Carbon-based materials are an attractive choice for fusion reactor plasma facing components (PFCs) because of their low atomic number, superior thermal shock resistance. and low neutron activation. Next generation plasma fusion reactors, such as the international thermonuclear experimental reactor (ITER), will require advanced carbon-carbon composite materials possessing extremely high thermal conductivity to manage the anticipated severe heat loads. Moreover, ignition machines such as ITER will produce high neutron fluxes. Consequently, the influence of neutron damage on the structure and properties of carbon-carbon composite materials must be evaluated. Data from an irradiation experiment are reported and discussed here. Fusion relevant graphite and carbon-carbon composites were irradiated in a target capsule in the high flux isotope reactor (HFIR) at Oak Ridge National Laboratory (ORNL). A peak damage dose of 1.58 dpa (displacements per atom) at 600-degrees-C was attained. The carbon materials irradiated included nuclear graphite grade H-451 and one-, two-, and three-directional carbon-carbon composite materials. Dimensional changes and strength are reported for the materials examined. The influence of fiber type, architecture, and heat treatment temperature on properties and irradiation behavior are reported. Carbon-carbon composite dimensional changes are interpreted in terms of simple microstructural models.

Carbon-carbon composites increasingly are being used for plasma-facing component (PFC) applications in magnetic-confinement plasma-fusion devices. They offer substantial advantages such as enhanced physical and mechanical properties and superior thermal shock resistance compared to the previously favored bulk graphite. Next-generation plasma-fusion reactors, such as the International Thermonuclear Experimental Reactor (ITER) and the Burning Plasma Experiment (BPX), will require advanced carbon-carbon composites possessing extremely high thermal conductivity to manage the anticipated extreme thermal heat loads. This report outlines a program that will facilitate the development of advanced carbon-carbon composites specifically tailored to meet the requirements of ITER and BPX. A strategy for developing the necessary associated design data base is described. Materials property needs, i.e., high thermal conductivity, radiation stability, tritium retention, etc., are assessed and prioritized through a systems analysis of the functional, operational, and component requirements for plasma-facing applications. The current Department of Energy (DOE) Office of Fusion Energy Program on carbon-carbon composites is summarized. Realistic property goals are set based upon our current understanding. The architectures of candidate PFC carbon-carbon composite materials are outlined, and architectural features considered desirable for maximum irradiation stability are described. The European and Japanese carbon-carbon composite development and irradiation programs are described. The Working Group conclusions and recommendations are listed. It is recommended that developmental carbon-carbon composite materials from the commercial sector be procured via request for proposal/request for quotation (RFP/RFQ) as soon as possible.

GraphNOL N3M (N3M) is a bulk graphite developed at Oak Ridge National Laboratory (ORNL) for advanced structural applications in aerospace thermal protection systems. It is currently of interest to the United States fusion energy community for plasma facing components, such as the first wall armor tiles of the International Thermonuclear Experimental Reactor (ITER) because of its superior thermal shock resistance and irradiation lifetime. This paper reports the results of irradiation experiments on N3M graphite at two temperatures, 600 and 875 °C in the High Flux Isotope Reactor (HFIR) at ORNL. Maximum fluences of 4.2 × 1026 and 2 × 1026 n/m2 (E > 50 keV) or 28.4 and 13.5 dpa (graphite) were attained at 600 and 875° C, respectively. Data are presented on the dimensional stability, volume change, strength, Young's modulus, critical stress intensity factor KIc, and coefficient of thermal expansion (CTE). The thermal shock resistance of GraphNOL N3M is discussed and comparisons made with other graphites. The influence of irradiation damage on thermal shock resistance is postulated.

Radiation damage due to H+2 and Mo+ implantation into hot-worked pyrolytic graphite and into single-crystal graphite flakes has been studied using 1-MeV 4He+ ion channeling. The implant energies used, 35 keV for H+2 and 120 keV for Mo+, yielded ranges of about 1600 and 600 Å, respectively. For H2 implantation, a partially crystalline surface layer remains after a fluence of 2×1016 H/cm2; this layer is completely disordered at 2×1017 H/cm2. At higher hydrogen fluences a surface layer exfoliates. For Mo implantation the disorder introduced at a fluence of 5×1014 Mo/cm2 is sufficient to prevent channeling throughout the range. For both implant species, complete recrystallization of samples disordered up to the surface occurs for annealing only at temperatures above 2800 K. If a surface layer remains crystalline after implantation, recrystallization proceeds both from the bulk and from the surface, and crystallinity is restored at 2300 K. While hydrogen is known to be released at temperatures between 1100 and 1500 K, Mo remains within its original range distribution up to the temperature of complete recrystallization. At a temperature of 2300 K an ordering of the implanted Mo atoms with respect to the c axis is observed, indicating short-range migration within the range distribution. At 2800 K no more Mo could be found in the analyzed surface layer.

In tensile testing of irradiated graphites, it is difficult to assure alignment of sample and train for tensile measurements. By recording location of fractures, run (sequential) statistics can readily detect lack of randomness. The technique is based on partitioning binomial distributions.

Dimethylsulfoxide extracts of Ashland-240 petroleum pitch and Barrett M-30 coal tar pitch were tested for mutagenicity using Salmonella histidine reversion assay (Ames test). Four strains of Salmonella were employed. The strains sensitive to frameshift mutations were reverted, with the coal tar pitch indicating a three fold greater mutagenic activity than the petroleum pitch. Metabolic activation with rat liver extracts was required. As a prescreen to aid investigators in ordering their priorities, the short-term tests appear to be a valid approach to testing the large number of hazardous compounds and complex mixtures that man encounters in his environment.