This report is a record of experimentation conducted intermittently over a period of two years and directed toward preventing deposition of transport corrosion products on fuel elements and other critical components in high-temperature, circulating water nuclear reactor. It includes the postulated mechanism for deposition, a description of experimental equipment, experimental data, results obtained from the experiments, and recommendations for future study.

The general program established at Argonne National Laboratory in connection with the Fast Power Breeder Reactor (PBR) includes performance of exponential experiments on assemblies having compositions which may exist in the reactor core. This report deals with that phase of the program known as the Fast Exponential Experiment which may be described very briefly as follows. An assembly of fissile (U-235) and fertile material (too small to be self-critical) intermixed with poisons (such as are encountered in the mechanical structure and coolant system of a self-sustaining reactor) is fed with neutrons from an auxiliary source. By measurements of the neutron flux within the assembly, important parameters can be calculated which are necessary to the proport design of an actual critical reactor of the same composition.

A method is described for preparing plaster of Paris replicas of irradiated fuel slugs. An impression mold is made by pouring the plaster about a fuel slug held in a specially designed holder. The slug is removed from the holder and the impression mold issued to cast a replica, also made of plaster of Paris. The replicas, including one end only, are accurate reproduction of the original slug for surface features down to about one-half mil and for dimensions within one or two mills. Two dental impression plasters were found to give satisfactory results. With the limits mentioned, the process will serve the purpose of preserving models of radioactive specimens for use as "museum pieces." However, the procedures are very exacting in achieving such results.

Uranium alloys containing 3 and 6 w/o niobium have been prepared in which the impurity content is rather low. These alloys show very promising resistance to corrosion by water at 260 and 300 degree C. The corrosion resistance is exhibited in degassed water and in water which is saturated with air or oxygen at room temperature before testing.

Report issued by the Argonne National Laboratory covering the quarterly report from the Reactor Engineering Division. A summary of reactor programs, designs, development, and experiments are presented. This report includes tables, illustrations, and photographs.