Numerical Simulation Of The Flow And Heat Transfer Characteristics Within Spent Fuel Pool

The spent fuel rods unloaded from reactor have massive decay heat and are temporarilystored in the spent fuel storage pool. Under the heat load increase, it is necessary toinvestigate the thermal-hydraulic in the spent fuel storage pool through a named high-densitystorage method adopted by most of nuclear power plants to store more and more spent fuels.In present paper, in order to investigate the thermal–hydraulic characteristics in the spent fuelstorage pool, CFD methodology was applied to develop a tool for spent fuel pool thermalhydraulic analysis and the Daya Bay spent fuel pool was chosen as the reference one. Theheat transfer at the interface between air and cooling water was modeled by using equivalentheat transfer coefficient, which was worked out by considering the heat transfer processincluding natural convection of the air and the evaporation of cooling water in the pool. In thepaper, investigation on the effects of locations of inlet pipe and the gap of racks upon thecooling performance were carried out. In addition, the flow and heat transfer behaviors in thespent fuel storage pool under abnormal condition and the loss of the cooling system wereanalyzed as well.The present results indicated that regardless of inlet pipe locations, obvious naturalcirculation exist in the pool, which makes the flow velocity more complicated, enhances theflow and heat transfer, which are very beneficial to remove decayed heat from the pool. Boththe mean water temperature and peak wall temperature on the surface of rack arranged at thebottom location are lower than cases of the inlet is arranged at the middle or top locations.While reducing the gap size between the storage racks, both the natural circulation flow andheat transfer processes were degenerated. Under cases of abnormal condition, the temperaturedistribution becomes more uneven and natural circulation stronger. The cooling system of thespent fuel storage pool can safely remove the decay heat under both normal and abnormalconditions. Under loss of cooling system condition，the influence of time step were validatedand one second time step is small enough to capture the rapidly changing of flow behaviors.Present study indicated that5000seconds after loss of cooling system, the flow behavior inthe spent fuel storage pool become steady and after11hours, the mean water temperature canrise up to the safety limited value of80℃，and some effective measures should be taken to prevent the water from boiling.The present studies are of great significance and can provide valuable references for thedesign, optimization and operation management of spent fuel storage pool.