Abstract Improved computer capabilities and parallel algorithms have enabled high fidelity coupled analyses of classical nuclear power plant designs, which can also be applied to analyze the new heat pipe cooled reactor design. The neutronic/thermal coupling is a key part of multi-physics, high-fidelity reactor simulations. In a heat pipe cooled reactor, the solid-state core can reach temperatures over 1000 K which causes significant thermal expansion. The expansion then affects the neutronic and thermal conditions. Therefore, the mechanical conditions should also be carefully considered in the highly coupled solid-state system. The Monte Carlo program RMC and the commercial finite element program ANSYS Mechanical were used to develop coupled solutions of the neutronic (N), thermal (T), and mechanical (M) effects in a heat pipe cooled reactor with the ANSYS APDL interface used to link the two programs. The neutronic (N) and thermal–mechanical (T-M) coupled strategy was based on an iterative solution of the nonlinear governing equations. The method was used to study the reactivity changes occurring during startup of the MegaPower heat pipe cooled reactor. The most important effect of the temperature reactivity feedback during startup was the fuel temperature Doppler effect, while the monolith and reflector Doppler effects were much smaller. The radial expansion of the monolith and the reflector and the axial expansion of the fuel pellets have the most significant effects on the mechanical reactivity feedback. The results further show that the thermal–mechanical feedback in the solid-state reactor provides a negative reactivity feedback (-1500 pcm) and yet deteriorates the heat transfer due to the expansion. The peak fuel temperature increases 11 K when the thermal/mechanical feedback is considered. Therefore, the N/T-M coupling must be considered to produce conservative designs.

中文翻译：

---

使用蒙特卡罗和有限元方法在固态反应堆中进行中子和热机械耦合分析

摘要 改进的计算机能力和并行算法使经典核电站设计的高保真耦合分析成为可能，这也可用于分析新的热管冷却反应堆设计。中子/热耦合是多物理场、高保真反应堆模拟的关键部分。在热管冷却反应堆中，固态核心的温度可以达到 1000 K 以上，这会导致显着的热膨胀。然后膨胀会影响中子和热条件。因此，在高耦合固态系统中也应仔细考虑机械条件。Monte Carlo 程序 RMC 和商业有限元程序 ANSYS Mechanical 用于开发中子 (N)、热 (T)、热管冷却反应堆中的机械 (M) 效应和用于链接两个程序的 ANSYS APDL 接口。中子 (N) 和热-机械 (TM) 耦合策略基于非线性控制方程的迭代求解。该方法用于研究 MegaPower 热管冷却反应堆启动期间发生的反应性变化。启动期间温度反应性反馈的最重要影响是燃料温度多普勒效应，而整体和反射器多普勒效应要小得多。整料和反射器的径向膨胀以及燃料芯块的轴向膨胀对机械反应性反馈的影响最为显着。结果进一步表明，固态反应器中的热-机械反馈提供了负反应性反馈（-1500 pcm），但由于膨胀而恶化了传热。当考虑热/机械反馈时，峰值燃料温度增加 11 K。因此，必须考虑 N/TM 耦合以产生保守的设计。