Technical Challenges for a Dual-Cooling Fuel Structural Components

This paper introduces mechanical component issues of a new concept PWR fuel, which is named as a 'Dual- Cooling Fuel'. The key feature of the dual-cooling fuel is readily discriminated by its annular cross-section of a fuel rod. So to speak, the fuel rod has an internal coolant passage in addition to an external one so that a fuel rod consists of coaxial inner and outer cladding tubes in which donut-shaped pellets are stacked. An intrinsic purpose of this shape is to increase the surface area of heat transfer which results in a reduction of the fuel temperature. The important effects of this idea are to enhance the fuel safety and to achieve a power uprating. This idea has been recently studied at Massachusetts Institute of Technology (MIT) for about 3-4 years. They picked up a conventional 17x17 PWR fuel of the Westinghouse type as a candidate and changed it into a 13x13 array fuel with increasing the outer diameter and making an additional internal flow passage. They found that the power uprating can be achieved by 50% with upgrading some necessary components of a nuclear power plant. Fuel performance, safety analysis and pellet fabrication were dealt with in their study but the fuel mechanical components have not been considered. PWR fuel development division of Korea Atomic Energy Research Institute (KAERI) recently started a new project of developing a above-mentioned fuel technology through a National R and D Program by the Ministry of Science and Technology. One of the relevant projects is to develop a design technology of the major structural components of a double-cooling fuel. As for the components, fuel rod supporting structure, top and bottom end pieces, guide thimbles and instrumentation tube were chosen. Differently than the MIT's works, the dual-cooling fuel components have to be compatible with the OPR 1000 system without replacing the reactor internals. Therefore, many challenging problems have to be tackled in this project. This paper describes some of the key issues that should be resolved