| In the primary system of PWR,the steam generator and the reactor coolant pump are usually connected by a U-shaped pipe.In case of a small-break loss of coolant accident(SBLOCA)in the cold leg,a loop seal will be formed in the U-shaped pipe to block the circulation flow of the primary circuit.The interruption of the primary loop cycle will lead to the accumulation of steam in the upper plenum,the decrease of the core collapse level and the rise of the fuel cladding peak temperature until the loop seal clearing(LSC)occurs.Therefore,it is of great significance to study the time of LSC and its influencing factors for the accurate safety analysis of fuel peak temperature.The aim of this study is to analyze the physical mechanism and influencing factors of LSC in PWR SBLOCAs.In order to establish a reasonable analysis model of full-scale PWR,this paper first uses the best estimate program RELAP5/MOD3.4 to model the small-scale LOBI integral test facility.Combined with the experimental data of LOBI and the results of physical mechanism analysis of LSC phenomenon,the key physical model of RELAP5 program which affects LSC phenomenon is debugged reasonably,and a better LOBI model of LSC phenomenon recurrence is established.On this basis,through the analysis of the scaling method and the main scaling distortion used in the design of LOBI facility,the LOBI model is inversely extended to its full-scale prototype reactor model.Finally,using the full-scale prototype reactor analysis model,from the point of view of SBLOCA intervention measures of PWR,the simulation research and mechanism analysis of various factors affecting LSC phenomenon under different break size and location are carried out.The results show that the break size is the key factor affecting LSC.The location of the break has some influence on the occurrence time of LSC and the loop sequence of LSC.When the break size is small,the safety injection condition can promote the occurrence of LSC;when the size of the break is large,the safety injection condition has no effect on LSC,but it can affect the recovery process of the core collapsed level after LSC,and has a significant effect on the fuel peak clad temperature(PCT).The influence of secondary side condition on LSC phenomenon is relatively small,which is mainly reflected in the influence of secondary cooling rate on primary and secondary side pressure reversal time.The research work of this paper can provide some suggestions for the accident response rules of PWR SBLOCA accident,besides,it can also provide a reference for the setting of the best estimation program for accurately simulating the phenomenon of LSC. |
