The Influence Of Scale Effect On The Phenomena Of A Closed Natural Circulation Loop

Natural circulation is a kind of key phenomena in the passive safety system of nuclear power device.For nuclear reactors,many tests are not convenient to carry out directly on the reactor,but on a scaled-down apparatus.Therefore,focus on the natural circulation phenomenon,the study of scale effect of experimental equipment is undoubtedly a very meaningful work.In this thesis,a RELAP5 model was established to simulate the natural circulation experimental device after proper simplification.According to the boundary conditions of selected test conditions,the corresponding RELAP5 program input cards were programmed.The rationality of the model was confirmed by comparing the calculated natural circulation flow in the experimental device with the measured natural circulation flow,and the ability of the RELAP5 program to simulate the natural circulation phenomenon was verified.On this basis,according to the scale model determined by different scaling methods,3different scale RELAP5 calculation models were established to simulate the single-phase steady-state natural circulation and the dynamic response of the natural circulation system under the condition of power changing in different ways.For working condition of power change,the amplitude of power change was 50% of the original power value,and the 5methods of power change were: step increase,step decrease,linear increase,linear decrease and sine.Obtained the temperature difference of the fluid at the inlet and outlet of the heating section θ,the mass flow rate of natural circulation W and the ratio of heat transfer rate in cooler to heating power ξ of the 4 models with different scales(including the prototype model).The results show that models with different scales,the variation trend of W is consistent,so as θ and ξ.For different power change methods,the ratio of hight ratio to diameter ratioα/β affects different parameters of natural circulation.As the change of α/β,some parameters change regularly.The greater the difference between α/β of model and α/β of prototype,the more distortion of the result.