Development of a FBR fuel pin bundle deformation analysis code "BAMBOO"; Improvement for the pin deflection analysis due to cladding-wire mechanical interactions

Uwaba, Tomoyuki ; Ito, Masahiro*

The bundle-duct interaction (BDI) occurs in a highly irradiated wire-wrapped fast breeder reactor (FBR) fuel subassembliy and probably limits the life time of the subassembly in achieving high burn up conditions. For the purpose of evaluating bundle deformation in BDI condition, the BAMBOO calculation code has been developed. We improved the BAMBOO code so that it could analyze the bundle deformation affected by the pin-wire mechanical interaction due to the tension of the wire, by incorpolating the analysis model that predicted a single pin-wire mechanical interaction deformation into the BAMBOO. We also performed the test analysis of the improved code on a typical 169 pin bundle model, to see how the pin-wire interaction affected the whole bundle deformation behavior. The result of the analysis showed that because the tension of the wire rapidly decreased by irradiation creep, the pin-wire interaction did not significantly affect the initial pin-to-duct contact unless the tension became tighter by the difference in swelling property between the fuel cladding and the wire.