Abstract: "Two cases are considered. In Case I, the reactor water velocity is optimized to obtain a minimum annual cost (including amortization and operating costs) for the cooling system along. The optimum velocity for a 310 megawatt reactor is calculated to be ~25 feet per second, compared to the present design value of 30 feet per second. In Case II, the velocity which will give the minimum cost of product under the assumptions of varying power and production rate is found to be in the range from ~25 to ~40 feet per second, depending on the assumptions with respect to the variation of total investment in the reactor complex with design production capacity."