Shengfei Wang

Thermal–Hydraulic Performance Analysis for AP1000 Passive Containment Cooling System

In order to improve the safety of new generation nuclear power plant, passive containment cooling system is innovatively used in AP1000 reactor design. However, since the system operation is based on natural circulation, physical process failure — natural circulation cannot establish or be maintained — becomes one of the important failure modes. Uncertainties in the physical parameters such as heat and cold source temperature and in the structure parameters have important effect on the system reliability. In this paper, thermal–hydraulic model is established for passive containment cooling system in AP1000 and the thermal–hydraulic performance is studied, the effect of factors such as air temperature and reactor power on the system reliability are analyzed.Copyright

Effect of air temperature on passive containment cooling system reliability in AP1000

Passive containment cooling system is innovatively used in AP1000 reactor design to enhance the safety. Since the system operation is based on natural circulation, physical process failure induced by uncertainties of physical parameters becomes one of the important failure modes (e.g. natural circulation cannot establish or keep and system design function cannot be accomplished because some parameters such as air temperature deviate from their design values), which should be considered in system reliability evaluation. As the heat sink, air temperature with high uncertainty has important effect on system reliability. In this article, we analyze the pressure variation in the containment along with the air temperature based on system thermal–hydraulic model, and the effect of air temperature on system operation is closely related to the thermal–hydraulic performance of the system. Moreover, the system thermal–hydraulic capacity is influenced by the system component configuration, so we evaluate the system physical process failure probability by Monte Carlo simulation and analyze the effect of air temperature distribution under different system component configurations. Finally, we evaluate the whole system reliability considering the logical relationship between physical process failure and equipment fault by fault tree method. The results illustrate that air temperature distribution has important influence on the system reliability, the system failure probability may be difference by several orders and the main contributors may be different at different plant locations, so climate should be considered in system design and reliability analysis.

Study on Impacts of ADS on AP1000 During SB-LOCA

AP1000 model, including Reactor Coolant System (RCS), Engineering Safety Features (ESFs) and containment, is built by using the modular accident analysis program. A severe accident scenario of small-break loss-of-coolant accident (SB-LOCA) at cold leg concurrent with different conditions of the automatic depressurization systems (ADS) was simulated and the calculation was mainly during the in-vessel phase, the effect of the ADS1-4 on the AP1000 was analyzed and evaluated. The analysis results showed that the execution of ADS 1-3 was effective to decrease the pressure of the primary system at the early stage and lead to quick and effective injection of cold water from core make-up tank (CMT) and accumulators into the core, but it was impossible to decrease the pressure of primary system effectively to allow the injection from the internal refueling water storage tank (IRWST) to the core and the core was uncovered. The zirconium-water reaction will produce the hydrogen. The execution of ADS4 accelerated the injection from the accumulators to the core and decreased the pressure of the primary system quickly so that the IRWST injection was available and the core was still covered with water. It was of great importance to the safety of AP1000. The passive containment cooling system (PCS) was an effective measure to control the pressurization of the containment.Copyright