Application of modern control theory to spatially dependent nuclear reactors

The basic objective of this research is to investigate the spatialcontrol problem in large power reactors using modern control tech-niques. Recently, in response to the need for nuclear reactors withimproved economics and greater efficiency, cores have become larger,power densities have increased, and power distributions have beenmade more uniform. Each of these improvements leads to reactors inwhich it is possible to sustain xenon-induced spatial power oscillations.For such reactor systems, it is necessary to design a detection andcontrol system that will minimize deviations from the design powerdistribution in order to maintain the required thermal margins at ratedpower.The phenomenon of spatial power oscillation has been recognizedfor many years and is widely discussed in the technical literature. 1, Z ,3This oscillation is partially due to the fission product xenon-135 becauseof its exceptionally large absorption cross section-about 3.5 X 106barns -for thermal neutrons.This isotope is formed to a small extent (0.30;0) as a direct pro-duct of fis sion, but the main proportion in a reactor originates fromtellurium-l35, produced in 5.60;0 of the slow-neutron fissions of ura-nium-235. Tellurium-135 has a half life of only 2 minutes and under-goes a series of stages of negative beta decay, as follows: