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Conference Spotlight
Nuclear Energy Conference & Expo (NECX)
September 8–11, 2025
Atlanta, GA|Atlanta Marriott Marquis
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The RAIN scale: A good intention that falls short
Radiation protection specialists agree that clear communication of radiation risks remains a vexing challenge that cannot be solved solely by finding new ways to convey technical information.
Earlier this year, an article in Nuclear News described a new radiation risk communication tool, known as the Radiation Index, or, RAIN (“Let it RAIN: A new approach to radiation communication,” NN, Jan. 2025, p. 36). The authors of the article created the RAIN scale to improve radiation risk communication to the general public who are not well-versed in important aspects of radiation exposures, including radiation dose quantities, units, and values; associated health consequences; and the benefits derived from radiation exposures.
Rei Kimura, Shohei Kanamura, Yuya Takahashi, Kazuhito Asano
Nuclear Technology | Volume 207 | Number 11 | November 2021 | Pages 1784-1792
Regular Technical Paper | doi.org/10.1080/00295450.2020.1843953
Articles are hosted by Taylor and Francis Online.
The small modular reactor (SMR) is considered one of the important energy sources for the realization of the de-carbonated society, especially SMR types that have 10 MW or less thermal power, called a microreactor or very small modular reactor (vSMR). Toshiba Energy Systems & Solutions has initiated the development of a multipurpose vSMR as a distributed energy source since 2017 called MoveluXTM (Mobile-Very-small reactor for Local Utility in X-mark).
In the current core design, a passive reactivity control device is required from the viewpoint of passive nuclear safety and operational cost reduction. The fundamental idea of vSMR passive reactivity control devices is based on the lithium expansion module (LEM) proposed by Kambe, et al. [“Startup Sequence of RAPID-L Fast Reactor for Lunar Base Power System,” Proc. Space Nuclear Conference, (2007)], however, the LEM has some issues regarding the lithium neutron absorber, such as production costs, chemical reactivity, and tritium generation. In the present study, the In-Gd alloy is proposed as an alternative to 6Li.
The In-Gd alloy is chemically stable in the air atmosphere; additionally, indium and gadolinium have enough neutron absorption cross section without isotope enrichment. However, the density, thermal expansion, and exothermal heat characteristics are not available, which is important information from the viewpoint of neutronics and safety. Hence, the material properties in the In-Gd alloy were measured, such as temperature-dependent density and chemical reactivity. Furthermore, control rod reactivity worth was evaluated based on the measured density.
As a result, the 1 wt% gadolinium contained in the In-Gd alloy shows control rod reactivity worth that is 2.5 times greater than natural lithium. Furthermore, the uncertainty of the In-Gd alloy density has a small impact on the reactivity worth; only in the range of 78 pcm (equivalent to 1% of insertion position) in the case of the 0.1 g/cm3 perturbation of the In-Gd alloy density. In conclusion, the present study shows the advantage and feasibility of the In-Gd alloy as a liquid neutron absorber for the Indium-Gadolinium Expansion Module.
