Reactor Power Monitor Based on Cherenkov Radiation Detection

Abstract

At the temperature and radiation levels expected in the core region of some projected reactor plants, conventional radiation sensors, such as fission chambers, suffer severe radiation damage. On the other hand, remote location of sensors introduces geometry effects. These circumstances emphasize the need for a power level sensor which is highly resistant to the hostile environment and still responds directly to power level changes. Such a detection channel has been proposed. It is based on sensing the gamma flux above some energy threshold, thus discriminating against gamma radiation associated with decay. In addition, the proposed system dispenses with cables and voltages applied across damageable insulators, through sensing the light transmitted along a cylindrical duct. The detecting medium is the gas with which the duct is filled; the light signal is the Cherenkov radiation generated by relativistic Compton recoil electrons. Cherenkov radiation intensity increases sharply from an electron velocity threshold, which depends on the index of refraction of the medium. For gases, this threshold can be continuously varied by adjusting the gas pressure. On the other hand, electrons with subthreshold velocities can generate (background) light through scintillation processes. In order to assay the overall discrimination available from the choice of gas, pressure, and geometry, a series of tests has been under way with 3-MeV electron pulses from a Van de Graaff accelerator.