Determination of the Void Fraction in the Msre Using Small Induced Pressure Perturbations.

Abstract

With the Molten-Salt Reactor Experiment (MSRE) operating a t 5 Mw, sawtooth pressure perturbations were introduced into the fuel-pump bowl to determine the amount of helium gas entrained i n the circulating fuel. The pressure and neutron flux signals were simultaneously amplified and recorded on magnetic tape. Then the signals were analyzed using auto-power spectral density, cross-power spectral density, cross-correlation, and direct Fourier transform techniques to obtain the neutron-fl ux-to-pressure frequencylesponse function. An analytical model, developed previously to a i d i n the interpretation of the fluctuations of the neutron flux i n an unperturbed system, was used t o infer from the exprimental data the amount of helium void (interpreted as a void fraction) entrained i n the fuel salt. A description of the analytical model and i t s experimental verification are included i n this report. The v o i d fraction w a s determined to be between 0.023 and 0.045%. The uncertainty of this inference i s attributed to assumptions made i n the model.