| Safety issues are the primary considerations in the construction of nuclear power plants and their operation.The design,construction and operation of nuclear power plants adopt the principle of defense in depth,and provide multiple levels of overlapping protection from equipment and measures.The main task of nuclear shielding design is to shield neutrons,this is because neutrons are electrically neutral,which can directly interact with matter nucleus,and have strong neutron penetration ability.Compared with the same dose of γ-rays andχ-rays,neutrons cause much more serious harm to the human body.As an important equipment of nuclear power plant radiation safety,the most important performance of the hot-cell shielding door is the neutron shielding performance.The neutron shielding performance of the shielding door is determined by the neutron energy,the type and thickness of the shielding material.In addition,the other important performance is the mechanical performance,this is because the insufficient structural strength of the shielding door will cause large gap or displacement of the shielding door,resulting in the leakage of radioactive materials.Therefore,in this paper,the theory-simulation-experiment method is used to carry out the systematic design and research on the hot-cell shielding door for nuclear power plants.Firstly,according to the design requirements and criteria of the hot-cell shielding door,the overall scheme design of the hot-cell shielding door are designed to ensure the shielding door have the good characteristics,including neutron and y-rays shielding performance and mechanical properties.The hot-cell shielding door adopts a single-leaf casement structure.The external dimension structure of the door leaf is stepped,and the internal structure is composed of steel plate,boron-containing plate and steel plate.The pressing and locking structure is used to apply a certain compression and lock load to the shielding door leaf of the hot-cell to ensure that the hot-cell shielding door meets the radiation protection requirements.In order to ensure the coaxiality and rotary accuracy of hinge axis of the hot-cell shielding door,the deep groove ball bearings and tapered roller bearings are chosen as the bearings in the hinge axis.Secondly,according to the design requirements,design criteria and overall scheme of the hot-cell shielding door,the structure design of the hot-cell shielding door are carried out in detail.Through the layout design,shape and size of each structure and the connection relationship between parts,the coordinated operation of the hot-cell shielding door is ensured.According to the application situation and the stress of the hinge,the design of hinge shaft and selection of the hinge shaft bearing are made.Then,the theoretical calculation,MCNP simulation and neutron shielding performance test are used to calculate the neutron transmittance of the hot-cell shielding door,and the neutron shielding performance of the hot-cell shielding door is comprehensively evaluated.The relaxation length method is used to calculate the neutron transmittance of the combined shielding material,and the neutron transmittance first increases sharply and then slows down.Using Monte Carlo method and MCNP program to study the influence of neutron energy,combined shielding material type,and thickness of the boron-containing plate of the combined shielding material on the neutron transmittance of the combined shielding material.Using 241Am-be standard neutron source to test the neutron shielding performance of the combined shielding materials.The results show that the three different combined shielding materials meet the requirements of the neutron shielding performance.Finally,on the basis of satisfying the neutron shielding performance,the mechanical properties of the hot-cell shielding door are studied by combination of finite element method and test method.The results show that the stress changes of hinge,anchor bolt and washer are the most obvious and do not meet the design requirements in the initial design.In order to reduce the high stress of the hot-cell shielding door under working condition Ⅳ,the optimization design of the structure of the hot-cell shielding door is carried out.The structural stress of the optimized hot-cell shielding door is less than the allowable stress.By performing static load deformation experimental test on the hot-cell shielding door,the result shows that the simulation results and test results are within a reasonable error range.Through the mechanical test of the boron-containing plate embedded in the hot-cell shielding door,the result shows that the maximum stress of the boron-containing plate embedded in the shielding door is far less than the tensile strength and bending strength of the test. |
