The Detection of Local Overheating in Liquid Metal Cooled Fast Neutron Reactors

Abstract

This thesis presents a theoretical and experimental study of special instrumentation systems proposed for the protection of sodium cooled fast neutron reactors. The growth and future potential of the fast reactor project is reviewed and the reasons why its protection represents a special instrumentation problem outlined. Various possible methods by which mal-function may be detected are examined. One such method, namely the detection and recognition of acoustic noise in a sodium cooled nuclear environment is believed to have been originated by the author. The development of these systems has necessitated the introduction of novel means of detecting signals from the reactor environment, A large experimental programme was carried out to assess the transducers and collate the information produced during simulated fault conditions. This investigation included both "out of pile" and "in pile" experiments, electrical heaters being used to simulate nuclear heating. The "in pile" experiment was carried out in the Dounreay Fast Reactor As a result of this programme a system was designed for the D.F.R. The design of such a system takes into account the theory of the measurement and correlation of random noise. Theoretical and experimental work is presented which examines the conditions to be satisfied in order that spectral correlation analysis is statistically significant. The prototype system has operated successfully in the D.F.R. for a few months and two recent non-crucial failures of experimental nuclear fuel elements tend to validate the system in that the installed instrumentation detected and correctly identified the source of the mal-function.