[en] Typical integral experiments using the 14 MeV neutrons concerning fusion neutronics are reviewed briefly, which have been performed in the last 20 years in Japan. Emphasis has been put upon some integral experiments on the tritium production rates in lithium oxide systems by JAERI group and a lithium metal sphere by university group. Integral tests of nuclear data files for several kinds of structural materials have been also carried out. It is expected that these results will be useful to enhance accuracy or the nuclear data evaluations and reactor blanket design. (author)

[en] Two major currents of the EAC relevant activities in Japan are reviewed in some chronological manner. One is the studies on the acceleration of fatigue crack growth in LWR. The work was first pioneered early in Japan, and extensive collaborative works have followed interacting with the international activities, which have yielded a clear views on the potential issues of the RPV structural steels used in the domestic NPPs. Another is the development of materials and techniques to combat the stress corrosion cracking of the structural materials in LWR water environment. Extensive collaboration among the government agencies, utilities, industries and academic societies lead the issues to a dramatic solution in rather short period. Both of those two aspects are stressed to have generic significance in the present and future nuclear technology. (author)

[en] As a highly sensitive, simple and non-radioactive neutron dosimeter, CR-39 plastic plates doped with a boron compound: ortho-carborane were prepared. After thermal neutron irradiation, the plates were etched in an aqueous solution of 30%KOH, at 60⁰C for 2 to 16h. The etch-pits generated by ¹⁰B(n,α)⁷Li reactions were then counted using an optical microscope or an automatic track counting system. The density of the etch-pits on an irradiated plate increases with the etching time. When the etching time is kept constant, the etch-pit density is proportional to the irradiated thermal neutron fluence. The proportional constant is termed ''sensitivity'', which is 4.2 x 10^-4 for a plate containing ortho-carborane at a concentration of 0.5% by weight and for etching time of 16h. By considering background counts, a thermal neutron dose of 0.025 mSv can be measured with this plate. The plates are insensitive to visible-, UV-, X-, β- and γ-rays and are easy to handle because the detector and converter are incorporated. There is no possibility of underestimating the dose equivalent due to fading. Furthermore, the isotopes of boron are not radioactive and thus are radiologically safe. (author)

[en] This study is based on the fuel centerline temperature measurement conducted in the Japan Materials Testing Reactor (JMTR). The specimen used in this experiment is the assembly composed of three fuel rods, two high performance fuel rods (one has the Cu-barrier cladding and the other has the Zr-liner cladding) and one reference fuel rod (i.e. it has the normal cladding). As to the fuel centerline temperature, it was investigated whether there are (1) differences between the reference fuel rod and the high performance fuel rods and (2) differences between two high performance fuel rods. Consequently, the differences of the fuel centerline temperatures were obvious among three fuel rods. And it was concluded that the inside surface roughness of the cladding of the fuel rods have the important effect on the differences of their fuel centerline temperatures because the fuel centerline temperature of the fuel rod with the Zr-liner cladding of which the inside surface is rougher than that of the normal cladding is higher than that of the fuel rod with the normal cladding etc. (author)

[en] Published in summary form only

[en] The prevention of leakage flows of coolant gas is important for a thermal hydraulic design of HTGR core which consists of prismatic graphite blocks. In particular, a seal mechanism for the core support blocks is necessary because gaps between core support blocks induce leakage flows in the core. Here, a seal mechanism, which consists of graphite seal element with triangular cross section and V-shaped seal seat, has been proposed. Air flow experiments were conducted to study the leakage flow characteristics of this seal mechanism. It is shown that the present seal mechanism is highly effective in preventing leakage flows as compared with the plate-type seal mechanism. It is also found that most of the leakage flow occurs at the seal element end-gaps and the pressure loss coefficient factor of this seal mechanism can be predicted with the use of the effective flow area of the end-graps. (author)

No abstract available

[en] Magnetic susceptibility was measured on the samples of U_1-xGd_xO₂ prepared by a coprecipitation method from 1.7 K to room temperature. The behavior of magnetic susceptibility is contributed almost from trivalent gadolinium ion because of its very large spin magnetic moment of ⁸S. For x < approx 40 %, the magnetic susceptibility-temperature curve obeyed Curie-Weiss law and values of magnetic susceptibility increase linearly with increasing gadolinium concentrations. For the higher concentrations of gadolinium the magnetic susceptibility-temperature curve has a peak at 3 ∼ 4 K, showing a magnetic field dependence of magnetic susceptibility at liquid helium temperature which would be expected for the case of a weak magnetic anisotropy in antiferromagnets. (author)

[en] In order to study the migration behavior of non-cationic species of ⁶⁰Co, the aqueous solution of ⁶⁰CoCl₂ from which cationic ⁶⁰Co was eliminated by using cation exchange resin was introduced continuously into sandy soil layers at a relatively fast water flow. It was found from the experimental results that the migration of non-cationic species of ⁶⁰Co was independent of that of cationic species. The reaction of non-cationic species of ⁶⁰-Co between sandy soil and pore water could be described by the first-order reversible equation and the prediction of the migration using the reversible equation was effective to the case of pulse injection of non-cationic species of ⁶⁰Co. Therefore, when the movement of underground water is fast, the use of the reversible equation is effective to predict the migration behavior of non-cationic species of ⁶⁰Co. (author)

[en] At present, differential pressure type flowmeters are widely used in feedwater systems of PWR plants. In these flowmeters, however, scales gradually deposit at the nozzle throat during the plant operation, causing the apparent flow rate to increase and consequently becoming a serious problem for efficient plant operations. Therefore, a new type of ultrasonic flowmeter (USFM) having good stability and free of the above phenomenon has been developed. A method to compensate for the effect of dependency of sound velocity on water temperature and pressure corresponding to PWR feedwater conditions was contrived. The validity of the method was confirmed in an experiment for investigating the sound velocity dependency in practice. The performance of the USFM was also examined using a water loop in various flow conditions with satisfactory results. After the basic studies, finally, the USFM was tested in an actual PWR feedwater system for almost 3 yr. The USFM met all the required characteristics for PWR feedwater systems, those being linearity, accuracy and stability. (author)