Speaker
Description
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$^{\mathrm{TM}}$ reactor system with 10 MWt and 3-4 MWe power output. The MoveluX$^{\mathrm{TM}}$ core uses less than 5% LEU as the nuclear fuel. Furthermore, calcium hydride (CaH$_2$) is also used as the solid-state neutron moderator. The hydrogen in CaH$_2$ dissociated above 800 ${}^\circ$C; thus, this temperature is the operation limitation temperature of the core. From the viewpoint of the core characteristics, the CaH$_2$ moderator shows a positive temperature reactivity coefficient from room temperature to near the operation temperature [2].
The MoveluX$^{\mathrm{TM}}$ core utilizes this positive temperature reactivity coefficient to assure critical safety during transport [3]. To evaluate this core characteristic, the TSL of CaH$_2$ is very important input data for the core calculation. However, only JEFF published TSL data on the CaH$_2$, and it was based on one experiment’s data.
On the other hand, the Toshiba Energy Systems & Solutions Corporation measured TSL of CaH$_2$ in the past research with Tokyo Tech and Kyoto University. Additionally, JAEA also evaluates this TSL based on the simulation. The MoveluX$^{\mathrm{TM}}$ 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$_2$ 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.
