Boron carbide is widely used as a neutron absorber in most nuclear reactors, in particular in fast neutron ones. The irradiation leads to a large helium production (up to 10²²/cm³) together with a strong decrease of the thermal conductivity. In this paper, we have performed thermal diffusivity measurements and X-ray diffraction analyses on boron carbide samples coming from control rods of the French Phenix LMFBR reactor. The burnups range from 10²¹ to 8.10²¹/cm³. We first confirm the strong decrease of the thermal conductivity at the low burnup, together with high microstructural modifications: swelling, large micro-strains, high defects density, and disordered-like material conductivity. We observe the microstructural parameters are highly anisotropic, with high micro-strains and flattened coherent diffracting domains along the (00l) direction of the hexagonal structure. Performing heat treatments up to high temperature (2200 °C) allows us to observe the material thermal conductivity and microstructure restoration. It then appears the thermal conductivity healing is correlated to the micro-strain relaxation. We then assume the defects responsible for most of the damage are the helium bubbles and the associated stress fields.

碳化硼在大多数核反应堆中，特别是在快中子反应堆中，被广泛用作中子吸收剂。辐照导致大量的氦气产生（高达10 ²² / cm ³），并且热导率大大降低。在本文中，我们对来自法国Phenix LMFBR反应器控制棒的碳化硼样品进行了热扩散率测量和X射线衍射分析。燃尽范围从10 ²¹到8.10 ²¹ / cm ³。我们首先确认在低燃耗时热导率会大大降低，并伴随着高的微观结构变化：溶胀，大的微应变，高的缺陷密度和无序状的材料电导率。我们观察到微观结构参数是高度各向异性的，沿着六角形结构的（00l）方向具有高的微应变和平坦的相干衍射域。进行高达2200°C的高温热处理，使我们能够观察材料的导热性和微观结构的恢复。然后看来，导热率的恢复与微应变的松弛有关。然后，我们假定造成大部分破坏的缺陷是氦气气泡和相关的应力场。