Masahito Matsubayashi

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.

Water movement in a plant sample by neutron beam analysis as well as positron emission tracer imaging system

We present water imaging of a plant sample both by neutron beam and positron emission tracer imaging system (PETIS). The former method provided static water profile in a plant sample as well as that in the vicinity of a root imbedded in soil. Not only X-ray film but also CT method using a cooled CCD camera is presented. Through non-destructive water image in an X-ray film, root development as well as 2-dimensional water movement toward the root was analyzed. Spatial water image was constructed from 180 CT projection images, taken at an interval of one degree while rotating the sample, through a CCD camera. In the case of a soybean root, there was a water gradient toward a root in soil and gave minimum value at about 1 mm far from the surface of a root. The water absorbing part in a root was gradually shifted downward with the root development. We also present real time water movement by PETIS, where water was labeled with a positron emitting nuclide, 15O. The transportation of 15O-water within a plant was relatively slow and water uptake was observed only at the lowest internode, between a root and the first leaf, during 20-minute measurement.

The review of the application of neutron radiography to thermal hydraulic research

Abstract This paper is concerned with the establishment of thermal neutron radiography as a high accuracy measurement method. This paper reviews the present status on the development of high-frame-rate neutron radiography with a steady thermal neutron beam and its application to multiphase flow research performed at the Research Reactor Institute of Kyoto University in collaboration with the Japan Atomic Energy Research Institute.

Visualization and measurement of gas–liquid metal two-phase flow with large density difference using thermal neutrons as microscopic probes

Abstract In a core melt accident of a fast breeder reactor, there is a possibility of boiling of the fuel–steel mixture in the containment pool. In relation to safety evaluation on severe accident, it is indispensable to evaluate the possibility of re-criticality of melted core. Gas–liquid two-phase flow with a large liquid-to-gas density ratio is formed due to the boiling of fuel–steel mixture. Although it is anticipated that the large density ratio may affect the basic characteristics of two-phase flow, little work has been performed so far on two-phase flow with a large liquid-to-gas density ratio. In this study, visualization and void fraction measurement of gas–liquid metal two-phase flow were performed by using neutron radiography and image processing techniques. Then, the effect of large density difference between gas and liquid phases on the basic flow characteristics of two-phase flow was clarified.

Three-dimensional visualization of void fraction distribution in steady two-phase flow by thermal neutron radiography

Abstract Three-dimensional void fraction distributions of a steady air–water two-phase flow in a 4×4 rod-bundle with circular ferrule type spacers were measured by neutron radiography using a CT method. The high flux thermal neutron radiography system at JRR-3M in JAERI was used. Two-phase flow was visualized with a SIT tube camera and time-averaged one-dimensional cross sectional averaged void fraction distributions were calculated. Visualization with high spatial resolution up to 0.18 mm was carried out by using a cooled CCD camera. Projections in 250 directions were obtained and were reconstructed by a filtered back projection method after using some image processing techniques. Animations were made to show the three-dimensional distributions. One-dimensional and three-dimensional void fraction distributions of the steady state two-phase flow in the rod bundle near the spacer were clearly visualized.

Application of neutron radiography for estimating concentration and distribution of hydrogen in Zircaloy cladding tubes

Practicability of neutron imaging plate (IP) and computed tomography (CT) for estimating the distribution of the hydrogen concentration in Zircaloy tubes was investigated. Zircaloy tubes with controlled amount of hydrogen which is segregated at the periphery were prepared. The width of the hydrogen region is small around 0.1 mm. In IP image the small segregated hydrogen region is recognized, and the distribution of the hydrogen in the Zircaloy tubes is displayed. The hydrogen region is also recognized in a CT image of the tube containing large amount of hydrogen. These results show that both neutron IP and CT methods are applicable tools to estimate hydrogen distribution. A quantitative evaluation of the hydrogen concentration by those images is also discussed.

Design and Characteristics of the JRR-3M Thermal Neutron Radiography Facility and Its Imaging Systems

Abstract The JRR-3M thermal neutron radiography facility was constructed in the JRR-3M of the Japan Atomic Energy Research Institute in 1991 and has been used as a research facility for various kinds of research fields. The characteristics of the facility have been briefly reported and declared to be excellent in neutron flux and in collimator ratio. Additionally, the authors have measured the beam flatness and the scattered components and have compared these measured characteristics with the design values. The neutron source, the beam tube, and the radiography rooms are described in detail and their data are applied to the analyses of the characteristics. The description of the radiography rooms includes beam size definition tubes and beam shutters, which are the most important components in the room. Also described are the restrictions on the size and shape of the sample, the background dose rates, and equipment information. The high-performance of the facility enables advanced imaging techniques such as high spatial resolution imaging and high temporal resolution imaging. The high-resolution static neutron radiography system using a cooled charge-coupled device camera has the capability to take neutron radiography images with 72 μm of spatial resolution. The high frame rate neutron radiography system has the capability to image high-speed phenomena with 4500 frames/s of temporal resolution. Both neutron radiography systems are described in detail especially for key components such as fluorescent converters and cameras.

A METHOD FOR QUANTITATIVE MEASUREMENT BY THERMAL NEUTRON RADIOGRAPHY

Abstract A quantitative measurement method by thermal neutron radiography was proposed for two-dimensional void fraction measurement in two-phase flow. The umbra method was modified for two-dimensional measurement by using a neutron absorber grid. Image processing methods to compensate for the effects of neutrons scattered in the object and optical rays scattered in camera were developed. A step made from acrylic resin was tested with a B4C grid 3mm in width and 3mm in interval. It was shown that two dimensional quantitative measurement was possible with this method in sacrifice of the spatial resolution.

Analysis of hydrogen distribution in hydrogen storage alloy using neutron radiography

Abstract The initial stage of hydrogen absorption was investigated on Mg–Ni based alloys, such as Mg2Ni and Mg3Ni (the eutectic mixture of Mg2Ni and Mg), using neutron radiography (NRG). The NRG images were obtained by not only a simple transmission method but also a tomographic one, which could clearly visualize hydrogen distribution in the alloys. The hydrogen diffusion coefficient in these alloys was estimated to be ≈2×10−7 cm2 s−1 from the change in hydrogen absorption depth with hydrogenation time. The comparison of the volume expansion rate due to hydrogen absorption for the alloys showed that Mg3Ni has better toughness than Mg2Ni until Mg3Ni was partly degraded to form magnesium hydride. Thus, NRG was found to be a powerful tool to clarify the behavior of hydrogen in hydrogen storage alloys.

NEUTRON RADIOGRAPHY OF A ROOT GROWING IN SOIL WITH VANADIUM

Abstract We show how the root activity of water uptake is inhibited by the presence of vanadium in soil. A soybean seedling was grown in an aluminum container where water absorbing polymer with V was imbedded with soil. The sample was irradiated with thermal neutrons to get the radiograph on an X-ray film. Through image analysis, the water uptake manner both around the main root and side root was studied. When the water uptake along the main root was measured, the effect of V was observed as early as two days whilst no observable change in morphological development of main root as well as side root was detected. Since the microscopic research of water movement around the root is not well studied, this result is expected to be applied further, especially in constructing water absorbing model of the root.