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THE CONTINUOUS MEASUREMENT OF THERMAL-NEUTRON FLUX INTENSITY IN HIGH-POWER NUCLEAR REACTORS
W.R. Loosemore, J.A. Dennis
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Abstract
The problem of measuring continuously the thermalneutron flux intensity in high-power reactors at temperatures up to 500 deg C is considered, and it is concluded that the mean-current ionization chamber provides the best solution. The development of a suitable chamber is described, which is made from stainless steel and has a gas filling of xenon. When the electrodes are coated with uranium oxide (U/sub 3/O/sub 8/) containing 0.48 mg of U/sup 235/, the current sensitivity i s 7 x 10/sup -17/ amp/n/cm/sup 2//sec, and at a neutron flux intensity of 10/sup 13/ n/cmsup 2//sec the equillbrium residual current measured in a graphite-moderated reactor is 0.6% of the total output. Life tests were carried out successfully to a total neutron dose of 3 x 10sup 20/ n/cm/sup 2/. At a flux intensity of 10/sup 14/ n/cm/sup 2/ /sec a chamber with uncoated titanium electrodes has the same fraction of residual current as one containing U/ sup 235/, and is preferred as it is not subject to depletion effects. (auth)