Progress in Passive Spent Fuel Pool Cooling System R&D Based on Heat Pipe Technology

Following the Fukushima Daiichi Nuclear Power Plant accident, particularly the hydrogen explosion at Unit 4, the safety of spent fuel pools garnered heightened attention, and the global nuclear industry extensively studied post-accident cooling of spent fuel pools consequently. During this period, the distinguished passive capabilities of heat pipes led to their superior adoption as primary heat exchangers, gradually becoming a technical consensus in the whole field. Starting in 2016, based on the series of PEX (Passive Experimental Facility), the group led by China Nuclear Power Engineering Co., Ltd. (CNPE) commenced continuous research on heat pipe mechanisms, the design of separate plate heat exchangers, and the overall characteristics of the Passive Spent Fuel Pool Cooling System (PSFS). And in 2023, CNPE proposed the conceptual design for the Linglong One PSFS system finally. The PEX series experiments were completed in two phases using four sets of experimental apparatus: the feasibility study phase with PEX00 and PEX00+, smaller-scale experimental setups with heat power 2–10 kW, primarily addressing issues related to heat pipe mechanisms, working fluid selection, optimal filling rate, vacuum maintenance, system startup characteristics, and the engineering feasibility of separate heat pipe heat exchanger; and the prototype testing phase with PEX50K and PEX100K. PEX50K, a medium-scale conceptual prototype test facility with heat power 50–100 kW employing a novel separated plate heat pipe (SPHP), focusing on research on innovative heat pipe devices. PEX100K, a large-scale engineering prototype test facility with heat power 100–200 kW employing traditional separated tube heat pipes (STHP), aimed at performance verification of engineering prototype units. After five years of research, the SPHP-based approach was ultimately selected, while the initial one with STHP was discarded. This paper provides a comprehensive overview of CNPE's pioneering, exhaustive, and systematic research and development process on SPHP and PSFS. details the PEX series experimental apparatus, and presents the main conclusions. More detailed experimental data, discussions on specific phenomena in certain experiments, detailed descriptions of equipment's processes, and ongoing actual system-level tests will be discussed in subsequent papers.