Patent Number: 
Section: claims

1. A method of determining a void rate in a biphase gas/liquid medium, the void rate corresponding to a fraction of a volume of gas corresponding to gas bubbles in the gas/liquid medium to a total volume of gas and liquid in the gas/liquid medium, the method comprising:defining a size of the largest gas bubbles in the gas/liquid medium by optical measurement;deploying a bulk elastic wave resonator in contact and coupled acoustically with the biphase gas/liquid medium;measuring, by nonlinear resonant ultrasound spectroscopy of the biphase gas/liquid medium in terms of frequencies and amplitudes of acoustic excitation in a given range of frequencies based on the size of the largest gas bubbles and in a given range of amplitudes, bulk elastic waves emitted and detected at said resonator, resulting in a set of resonance curves exhibiting maxima;determining a straight line defined by the maxima of said set of resonance curves having different excitation amplitudes;determining a slope of said straight line; anddetermining the void rate based on said slope. 2. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, further comprising determining a resonant frequency of said gas bubbles. 3. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein:the gas bubbles have a radius on the order of a hundred microns,the given range of frequencies is below 33 kHz,the liquid medium is water, andthe gas bubbles are air bubbles. 4. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein the bulk elastic wave resonator is placed in said biphase gas/liquid medium, and the bulk elastic wave resonator comprises a first metallic plate connected to an emitter and a second metallic plate connected to a receiver. 5. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 4, wherein the first plate is connected to a transducer. 6. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 4, wherein the second plate is connected to a hydrophone. 7. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 4, wherein the first metallic plate is a front face of the emitter and the second metallic plate is a front face of the receiver. 8. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein the bulk elastic wave resonator is of Helmholtz type, and the biphase medium is introduced into said bulk elastic wave resonator. 9. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein the liquid is a metal in a liquid state. 10. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 9, wherein the metal is sodium. 11. A nuclear reactor configured to apply the method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1. 12. The nuclear reactor as claimed in claim 11, wherein the resonator is of plate type, and the resonator is placed within the liquid of sodium type of a primary circuit of the nuclear reactor. 13. The nuclear reactor as claimed in claim 11, wherein the resonator is of Helmholtz resonator type, and the resonator is placed branched off from a primary or secondary circuit of the nuclear reactor. 14. A fast neutron reactor configured to apply the method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1. 15. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 1, wherein each resonance curve in the set of resonance curves exhibits a single maximum. 16. A method of determining a void rate in a biphase gas/liquid medium, the void rate corresponding to a fraction of a volume of gas corresponding to gas bubbles in the gas/liquid medium to a total volume of gas and liquid in the gas/liquid medium, the method comprising:deploying a bulk elastic wave resonator in the biphase gas/liquid medium, the bulk elastic wave resonator comprising a first metallic plate connected to a transducer and a second metallic plate connected to a receiver;measuring, by nonlinear resonant ultrasound spectroscopy of the biphase gas/liquid medium in terms of frequencies and amplitudes of acoustic excitation in a given range of frequencies and in a given range of amplitudes, bulk elastic waves emitted and detected at said resonator, resulting in a set of resonance curves exhibiting maxima;determining a straight line defined by the maxima of said set of resonance curves having different excitation amplitudes;determining a slope of said straight line; anddetermining the void rate based on said slope. 17. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 16, wherein the first metallic plate is a front face of the resonator and the second metallic plate is a front face of the receiver. 18. The method of determining the void rate in the biphase gas/liquid medium as claimed in claim 16, wherein the bulk elastic wave resonator is of Helmholtz type. 19. A fast neutron reactor configured to determine a void rate in a biphase gas/liquid medium, the void rate corresponding to a fraction of a volume of gas corresponding to gas bubbles in the gas/liquid medium to a total volume of gas and liquid in the gas/liquid medium, the fast neutron reactor being configured to determine the void rate in the biphase gas/liquid medium by:deploying a bulk elastic wave resonator in contact and coupled acoustically with the biphase gas/liquid medium;measuring, by nonlinear resonant ultrasound spectroscopy of the biphase gas/liquid medium in terms of frequencies and amplitudes of acoustic excitation in a given range of frequencies and in a given range of amplitudes, bulk elastic waves emitted and detected at said resonator, resulting in a set of resonance curves exhibiting maxima;determining a straight line defined by the maxima of said set of resonance curves having different excitation amplitudes;determining a slope of said straight line; anddetermining the void rate based on said slope. 20. The fast neutron reactor as claimed in claim 19, wherein the resonator is placed within a primary circuit of the fast neutron reactor.