An Incore Detector for Measuring Power and Breeding Distributions in Power Breeders

For optimum operation of fast breeder reactors, knowledge of the incore power and breeding distributions is desirable. Because of the high temperature liquid sodium environment in the breeders, an activation method rather than a technique involving ion chambers seems to be the most appropriate experimental technique at present. An activation system has been worked out in which 1/16" BeO balls containing oxides of 235U and 238U are inserted into the reactor for activation and withdrawn to be counted in a Ge(Li) counter. Measurements of the activated fission and 239Np gamma-rays yield the desired information. Parameters and procedures are obtained based on a specific fast Demonstration Breeder design. However, only slight modification would be required for the application to other breeders.