A GAMMA-RAY ATTENUATION METHOD FOR VOID FRACTION DETERMINATIONS IN EXPERIMENTAL BOILING HEAT TRANSFER TEST FACILITIES

Gamma rays emanating from a radioactive source are beamed through and are attenuated by steam --water mixtures contained in a simulated reactor flow channel. The emergent radiation is detected by a scintillation crystalphotomultiplier tube assembly. An expression is developed which yields the void fraction when the detector output with the channel empty, filled with water, and containing the mixture in question is known. The principal sources of errors inherent in the method are analyzed and their magnitudes computed for a specific test facility. With a uniform bubble distribution on this facility, the maximum possible error in void fraction is approximately plus or minus 0.03. The method is also applied to three idealized preferential phase distributions simulated in Lucite. However, the large discrepancy between calculated and measured void fractions illustrates the need for more refined experimental techniques where non-uniform distribution of voids are encountered. Such techniques are being developed. (auth)