Abstract

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 MoveluX^TM (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.

摘要

小型模块化反应堆（SMR）被认为是实现脱碳社会的重要能源之一，特别是具有10MW或以下热功率的SMR类型，称为微反应器或超小型模块化反应堆（vSMR）。自 2017 年以来，东芝能源系统与解决方案公司开始开发一种多用途 vSMR 作为分布式能源，称为 MoveluX ^TM（X-mark 本地公用事业移动式超小型反应堆）。

在目前的堆芯设计中，从被动核安全和降低运行成本的角度来看，需要一个被动反应控制装置。vSMR 被动反应控制装置的基本思想是基于 Kambe 等人提出的锂膨胀模块 (LEM)。[“用于月球基地动力系统的 RAPID-L 快堆的启动顺序”，Proc。空间核会议，（2007 年）] 然而，LEM 在锂中子吸收剂方面存在一些问题，例如生产成本、化学反应性和氚生成。在本研究中，建议使用 In-Gd 合金作为⁶ Li的替代品。

In-Gd合金在空气气氛中化学稳定；此外，铟和钆具有足够的中子吸收截面，没有同位素富集。然而，密度、热膨胀和放热特性不可用，从中子学和安全的角度来看，这是重要的信息。因此，测量了 In-Gd 合金中的材料特性，例如与温度相关的密度和化学反应性。此外，根据测量的密度评估对照棒反应性价值。

结果，包含在 In-Gd 合金中的 1 wt% 钆显示出比天然锂高 2.5 倍的控制棒反应性。此外，In-Gd 合金密度的不确定性对反应性价值的影响很小；在In-Gd 合金密度为 0.1 g/cm ³微扰的情况下，仅在 78 pcm（相当于插入位置的 1%）范围内。总之，本研究显示了 In-Gd 合金作为用于铟钆膨胀模块的液体中子吸收剂的优势和可行性。