氚化钯中氦行为的小角中子散射研究

Palladium is one of the most important candidate materials for supply, storage and recovery of deterium-tritium fuel cycle in ITER plant. However, the tritium aging palladium plays adversely effect on the performance of palladium, which causes hazards to stability and reliability of nuclear fusion reactor and tritium-related system. The microscopic nature of the aging effect is derived from the evolution of helium generated by tritium decay in palladium, which hinders or changes the diffusion and retention beheavior of hydrogen isotopes. In the present research on helium beheavior in palladium, there still exists imperfections in traditional analytical techniques, such as localization of microscopic and distortion in obtaining helium bubble information. In present proposal, small angle neutron scattering (SANS) technique is applied to investigate the evolution mechanism of helium bubbles in palladium tritium, to obtain the dependence of the size and population of the helium bubbles on the aging time, and to establish the evolution model of nucleation and growth of helium bubbles. Meanwhile, the grain boundary and dislocation, which are closely related to helium behavior, are introduced into palladium by reconstruction technology to study the influence on helium behavior. Finally, the exploration on quantification of helium aggregates density is conducted. Through the implementation of this project, a new breakthrough on helium behavior research technique of tritium-related materials can be achieved, which will provide the physical image for interpretation the nature of tritium aging effect. Besides, the results figured out from this work should be useful to guide the design the reconstructed palladium with long-life and stable performance in tritium storage application.

金属钯在磁约束核聚变堆等涉氚系统中氘氚核燃料贮存、输运、回收领域具有重要的应用背景。然而钯的氚老化效应对其使用性能造成不利影响，从而给涉氚系统的稳定性及可靠性造成隐患，其微观本质源于氚衰变生成的氦在钯中的演化行为，阻碍/改变了氢同位素的扩散与驻留方式。目前在钯中氦行为的研究中，传统分析技术还存在一些不足，如氦泡信息的获取存在片面性、失真等问题。本项目拟采用小角中子散射技术进行氚化钯中氦泡的演化机制研究，研究氦泡的尺寸、数量等关键信息随老化时间的变化规律，建立氦泡形核、生长的演化模型。其次，将与氦行为密切相关的晶界、位错通过重构技术引入钯中，研究晶界、位错对氦行为的影响规律。最后，开展氦聚集体的密度定量化的探索性研究。通过本项目的实施，可实现涉氚材料氦行为研究技术的新突破，将为氚老化效应本质内涵的阐释提供重要物理图像。同时，为获得长寿命、性能稳定的重构型钯贮氚材料提供重要的指导依据。

本项目针对贮氚材料钯的氚老化效应，系统研究其微观本质——氦在钯中的演化行为，以及该行为与贮氚性能之间的关联。首先，着重采用中子小角散射技术，对氚老化后的钯及钯铑合金开展了“原位”的测试及表征，首次获得了贮氚材料在吸氚态下氦泡的尺寸及分布，建立了氦泡演化行为与材料的吸氚热力学性能之间的内在关联，基于该结果，选用吸氚坪压高的贮氚材料，可减小材料中氦泡的尺寸，同时增加氦泡的数量，避免氦泡生成较大尺寸而破裂逸出；其次，为了获得原子态氦的演化行为，采用中子衍射技术对钯及钯铑合金也开展了“原位”的测试及表征，首次获得了贮氚材料在吸氚态下的中子衍射图谱，证实了氚及氦均占据晶格八面体间隙位置，并根据该结果提出采用非饱和态吸氚，可降低氦泡和氚尾的形成几率，有效减缓氚老化效应；最后，为了丰富和补充不同形态的氦泡在钯中的演化行为机制，采用氦离子注入向系列钯样品中引入氦，通过控制辐照条件获得了不同特征的氦泡，揭示了晶界对氦泡的聚集及捕获作用。同时，基于该研究建立了氦离子辐照与氚老化生成氦泡特征的内在关联，该结果可对氚老化氦泡的微观表征分析提供补充，同时可为长服役寿命下氚化钯中氦泡的演化行为预测提供指导及借鉴。