Thermomechanical analysis of innovative nuclear fuel pin designs

[摘要] (cont.) The FRAPCON fuel performance code has been modified to assess the behavior of the RMWR fuel pins. Properties were modified to allow for a higher concentration of plutonium oxide. A new mechanistic model was adopted to simulate the fission gas release and swelling behavior of the fuel. The gas bubble swelling at the grain edges and grain faces were modeled separately. In addition, solid fission product swelling model was modified and the effect of axial migration of the volatile fission product behavior on fuel performance was also analyzed. Specifically, the cesium migrates axially based on the evaporation/condensation mechanism. Cesium precipitation at the fuel blanket interface and the resulting excessive swelling of the fuel pin at these locations could potentially be a major source of local stresses. Furthermore, as-fabricated porosity migration, central void formation, and hot-pressing of the fuel pellet were also modeled. Finally, axial variation of the material properties was allowed to represent the active fuel region and the blanket regions. The updated version of FRAPCON (called FRAPCON-EP) was checked against experiments then used to analyze the RMWR fuel behavior to optimize various parameters such the fuel pellet smear density, plenum height, and achievable peak burnup in order to achieve performance that could satisfy the NRC requirements for fuel pins.

[发布机构] Massachusetts Institute of Technology