HTR-PM is a demonstration plant of the modular high temperature reactor with two pebble-bed cores of 250 MWth. Since the early HTRs, such as AVR and THTR in Germany, thorium-based fuel has been regarded as an important fueling option. In this work, the feasibility of maximizing thorium utilization and minimizing the refueling effort of uranium fissile under the framework of HTR-PM is investigated. The preliminary neutronics features of the Th-233U fuel cycle in the equilibrium state of the HTR-PM are analyzed. Two types of fuel loading schemes are considered: the ThU-MOX scheme, namely the so-called “ThOX” fuel in literatures, and the SEP scheme, which means “separate” fuel pebbles loaded with thorium oxide and uranium oxide, respectively. The ThU-MOX scheme utilizes the mixed Th+HEU oxide fuel particles in all the fuel pebbles in the core, in which the enrichment of HEU is 93%. The SEP scheme utilizes the separate thorium pebbles and LEU pebbles mixed homogeneously in the core. The preliminary results on the ThU-MOX scheme indicate that thorium mixed with HEU in the fuel particle can lower the 235U loading requirement per energy generated, compared with the normal LEU loading scheme of the HTR-PM, and enhance the safety performance for high heavy metal loading cases. On the other hand, the results of SEP scheme reveal that the self shielding effect of the thorium particles depresses the absorption of thorium and the utilization of 233U. However, the situation can be improved by lengthening the residence time of the thorium pebbles. Furthermore, more realistic features are investigated as the basis of future works, including the initial core and the running-in phase, the impact of control poisons.

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