Research On Structure And Mechanical Properties Of Fuel Assembly For CiADS Lead Bismuth Fast Reactor

In order to slove the problems caused by reactor spent fuel accumulation,China has been researching on China Initiative Accelerator Driven Sub-critical System(CiADS).One of the internationally recognized fourth generation reactor-lead based cooled fast reactor(LFR)has been selected for CiADS.It has excellent abilities of nuclear waste transmutation and nuclear fuel proliferation.It also can effectively improve fuel efficiency and sustainability.The design of fuel assembly is a core task for LFR research and development.There are many types of fuel assembly structures due to different research purposes and demands in the world.Basically,they are at the stage of conceptual design or prototype verification,which can not satisfy the actual needs of CiADS.This paper performed a structure conceptual scheme of fuel assembly for CiADS.First of all,this paper defined the design objectives for CiADS fuel assembly refering to domestic and foreign fuel assembly structural design schemes of LFR.We adopted core fixing scheme,fuel bundle positioning scheme and fuel assembly shape structure scheme.They are suitable for CiADS requirments.The design principle of fixing&unlocking components and three-dimensional mechanism design for the fuel assembly were also performed.Secondly,the mechanical analysis for fuel assembly proved that the structural design of fuel assembly is safe and reliable.Structural analysis includes:(1)Acording to the contact mechanics calculation,the optimal size parameters and maximum safe load of the ball anchor locking structure were obtained;(2)With the static and modal analysis of the lower support grid,it proved that the structural strength and stiffness met the design requirements;(3)Through parametric analysis,the optimal structure size of the grid element was determined.We used the linear symmetrical three spring vibrator to equivalently simulate the contact stiffness of the grid element.The required number and distribution of the spacing grid assembly in the fuel assembly were obtained by the additional mass method;(4)We calculated the maximum interference fit between the grid element and the fuel rod.Based on mechanical calculation,it proved that the method of fixing the spacing grid assembly with screws on the hexagonal sleeve inner wall is safe and reliable;(5)Acoustic-solid coupling method was applied to calculate the wet modes of fuel bundle in lead bismuth liquid.The added mass of lead bismuth liquid and the coupling effect between fuel rods have effects on the wet modes.Finally,the thermal hydraulic calculation of the fuel assembly was carried out to prove the rationality of the internal flow channel.Flow field analysis includes:(1)According to the fuel assembly structure,we established the fuel assembly flow field model,completed the grid independence analysis,and determined the basic grid size and the minimum grid size(2)The inlet flow parameters suitible for thermal hydraulic design requirements of CiADS subcritical reactor fuel assembly were calculated(3)We conducted thermal hydraulic analysis for different areas of the fuel assembly,the results shows that flow channel have muddy and drainage effect on the lower end of the lateral flow channel,that the eddy currents have no effect on the flow field in the active section of the fuel assemble,that the location and cause of the maximum flow rate inside the fuel assembly are obtained,and that the formation process of the annular high temperature zone in the middle of the fuel rod bundle are conducted.(4)We quantitatively analysed the flow and heat transfer characteristics in the inner subchannel for the rod cluster at the outlet of the fuel assembly active section.In this paper,based on the actual requirements of CiADS,a structure conceptual scheme of fuel assembly for LFR was designed.Through structural mechanics calculation and flow field analysis,the rationality and feasibility of the structure conceptual scheme of fuel assembly were proved.It accumulated technical foundation for fuel assembly design of CiADS industrial demonstration device in the furture.