[en] In order to obtain fundamental perspectives on fuel cladding deformation behavior under changing temperature and pressure conditions in a hypothetical loss-of-coolant accident of PWR, Zircaloy-4 tube burst test was conducted in both air and 99.97% Ar atmospheres. The tubes were directly heated by ac-current and maintained at various temperatures, and pressurized gradually until rupture occurred. Rupture circumferential strains were generally larger in Ar gas than in air and attained a maximum around 1,120 K in both atmospheres. Some tubes tested in air produced axially-extended long balloons, which proved not to be explained by such properties or ideas as effect of cooling on strain rate, superplasticity, geometrical plastic instability and stresses generated by surface oxide layer. A cause of the long balloon may be obtained in the anisotropy of the material structure. But even a qualitative analysis based on this property can not be made due to insufficient data of the anisotropy. (author)

No abstract available

[en] This paper describes the experimental results and discussions on the changes in dimension, volume and thermal expansion coefficient of five nuclear grade graphites which were made from petroleum coke or gilsonite coke and irradiated in the JMTR at 670 -- 1,260⁰C up to the maximum neutron fluence 3.3 x 10²¹ n/cm² (E > 0.18 MeV). Dimensional or volume shrinkages for all samples were observed after irradiation and their changes depended on the kind of graphite studied. The changes in thermal expansion coefficient were also observed for three of five samples. The relations between the changes in dimension or volume and thermal expansion coefficient were obtained, and it was clarified that both the rates of irradiation shrinkage in dimension and volume of the sample having larger thermal expansion coefficient were smaller than for the sample having smaller thermal expansion coefficient. (author)

[en] A simple but realistic method of active feedback control of a self-ignited tokamak reactor by major radius compression-decompression is presented, in which the thermal fusion output power and the ion temperature are envisaged as the variables that could be adopted as object of control. Error inherent in the measuring system for the controlled variable is taken into account in the analysis. Numerical calculations based on a point reactor model are performed, which indicate that the proposed method of control is capable of completely suppressing thermal runaway without involving any significant change in the major radius or in the fusion output power. Matching the reactor output to changes in load is shown also to be possible from a numerical example. The thermal stability of an igniting plasma governed by this feedback control is analyzed without prescribing any particular transport scaling. It is revealed that the control is achievable for a suitably chosen gain even with a response time lag longer than the thermal runaway time. Strong dependence of the stability on the scaling law is indicated. (author)

No abstract available

[en] Five-percent small break tests have been conducted at the ROSA-III test facility with various emergency core cooling system (ECCS) actuation conditions. Break was assumed at the main recirculation pump inlet line. The ROSA-III facility simulated a BWR/6-251 by the volume scaling ratio of 1/424 and a 5 % break area in a ROSA-III test means 5 % of 1/424 of the BWR recirculation line pipe cross section. No dryout of fuel surface was observed in the tests with high pressure core spray system (HPCS) actuation irrespective of the conditions of the other ECCS. Without HPCS the whole core was uncovered to the steam environment; however, the peak cladding temperature (PCT) was limited to 1,022 K well below the present safety criteria of 1,473 K. The results of the test with the highest PCT without HPCS actuation were analyzed by the RELAP4/Mod6 computer code. The calculated fuel surface temperatures agreed well with measured results in the blowdown phase. The calculated PCT was 930 K, 92 K below the measured PCT of 1,022 K. (author)

[en] Preliminary studies are made in order to apply an X-ray CT scanner to the measurement of cross-sectional distributions of void fractions in steady state two-phase flows. Using air-water flows in a horizontal U-shaped tube, results of CT scanner measurements are compared with those of the volumetric measurements with quick-closing valves and of hotfilm anemometer measurements. Studied are cross-sectionally averaged void fractions and void fraction profiles. The comparisons give good agreements. The effect of density fluctuations on the reconstruction of void fraction distributions in two-phase flows is also discussed. Consideration of the statistical fluctuation in the projection data for a stationary object gives the sufficient conditions required for the evaluation of the cross-sectional distribution of the scanning time-averaged void fraction in steady state two-phase flows. (author)

[en] A new type of gas chromatograph for quantitative measurements of hydrogen isotopes mixture has been developed through the adoption of catalytic oxidation type detector. Experiments using He as the carrier gas were successfully performed for the separation of D₂-HD and H₂-HD-D₂ mixtures. The minimum detection limits were 0.4 -- 0.9 μl-STP for these components. The linear calibration curves were obtained in the range of 10 μl-STP -- 20 ml-STP. The sensitivities for H₂, HD and D₂ were 843, 774, and 654 (μl-STP)^-1, respectively. The maximum time needed for the analysis was about 16 min. (author)

No abstract available

[en] The intensity and the energy spectra of Very Cold Neutrons (VCN) transmitted through a curved guide tube were measured by using the time-of-flight method of VCN. In the measurements, the curved guide tube having a characteristic neutron velocity of about 70 m/s is combined to a pulsed cold source of an electron linac in an internal target geometry. A space dependence of the VCN spectra was observed on the radial positions of a detector at the guide tube exit. A simple theoretical analysis on the transmission of VCN in the curved guide tube is also presented with taking into consideration about the effects of a finite size and a finite distance of the VCN-emitting source, and simple analytical formulas for the exit spectra of the guide tube are given. Comparisons between the experimental results and the theoretical calculations show good agreements, and the satisfactory performance of the present VCN guide tube assembly was ascertained. These results present also instructive features for understanding the structures and the space dependence of the exit spectra of a neutron guide tube. The VCN spectra at the guide tube exit can be divided into a few energy regions according to the transmission processes of VCN. Thus, the present study provides useful informations for the preparations of a VCN source with a curved guide tube. (author)