| Neutron radiography has the ability to differentiate between gas and liquid in two-phase flow due both to the density difference and the high neutron scattering probability of hydrogen. Previous studies have used dynamic neutron radiography -- in both real-time and high-speed -- for air-water, steam-water and gas-liquid metal two-phase flow measurements. Radiography with thermal neutrons is straightforward and efficient as thermal neutrons are easier to detect with relatively higher efficiency and can be easily extracted from nuclear reactor beam ports.;The primary objectives of this work are: (1) to optimize a neutron radiography facility for dynamic neutron radiography applications and (2) to investigate a new technique for three-dimensional neutron radiography using information obtained from neutron scattering.;In this work, neutron transport analysis and experimental validation of a dynamic neutron radiography facility is studied with consideration of real-time and high-speed neutron radiography requirements. A beam port based dynamic neutron radiography facility, for a target thermal neutron flux of 1.0x107 n/cm2-s, has been analyzed, constructed and experimentally verified at the McMaster Nuclear Reactor.;The neutron source strength at the beam tube entrance is evaluated experimentally by measuring the thermal and fast neutron fluxes using copper activation flux-mapping technique. The development of different facility components, such as beam tube liner, gamma ray filter, beam shutter and biological shield, is achieved analytically using neutron attenuation and divergence theories. Monte-Carlo simulations (using MCNP-4B code) are conducted to confirm the neutron parameters along the beam path and at the imaging plane. Good agreement between the analytical and the numerical values for the thermal neutron flux at the imaging plane to within 5% has been achieved. The MCNP simulations show that neutron back scattering, due to the presence of the back-wall biological shielding and the beam catcher, have an insignificant effect on the thermal neutron flux at the imaging plane, however, the epithermal and fast neutron fluxes have increased by 4-11%.;The quality of images obtained using neutron radiography and the imaging speed depend on the neutron beam intensity at the imaging plane. A high quality neutron beam, with thermal neutron intensity greater than 3.0x 10 6 n/cm2-s and a collimation ratio greater than 100 at the imaging plane, is required for effective dynamic neutron radiography up to 2000 frames per second.;Experimental results show that the thermal neutron flux is nearly uniform over an imaging area of 20.0-cm diameter. The thermal neutron flux ranges from 1.0x107 -- 1.26x107 n/cm 2-s at a reactor operating power of 3.0 MW. The measured value for the neutron-to-gamma ratio is 6.0x105 n/cm2-muSv and the Cadmium-ratio is observed to be 1.22. These values promote real-time neutron radiography with relatively high neutron attenuating materials such as light water and high-speed neutron radiography with relatively low neutron attenuating materials such as heavy water and Freon type fluids with a minimal contrast degradation resulting from non-thermal neutron content of the beam.;A dynamic neutron radiography system has been developed and modified to obtain less neutron damage to the low-light level video camera. The system is used to visualize air-water two-phase flow in a natural-circulation loop to examine the dynamic capabilities of the radiography facility. Measurements of bubble velocity, void fraction, and phase distribution are successfully made. Single frames (∼33 ms) of neutron images were captured using the dynamic neutron radiography system for air-water two-phase flow. The system was able to resolve single bubbles interfaces with an image spatial resolution of approximately 0.44 mm.;Thermal neutron detectors are placed at the periphery of the neutron beam to detect neutrons scattered by a non-flowing two-phase object placed on a turntable to simulate motion of the gas phase. The results show the potential ability to use neutron scattering technique to provide two-dimension neutron radiography with additional information to the third dimension. |
