Shigeru Izumi

Detection of Fine Particles in Liquids by Laser Breakdown Method

Basic characteristics of a particle detection method using laser breakdown were studied for a system of polystyrene standard particles dispersed in ultrapure water. The method was able to detect 0.02 µm particles. The detection sensitivity decreased with the particle size due to size dependence of the laser breakdown threshold. The plasma emission delay time from the laser pulse decreased with particle size (9.8±0.8 ns for 0.04 µm, 5.7±0.8 ns for 3.0 µm). The above results suggested the possibility of concentration and size measurement of fine particles in liquids by the proposed method.

Particle Size Dependence of Correlation between Plasma Emission Delay Time and Plasma Emission Intensity of Laser Breakdown Induced by a Particle

Plasma emission delay time and plasma emission intensity of laser breakdown induced by a polystyrene particle in water were measured simultaneously. Short plasma emission delay time tended to correspond to high plasma emission intensity, as expected from the spatial and temporal profiles of the laser pulse power density. Particle size dependence of the correlation between the two parameters may serve in the measurement of the particle size.

Evaluation of Sodium Sulfur Cell Characteristics Using an In Situ X‐Ray Computed Tomogram System

An in situ X-ray computed tomogram system to observe a sodium sulfur cell was constructed with a 0.14 g/cm 3 density resolution and 0.17 mm spatial resolution. Density distributions in the radial cross sections of the sodium sulfur cell were obtained by the system during charge and discharge operations at 350°C. The typical behavior of sodium supplied to the surface of the solid-electrolyte tube was observed. The experimental density changes of the sulfur electrode agreed with the theoretical values during charge and discharge operations except in one part of the cell.

Radioactivity measurement of drum package waste by a computed-tomography technique

Abstract A method of evaluating the radionuclide content of low-level drum package waste using emission computed tomography (ECT) and transmission computed tomography (TCT) has been investigated. This method requires accurate correction for the γ-ray attenuation in the drum. The TCT and ECT analyses are performed according to the constrained least-squares technique. Satisfactory results were obtained in preliminary experiments carried out using test equipment with 20 NaI(Tl) scintillation detectors and sample 200-L drums which contained sealed γ-ray point sources of 60 Co and 137 Cs, and pipes and concrete blocks. The radioactive content of one or two 60 Co sources (about 3.5 MBq) in a drum of about 200 kg was evaluated in 6 × 6 × 9 voxel with an uncertainty of about ±15% for an ECT measurement time of about 12.5 min.

Unknown sound evaluating method and apparatus

Method and apparatus for evaluating location of an unknown sound generated in a structure such as a pressure vessel. A plurality of sound detectors are mounted on the structure for detecting sounds generated in the structure. On the basis of sound information of the unknown sound source derived from the outputs of the detectors, the location where the unknown sound is produced is determined. To this end, reference sounds are first generated at a plurality of known reference sound source positions, wherein information of the reference sounds derived from the outputs of the detectors are stored in a storage unit. Equi-pattern-distance curves each of which is in an equal pattern distance between a supposed unknown sound source and each of the reference sound sources are calculated on the basis of the reference sound information. The equi-pattern-distance curves are further corrected in accordance with the reference sound information. Upon occurrence of an unknown sound, pattern distances between the desired reference sound source positions and the unknown sound source position are calculated through pattern recognition procedure from the sound information derived from the outputs of the detector and the reference sound information stored. On the basis of the calculated pattern distances and the equi-pattern-distance curves, the position of the unknown sound source is determined. On the basis of the position of the unknown sound source, kinetic energy thereof may be arithmetically determined.

Development of a Collector Ring Monitor for Sparking Detection on Generators

Continuous monitoring techniques are described for sparking detection of collector rings on generators.

Application of Fission Chamber to Uranium Microanalysis

The possibility of using a fission chamber for quantitative analysis of uranium impurity in dynamic memory materials was studied. The fission chamber had two pairs of parallel disk electrodes. One electrode of each pair was used as a collector and was made of Teflon with a pure aluminum coating, while the other electrode was the material to be measured. Carbon dioxide was used as the ionization gas. Uranium in the materials was irradiated with neutrons and the number of fissions was counted to give the impurity content. Uranium contents in aluminum (99.8%) and Teflon were calculated, and measured values showed a fairly good reproducibility. The detection limit, determined by background fluctuations, for uranium impurity contained in the aluminum coated Teflon electrode was 4.0 ppb.

Application of pattern recognition techniques to location of impact sound sources on pressure vessels.

Pattern recognition techniques for loose parts location in nuclear power reactors are investigated. The location method is based on determining a reference impact position closest to the unknown impact from a library in which data for reference impacts are listed. The values of sound amplitude and arrival time as obtained from accelerometers are used for the pattern information which is inherent in impact position. The distance between unknown and reference impact positions is estimated from the similarity of each pattern. The pattern distance between two sound sources is defined as an index of the pattern similarity. Relationships between the pattern distance and the actual distance of the impacts are studied using impact data from a commercial boiling water reactor. It is found that the pattern distance and the actual distance have a very close correlation and the false probability that the zero impact distance is determined to be a distance of more than 0.6 m is 0.15. These results suggest that the pat...

Estimation of Sodium Sulfur Cell Characteristics Using Computed Tomograms from High Energy X‐Rays

The density distributions in the axial and radial cross sections of two typical sodium sulfur cells were obtained by a high-energy x-ray computed tomography (CT) system with a linear accelerator. The tomograms of the low-resistance cell showed a uniform density distribution of sulfur and sodium pentasulfide in the graphite felt of the sulfur electrode, while those of the high-resistance one were indicative of a nonuniform density distribution. The difference in the cell characteristics between the cells could be accounted for by the difference in the density distribution of the active material in the sulfur electrode. The low discharge voltage of the high-resistance cell, calculated using an internal-parallel-cell model, agreed well with experimental results. The tomograms of cells taken by x-ray CT can be applied to evaluate sodium sulfur cell characteristics.

Methods of metallic loose parts location and impact energy estimation from information on reference impact sounds

Abstract Reference impacts were employed to achieve accurate location and energy estimation of metallic loose parts in inhomogeneous systems such as nuclear reactor vessels. Impact positions are determined using distances from reference impacts and pattern recognition technique. To confirm the method, experiments were carried out using a cylindrical steel tank (diameter = 2m, height = 5m, thickness = 2m). The reference impacts were arranged on lattice points, separated by 1 meter, on the tank wall. The signal amplitudes of various impacts positions with a uniform impact energy and the same propagation path length exhibited deviations of around one order of magnitude. This fact would seem to limit the posibility of achieving accurate location and energy estimations from the amplitude data. However, the results were surprisingly good. Using amplitude data, the impact positions on the tank were located within an error of 13cm and impact energies were estimated within an error of 25%.