A system to utilize high-temperature nuclear heat effectively is proposed here. The system comprises a High-Temperature Gas-cooled nuclear Reactor (HTGR), reaction vessels to produce H2 using the steam-reforming reaction of CH4 or the Iodine-Sulfur (I-S) process, chemical heat pumps and He gas turbines. The chemical heat pumps are operated between the two decomposition temperatures of SO3 (~900°C) and HI (~500°C) of the I-S process. The pump system transfers heat from lower temperature to higher one with repeated H2 absorption-desorption cycles, and the overall thermal conversion ratio from H2O to H2 can be enhanced. The material candidate for H2 absorption in heat pump is considered TiH2 and ZrCoH3 (or UH3) according to the two reaction temperatures. The decomposition of the metal hydrides proceeds at their respective plateau pressures that are a function of temperature regardless of the H content in metals. Variations of the temperature and the equilibrium H2 pressure with repetitions of the heat-pump cycle are shown in the present paper comparatively. In addition, proton-conducting fuel cell system supplied with CH4 is incorporated in the high-temperature utilization system.