Quantitative risk reduction by means of recovery strategies

Highlights: • This paper illustrates an application of the ISA methodology to quantify the risk reduction by means of FLEX and usual recovery strategies. • The impact of portable equipment and AFW recovery strategies on Damage Exceedance Frequency of TLFW sequences has been evaluated, as well as the RCP trip and F&B start time. • The FLEX strategies lead to a significant risk reduction in TLFW sequences. • The installation time of portable equipment is a key factor for FLEX strategies success. -- Abstract: After the accident at Fukushima Dai-ichi, considerable efforts were put on enhancing the capability of the Nuclear Power Plants to cope with conditions resulting from the loss of plant safety-related systems. The most widespread solution adopted worldwide has been to define and implement new procedures and emergency actuation plans, the so called FLEX strategies. Among these strategies, there are several recovery strategies which involve the use of portable equipment for accomplishing the safety functions of the unavailable systems. In some cases, these strategies have been devised to be performed concurrently to the usual system recovery procedures included in the EOPs of most NPPs. In this regard, the heat sink recovery after the occurrence of a Total Loss of Feedwater (TLFW) in a Westinghouse 3-loop PWR design is a significant example, and it has been chosen in the present study to assess the quantitative risk reduction provided by the usual and FLEX recovery strategies in a Westinghouse 3-loop PWR design. With this aim, the Integrated Safety Assessment (ISA) methodology, developed by the Spanish Nuclear Safety Council (CSN), has been applied to TLFW sequences as part of the collaboration between Technical University of Madrid (UPM), NFQ Solutions and CSN.