Session: 05-07: System Performance and Safety Enhancements

Paper Number: 134999

134999 - Design and Evaluation of Mitigation Measures for Tsinghua High Flux Reactor Loss-of-Coolant Accidents 

Abstract: 

Tsinghua High Flux Reactor is a planned new high flux research reactor in China. It will be used primarily for material irradiation and isotope production. The thermal hydraulic characteristics of high flux research reactor are different from those of pressurized water reactor. Therefore, the emergency core cooling system of Tsinghua High Flux Reactor must be reconsidered and redesigned to ensure the core safety in the event of loss-of-coolant accident (LOCA). This paper designs a set of mitigation measures for LOCA and preliminarily proposes the emergency core cooling scheme for Tsinghua High Flux Reactor. The primary coolant system includes four loops, each of which consists of a main pump, a heat exchanger and the corresponding pipes and valves. Four accumulators are respectively located at the upstream of the four main pumps. Two low-flow emergency pumps are connected in parallel with the four main pumps, and each two loops share one emergency pump. All pipes and equipment are placed in either the reactor pool or the finite volume dry pools. Once LOCA occurs, coolant in accumulators can compensate for the leaked coolant. The dry pool where the break occurs can collect the leaked coolant and gradually form a stable pressure boundary after all the accumulators are isolated. The emergency pumps can maintain low-flow forced circulation for 2 to 3 hours. When sufficient safety margin can be ensured, the valves between the primary coolant system and the reactor pool is opened and the natural circulation between the core and reactor pool will replace the forced circulation. To verify the effectiveness of the current scheme, the corresponding Relap5 model is established, based on which four double-ended rupture accidents are simulated. The four breaks are located at core inlet, core outlet, primary heat exchanger inlet and main pump inlet. The simulation results and event sequences for all breaks are presented. The core pressure, mass flow, coolant temperature, etc. in the transient process are studied and analyzed. According to the characteristics of the accidents, all break accidents are divided into five phases: non-shutdown phase, high-injection phase, low-injection phase, stable forced circulation phase and natural circulation phase. The non-shutdown phase is the most dangerous, and thus high core pressure and flow must be guaranteed. During the high-injection and low-injection phases, the safety margin is relatively large. In the stable forced circulation phase, the stable back pressure is formed and the residual core heat can be removed by forced circulation. As for the natural circulation phase, it is also safe. Sudo CHF correlations are used to predict critical heat flux. Results show that the minimum departure nucleate boiling ratios of four break accidents are all larger than the safety limit of 1.5. Therefore, the current scheme can ensure the core safety even if a double-ended rupture accident occurs.

Presenting Author: Zhuang Wang Tsinghua University

Presenting Author Biography: He is a PhD candidate from Tsinghua University. His main research interest is high flux reactor system design.

Authors:

Zhuang Wang Tsinghua University
Heng Xie Tsinghua University
Gan Zhu Tsinghua University
Szu-En Yeh Tsinghua University