Fuel Management Study of Refuelling of One-Quarter and One-Half of the Core at Point Lepreau

Abstract

In 1995 September after a prolonged outage, an incident occurred during the restart of the Point Lepreau reactor, that led to entry of foreign materials into the Heat-Transport System (HTS). To rehabilitate the HTS and to ensure that flow impairment or blockage did not exist, it was proposed that channels in certain coolant-passes could be defuelled and flushed. Such an operation would imply defuelling all 95 channels in a pass in Loop 1, or possibly 190 channels in both Loop 1 and Loop 2. Such refuelling would create certain highly asymmetric fuel burnup configurations, not previously analyzed in the design or operation of the CANDU 6 reactors. Three defueling options are discussed. The core characteristics in terms of system reactivity, flux tilts, power distribution, controllability, response to subsequent refuelling, fuel burnup redistribution, zone-fill variations needed to be analyzed. Fuel-management studies were conducted to investigate these issues, in particular the optimal initial-fuel-loading configuration and subsequent flux shape controllability, with routine refuelling at full-power operation for an extended period of time until the nominal equilibrium fuel burnup distribution is re-established. In general, the operability of the core according to design intent was investigated and re-confumed.