Application Of Dynamical System Scaling On Single Phase Natural Circulation

Natural circulation refers to the process that fluid can flow spontaneously through the density difference of fluid formed by heat change.Passive safety system with the key elements of the natural cycle is of great significance for the safety of the three generation reactor.Considering the practicability,economical efficiency,and timeliness factors of the experimental bench,it usually chooses to simulate the prototype experiment on a reduced experimental bench.The scaling analysis method provides a theoretical basis for reducing the scale of the experimental bench effectively simulated the experimental phenomena and experiment process.However,many international passive experimental bench used for safety verification are designed based on the scaling analysis results under steady state conditions,and the simulation study on the transient process of natural circulation has not been reported.This paper is mainly a numerical verification of the scaling analysis of a single phase natural circulation system under the transient process of the step change of power.The scaling number and similarity criteria required for numerical verification are mainly obtained by the classical scaling analysis method(H2TS)and the dynamic scaling analysis(DSS)method.The required validation data are obtained by numerical simulation of the RELAP5 program.The results show that:(1)The H2TS method and the DSS method can effectively proportional the single phase natural cycle process.In addition to geometric similarity,the two methods are different,such as motion similarity,dynamic similarity,etc.The DSS method can guarantee the same process time as the original process.(2)Variation trend of the error curve between the H2TS method and the DSS method is basically the same.The error range of the numerical simulation is within 5%.But the error occurred greatly in the initial stage,especially the error related the temperature.This is mainly due to the step change of the input power.(3)The difference between the two methods in the same chart is caused by the non-equivalent physical model and the different scaling similarity criteria.The non-equivalent physical model will cause the deviation of physical parameters.The different similarity criteria are based on different theories,it may also cause errors,so that there will be a certain difference in the same chart.(4)The dynamic scaling analysis method can evaluate the scaling deviation and its influencing factors in the whole process of the single-phase natural circulation system,and form the optimized dynamic scaling analysis method of the single-phase natural circulation system and the corresponding similarity criterion group.