Accident Tolerant LWR Fuel Pellets Development: Micro-cell and High-Density Pellets

Accident tolerant fuel pellets (ATF pellets), in comparison with the standard UO₂ pellets currently used by the nuclear industry, can tolerate a loss of active cooling for a considerably longer time period, while maintaining or improving performance during normal operations and operational transients and also enhancing fuel safety for accidental events. At the beginning of 2012, the Advanced LWR fuel pellet development laboratory in KAERI has launched a research program to develop advanced LWR fuel pellets with enhanced accident tolerance. The objectives of this 5-year project are to design and select the potential candidates for ATF fuel pellets, test out-of-pile performances, and establish databases for fuel materials, start the irradiation test of ATF pellets in research reactors. This paper shows the design and preliminary feasibility for fuel pellet fabrication of micro-cell UO₂ pellet and high uranium density ceramic composite pellets. Micro-cell UO₂ pellets are characterized by enhanced fission products retention capability and thermal conductivity. High uranium density ceramic pellet is composite pellets consisted of UO₂ and non-oxide ceramics such as nitrides. These composite pellets are expected to increase the thermal conductivity and uranium density of fuel pellets. Those ATF pellets are expected to effectively enhance the robustness of the fuel rods even under accident conditions such as a LOCA, as well as under normal operation conditions. Our long-term and challenging goal is to establish generic technology of ATF pellets and apply those pellets for lead test rods (LTRs) by the end of 2022, which would be subjected to in-reactor testing in a commercial power plant