Investigation On Asymmetrical Operation Characteristics Of Natural Circulation Lead-bismuth Reactor Under Ocean Conditions

Natural circulation lead-bismuth reactor(NCLR)is one of the important candidates for future marine nuclear power because of its high thermal efficiency,good safety,stable operation and superior concealment performance.Due to the influence of marine conditions including tilt,heave,sway,the thermal and hydraulic characteristics of natural circulation lead-bismuth reactor are quite different from those of land-based conditions.At the same time,in order to ensure the vitality for ship,natural circulation lead-bismuth reactor often uses asymmetrical operation to isolate the fault loop in case of specific accidents such as Steam generator heat transfer tube rupture(SGTR)and steam generator primary side blockage.While the loop accident is cleared,the reactor will restore the faulty loop and switch to full loop operation.Therefore,the analysis of the natural circulation characteristics during full-loop and asymmetrical operation and conversion for natural circulation lead-bismuth reactors under marine conditions is important to research the reliability of leadbismuth reactor operation.In this paper,firstly,based on the pressurized water reactor system analysis program RELAP5,the marine condition lead-bismuth reactor system analysis program RELAP5-LBE-OCEA was developed.Secondly,the natural cycle lead-bismuth reactor SNCLFR-10 was carried out to analyze the thermal and hydraulic characteristics under marine conditions.The specific work includes: 1)Based on the system analysis program RELAP5,the system analysis program RELAP5-LBE-OCEAN was developed for the lead-bismuth reactor under marine conditions by adding the lead-bismuth fluid property model,convective heat transfer model,modified flow resistance model,and additional force model,and the calculation accuracy and reliability of the program were verified by comparing the experimental data with the simulation results;and,2)Using the natural circulation lead-bismuth reactor SNCLFR-10,the system analysis program RELAP5-LBE-OCEAN was developed for the leadbismuth reactor.(2)The natural circulation lead-bismuth reactor SNCLFR-10 was used as the research object,and based on the system analysis program,a calculation model of natural circulation lead-bismuth reactor with asymmetrical operation was established,and the operating characteristics of the asymmetrical and full loop conditions under tilt,heave and rocking conditions are analyzed to investigate the response characteristics of the key parameters of the reactor under different motion conditions.The analysis results showed that the RELAP5-LBE-OCEAN system analysis program established in this paper has high accuracy and reliable calculation results.The simulation results of lead-bismuth reactor under marine conditions show that the operation of lead-bismuth reactor under marine conditions is characterized by the decrease of core flow and the increase of core outlet temperature.When the reactor was converted from full-loop operation to asymmetrical operation,under tilting conditions,the flow rate and temperature parameters are less sensitive to the change of tilt angle,under undulation conditions,the fluctuation of flow rate was reduced by 9% and the outlet temperature is reduced by about 16 K.The larger the undulation is,the more drastic the flow rate fluctuation is;the larger the undulation period,the more obvious the flow rate oscillation,but the effect was also weakening.Under swing conditions,core flow and outlet temperature will be decreased and the reactor has a higher safety margin;the larger the swing amplitude and the smaller the swing period,the larger the flow fluctuation,and the core outlet temperature is significantly more sensitive to the cycle change than the swing amplitude change.The reactor parameters quickly recover to the full-loop operation level during the process of switching the system from asymmetrical operation to full-loop operation.The end of the off-loop operation condition under tilt conditions leads to an increase in the sensitivity of key parameters to changes in tilt angle.Full-loop operation at extreme tilt angles has extremely harsh effects on reactor safety.Under heave and sway conditions,the sensitivity of key parameters changes to accompany ocean motion conditions,but the reactor still retains a large safety margin.