Structural Evaluation of Fuel Rod Drop in the PHWR Spent Fuel Pool

This technical paper documents an assessment of the structural integrity of an individual spent fuel rod under a hypothetical drop accident occurring during fuel-bundle handling in the spent fuel pool (SFP) at domestic pressurized heavy-water reactor (PHWR) nuclear power plants. The analysis is grounded in the operating procedures for managing and transferring spent fuel (SF) in the SFP. Although an anti-drop metallic screen is installed on actual pool floors, a rigid floor was assumed for conservatism. The evaluation encompasses determining the underwater drop velocity with due consideration of hydrodynamic damping in the pool environment, estimating the resulting impact load, and calculating stresses and strains in the Zircaloy-4 cladding (sheath), followed by comparison with acceptance criteria for preventing failure and leakage and the associated design margins. Conservative assumptions were applied for impact location, drop height, and material properties; the methodology and input assumptions are presented, and representative case calculations are provided to confirm whether structural integrity is maintained.