Enrico Fermi Reactor Use For Irradiation Testing PDF Download

Three Enrico Fermi prototype fuel pins have been irradiated in the CP-5 reactor to average burnups of 0.27, 0.58, and 0.85 per cent of the total atoms fissioned in the uranium -- 10 per cent by weight molybdenum fuel alloy. The purposes of the tests were to study the radiation stability of the full-size pins under environmental conditions similar to those expected in the Enrico Fermi Fast Breeder Reactor, and to verify the swelling-temperature-burnup relationships established in a previous capsule irradiation program conducted in the Materials Testing Reactor (MTR). Through correlation of diameter measurements, temperature, and postirradiation metallographic analysis, it is concluded that the radiation stability of the alloy is heavily dependent on the metallurgical condition of the material. The ? phase, stable above 1060 F, resists radiation more effectively than the ? + ? phases, which are thermally stable at temperatures less than 1045 F. Data from the CP-5 program suggest a more severe burnup limitation on this alloy than was previously concluded on the basis of the MTR results. The disparity is believed to be due to the influence of the fission-rate parameter on the microstructure of the material during irradiation. Fission events, if they occur with sufficient frequency, maintain the ? phase at temperatures below 1060 F. If the critical rate is not attained, the alloy will transform thermally in accordance with the uranium-molybdenum equilibrium diagram and the macroscopic temperature of the material.