[en] The uranium enrichment pilot plant at PNC Ningyo-Toge Works, Japan, started operation in August 1979. Since then, inspection activities by the government of Japan and the International Atomic Energy Agency (IAEA) have been carried out. A basic measure of safeguards is evaluation of material unaccounted for (MUF) by closing the material balance. As the plant now produces uranium of <5% enrichment, a material balance is closed only once a year. Until now, eight physical inventories have been taken. This paper describes the operator's procedures for material accountability and the values of MUF reported to the government of Japan and the IAEA

No abstract available

[en] A new ESR isochrone dating for fracture age based on the effective annual dose for different grain sizes has been applied to quartz grains in fractured granite at the Nojima fault that moved during the earthquake in 1995 and in fault gouge at the Rokko fault in the vicinity. Incomplete resetting of ESR signals was observed for the Rokko fault as (1.6 ± 0.2) x 10⁵ yr. At the Nojima fault there appears to be a considerable effect from previously-fractured surfaces in the newly-fractured material. The relation between the fracture age and the age of the fault movement is discussed. (author)

[en] Models of uranium-uptake at the early stage and at a constant rate (linear-uptake) were re-examined for ESR dating of fossil bones and teeth. An analytical equation for the total dose of natural radiation (D_T) was obtained for uranium uptake in the form of a saturation function, C_υ(t) C_US (1 -e^-if), where C_US is the saturation level of the uranium and λ is the uranium uptake rate, presumably associated with the decomposition rate of organic materials and the diffusion of uranium. The present uranium content C_υ(T) C_υ* at the unknown age T gives C_US C_υ*/(1 - e^i./T) and so λ = -(1/T)In(1 -C_υ*/C_US). The D_T calculated by taking ²³⁸U-series secular disequilibrium into account is reduced to that of an early uptake for λT >> 1 and to that of a linear uptake for λT << 1. The activity ratios of ²³⁴U/²³⁸U and ²³⁰Th/²³⁸U for the saturation-uptake model are also given. The model of linear uptake is applicable for C_υ* < C_US. The curves of D_T as a function of T was calculated for C_US as a parameter. (author)

[en] Optically stimulated luminescence (OSL) of synthetic stishovite was investigated for a future dating technique of meteor impact craters. Luminescence around 330 nm was measured on the γ-ray irradiated stishovite under two stimulating light sources of infrared laser (830 nm) and blue light emitting diode set (470 nm). Thermoluminescence (TL) studies before and after the OSL measurements showed the intensities around 100-200 deg. C and 220-350 deg. C to increase and those around 350-450 deg. C to decrease. This indicates that a part of deep-trapped charges excited during the OSL measurements were retrapped by shallower traps. The infrared stimulated luminescence (IRSL) after the TL measurement up to 450 deg. C could not be detected, while the blue light stimulated luminescence (BLSL) after TL had about one-tenth of the intensity before TL. This indicates that a part of the charges in shallower traps were detrapped thermally and returned to the deeper traps which were related to BLSL. The result implies that some of the BLSL-related traps are quite stable at room temperature and could be used for geological dating. In addition, two paramagnetic centers produced by sudden release of high pressure in synthesis process were found in the unirradiated stishovite by electron spin resonance (ESR). Their g-factors are g_parallel=2.00181 and g_{perpendicular}=2.00062 for an axial signal and g=2.00305 for the other isotropic signal. These signals could be used for an evidence of impacts if those signals could be stored in geological time

[en] Selective adsorption-desorption method has been developed as an effective means of enriching krypton and xenon gases. A seriesof laboratory-scale tests were performed to provide some basic data of the method when applied to off-gas streams of nuclear power plants. For the first step of the enrichment process of the experiments, krypton was adsorbed on solid adsorbents from dilute mixtures with air at temperatures ranging from -50⁰C to -170⁰C. After the complete breakthrough was obtained, the adsorption bed was evacuated at low temperature by a vacuum pump. By combining these two steps krypton was highly enriched on the adsorbents, and the enrichment factor for krypton was calculated as the product of individual enrichment factors of each step. Two types of adsorbents, coconut charcoal and molecular sieves 5A, were used. Experimental results showed that the present method gave the greater enrichment factor than the conventional method which used selective adsorption step only. (U.S.)

[en] The removal efficiency of impregnated activated charcoal and silver zeolite for radioactive methyl iodide is influenced by various parameters such as temperature, relative humidity, face velocity and packing density. This study is to evaluate the dependency of the removal efficiency on each parameter and these combined parameters, quantitatively. Four types of adsorbents, BC-727, AgX, CHC-50 and SS 208C 5KI₃, were tested. From experimental data and mass transfer theory, an experimental equation for evaluating the removal efficiency of adsorbents was derived under a series of experiments for radioactive methyl iodine-131. It was concluded that the removal efficiency calculated from the experimental equation agreed well with the experimental value. Effects of experimental specific parameters, such as Pre-flow time, methyl iodide injection time and After-flow time, on the removal efficiency of adsorbent are also described

[en] A NDA instrument has been developed to determine the enrichment of gas phase uranium in pipes for a gas centrifuge enrichment plant. The enrichment of gas phase uranium could be measured by combining the passive gamma rays measurement with X-ray fluorescent analysis. The passive gamma rays measurement has extensively been performed in previous works. Successively the amount of deposited uranium has been measured for a long-term plant operation. Some increase of deposited uranium was observed. Determination of total mass of uranium in a pipe was studied by X-ray fluorescent analysis on a test loop system. It was found that total mass of gaseous UF/sub 6/ in the pipe could be determined accurately enough in implementation of safeguards

No abstract available

[en] The enrichment measurement of UF₆ is one of the most important techniques for a gas centrifuge enrichment plant. Developments of enrichment measurements using non-destructive assay technologies have been carried out at the Ningyo-Toge Uranium Enrichment Pilot Plant, PNC. Included in these developments are an enrichment monitor on 30B type cylinders, a neutron monitor, in-line enrichment monitors, and those for pipework and for sample bottles, and the field test of the IAEA gas phase enrichment monitor. The evaluation applications of these monitors, used for both safeguards and process control, are described. (author)