# Nuclear Science and Techniques

《核技术》(英文版) ISSN 1001-8042 CN 31-1559/TL     2019 Impact factor 1.556

Nuclear Science and Techniques ›› 2018, Vol. 29 ›› Issue (8): 110

• NUCLEAR ENERGY SCIENCE AND ENGINEERING •

### Effects of fuel salt composition on fuel salt temperature coefficient (FSTC) for an under-moderated molten salt reactor (MSR)

Xiao-Xiao Li 1,2 • Yu-Wen Ma 1,2,3 • Cheng-Gang Yu 1,2 • Chun-Yan Zou 1,2,3 • Xiang-Zhou Cai 1,2,3 • Jin-Gen Chen 1,2,3

1. 1 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
2 CAS Innovative Academies in TMSR Energy System, Chinese Academy of Sciences, Shanghai 201800, China
3 University of Chinese Academy of Sciences, Beijing 100049, China
• Contact: Xiang-Zhou Cai E-mail:caixz@sinap.ac.cn
• Supported by:

This work was supported by the Chinese TMSR Strategic Pioneer Science and Technology Project (No. XDA02010000) and the Frontier Science Key Program of the Chinese Academy of Sciences (No. QYZDY-SSW-JSC016).

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Xiao-Xiao Li, Yu-Wen Ma, Cheng-Gang Yu, Chun-Yan Zou, Xiang-Zhou Cai, Jin-Gen Chen. Effects of fuel salt composition on fuel salt temperature coefficient (FSTC) for an under-moderated molten salt reactor (MSR).Nuclear Science and Techniques, 2018, 29(8): 110
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Abstract:

With respect to a liquid-fueled molten salt reactor (MSR), the temperature coefficient of reactivity mainly includes the moderator temperature coefficient (MTC) and the fuel salt temperature coefficient (FSTC). The FSTC is typically divided into the Doppler coefficient and the density coefficient. In order to compensate for the potentially positive MTC, the FSTC should be sufficiently negative, and this is mostly optimized in terms of the geometry aspect in pioneering studies. However, the properties of fuel salt also directly influence the FSTC. Thus, the effects of different fuel salt compositions including the 235U enrichment, heavy metal proportion in salt phase (HM proportion), and the 7Li enrichment on FSTC are investigated from the viewpoint of the essential six-factor formula. The analysis is based on an undermoderated MSR. With respect to the Doppler coefficient, the temperature coefficient of the fast fission factors (αT(ε)) is positive and those of the resonance escape probability (αT(p)), thermal reproduction factor (αT(η))), thermal utilization factor (αT(f)), and total non-leakage probability (αT(Λ)) are negative. With respect to the density coefficient, αT(p)  and αT(η) are positive, while the others are negative. The results indicate that the effects of the 235U enrichment and HM on FSTC are mainly reflected in αT(ε) and αT(p), which are the dominant factors when the neutron spectrum is relatively hard. Furthermore, the 7Li enrichment influences FSTC by αT(f) and αT(Λ), which are the key factors in a relative soft spectrum. In order to obtain a more negative FSTC for an under-moderated MSR, the possible positive density coefficient, especially its αT(p), should be suppressed. Thus, a lower 235U enrichment (albeit higher than a certain value, 5 wt% in this article) along with a lower HM proportion and/or a higher 7Li enrichment are recommended. The analyses provide an approach to achieve a more suitable fuel salt composition with a sufficiently negative FSTC.