A review of the FLEX strategy for nuclear safety

Abstract

After the Fukushima nuclear accident, in order to enhance the implementation strategy of Defence in Depth (DID) for nuclear safety and response to the U.S. Nuclear Regulatory Commission Order EA-12-049, U.S. Nuclear Energy Institute (NEI) put forward the concept of Diverse and Flexible Coping Strategies (FLEX) and the corresponding FLEX support guidelines (FSG) for the special accidents caused by external events. Subsequently, the idea of the FLEX strategy was accepted and spread widely. Since 2021 is the 10th anniversary of the Fukushima nuclear accident, the progress in the FLEX strategy should be summarized systematically, and the existing challenges of the FLEX strategy are deserved to review. This paper has reviewed and summarized the methodology of the FLEX strategy in the following aspect: the Beyond-Design-Basis External Event (BDBEE), the procedures of the FLEX strategy (including the development, analysis, and assessment of the FLEX strategy, the creation of FSG, and its implementation), the staffing and training, the resources management (including on-site and off-site portable equipment/devices). A comparison of Extensive Damage Mitigation Guideline (EDMG) and FSG has been given in this paper since they are sometimes confusing. Furthermore, the integration of the FLEX strategies with other procedures/guidelines has been reviewed specifically. Finally, based on the literature and the above-mentioned review, some concluding remarks and recommended future work have been given.