Preliminary Study of Cost Benefits Associated with Duplex Fuel Pellets of the LOWI Type

Duplex UO₂ pellets, which consist of an outer enriched annulus and a depleted or natural core, can provide a solution to the problem of stress corrosion cracking failures, which have led to constraints being placed on ramp rates in power reactors. An analysis of the reactor physics and the performance of duplex pellets is presented in the context of a 17 × 17 pressurized water reactor fuel rod design. The study has been based on the particular type of duplex pellet in which the core and the annulus are physically separate; this is called “LOWI” after the Danish design. At low bumup, this fuel shows a significant improvement in power ramp performance compared with standard fuel. At higher bumup, the benefits are less certain but as the severity of the ramp will usually be less in high bumup fuel simply because of the reduced rating, the reduction in benefit may not be significant. If the gap between the core and annulus persists to high bumup, there will be no loss of benefit. Economic calculations and a cost-benefit analysis are presented to show the number of extra full-power hours of reactor operation that must be obtained in order to outweigh the additional fabrication costs associated with this fuel.