Level 3 PSA - EDF Hinkley Point

HPC-NNBOSL-U0-000-RES-000028 Version 1.0
Level 3 PSA
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accident that could give rise to a worker dose, SDO-5. The worker risk methodology is
described in [Ref. 23], dose calculations performed in [Ref. 24] and the results are
presented in [Ref. 25]. It should be noted that the methodology presented here relates
only to risk arising from the radiological consequences of accidents. Therefore the risk to
workers arising from annual radiation dose uptake during normal operations is not
addressed in this document. This section also does not address the risk from accidents
that give rise to purely conventional hazards.
Accidents in the ILWSF, the ISFS and the Contaminated Tool Store (CTS) are not yet
considered, they shall be addressed at a later stage when more detailed information is
available for these facilities. The inclusion of accidents from these buildings into the
Worker Risk Assessment is an item on the Forward Work Plan [Ref. 20].
The below Safety Design Objectives, taken from the NSDAPs [Ref. 1], show the targets
for the results evaluated within the Worker Risk Assessment to be compared against.
SDO-4; The risk of an individual worker fatality due to exposure to radiation from
on-site accidents shall be below 1x10-6 per year and/or demonstrated as ALARP.
SDO-5; The targets for the predicted frequency of any single accident in the
facility, which could give doses to a person on the site, are:
Effective Dose (mSv)
Annual Accident Frequency
BSO
BSL
2 – 20 1 x 10-3 y-1 1 x 10-1 y-1
20 – 200 1 x 10-4 y-1 1 x 10-2 y-1
200 – 2000 1 x 10-5 y-1 1 x 10-3 y-1
>2000 1 x 10-6 y-1 1 x 10-4 y-1
A diagrammatic representation of the methodology for the Worker Risk Assessment is
presented in Figure 4.
5.1 Identification of Faults
The first stage of the assessment is to identify all the accidents that could result in a
dose that is greater than 0.1mSv. Accidents resulting in a dose below this limit are
considered to be part of normal operation.
The accident list has been collated from the following sources [Ref. 23];
1) The Level 1 PSA accident list including both internal hazards and external hazards
where these were assessed in the PSA. It was necessary to review all sequences
from the Level 1 PSA, including non core damage ’success’ sequences that could
still result in a dose to workers. Sub-chapter 15.1 [Ref. 7] presents the Level 1
PSA for HPC.
2) The Level 2 PSA Release Categories - Table 15.
3) Design Basis Plant Condition Category (PCC) accidents which were not included
in the PSA. (These are the non core damage faults that could still cause
radiological consequences) - Table 19.
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