As part of a program to develop an economical fuel cycle for an Organic Moderated Reactor (OMR), experimental fuel elements are being irradiated in the Organic Moderated Reactor Experiment (OMRE). The first two experimental fuel elements have been removed from the OMRE, examined, and evaluated. These extended-surface, platetype fuel elements had finned aluminum cladding, metallurgically bonded to flat uranium alloy fuel plates. A 0.0005 in. nickel layer was used to prevent interdiffusion between the aluminum and uranium. The fuel core alloys irradiated were U--5.5% Mo and U--3.5% Mo--0.5% Si. These two experimental elements were removed from the reactor after one of the elements released fission products, and cladding temperatures increased on both fuel elements. The maximum measured cladding temperature was 780 deg F. The maximum fuel burnup was later determined to be 0.25 at.% U. Hot-cell examination revealed that the coolant inlet ends of the fuel elements had filtered particulate matter out of the coolant, which blocked the ends of the coolant channels. Restriction of the coolant flow through the elements caused partial melting of the cladding in one fuel element and a blister on one of the fuel plates from the other fuel element. Dimensions were taken on three of the fuel plates. Metallographic sections from the blistered fuel plates were examined, and burnup profiles were determined for the three plates measured. The fuel had good dimensional stability, which is significant, since the melted cladding and the core microstructure evidenced temperatures substantially above the maximurn temperatures recorded by thermocouples. Nothing was observed that would indicate the fuel elements would not have functioned properly in the same coolant if the coolant were free of particulate matter of sizes that could be trapped. (auth).

Two fuel elements were removed from the Experimental Boiling Water Reactor and examined in a hot cell. The elements had maximum burn-ups of 0.11 and 0.39 at.%. Both were disassembled and sampled for the evaluation of the effects of in-pile operation and radiation damage to the fuel. The fuel elements were in gcod condition with no ruptured.cladding, core-clad nonbonds, or excessive fuel-plate swelling or warpage. Thin samples cut from the fuel plates in element ET-51 warped and cracked, suggesting a relieving of locked-in stresses and indicating that after 0.39 at.% burn-up the fuel cores were hard, brittle, and highly stressed. The rate of fuel-plate volume increase owing to the burn-up of uranium was 6 to 7% DELTA V per at.% burn-up. Hydrogen was picked up by the fuel plates under reactor operating conditions with the probable forraation of isolated areas of small announts of zirconiura hydride. Annealing studies on sections of fuel plate at 500 and 550 deg C indicated bulk volume increases of 1 to 2% and 5 to 10%, respectively, after 500 hr. A 600 deg C anneal resulted in a bulk volume increase of 17% after 45 hr. (auth).