The Role of the New CANFLEX Fuel Bundle in Advanced Fuel Cycles for CANDU Reactors

Abstract

The fuel cycles of principal interest for use in CANDU* reactors are: slightly enriched uranium (up to approximately 1.2 wtX U-235), various cycles using the U-235 or Pu recovered from spent light-water reactor (LWR) fuel, and the high-burnup thorium fuel cycles. In all of these cycles the fuel bundles contain more fissile material than with natural uranium fuel in order to achieve the higher burnups required for optimum economics. This higher burnup results in the fuel being subjected to power ramps and high fuel ratings at burnups higher than are adequately covered by current CANDU fuel experience, and the extra fissile loading generally requires more complex fuel- management procedures, with the associated higher risk of greater localized power peaks than are currently acceptable. The new CANFLEX fuel bundle is the most appropriate vehicle for the optimal use of these fuel cycles in CANDU reactors because of the lower fuel ratings and enhanced operational flexibility which it provides. The peak fuel-element ratings are lowered by approximately 20% (dependent upon burnup and fissile content) through the use of smaller-diameter fuel elements than in current CANDU bundles. The flexibility is further enhanced by the thermalhydraulic optimization of the CANFLEX bundle to increase its critical heat flux (CHF) capability by approximately 15% above that of current CANDU bundles. The CANFLEX bundle is compatible with current CANDU reactors, so that it can be used to support advanced fuel cycles in either new or existing CANDU reactors.