Research On Transients And Accidents Of Supercritical Water-Cooled Reactor

It is pointed out that the nuclear safety should maintain the international advanced level,and the incidence of radioactive radiation accident should be further reduced before the end of the ‘13th Five-Year',which is published in ‘Nuclear Safety and Radioactive Pollution Prevention 13 th Five-Year Plan and the 2025 Vision.The Supercritical Water-Cooled Reactor(SCWR)is an alternative reactor type of the China's fourth generation development,according to its economic,continuity,sustainability,and many other comprehensive advantages.From a safety point of view,the SCWR has features like less water load,transient response fast.its transient and accident research has important scientific significance.The CSR1000 reactor has been selected as the research object.The Stability analysis code SAC-CSR1000 and the Safety characteristic of transient and accident code SCAC-CSR1000 have been made.After the verification,the stability analysis for the core system has been done,along with the safety control system analysis,transient and accident analysis,the safety feature and design improvement.In the supercritical water-cooled reactor core system stability calculation,the stability of full load operation transient and whole process of start transient are been analyzed.The calculation results show that In the full load operation transient,the highest attenuation frequency is less than 0.5 in both the first flow channel and the second flow channel.In the start transient,there is a phenomenon in the process of steam turbine start-up phase,pressure-up phase and the beginning of the temperature rise phase,the highest attenuation frequency is higher than 0.5.So during full load operation transient,the core system can maintain stability.In the start transient,it is indicated that steam turbine start-up phase,pressure-up phase and the beginning of the temperature rise phase exist the instability of the core system.In the supercritical water-cooled reactor safety control system anaylsis,the judgment of trigger condition of safety systems,the safety system operation process active safety system matching calculation are done.The results show that the supercritical water-cooled reactor safety system has low flow,high power and high pressure shutdown trigger signal.The active safety system parameters of supercritical water-cooled reactor are optimized.Among them,the pressure controller K value is 100/4,the main steam temperature control coefficient KP is 0.12,the power controller adjustment coefficient B is 2.9.In the typical supercritical water-cooled reactor transient calculation,the partial loss of flow transient and coolant pump stuck transitent are calculated.The results show that in partial loss of flow transient,the maximum cladding temperature is 729.08?,and the core pressure is stable at 24.17 MPa.In coolant pump stuck transitent,the maximum cladding temperature is 739.72 ?,and the core pressure is stable at 24.14 MPa.After the occurrence of these two transients,the maximum cladding temperature does not exceed 850?,while more than 800? for no more than 491 hours.The reactor pressure does not exceed 26.25 MPa.Therefore,in the typical transient conditions,CSR1000 supercritical water-cooled reactor can ensure the integrity of the fuel cladding to meet the requirements of transient standards by the safety systems.In the typical supercritical water-cooled reactor accident calculation,the total loss of flow(short term),total loss of flow(long term)and loss of coolant accident are calculated.The results show that,in the total loss of flow accident,the maximum cladding temperature is 1094.56?,and the maximum core pressure is 25 MPa.In the loss of coolant accident,the maximum cladding temperature is 630 ?,and the maximum core pressure is 25 MPa.After the occurrence of these two accidents,the maximum cladding temperature does not exceed 1260?,the reactor pressure does not exceed 27.5MPa.Therefore,in the typical accident conditions,CSR1000 supercritical water-cooled reactor can ensure the integrity of the fuel cladding to meet the requirements of accident standards by the safety systems.In safety characteristics and design optimization of SCWR,the safety feature of CSR1000 has been done,and the suggestions of design optimization are put forward.The analysis results and optimization program are as follws: It is recommended that the ratio of the density feedback coefficient is 1 and the ratio of the doppler feedback coefficient is 4.Increase the flow control device in both processes,add the logic control unit to control the flow and pressure during the start-up process to ensure that the core flow instability does not occur.In the safety control system chosen,it is recommended to use active and passive coupling control system design.