Research On Nuclear Core Thermal Performance Of Fast Reactor Under Typical Accident Conditions

Sodium-cooled fast reactor is the fourth generation nuclear reactor system with good application prospects because of its closed cycle and high energy utilization.In the use of nuclear energy,when a nuclear accident occurs,the radioactive nuclides leaked will have a greater impact on the personnel and environment in a certain area;on the other hand,three major nuclear accidents in the world make people "talk about nuclear discoloration".Therefore,the safety of nuclear reactor,accurately speaking,the safety of nuclear reactor core,is the primary research goal of nuclear energy utilization nowadays,and an important guarantee for the sound development of nuclear energy in the future.Establishing prediction criteria for core temperature and damage status is the key to nuclear reactor safety research.In the existing research methods,because of the high temperature and extremely high radioactivity in the core,it is impossible to directly measure the core to determine whether there is a possible accident.Core damage assessment mainly includes the following two points:(1)feedback the temperature distribution inside the core through the thermocouple in the core exit area;(2)feedback the core damage through the concentration change of delayed neutrons in the loop.This paper chooses China Demonstration Fast Reactor as the research object,which adopts pool structure design.In this paper,computational fluid dynamics sofrware(Fluent)is used to analyze the temperature distribution of thermocouples in the core exit area under different loss-of-flow accidents.Meanwhile,the distribution of delayed neutron precursor nuclei in the sodium pool is studied.Through the analysis of the rated condition,electric power can not lose OTC emergency shutdown,loss of power emergency shutdown and off the power of natural circulation and other categories of cases.The temperature distribution at the core outlet area is obtained,and the temperature distribution at the temperature measuring point is mainly studied.It is found that mass flow has great influence on the accuracy and validity of temperature measurement points.At the same time,under the condition of high mass flow,high temperature components will form a high temperature zone at a certain height.The arrangement of temperature measuring points on the top of high temperature components can effectively feedback the change of temperature.Under the condition of low mass flow,the feedback effect of measurement points decreases and the uncertainty of temperature distribution increases due to turbulent disturbance.The validity of temperature measurement points is analyzed,which provides a reference for optimizing the layout of measurement points.At the same time,the whole hot sodium pool is modeled in one-half area,and the trend of coolant flow in the whole sodium pool area is analyzed.The flow trends of delayed neutron detectors from core to intermediate heat exchanger are analyzed under different working conditions and positions of leaked delayed neutron precursor nuclei.It is found that the location distribution of fuel assembly has a great influence on the detection time.When the components close to the shield cylinder leak,they can be detected more quickly,and the time to detect the damage of the inner position of the center is much longer than that of the outer position.The design of neutron shielding column has great influence on the flow field and temperature field.The original method of simulating the main components by using porous medium method has great error with the actual modeling.When the hardware conditions permit,the simulation method of solid modeling should be adopted.The time trend of different time flow to the position of the intermediate heat exchanger is obtained,which provides a reference for delayed neutron feedback.