysis results presented in
Section 3.3 of this sub-chapter. Hence, particularly in the lowest dose bands, the
assigned off-site consequences are likely to be upper bound estimates.
Two further potential accidents in the spent fuel pool, loss of cooling and pool drainage,
have been included in the analysis using results available in Sub-chapter 15.3 [Ref. 13].
It should be noted that this latter sub-chapter does not cover fuel handling accidents.
The frequency contribution to potential radioactive release from accidental aircraft crash
has also been assessed and is shown in Table 16 [Ref. 14], the consequences of an
accidental aircraft crash have also been assessed and has been assigned
conservatively to dose band DB2 [AS-016].
In addition, as part of the site specific assessment for Hinkley Point C (HPC), the risk
due to turbine disintegration from both HPC and Hinkley Point B (HPB) has been
assessed for each safety-related building. For all targets other than the contaminated
tool storage building, the impact frequency is of the order of magnitude of 10 -7 per year
and so can be screened out at this stage [Ref. 15]. The dose due to impact on the tool
storage building has been assumed to be DB1 [AS-017].
The results, in terms of the summated frequency contribution to the dose bands resulting
from these additional sequences, are shown in Table 16.
3.6 Combination of Results
The results from the three strands of the assessment (the Level 1 PSA, the Level 2 PSA
and the additional non core damage sequences as described in sections 3.3 to 3.5 of
this sub-chapter respectively) are presented in Table 17. In addition to the contributions
from each strand, the total for each dose band is presented.
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