Design of passive residual heat removal systems and application of two-phase thermosyphons: A review

We conducted a review on the application of two-phase thermosyphons in passive residual heat removal systems (PRHRs). Thermal management to handle the heat of decay in nuclear power plants is crucial for maintaining the integrity of the reactor core. Nuclear power plants are equipped with decay heat removal systems under normal and accident conditions. These systems are generally known as residual heat removal systems. The technology of decay heat removal that relies on electric power, known as an active system, will become ineffective when there is a total loss of electrical power for an extended period (e.g., extended station blackout (SBO)), such as the accident at the Fukushima Daiichi Nuclear Power Plant. To deal with SBO accidents, the design of Generation III+ and small- and medium-size nuclear power plants already includes PRHR systems, which is designed to function for at least 72 h without operator intervention. On the other hand, the use of two-phase thermosyphons as part of thermal management in nuclear power plants is also increasing. This review aims to determine the current status and challenges of the PRHR system design and the application of two-phase thermosyphons in PRHR design. The tools and models used for analyzing PRHR designs are also included in this review. Therefore, a review of thermal-hydraulic performance PRHR that uses the two-phase thermosyphon has been prepared based on simulation and experimental approaches found in the literature. This review focuses on the design and analysis of PRHR systems for light water reactors (LWR) and the usage of two-phase thermosyphon as cooling devices for nuclear-spent pools and non-transient cooling for both LWR and non-LWR reactors. We highlight the PRHR system design and the application of two-phase thermosyphons in PRHR design. As major contributions, different configurations of long-term cooling of PRHRs are discussed. It has been found that to extend the working life of PRHR beyond 72 h, several researchers have proposed new designs with unlimited cooling capabilities. One of the proposed technologies to support PRHR systems of this type is the sub-atmospheric two-phase thermosyphon. It has also found that RELAP5 is the most frequently used PRHR system design analysis tool. This paper, as a whole, acts as a current reference for researchers and lays the groundwork for future research in the use of two-phase thermosyphon for long-term decay heat removal systems.