The Role of Void Distributions on Void Fraction Measurements

Abstract

<p>The distribution of voids in a nuclear reactor is of great importance due to their effect on the neutron flux and on the reactor dynamic characteristics in addition to the well known thermohydraulic problems they create.</p> <p>The possibility of using scattered neutrons to measure voids in a liquid flow is investigated experimentally. The appealing property of a scattering technique as compared to the well known transmission method, is that multiple detectors could be used for additional information about the distribution of the voids as well as their void fraction.</p> <p>For this purpose a beam of neutrons has been extracted from the McMaster University 5MW pool type nuclear reactor. Cylindrical pieces of Lucite have been used to simulate a column of water; this material has neutron transport properties which are very similar to those of liquid water.</p> <p>The neutron diagnostic method of detection has the advantage of not disturbing the flow of the fluid like devices such as probes and isolating valves would do.</p> <p>A BF₃ detector mounted on an arm which rotates about the axis of the cylindrical samples was used as the experimental set up. Lucite samples of different void fractions and possessing different void distributions were prepared. Different numbers of circular holes and of different relative sizes were drilled in the samples providing the possibility of simulating many void distributions by simply rotating the samples. Counting times of the order of 100 seconds were used in order to provide sufficient statistical accuracy to observe the differences in counts.</p>