PWR Transition to a Higher Power Core Using Annular Fuel

Abstract

The internally and externally cooled annular fuel is a new type of fuel for PWRs that enables an increase in core power density by 50% within the same or better safety margins as traditional solid fuel. Each annular fuel assembly of the same side dimensions as the 17x17 solid fuel assembly has 160 annular fuel rods arranged in a 13x13 array. Even at the much higher power density, the fuel exhibits substantially lower temperatures and a Minimum Departure From Nucleate Boiling (MDNBR) margin comparable to that of traditional solid fuel at nominal (100%) power. The major motivation for such an uprate is reduction of electricity generation cost. Indeed, the capital cost per kWh(e) of a new reactor would be smaller than the standard construction of a new reactor with solid fuel. Elaborating on previous work, we study the economic payoff of an uprate of existing PWRs given the expected cost of equipment and also cost of money using different assumptions. The fate of the already bought solid fuel is investigated. It is demonstrated that the highest return on investment is obtained by gradually loading annular fuel in the reactor core such that immediately before shutting the reactor down for the uprate construction, two batches in the core are of the annular fuel. This option implies running a core with a mixture of both annular and solid fuel assemblies. In order to prove the technical feasibility of such an option, the thermalhydraulics of this mixed core is investigated and the MDNBR is found to be either unaffected or improved. Consequently, a neutronic model is developed to verify and validate the neutronic feasibility of the transition from solid to annular fuel. This involvements assessment of the peaking factors and capability to provide control poisons within allowable concentrations The overall conclusion of this work is that annular fuel is a very promising option for existing reactors to increase their power by 50%, as it enables a significant uprate with an attractive return on investment. We show that, by a smart management of the transition, an internal return on investment of about 22–27% can be achieved.