Study On The Characteristics Of Secondary Passive Residual Heat Removal System Under Ocean Conditions

In order to investigate whether the secondary passive residual heat removal system(PRS)can operate effectively under ocean conditions,this paper takes the PRS of a small marine nuclear power platform as the research object,and builds a scaled-down experimental apparatus.Under typical ocean motion conditions such as inclination and rolling,the operating data of the experimental apparatus under different operating pressures and different steam generator heating powers are obtained.Based on the experimental data,the influence mechanism and law of typical ocean motion conditions on t he flow and heat transfer behavior of the system is analyzed.In addition,the RELAP5 program,which has been re-developed,was used to simulate and model the experimental device,and the experimental data was used to verify the calculation results obtaine d by the system analysis program,and a comparative analysis was conducted.On the basis of verifying the applicability of the program,the system analysis program was used to further calculate the operating characteristics of the experimental device in th e form of ocean motion that the experimental device could not cover,and the operation performance of the PRS under fault cases which included main pipe blocked of C-type heat exchanger,delayed operation of PRS and non-simultaneous opening of isolation va lves was analysed.The results of the study under stationary conditions show that the system steady-state condition depends mainly on the steam generator heat ing power,while the different operating pressure only affect s the transient response characteristics.During the operation of the system,the C-type heat exchanger has the characteristics of uneven local heat transfer outside the tube,and the heat transfer coefficient outside the tube shows a tendency to increase a long the vertical height of the heat exchanger during the stabilization phase.The research results under typical ocean conditions show that the effective height difference of the cold and heat sources of the system and the change of the heat transfer boun dary conditions outside the tube of the C-type heat exchanger caused by the heeling condition are the main factors that cause the changes in the operating characteristics of the system.The positive angular heeling can enhance the overall heat transfer of the system,while the negative angular heeling has the opposite effect;the trim ing condition only affects the effective height difference between the cold and heat sources,and the influence of the trim ing angle change on the system operating characterist ics is consistent with the heeling condition,and its impact is relatively small.The additional inertial force introduced under the rolling and pitching condition is the main factor that causes the system operating characteristics to change.Under the rolling condition,the periodic change of the heat transfer boundary conditions outside the condenser section of the C-type heat exchanger and the combined effect of flow fluctuations will make the system main thermal parameters also fluctuate periodically.Rolling motion can enhance the overall heat transfer performance of the system,and the enhancement effect increases with the decrease in the amplitude of the rolling angle and the increase of the roll ing period;the pitching motion can enhance the overall heat transfer performance of the system as well,while the change in pitch ing period and angle amplitude has less influence.The results of the study of the fault operation characteristics show that under static conditions,when delay ed operation of PRS occurs,the main thermal parameters of the system also exhibit the delay characteristics during the delay period,and the system status is not affected in the stable phase;when the pipe is blocked in the C-type heat exchanger,the overall heat exchange performance of the system will be weakened,and the pressure in the stable phase will increase significantly compared with the normal operating conditions.The overall heat transfer of the system will be most weakened when the heat transfer tube of C-type heat exchanger is blocked under the condition of heeling-24°,and the pressure value of the stabilization phase is higher than the operation pressure.Nonsimultaneous opening of the isolation valve only affects the system response characteristics and has no effect on the steady state.