atw - International Journal for Nuclear Power | 05.2020

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<strong>atw</strong> Vol. 65 (2020) | Issue 5 ı May ENVIRONMENT AND SAFETY 284 simulation results shows that the containment pressure at all conditions begin to rise after a brief decline. Never theless, the trend of the containment pressure is about the same in the simulation results and the experimental result, but the simulation results underestimate the heat transfer capacity of PCSHP compares to experimental results. In the start-up conditions, under different initial containment pressure, the curves of the flow rate of the loop over time are shown in Figure 5. After the loop heat pipe is activated, the natural circulation flow rate reaches a large value instantly and decreaces rapidly at a certain moment, then the flow rate oscillates and gradually stabilizes. Under same boundary conditions, the flow rate in the loop tends to increase with the rise of initial containment pressure. The comparison of the simulation results and the experimental results shows that the trend of the flow rate of the loop is about the same. However, the flow rate obtained by the simulation results is relatively small compared to the experimental results. Generally, the heat transfer capacity of the system is positive correlated with the circu lating flow rate, which also indicates that the simulation results under estimate the heat transfer capacity of PCSHP. In the start-up condition, under different initial containment pressures, the curves of loop pressure over time are shown in Figure 6. After the system is started, the loop pressure drops rapidly, and it rises at a certain moment and gradually stabilizes, maintaining a tendency to rise slowly. Under the same boundary condition, the flow rate in the loop tends to increase with the rise of initial containment pressure. The comparison between the simulation results and the experimental results shows that the trend of the loop pressure is about the same, but the loop pressure obtained by simulation results are relatively small compared to the experimental results. In the start-up condition, with initial containment pressure at 0.35 MPa, the curves of the fluid temperature at various positions of the loop over time are shown in Figure 7. The evaporator outlet temperature is substantially equal to the condenser inlet temperature, and is stabilized at about 110 °C. The condenser outlet temperature is slightly higher than 30 °C. The comparison of the results shows that the simulation results are in good agreement with the experimental results of the above three parameters, but the evaporator inlet temperature differs greatly. In the experimental results, the evaporator inlet temperature decreases rapidly after the start-up of PCSHP and remains equal to the condenser outlet. | Fig. 6. Loop pressure in start-up conditions. (a) Experiment results (b) GOTHIC simulation results (a) Experiment results | Fig. 7. Fluid temperature at various positions of the loop in start-up conditions. (b) GOTHIC simulation results Environment and Safety Experimental and Computational Analysis of a Passive Containment Cooling System with Closed-loop Heat Pipe Technology ı Lu Changdong, Ji Wenying, Yang Jiang, Cai Wei, Wang Ting, Cheng Cheng and Xiao Hon
<strong>atw</strong> Vol. 65 (2020) | Issue 5 ı May (a) Experiment results | Fig. 8. Steady natural circulation flow rate of the loop over containment pressure in steady-state conditions. (b) GOTHIC simulation results ENVIRONMENT AND SAFETY 285 (a) Experiment results | Fig. 9. Steady natural circulation flow rate of the loop over heating power in decay heat simulation conditions. (b) GOTHIC simulation results However, in the simulation results, the evaporator inlet temperature rises after a brief drop. This is mainly because the evaporator inlet temperature is greatly affected by the evaporator in the GOTHIC simulation. 4.2 Steady-state conditions In the steady-state conditions, under different initial vacuum degrees of the loop, the curves of the steady natural circulation flow rate over containment pressure are shown in Figure 8 (P 0 indicates the initial vacuum degree of the loop). With the same vacuum degree, when the containment pressure rises, the steady natural circulation flow rate of the loop tends to increase. This is mainly because the containment temperature goes up with the rise of containment pressure and the temperature difference between the evaporator and the containment increases. Larger tem perature difference results in a higher heat transfer coefficient in the evaporator, which leads to an increased loop circulating dive head, and a larger natural circulation flow rate is observed accordingly. This demonstrates that the heat transfer capacity of the system is highly adaptive with changes in containment pressure. It can also be seen from Figure 8 that when at same containment, the higher the initial vacuum degree of the loop (the lower the initial loop pressure), the larger the steady natural circulation flow rate. It can be seen from the comparison of the results that the simulation results agree well with the experimental results. However, the natural circulation flow rate obtained by the simulation is relatively small compares to the experimental results. 4.3 Decay heat simulation conditions In the decay heat simulation condition, under different initial vacuum degrees of loop, the curves of the steady natural circulation flow rate over heating power are shown in Figure 9. The simulation results are in good agreement with the experimental results. Both the simulation results and the experimental results indicate that under same initial vacuum degree, the steady natural circulation flow rate of the loop increases linearly with the increase of heating power. Generally, the heat transfer capacity of the system is positive correlated with the circulating flow rate. Hence, the heat transfer capacity of the system is highly adaptive with the change of decay heat. Under the same heating power, the steady natural circulation flow rate of the loop with different initial vacuum is basically the same. The initial vacuum of the heat pipe has little effect on the natural circulation flow rate when the system is stable. Environment and Safety Experimental and Computational Analysis of a Passive Containment Cooling System with Closed-loop Heat Pipe Technology ı Lu Changdong, Ji Wenying, Yang Jiang, Cai Wei, Wang Ting, Cheng Cheng and Xiao Hon
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atw - International Journal for Nuclear Power | 05.2020

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