High-temperature carbon-irradiation issues for the Sombrero ICF reactor

In order to assess the feasibility of carbon materials for the first-wall of the Sombrero KrF laser-driven ICF fusion reactor [W.R. Meier et al., OSIRIS and SOMBRERO Inertial Fusion Power Plant Designs, W.J. Schafer Associates Report, WSJA-92-01, DOE/ER/54100-1 (1992); W.R. Meier, et al., Fus. Eng. Des. 25 (1994) 145–157; I.N. Sviatoslavsky, et al., Fus. Tech. 21 (1992) 1470–1474], published experimental results relating to mechanical and thermal properties of graphites and carbon-fiber-composites (CFCʹs) under neutron irradiation and high heat loads are reviewed. Results are compared to published design requirements for the Sombrero ICF reactor, with particular attention to three separate issues of concern: (1) Erosion rates of the first wall are highly sensitive to the thermal conductivity value, which is itself environment-sensitive (radiation and high temperature). Erosion rates at the first wall are calculated here using a high-temperature post-irradiation conductivity value of 50 W/m K, with complete erosion of the first wall layer predicted within 1.25 full-power years (FPY), illustrating the sensitivity of erosion rates to thermal conductivity assumptions; (2) Radiation-induced swelling in 2-D and ‘pseudo 3-D’ CFCʹs is consistently ∼20% under high-temperature neutron damage of 5 dpa (0.33 FPY). This level of swelling would pose technical challenges to the engineering of the target chamber modules; (3) Total tritium retention is predicted to be ∼0.5–5 kg in the Sombrero chamber within 0.67 FPY, which may call into question safety-status assumptions of the CFC-based chamber design. These results indicate the urgency of high-temperature neutron-irradiation tests of fully symmetric 3-D CFCʹs in order to support the plausibility of a carbon first-wall IFE chamber such as proposed for Sombrero.