PSA of Accidents in the Spent Fuel Pool - EDF Hinkley Point

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HPC-NNBOSL-U0-000-RES-000034 Version 2.0 PSA of Accidents in the Spent Fuel Pool NOT PROTECTIVELY MARKED The frequency of boiling is dominated by the contribution from at-power state AB (96%). In addition, the LOCC provides the majority contribution (67%) to the overall frequency in state AB. The frequency of fuel damage is dominated by the contribution from at-power states AB (52%) and from the refuelling state (47%). However, the absolute values remain low. The contribution to the overall frequency in state AB is 17% and in the refuelling state is 18%. 4.4.4.6 Loss of Offsite Power LOOP Frequency of Fuel Damage (/r.y) Frequency of Boiling (/r.y) AB 2.14E-10 1.13E-05 C 2.42E-12 1.28E-07 D 7.76E-13 4.10E-08 E/2 1.14E-12 6.00E-08 REF 1.97E-10 1.69E-07 OVERALL 4.15E-10 1.17E-05 The frequency of boiling is dominated by the contribution from the at-power state AB (97%). However, the contribution for the overall frequency in state AB is low (4%). The frequency of fuel damage is dominated by the contributions from the at-power state AB (52%) and the refuelling state (47%). Moreover, the contribution to the overall frequency in state AB is 76% and the contribution to overall frequency in the refuelling state is 74%. The contribution of the long Loss Of Offsite Power events to the frequency of fuel damage in the fuel pool has increased by about 200%. This is mainly linked to the increase in initiating event frequency for long LOOP, which has increased from 1E-03/r.y to 5E-03/r.y [Ref. 8]. 4.4.4.7 Loss of Ultimate Heat Sink LUHS Frequency of Fuel Damage (/r.y) Frequency of Boiling (/r.y) AB 2.38E-13 9.30E-07 C 3.67E-15 1.45E-08 D 3.16E-20 1.23E-13 E/2 4.35E-20 1.70E-13 REF 1.50E-15 1.58E-11 OVERALL 2.43E-13 9.45E-07 The frequency of boiling is dominated by the contribution from at-power state AB (98%). However, the contribution for the overall frequency in state AB is low (0.3%). The frequency of fuel damage is dominated by the contribution from at-power state AB (98%). However, the contribution to the overall frequency in state AB is only 0.1%. UNCONTROLLED WHEN PRINTED NOT PROTECTIVELY MARKED Page 22 of 37
HPC-NNBOSL-U0-000-RES-000034 Version 2.0 PSA of Accidents in the Spent Fuel Pool NOT PROTECTIVELY MARKED 4.4.4.8 Dominant Accident Sequences 4.4.4.8.1 Boiling The following table lists the main Spent Fuel Pool accident sequences leading to boiling, in all reactor states. They represent around 87% of the overall risk of boiling in the Spent Fuel Pool. Initiating Event Description Freq. (/r.y) % Loss of Cooling Chain in state AB Loss of pump in state AB Loss of pump in state AB Loss of Cooling Chain in state AB Loss of Cooling Chain in state AB Failure of the SPPA-T2000 platform and the operator fails the local action to initiate the stand-by pump before 97°C. Failure of the SPPA-T2000 platform and the operator fails the local action to initiate the stand-by pump before 97°C. Failure of the operator to initiate the stand-by pump before 97°C. Failure of the operator to initiate the stand-by pump before 97°C. Failure of PTR [FPCS] train 2 due to a mechanical failure (including support systems) and preventative maintenance on train 3. 1.6E-04 56.3 5.7E-05 19.7 1.1E-05 3.9 9.6E-06 3.3 9.1E-06 3.2 The dominant cause of boiling to the atmosphere within the fuel building is the failure of the operator to initiate another PTR [FPCS] pump or train from the main control room or locally. This action has to be performed locally in the case of failure of the SPPA-T2000 platform. The overall boiling frequency is judged conservative; the reliability allocated to the local action is underestimated considering the significant grace period before unacceptable consequences are reached. UNCONTROLLED WHEN PRINTED NOT PROTECTIVELY MARKED Page 23 of 37
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PSA of Accidents in the Spent Fuel Pool - EDF Hinkley Point

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