Evaluation of Pressure Tube Axial Elongation Mitigation Options at Pickering Nuclear Generating Station

Abstract

The CANDU (CANada Deuterium Uranium) is a pressurized heavy-water reactor design where the fuel bundles are oriented horizontally inside the fuel channels. Each fuel channel is comprised of concentric tubes called the pressure and calandria tubes. The fuel channels undergo deformation due to aging in which they (i) elongate axially, (ii) creep radially, and (iii) sag vertically, primarily due to high-energy neutron fluence, high coolant pressure, high coolant temperature, and the weight of the fuel, coolant, and pressure and calandria tubes. The fuel bundles reside, end-to-end, within the pressure tubes. This paper examines the axial elongation of the pressure tubes and proposes mitigation options to reduce the rate of elongation at the Pickering Nuclear Generating Station (PNGS), which is comprised of six operating CANDU reactors. The two energy-group diffusion code RFSP, used for simulation of CANDU fuel physics and for safety analysis, is applied here to evaluate these mitigation options.