LAMPRE, a 1 MW experimental fast reactor, fueled with plutonium and cooled by sodium, operated successfully for two and a half years.** In this simple system, the use of plutonium fuel and liquid metal coolant proved to be straightforward. Some of the experience gained with this system should be applicable to larger, more complex fast reactors. Adequate coolant purity was maintained in the LAMPRE system so that a refractory metal container for the fuel could be satisfactorily used. Nitrogen

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... the atmosphere"was observed to diffuse into the coolant loop through the pipe walls, which operated at temperatures in the range 450°C to 55G°C; the nitrogen concentration in the gas space above the sodium was controlled by periodic flushing, and no ill effects attributable to the nitrogen were observed. During the course of the experiment, fission products and plutonium were released into the coolant loop. This had only a minor effect on the established procedures for reactor operation, fuel handling, etc. Additional conservatism was applied to maintenance tasks, but it appears in retrospect that more than necessary caution was used. The distribution of fission products in the system was not examined in detail, because not all of the loop was accessible to gamma scanning equipment. Where measurements could be made, the results -particularly with respect to cesium -are consistent with fission product transport and distribution observed in laboratory experiments. A major part of the core structure, and some of the coolant loop, was disassembled after the conclusion of the reactor experiment. This was accomplished without particular difficulty. The level of dispersable plutonium contamination was lower than had been expected. In the hot trap system, plutoniimi contamination was firmly fixed on the pipe walls; sections of these components were removed from the loop without any-special techniques to prevent the spread of radioactive materials. The larger sections of gas piping attached to the top of the reactor vessel contained detectable levels of plutoniimi, but conventional bagging tech- %S.oOi ./^^ niques were adequate to permit uneventful disassembly of the system. Smaller gas lines connected to the fuel charging machine were safely removed without bagging.