To realize a decarbonized society, various organizations are developing small modular reactors and micro-reactors [1]. Toshiba Energy Systems & Solutions has been developing a MoveluX reactor system with 10 MWt and 3-4 MWe power output. The MoveluX core uses less than 5% LEU as the nuclear fuel. Furthermore, calcium hydride (CaH) is also used as the solid-state neutron moderator. The hydrogen in CaH dissociated above 800 C; thus, this temperature is the operation limitation temperature of the core. From the viewpoint of the core characteristics, the CaH moderator shows a positive temperature reactivity coefficient from room temperature to near the operation temperature [2].
The MoveluX core utilizes this positive temperature reactivity coefficient to assure critical safety during transport [3]. To evaluate this core characteristic, the TSL of CaH is very important input data for the core calculation. However, only JEFF published TSL data on the CaH, and it was based on one experiment’s data.
On the other hand, the Toshiba Energy Systems & Solutions Corporation measured TSL of CaH in the past research with Tokyo Tech and Kyoto University. Additionally, JAEA also evaluates this TSL based on the simulation. The MoveluX core had around 200 pcm between these TLS data, furthermore, more than a 2% difference in temperature reactivity coefficient was confirmed. These differences were not small, thus, improvement of the CaH TSL data will be required.
References
[1] J. Buongiorno, et al, “The Future of Nuclear Energy in a Carbon-Constrained World”, Massachusetts Institute of Technology, MA, USA, (2018) p. 26.
[2] R. Kimura, S. Wada, “Temperature Reactivity Control of Calcium–Hydride–Moderated Small Reactor Core with Poison Nuclides”, Nucl. Sci. Eng., 193 (9), (2019) pp.1013-1022.
[3] R. Kimura, K. Asano, “Ensuring Criticality Safety of vSMR Core During Transport Based on Its Temperature Reactivity”, Nucl. Sci. Eng.,194 (3), (2020), pp.213-220.
