Spherical graphite and fuel elements distinguished in analysis - by large systematic error associated with graphite only elements

摘要

The neutron interaction properties are measured as they are successively passed through zones of a measuring reactor in which neutron-absorbing, neutron-scattering and fissile substances each possess a maximum influence on the reactivity of the measuring reactor. The power variations occurring as the spherical elements pass through the reactor provide characteristic curves. These evaluated by an analysis programme to give the composition of the elements. The apparent difference between the graphite content of a graphite element as given by this analysis programme and the actual graphite content in the element is utilised for distinguishing between graphite elements and fuel elements which possess approximately the same graphite content as the graphite elements and are in a specific burn-up state. In the existing method, the evaluation of the graphite content of a graphite element involves a systematic error. The new method enables this error to be utilised to distinguish between graphite elements and partly burnt-up fuel elements having the same graphite content, since the systematic error associated with the former is much greater than that associated with the latter.