Preliminary analysis of a zirconium hydride moderated megawatt heat pipe reactor

•A moderated megawatt-class HPR core design is proposed and the influence of moderators is analyzed.•The moderators can reduce the fuel loading and shield weight while increasing the fuel capacity utilization.•Preliminary thermal analysis shows the stability of zirconium hydride with a sufficient temperature margin. At present, megawatt-class Heat-Pipe Reactors (HPRs) are under-investigated widely as a candidate for robust, self-contained, and long-term power for special purpose applications. In this work, zirconium hydride is introduced to design a moderated megawatt-class HPR core. The influence of moderators on core parameters is analyzed. According to the calculation, although the use of a moderator will lead to higher burnup reactivity loss, the reactivity decreasing caused by the reduction of fuel can be offset by the proper moderator. The introduction of moderator has no significant influence on radial and axial power distribution and power peak factor. Meanwhile, the moderation of core will decrease the maximum neutron flux as well as the reactivity worth of control devices. The moderated core possesses a stronger doppler effect while the thermal expansion reactivity feedback of monolith and fuel decreases. Results also show that the introduction of moderators is beneficial to reducing the thickness and weight of the shield. Preliminary thermal analysis is conducted to verify the feasibility, the results show that zirconium hydride can stay stable in the moderated megawatt heat pipe reactor, and the yttrium hydride shows better thermal stability.