The following criteria defines the objectives, bases and functional requirements that shall govern the preparation of the final design for the zirconium process tube installation program at the 100-K Areas. As a result of this program, reduced operating costs and increased production can be achieved. The present central zone aluminum tubes in the 100-K Reactors require replacement every to to three years to prevent excessive failures resulting from the thinning of the tube walls by corrosion. Replacement of the aluminum central zone tubes with zirconium tubes which have a negligible corrosion rate will substantially reduce the need for tube replacement and the attendant loss of production. Installation of the ribless zirconium tubes will, in addition, permit increased production through the use of self-supported fuel elements of improved performance.