Akira Tsuruno

Visualization of fluid phenomena using a high frame-rate neutron radiography with a steady thermal neutron beam

Abstract Experiments on visualization of fluid phenomena in a metallic vessel were conducted using a high-speed video camera with a steady thermal neutron beam. The Japan Research Reactor 3M, whose flux at the imaging plate is 1.5 × 10 8 n/cm 2 s, of Japan Atomic Energy Research Institute was used as a neutron source. The imaging system for high frame-rate neutron radiography with the steady thermal neutron beam consisted of a high sensitivity scintillator, 6 LiF/ZnS:Ag, an image intensifier whose gain was a factor of 100 000 at the maximum, and a high-speed video which could record phenomena at 1000 frames/s for 14 min by using an ordinary VHS tape with the recording time of 120 min at the normal speed. Visualization of air-water two-phase flows in a rectangular duct with 2.4 mm gap and 40 mm width were successfully performed with the steady thermal neutron beam and this imaging system at frame rates up to 1000 frames/s. The shapes and the behavior of bubbles and liquid films were clearly observed. The rising velocities of slug bubbles and the flow regimes could be also measured. It was clarified that this new technique may have significant advantages both in visualizing and measuring high-speed phenomena when the visible light is not applicable.

Three-dimensional void fraction measurement of two-phase flow in a rod bundle by neutron radiography

Abstract Three-dimensional void fraction distribution and one-dimensional cross-sectional averaged void fraction distribution of air-water two-phase flow in a 4 × 4 rod bundle near a spacer was measured by neutron radiography using a CT method. Two-phase flow behavior in the rod bundle near the spacer, which is important to study from the safety considerations of nuclear reactors and which is difficult to observe by other methods, was clearly visualized.

High resolution static imaging system using a cooled CCD camera

Abstract An intelligent filter, originally a median filter, was developed and introduced as noise correction in order to distinguish white spots from pixels which hold image information. The algorithm of the intelligent filter is able to correct dark spots as well as white spots using independent criteria and does not affect any other signals. The experimental results confirmed that the intelligent filter worked as a white spot correction effectively.

Neutron radiography of thick hydrogenous materials with use of an imaging plate neutron detector

Abstract The value of the neutron mass attenuation coefficient of hydrogen being very high, it is extremely difficult to image normal size, living animals with neutron radiography. However, the authors suggest the possibility of applying neutron radiography for biomedical specimens. The organs in the breast, bones and cartilages in the extremities, and the tail of mice and rats were clearly imaged by neutron radiography with Gd foils as neutron converters and X-ray films. However, no contours of the organs in the mouse abdomen were visible with neutron radiography with an exposure time of 200 s. By adding Gd or Li compounds as neutron converters to imaging X-ray plates, imaging plates have been developed for neutron detectors. A trial using these imaging plates for neutron radiography of water-filled containers and the abdomen of mice was completed. The roundness of a 100 ml-beaker was imaged with a neutron exposure of 180 s. Obscure contours of the liver and kidneys of the mouse were imaged with a neutron exposure of 100 s.

VOID FRACTION DISTRIBUTION MEASUREMENT IN TWO-PHASE FLOW BY REAL-TIME NEUTRON RADIOGRAPHY AND REAL-TIME IMAGE PROCESSING

Abstract A real-time two-dimensional void fraction distribution measurement of gas-liquid two-phase flow was carried out by real-time neutron radiography and real-time image processing. The JRR-3M real-time thermal neutron radiography system and a Musashi dynamic image of processing system were used. Image processing methods to calculate two-dimensional and cross-sectional void fraction distributions were proposed. The void fraction distribution was calculated by non-linear processing of the neutron radiography image and displayed by pseud-color in real-time. A simple gas-liquid two-phase flow induced by injecting gas through needles at the bottom of water pool in a rectangular vessel was tested.

VOID FRACTION PROFILE IN TUBE-BANKS OF A SIMULATED FLUIDIZED-BED HEAT EXCHANGER

Abstract Flow visualization of cross-flow tube-banks in a simulated fluidized-bed was conducted by using the neutron radiography system of JRR-3M. Applying the image processing technique to the visualized image, the void fraction profile in the tube-bank was obtained. The observed flow pattern and the void fraction profile demonstrate the importance of the tube arrangement in fluidized-bed heat exchangers.

Transmittance measurements of cold neutrons for some materials by means of neutron radiography

Abstract We examined cold neutron radiography (CNR) to determine its characteristics with respect to the ability to obtain the quantitative measurements. In order to describe the complicated transmission phenomena in CNR, a thickness dependent attenuation coefficient μ ( t ) is introduced instead of an average attenuation coefficient. A simple function using a linear approximation model to μ ( t ) is proposed to express transmission curves in CNR. This function agreed well with the experimental data for materials having deep and shallow Bragg cutoffs and for a 1 / ν dependent material. Thus, the linear approximation to μ ( t ) is effective for describing the transmission phenomena in CNR.

Large-particle movement and drag coefficient in a fluidized bed

Flow visualization studies of the behavior of a large particle in a fluidized bed were conducted using neutron radiography. The large particle moved according to the bed materials, especially in the wake of a bubblc. When the density of the large particle was high, the particle moved with a velocity different from that of a bubble, and in some cases the particle moved downward through a bubble. When the density was low enough, the particle moved on the surface of the bubble wake. The drag force of the large particle immersed in a fluidized bed was measured. The drag force increased with an increase in the volumetric gas flux as well as with an increase in the particle diameter. The drag coefficient was derived and was well correlated on the basis of a two-phase model and experimentally determined effective viscosity of the bed materials.

Fast neutron radiography tests at the YAYOI-reactor, university of Tokyo

Fast neutron radiography (FNR) has been jointly studied by the members of neutron radiography laboratories in Japan by using the CR-39 nuclear track detector at the fast neutron source reactor “YAYOI” of the University of Tokyo. Three beam holes installed at the reactor are utilized, whose collimator ratios, LD, are up to 135, and the fast neutron fluxes are more than 106 ncm−2 s−1. Some well-defined FNR images of various types of objects are obtained with a fast neutron fluence of about 1010 n/cm2. Small holes of 0.5 mm in diameter and 10 mm in depth in an acrylic plate are well imaged through 60 mm thickness of iron plate. Hydrocarbon specimens placed behind thick iron plates (30 mm) are clearly imaged. For the ASTM image quality indicators (IQIs for thermal neutron radiography), very thin A1 spacers with 0.05 mm thickness in the SI indicator have been discernible. The scattering component of fast neutrons from object materials does not seriously degrade the resolution of the FNR image.

Liquid metal flow measurement by neutron radiography

Abstract Visualization of a liquid metal flow and image processing methods to measure the vector field are carried out by real-time neutron radiography. The JRR-3M real-time thermal neutron radiography facility in the Japan Atomic Energy Research Institute was used. Lead—bismuth eutectic was used as a working fluid. Particles made from a gold—cadmium intermetallic compound (AuCd 3 ) were used as the tracer for the visualization. The flow vector field was obtained by image processing methods. It was shown that the liquid metal flow vector field was obtainable by real-time neutron radiography when the attenuation of neutron rays due to the liquid metal was less than 1/e and the particle size of the tracer was larger than one image element size digitized for the image processing.