This part of the completion report pertaining to the NERVA graphite fuel element program covers data collected during the extrusion studies. The physical properties of the fuel element reached the following values: coefficient of thermal expansion (CTE) - 7.0 x 10-6/o C (25 - l,OOOo C); modulus of elasticity - 1.5 x lo6 psi; flexural strength - - 8,000 psi; ultimate strain to failure - 5,500 pidin; good thermal stress resistance. Matrices were produced which could be vapor coated with crack-free films of zirconium carbide. The CTE of the matrix was almost equal to the CTE of the zirconium carbide coating.

Microstructural and mechanical property observations of ingotsource beryllium at selected points in the can-rolling process are reported. Recrystallization occur s concurrently with rolling at temperatures above 1800 deg F, and only partial recrystallization is observed during reheats at 1400 deg F. Most grain refinement induced by the rolling schedule occurs in the first 15 rolling passes. These represent 88 percent reduction from the ingot. A relatively small contribution comes from the final six passes which bring the total reduction from the ingot to 95 percent. Information was also obtained on the effects of the rolling schedule on the properties of the stainless steel can. (auth)

Methods used to obtain evaluated neutron interaction and photon production data for /sup 238/U are described. (auth)

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Progress in the isotopes fuel program during July to Oct 1973 is reported. Preparation and fuel characterization studies of /sup 238/Pu fuels continued. The effect of lower pressing temperatures on pressed plutonium oxide (PPO) spheres was evaluated. Plutonium-238 dioxide feed material that was sintered to a maximum of only 900 deg C was pressed under otherwise normal conditions into a Multihundred Watt (MHW) type fuel sphere. This pressing resulted in a sphere with near-perfect surface texture. The surface was bright and totally free of any visible cracks. However, upon subjection to the normal 1500 deg C vacuum heat treatment, the sphere cracked severely. Metallographic examination of selected areas of MHLV- PPO spheres showed that the spheres were not uniform in microstructure. They possessed nonuniform grain size and porosity distribution. Spheres exposed to high-temperature heat treatments also were nonuniform in microstructure. Calculations were performed to determine the stresses that appear in MRW PPO spheres due to temperature gradients. Thermal shock analyses were also performed. The data obtained as a result of these analyses were used in establishing a controlled heating and cooling cycle for the 1500 deg C, 1-h outgassirg process for development and production spheres. In order to evaluate the …

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As part of the overall fuel ulement research and development program for the Public Service Company of Colorado Fort St. Vrain Nuclear Generatlng Station, Unit One Reactor, one or more prototype proof test fuel elements are to be irradiation tested in a high-temperature gas-cooled reactor (HTGR) environment. The design details, fuel characteristics, and assembly of the second proof test element (PTE-2) in a series of five prototype proof test elements built for the Fort St. Vrain Nuclear Generating Station are described. The purpose of the fue1 element irradiation program is to demonstrate that the Fort St. Vrain (FSV) fuel element will meet its design objectives. This will be demonstrated by irradiating a test element(s) in the Peach Bottom HTGR at temperature gradients typical of that expected in FSV to at least one-third of the design lifetime fuel burnup. PTE-2 will achieve the desired total burnup in approximately 300 full- power days of irradiation in Peach Bottom. It should be noted that PTE-2 was built in 1968, prior to the introduction of pitch-bonded, natural-flake graphite matrix which was eventually chosen for use in the FSV initial core. (25 references) (auth)

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Two methods were employed to densify graphite bodies: gaseous impregnation and liquid impregnation. Gaseous impregnation consisted of two processes: direct flow and pulse vacuum. Liquid impregnation was based on the use of a polymer of cinnamylideneindene. Both types of gaseous impregnation processes were successful in densifying the fuel element graphites; however, the process time of the pulse-vacuum method was shown to be significantly shorter than that of the direct-flow process. The liquid impregnation process was also successful. Two to four impregnation cycles were required to obtain a maximum density.

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