Journal of Nuclear Science and Technology
Online ISSN : 1881-1248
Print ISSN : 0022-3131
Volume 30, Issue 3
Displaying 1-10 of 10 articles from this issue
  • Akira OHNUKI, Hajime AKIMOTO, Yoshio MURAO
    1993 Volume 30 Issue 3 Pages 187-202
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    The applicability of core thermal-hydraulic models in REFLA code was evaluated to a 17×17 type fuel assembly of PWR, the models which have been developed for the reflood phase of LOCA of PWR with a 15×15 type fuel assembly. The two assemblies are different each other in respect of (1) the rod bundle configuration (fuel rod diameter and pitch) and (2) the grid spacer type (existence of mixing vane and interval between spacers). The effects of (1) and (2) were investigated experimentally and the applicability was assessed with the data.
    The film boiling heat transfer and void fraction models in REFLA code could apply to the 17×17 type fuel assembly within the error band of each model (±30%). The difference of grid spacer type did not affect the turnaround temperature which is the maximum clad temperature at each elevation but quench velocity. The quench velocity became lower in the case of grid spacer type of 17×17 type fuel assembly and the increase of heat transfer coefficient was delayed. From the analyses by the REFLA code with adjusted quench velocity correlation, the delay of increase of heat transfer coefficient was found to give no significant effects on the peak clad temperature even under the condition calculated by evaluation model code of reactor safety analysis.
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  • Natural Circulation Oscillation Induced by Hydrostatic Head Fluctuation
    Jing Hsien CHIANG, Masanori ARITOMI, Michitsugu MORI
    1993 Volume 30 Issue 3 Pages 203-211
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    The authors have been investigating the fundamentals of thermo-hydraulic instabilities which may appear during the start-up in natural circulation BWRs in order to understand their driving mechanisms and to examine the methods preventing their occurrence with an aim of establishing a rational start-up procedure and reactor configuration. In this paper, 'Natural Circulation Oscillation' was investigated experimentally under various conditions of heat input, inlet subcooling and non-heated riser length to reveal the driving mechanism and its feature. As a result, it was made clear that the in-phase natural circulation oscillation was induced in parallel channels by hydrostatic head fluctuation in a long vertical non-heated channel such as steam separators and a divided chimney in natural circulation BWRs due to alternate flow of vapor and liquid therein while the vapor generation rate is insufficient.
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  • Katsuhiko NAKAHARA, Junko WATANABE, Kunihiko NAKAYAMA, Tadashi YOSHIDA
    1993 Volume 30 Issue 3 Pages 212-220
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    Optimization of laser power balance is studied numerically for effective multi-step photo-ionization of degenerate atoms. To date, a large number of similar studies have been executed for simple nondegenerate atoms and, therefore, the emphasis in this study is placed on investigating the role of the level degeneracy. It is concluded that a monotonically increasing J-value in the excitation ladder of levels is preferable, which is followed by some variations thereof. It should also be noted that a reasonably high ionization rate is attainable, in any case, provided that the Rabi-frequencies are optimized at the expense of the sizable laser powers required. The computer code employed here, which deals with the population evolution among numerous magnetic sublevels, has been tested against experiments in advance of the above numerical study.
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  • Katsumi UNE, Shinji KASHIBE, Kenichi ITO
    1993 Volume 30 Issue 3 Pages 221-231
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    Fission gas behavior of UO2 fuel pellets with controlled microstructure irradiated to 23 GWd/t in a test reactor has been studied by using a postirradiation annealing experiment. Four types of fuel pellets with or without additives were examined : (1) un-doped standard (grain size : 16 μm), (2) un-doped large grained (43 μm), (3) 0.7 wt Nb2O5-doped large grained (110 μm), (4) 0.2 wt c), " TiO2-doped large grained (85 μm) fuels. The annealing was conducted at 1, 600 or 1, 800°C for 5 h in reducing or oxidizing atmospheres. Fission gas release and bubble swelling caused by the high temperature annealing for the two un-doped fuels were reduced to about 1/31/2 by increasing the grain size from 16 to 43 pm, which roughly corresponded to the ratio of their grain sizes. By contrast, the performance of the two large grained fuels doped with Nb2O5 or TiO2 was roughly equivalent to, or rather inferior to that of the standard fuel, despite their large grain sizes of 110 and 85 μm. The fission gas behavior of un-doped fuels was aggravated by increasing the oxygen potential in the annealing atmosphere, while that of additive doped fuels did not depend on it. The effects of grain size, additive doping and oxygen potential on fission gas release and bubble swelling were discussed in connection with the diffusivities of fission gas atoms and cation vacancies.
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  • 31P-NMR Study of Coordination Behavior of Zirconium Dibutylphosphates
    Mitsuhiro HIROSE, Chie MIYAKE, Masayasu IIDA
    1993 Volume 30 Issue 3 Pages 232-238
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    The coordination and complexation behavior of Zr-dibutylphosphate was investigated by 31P-NMR measurement, in order to clarify the mechanism of the previously reported phenomena that the precipitates once formed at low HDBP/Zr mole ratio of 2 in an organic solution disappears with increasing HDBP/Zr. As the results of 31P-NMR spectrum measurements, following two steps were identified. (1) Species having Zr : DBP=1:3 immediately reacts with free HDBP to form species having Zr: DBP=1:4 with increasing HDBP/Zr, (2) Under the presence of higher HDBP/Zr concentration, species having more DBPs than 4 to one Zr are observed. DBP- (or HDBP) ligands in these species bridge two Zr ions to form three-dimensional net-work structure and have an interaction with HDBP in the solvent. Consequently, the mechanism was elucidated for the re-dissolution of Zr-DBP precipitates with sufficient free HDBP producing highly viscous oilyliquid.
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  • Hitoshi MIMURA, Kenichi AKIBA, Hiroshi IGARASHI
    1993 Volume 30 Issue 3 Pages 239-247
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    The simultaneous removal of heat-generating nuclides Cs and Sr from high-level liquid wastes was achieved through columns packed with mixed zeolites of ferrierite (F) and zeolite A (A). A simulated waste solution was efficiently denitrated with formic acid up to pH 6.5 8.3 in the region of the initial molar ratio of [HCOOH-]/[HNO3] from 2.3 to 2.7. Large portions of multivalent nuclides including lanthanoids and actinoids were filtered off as precipitates in this pH region. Both Cs and Sr remaining in the filtrate were then completely removed by passing through the column packed with mixed zeolites. Break points for a column with an appropriate mixing ratio of A:F-=2:3 were found to be 12.6 bed volumes (BV) for Cs and 11.0 BV for Sr; the amounts of Cs and Sr adsorbed were estimated to be 0.28 and 0.12 mmol/g, respectively. The mixed zeolites adsorbing Cs and Sr were readily converted into a solid form by calcination at 1, 200°C.
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  • Kiyonobu YAMASITA, Hiroo HARADA, Isao MURATA, Ryuichi SHINDO, Takuya T ...
    1993 Volume 30 Issue 3 Pages 249-260
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    Xenon oscillations of large graphite-moderated reactors have been analyzed by a multi-group diffusion code with two- and three-dimensional core models to study the effects of the geometric core models and the neutron energy group structures on the evaluation of the Xe oscillation behavior.
    The study clarified the following. It is important for accurate Xe oscillation simulations to use the neutron energy group structure that describes well the large change in the absorption cross section of Xe in the thermal energy range of 0.10.65 eV, because the energy structure in this energy range has significant influences on the amplitude and the period of oscillations in power distributions. Two-dimensional R-Z models can be used instead of three-dimensional R-θ-Z models for evaluation of the threshold power of Xe oscillation, but two-dimensional R-θ models cannot be used for evaluation of the threshold power. Although the threshold power evaluated with the R-θ-Z models coincides with that of the R-Z models, it does not coincide with that of the R-θ models.
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  • Mitsuaki YAMAOKA, Masatoshi KAWASHIMA
    1993 Volume 30 Issue 3 Pages 261-265
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
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  • Hiroshi KAMIMURA
    1993 Volume 30 Issue 3 Pages 266-269
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
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  • Akihiko NISHIMURA, Hideo KABURAKI, Hironori OHBA, Takemasa SHIBATA
    1993 Volume 30 Issue 3 Pages 270-273
    Published: March 25, 1993
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
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