[en] The effect of first wall lifetime of 0.5 to 8 years on the cost of generating electricity in the UWMAK-I and UWMAK-II reactors is investigated. It was assumed that there was little incentive to develop walls with lifetimes (determined by radiation damage) greater than 10 years because of failures due to conventional mechanisms. Based on this assumption the cost of electricity from these two reactors increased over the 10 year lifetime value by 8 to 10 percent for a wall life of 4 years, 17 to 28 percent for 2 years, 35 to 65 percent for 1 year, and 85 to 150 percent for 0.5 year lifetimes. It appears that wall lifetimes of less than 2 years are economically unattractive for these reactors and that there is a great incentive to find materials which will have in-service lifetimes between at least 4 and 10 years