11th International Conference on Nuclear Engineering

A comprehensive study on the effects of energetic protons on carbon fiber composites and compounds under consideration for use as low-Z pion production targets in future high power accelerators and lowimpedance collimating elements for intercepting TeV-level protons at the Large Hadron Collider has been undertaken addressing two key areas namely thermal shock absorption and resistance to irradiation damage. Carbon fiber composites of various fiber weaves have been widely used in aerospace industries due to unique combination of high temperature stability, low-density and high strength. The performance of carbon-carbon composites and compounds under intense proton beams and long-term irradiation have been studied in a series of experiments and compared with the performance of graphite. 24 GeV proton beam experiments confirmed the inherent ability of 3D C/C fiber composite to absorb shock. A series of irradiation damage campaigns explored the evolution of the different C/C structures as a function of proton fluence and irradiating environment. The studies confirmed the influence of the environment on structural integrity loss with radiolytic oxidation as most pronounced detrimental factor above a threshold proton fluence of 5•10 pcm. The carbon-fiber composites were shown to exhibit significant anisotropy in their dimensional stability driven by the fiber weave and the microstructural behavior of the fiber and carbon matrix accompanied by the presence of manufacture porosity and defects. Carbon-fiber reinforced compounds exhibited significant decrease in post-irradiation deformation even after low dose levels and high degree of structural degradation at fluence ~5•10 pcm while irradiated in vacuum and at higher temperature. Finally, X-ray diffraction studies on irradiated C/C composites and carbon-fiber reinforced Mo-graphite compound revealed (a) low graphitization in the as-received 3D C/C and high graphitization in the MoGRCF compound (b) irradiation-induced graphitization of least crystallized phases in the carbon fibers accompanied by increased inter-planar distances along the c-axis of the graphite crystal with increasing fluence and coalescence of interstitial clusters to new crystalline planes between basal planes.