Structural and Neutronic Assessment of Calandria Tube Enhancement Design Options

Over the lifetime of a CANada Deuterium Uranium (CANDU) Type Reactor, the pressure tubes and calandria tubes deform via creep and sag, eventually requiring replacement. The sagging phenomena leads to fuelling issues, potential contact between the Calandria Tube (CT) and the liquid injection shutdown system or the Pressure Tube (PT). As such, this ageing phenomenon limits the lifetime of the components. Conceptual designs were assessed to determine their potential for reducing the effects of aging by minimizing the magnitude of sagging. Three different design options for a CT have been investigated using numerical simulation techniques. The CT design options include fins and ribs of different sizes and combinations. The fins and ribs provide improved structural integrity over the reactors lifetime. Analyses results have shown that the design options yield an increased overall strength with a minimal impact on neutronics. The analysis has determined that the finned design option is superior in terms of CT strength enhancement and minimizing the impact on neutronics. Furthermore moderator displacement analysis for the finned design option showed an ability to minimize the impact on moderation or even cause moderator displacement potentially decreasing the positive void coefficient.