UK version of the Hua-long Pressurised Reactor (UK HPR1000), designed by China General Nuclear Power Corporation (CGN), has been successfully completed the Generic Design Assessment (GDA), with the issue of a Design Acceptance Confirmation (DAC) from Office for Nuclear Regulation (ONR) and a Statement of Design Acceptability (SoDA) from the Environment Agency on 7 February 2022. In the UK GDA process, one of the main fundamental requirements is that the nuclear safety risk should be reduced to ALARP (As Low As Reasonably Practicable). During the UK HPR1000 design process, Probabilistic Safety Assessment (PSA) has been widely used as a key tool to inform the design and evaluate risk levels, and to demonstrate that the nuclear safety risk has been reduced to ALARP. The process of PSA ALARP demonstration is established in accordance with the methodology that reflects the UK context requirements and consistent with relevant good practice. The process is fully applied by using PSA to systematically review the risk insights and to support other topic areas. After the systematic review of PSA risk insights from internal events Level 1 PSA, internal fire Level 1 PSA, internal flooding Level 1 PSA, external hazards Level 1PSA, external flooding Level 1 PSA, seismic PSA, Spent fuel pool PSA and Level 2 PSA, the related conservatisms, potential design improvements have been identified and addressed. Current UK HPR1000 PSA results and risk insights show that the risk level of UK HPR1000 design is relatively low and the risk of UK HPR1000 design has been reduced to ALARP in GDA stage.
Spent fuel pool stores fuel assemblies that have been removed from the reactor in previous years, and the release of radioactive material to the external environment is easier than reactor core after fuel damage occurs. In the earthquake situation, the spent fuel pool itself and its accident corresponding mitigation measures are likely to fail at the same time, causing serious accident consequences. Based on the design and operation characteristics of typical CPR1000 units, this paper uses the probability safety analysis method to quantitatively evaluate the risk of spent fuel pool caused by seismic events, and identify the weak links in the design and operation of CPR1000 units. Quantitative analysis shows that the risk of the spent fuel pool caused by seismic events is relatively low relative to the core, with the main risks coming from the collapse of the fuel building and structural damage to the spent fuel pool. In addition, seismic events affect both the core and spent fuel pool, and the steam and radioactivity of spent fuel pools will have an impact on mitigation of core accidents.
Damage to fuel assemblies and the release of radioactive substance may occur during fuel lifting and storage in nuclear power plant. For the purpose of quantitatively evaluate internal events, internal and external hazards induced risk of spent fuel pool and related fuel lifting facilities, to identify weaknesses of the fuel route design and provide corresponding risk insights, the methodology of fuel route probabilistic safety assessment (PSA) is systematically summarized in this study, and based on the design characteristics of a specific pressurized water reactor nuclear power plant, fuel damage frequencies and radioactive substance release frequencies in the fuel route are assessed, some possible further safety improvements for the fuel route are identified. The results of analysis case show that the fuel building ventilation system failure has the largest contribution to the overall fuel thermal damage frequency, while the spent fuel crane failure has the largest contribution to the overall fuel mechanical damage frequency. The drop of the spent fuel cask full of spent fuels in loading pit has a prominent contribution to the risk of radioactive substances release due to the mechanical damage. The safety risk in the fuel route can be effectively reduced by the diversified design of local cooling unit fans in fuel building ventilation system and type modification of the spent fuel pool crane.
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