Study on premixing phase of steam explosion at JAERI

Melt jet breakup and fragmentation has been studied in ALPHA program at JAERI. In the first two experiments of the MJB series, a jet of molten lead–bismuth eutectic alloy was released into a deep pool of saturated water. The steam generation rate was measured and correlated with the jet behavior observed by a high-speed camera. The jet breakup length and debris size distribution were also evaluated. In parallel with the experimental study, JASMINE code has been developed for the simulation of a steam explosion process. The models of melt jet breakup and the particle breakup in the code were assessed by analyzing FARO-L14 and ALPHA MJB experiments.     

Vacuum insulation of the high energy negative ion source for fusion application

Vacuum insulation on a large size negative ion accelerator with multiple extraction apertures and acceleration grids for fusion application was experimentally examined and designed. In the experiment, vacuum insulation characteristics were investigated in the JT-60 negative ion source with >1000 apertures on the grid with the surface area of ～2 m(2). The sustainable voltages varied with a square root of the gap lengths between the grids, and decreased with number of the apertures and with the surface area of the grids. Based on the obtained results, the JT-60SA (super advanced) negative ion source is designed to produce 22 A, 500 keV D(-) ion beams for 100 s.     

Swelling of hydrophilic polymers. IV

The swelling of five types of spherical crosslinked dextrans (Sephadex) that are either nonionic (G) or ionic [carboxymethyl (CM), sulphopropyl (SP), diethylaminoethyl (DEAE), and diethyl-(2-hydroxypropyl)aminoethyl (QAE)] in the same skeleton has been studied in water at different dissolved oxygen concentrations by microscopic observation and by dilatometry. The maximum specific volume, V_max/V₀ obtained by microscopic observation increased with the lowered dissolved oxygen concentration for each Sephadex. The change of the maximum specific volume was closely related to the changes of the dissolved oxygen concentrations. The maximum changes of the total volume took the larger negative values at the lower dissolved oxygen concentration. The effect of the difference in the dissolved oxygen on the change of the total volume with swelling was closely related to the viscosity B coefficient of the Jones-Dole equation. From these results, we conclude that the structure of water on the inside of the gel differs from that on the outside of the gel. © 1995 John Wiley & Sons, Inc.     

Mechanisms and mechanics of early growth of debonding crack in an APSed Ni-base superalloy TBCs under cyclic load

Nucleation and early growth of debonding cracks in a Ni-based superalloy thermal barrier coating (TBC) system were investigated. The TBC system consisting of CoNiCrAlY bond and ZrO₂ top coat stabilized by 8%Y₂O₃, was subjected to cyclic load at high temperature. During the study, special effort was made to understand both mechanistic and mechanical behavior on the nucleation and subsequent crack propagation process. The experimental observations clearly demonstrated that both the lamellar structure of top coat and the interlamellar cracks at the splat boundaries played intrinsic role in the nucleation of the spallation cracks. It was also shown that the naturally-initiated small spallation cracks in the smooth specimen revealed propagation rates considerably higher than long crack in the notched specimen under the same remote external loading conditions. This behavior reminds us the fatigue small crack problems, same as in metallic materials. Some fracture mechanics aspects of these characteristics and behaviors are discussed on the basis of FEM calculations.     

Development of a hand-held fast neutron survey meter

A neutron survey meter with a ZnS(Ag) scintillator to measure recoil protons was built. The detection probe weighs ~2 kg, therefore providing us with true portability. Performance tests exhibited satisfactory neutron dosimetry characteristics in unmoderated or lightly moderated fission neutron fields and in particular work environments at a mixed oxide fuel facility. This new survey meter will augment a routine of neutron monitoring that is inconveniently being carried out by moderator-based neutron survey meters.     

An azide-insensitive superoxide dismutase from a hyperthermophilic archaeon, Sulfolobus solfataricus

We studied the mechanisms by which the plant alkaloid tetrandrine (TTD) inhibits Mac-1-dependent neutrophil adhesion to fibrinogen. TTD (0.1-10 microM) significantly inhibited Mac-1 up-regulation and neutrophil adhesion, as induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol-myristate-acetate (PMA). Treatment of neutrophils with fMLP or PMA caused a rapid influx of Ca++ and accumulation of reactive oxygen species (ROS), both of which have been shown to enhance neutrophil adhesion via Mac-1 up-regulation. Because TTD antagonizes Ca++ influx and abrogates ROS, we examined the relationship between Ca++ influx, ROS formation, and Mac-1 expression in TTD-inhibited neutrophil adhesion. TTD alone caused a slight but statistically significant increase in [Ca++]i with no effect on adhesion. In contrast, TTD as well as two Ca++ channel antagonists, verapamil and nifedipine, markedly diminished fMLP- and PMA-induced Ca++ influx, Mac-1 up-regulation, and adhesion. TTD also inhibited increases in [Ca++]i and adhesion induced by the ionophore A23187 but failed to inhibit those induced by thapsigargin, an agent mobilizing Ca++ from intracellular stores. Thus, TTD impeded Ca++ influx from outward to avert neutrophil adhesion. Similarly, TTD and two ROS scavengers, superoxide dismutase and catalase, abolished ROS production, Mac-1 up-regulation, and neutrophil adhesion. Ca++ and ROS, therefore, represent two essential signals for Mac-1 up-regulation upon fMLP or PMA stimulation. Our data suggest that the antiadherent effect of TTD is mediated, in part, by the inhibition of Ca++ influx and ROS formation, resulting in suppressed up-regulation of Mac-1 and, in turn, neutrophil adhesion to fibrinogen.     

A scenario of core disruptive accident for Japan sodium-cooled fast reactor to achieve in-vessel retention

As the most promising concept of sodium-cooled fast reactors, the Japan Atomic Energy Agency (JAEA) has selected the advanced loop-type fast reactor, so-called JSFR. The safety design requirements of JSFR for Design Extension Condition (DEC) are the prevention of severe accidents and the mitigation of severe-accident consequences. For the mitigation of severe-accident consequences, in particular, the In-Vessel Retention (IVR) against postulated Core Disruptive Accidents (CDAs) is required. In order to investigate the sufficiency of these safety requirements, a CDA scenario should be constructed, in which the elimination of power excursion and the in-vessel cooling of degraded core materials are evaluated so as to achieve IVR. In the present study, the factors leading to IVR failure were identified by creating phenomenological diagrams, and the effectiveness of design measures against them were evaluated based on experimental data and computer simulations. This is an unprecedented approach to the construction of a CDA scenario, and is an effective method to objectively investigate the factors leading to IVR failure and the design measures against them. It was concluded that mechanical/thermal failures of the reactor vessel due to power-excursion/thermal-load could be avoided by adequate design measures, and a clear vision for achieving IVR was obtained.     

The risk of hepatitis C virus infection among blood donors in Osaka, Japan

A 70-year-old male presented with a plasma cell granuloma extending from the extracranial to the intracranial space. Findings of preoperative magnetic resonance imaging and intraoperative observation indicated that the lesion extended from the temporal muscle to the subarachnoid space, penetrating the frontal bone. The subarachnoid lesion was composed of neutrophils indicating the presence of acute or subacute inflammation. The final diagnosis of the resected tumor was plasma cell granuloma. High levels of antibodies against Epstein-Barr (EB) virus in the cerebrospinal fluid and the immunohistochemical demonstration of EB nuclear antigens in the plasma cell granuloma suggested that EB virus infection was associated with the development of plasma cell granuloma in this patient.