This report to the FEDC Working Committee details activities in N-Reactor fuel element fabrication and materials testing for the time period of September 1965 to January 1966.

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A study of relative plutonium and orallay values is being made by representatives of the production sites under direction of AEC Headquarters. Division of Production. (Oralloy is uranium enriched to 93-15 percent U-235.) Under study assumptions that will be detailed later, oralloy would cost less than formerly, and may be cheap enough to enrich production reactor discharged uranium to reactor input assays. To date uranium recycle enriching assays have been held below two percent U-235 -- usually 1.2 to 1.5. Use of orallay for enriching reactor tails would conserve U-236. which would increase neptunium and Pa-238 production. There may be other profitable reactor uses for the cheaper oralloy.The intent of this document is to give the oralloy cost data to those who may study or evaluate oralloy use, and to explain the basis for oralloy cost so that the validity of any use may be assessed.

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In the bombardment of materials with heavy particles a large amount of energy can be deposited in a very small region by a primary knock-on atom and the local atomic arrangement can be thereby drastically disrupted. Various measurements of physical properties of such irradiated materials indicate the presence of distributions of defects which are removed in a step-like manner by annealing. One of the more interesting physical property changes accompanying fast particle irradiation is the attendant change in mechanical properties of irradiated crystals. The defect which is responsible for the mechanical property changes of irradiated crystals is only removed at high temperatures, temperatures coresponding to self diffusion. This observation, as well as others, has led to the model of a depleted zone as being responsible for the changes of mechanical properties of irradiated crystals. A depleted zone is envisioned as a region of crystal where a high local concentration of point defects exists - a belt of interstitials surrounding a multiply connected complex of vacancy clusters. We would like to present here some evidence which lends support to the existence of such defects.