It is shown that fine-scale bubbles are to be expected in reasonably pure uranium, the bubbles nucleating either homogeneously with a spacing less than a micron or on any suitable nucleation sites that may exist on this or a finer scale. The precise value of the homogeneous nucleation spacing depends on the diffusion coefficient of the gas atoms, which is modified during irradiation by the excess concentration of vacancies produced by the fission prooess. The dislocation lines and nodes should provide suitable nucleation sites as they have about the right spacing and their stress fields should attract the large inert gas atoms to form Cottrell atmospheres. The bubbles when once nucleated grow by a vacancy diffusion mehanism, the vacancies being created by the fission process or possibly diffusing from the grain boundaries in very small grains. At temperatures above some value, which in certain cases may be as low as about 300 deg C, the influx of vacancies is sufficient to prevent the gas pressure in a bubble from exceeding the surface energy restraining force by more than an order of magnitude, in which case dislocation mechanisms of plastic deformation should not operate. The fission prooess enhances the concentrations of both vacancies and interstitials in the solid with the result that bubble growth is governed by the thermal equilibrium or vacancies, but an enhanced growth will occur at the lower temperatures if the sinks for point defects accept interstitials more readily than they do vacancies. (auth) 186l8 The gamma activity anticipated during the refabrication of EBR-II fuel has rendered suspect many operations considered adequate in less demaning environments. Two such operation involve the use of a differential transformer to measure linear displacement and an eddy current coil to measure the internal integrity of a cast fuel pin. A test apparatus containing the above components was irradiated at between 4.7 x lO/sup 5/ and 1.6 x 10/sup 6/ rad/hr in the ANL Gamma Irradiation Facility. The electrical output of the components was periodically monitored until a total exposure of 1.24 x 10/sup 9/ rads had been realized. No changes in the shape of the traces recorded were noted over the entire irradiation period. With the exception of a base-line shift in the case of the eddy current output trace, the measurements were also insensitive to temperature changes of the order of l9 deg C. Radiation damage to paints, varnishes, conventional insulations and a radiationresistant grease was noted, but the extent of this effect was not such that the test was affected. It appeared that the performances of the linear transducer and eddy current device were such that they would be expected to operate successfully in an environment similar to that anticipated in the EBR-II Fuel Cycle Facility. (auth) l86l9 Cr --Al/sub 2/O/sub 3/ cermet specimens were examined by metallographic methods. Two unfueled specimens were previously irradiated in the LITR to about 1020 nvt (thermal), and two UO/sub 2/ fueled specimens were irradiated to 2.53 x 10/sup 20/ nvt at lOO0 deg C. The unfueled samples showed no evidence of structural changes as a result of irradiation. Various changes in the fueled sample are discussed. (J.R.D.)