[en] A new core is being designed to improve the performance of the Annular Core Pulse Reactor (ACPR). This design utilizes a two region core with the inner region containing high enthalpy fuel elements around the 228 mm diameter central irradiation cavity. An outer core region of uranium-zirconium hydride fuel elements is placed around the high-enthalpy inner core region to provide an adequate negative temperature coefficient for the entire core. A program has been conducted to develop a high-enthalpy fuel element using a graphite matrix fuel containing (U-Zr)C solid solution particles. The program has successfully developed a (U, Zr) C-graphite fuel element with a high volumetric enthalpy which can be used in a water cooled pulse reactor. Extensive tests have demonstrated the feasibility and safety of the fuel element design