Abstract:

The aim of the paper is to analyse the physical properties of liquid heavy metal fast reactor fuel rods and control rods from a neutronics point of view to support their structural design and material selection.In this paper, the liquid-uranium ratio selection, radial power distribution, cladding material selection, reflective layer material selection for fuel rods, radial structural design of control rods, absorber material selection, and moderated structural design are computationally analysed using the fast neutron reactor analysis program SARAX. Calculation results show that: the K_eff of the fuel rod grid element is linearly related to the liquid-uranium ratio, and the selection of the liquid-uranium ratio needs to consider the heat-carrying factor more. The fuel rod cladding is preferred to be made of ferritic/martensitic steel materials. The materials for the reflective layer at the axial ends of the fuel may be chosen to be made of steel materials.Based on the results of the analysis of the Pu migration phenomenon, none of the current physical calculation procedures are coupled with the Pu migration phenomenon, and the power distribution obtained from the calculation is relatively homogeneous, which leads to a bias of unconservative results in the calculation of the fuel centre temperature.The use of thin rod design for control rods can effectively reduce the self-screening effect, but the use of thin rod structure will lead to lower space utilisation. B₄C is commonly used as the absorber material in fast reactors.The wrapping of the control rod absorber with a moderator softens the neutron energy spectrum and increases the B-10 neutron absorption cross section significantly, increasing the value of the control rod. At the same outer diameter, the rod value of a pure absorber core block is less than that of a core block wrapped with a moderator (ZrH₂).

Key words: liquid heavy metal reactor, fuel rod design, control rod design