• Electrical & Electronic Materials
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• v.10 no.4
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• pp.327-333
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• 1997

Experiments on mechanical fatigue were conducted using the specimens which were cut from hydrogen cooled generator(rated 22kV and 50OMW) stator windings. We have investigated the aged mechanism of mica/epoxy insulation systems under air or hydrogen by both the tensile and compressive loadings. The fracture of generator stator windings is generally affected by mechanical stress. Thus, the tensile strength test were conducted. In this case, the maximum strength and strain are quite different between sound and aged specimens. It is observed that low bonded interface parts of tapes generally have lower strength than those of normal tapes which causes stress. In order to estimate the effects of cyclic load by the electromagnetic forces while the generator starts/stops, the mechanical fatigue test was also conducted. It is confirmed that the equation of expected life depends on stress amplitude and number of cycles. Though the stress amplitude and number of cycles are very tiny, the tensile fatigue of aged specimens under hydrogen atmosphere is bigger than those under air. In the case of hydrogen atmosphere, the tensile stress gives bigger effect than the compressive one.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.893-899
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• 2024

In a secondary cooling system of a sodium-cooled fast reactor (SFR), rapid detection of hydrogen due to sodium-water reaction (SWR) caused by water leakage from a heat exchanger tube of a steam generator (SG) is important in terms of safety and property protection of the SFR. For hydrogen detection, the hydrogen detectors using atomic transmission phenomenon of hydrogen within Ni-membrane were used in Japanese proto-type SFR "Monju". However, during the plant operation, detection signals of water leakage were observed even in the situation without SWR concerning temperature up and down in the cooling system. For this reason, the study of a new hydrogen detector has been carried out to improve stability, accuracy and reliability. In this research, the authors focus on the difference in composition of hydrogen and the difference between the background hydrogen under normal plant operation and the one generated by SWR and theoretically estimate the hydrogen behavior in liquid sodium by using ultra-accelerated quantum chemical molecular dynamics (UA-QCMD). Based on the estimation, dissolved H or NaH, rather than molecular hydrogen (H₂), is the predominant form of the background hydrogen in liquid sodium in terms of energetical stability. On the other hand, it was found that hydrogen molecules produced by the sodium-water reaction can exist stably as a form of a fine bubble concerning some confinement mechanism such as a NaH layer on their surface. At the same time, we observed experimentally that the fine H₂ bubbles exist stably in the liquid sodium, longer than previously expected. This paper describes the comparison between the theoretical estimation and experimental results based on hydrogen form in sodium in the development of the new hydrogen detector in Japan.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1320-1325
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• 1995

For hydrogen-cooled large turbine generators, partial discharges in ground wall insulations are suppressed by high hydrogen pressure. The first goal of the experiment is to investigate the effect of hydrogen pressure on partial discharge activity and aging rate in turbine generator winding insulations. A series of tests have been performed on two groups of the accelerated aging experiments. The first group of stator windings was aged under hydrogen pressure of 4 atm while the second group of stator windings was aged under air atmosphere. The stator windings aged under air atmosphere suffer from larger partial discharge magnitude with larger voids at high electrical stress than those under hydrogen pressure. The second goal of the experiment is to evaluate the validity of on-line measurement technique which is normally measured under hydrogen environment. The test results show that further experiments are needed to apply the on-line scheme to turbine generator being under high hydrogen pressure.

• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.170-179
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• 2017

We investigated design requirements of feed water drain and hydrogen vent systems for the sodium-water reaction pressure relief system (SWRPRS) of the prototype generation IV sodium cooled fast reactor (PGSFR). We evaluated the areas of the gas vent pipe of the water dump tank and the length of the water drain pipe of the steam generator to rapid drain of the water steam inside the steam generator for the normal and refueling operations, respectively. We also calculated the diameter of the gas vent pipe of the sodium dump tank which met its design pressure.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1676-1678
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• 2004

Class-F resin-rich type insulating tapes are generally used for the groundwall insulations of the large turbine generators with air-cooled and hydrogen-cooled stator windings. In this paper, mechanical strength properties degraded over aging time in higher temperature than designed one in normal condition were experimentally investigated and the results of comparative tests were presented on the existing class-F resin-rich type tape and a developed one after curing. The resin-rich insulating tapes with composite material of Mica/Epoxy/support currently were used in this test. The tests for tensile and flexural strength properties were conducted with the specimens which were composed of unaged and the aged specimens accelerated for one, two, and three thousand hours at 180 $^{\circ}C$. The tensional strength was only measured for the unaged specimens and the results are also presented to make a comparative test for their initial mechanical characteristics.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1846-1849
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• 2000

Off-line and on-line partial discharges were measured on a 828MVA, 22kV and direct hydrogen-cooled large turbine generator. Partial discharge tests were conducted using digital partial discharge detector(PDD) and turbine generator analyzer(TGA). PDD and TGA showed that off-line partial discharge pattern seems to be very, similar to that found with on-line. Most of the partial discharge is originating with the stator slot in the three phases. As the partial discharge activity is very low, the stator insulation condition of this generator is very good.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.2
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• pp.69-76
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• 2006

TRISO(tri-isotropic)-coated fuel particle technology is utilized owing to its higher stability at a high temperature and Its efficient retention capability for fission products In the HTGR(high temperature gas-reeled reactor). The typical spherical TRISO fuel panicle with a diameter of about 1mm is composed of a nuclear fuel kernel and outer coating layers. The outer coating layers consist of a buffer PyC(pyrolytic carbon) layer, Inner PyC(1-PyC) layer, SiC layer, and outer PyC(O-PyC) layer Most of the Inspection Items for the TRTSO-coated fuel particle depend on destructive methods. The coating thickness of the TRISO fuel particle can be nondestructively measured by the X-ray radiography without generating radioactive wastel. In this study, the coaling thickness for the simulated TRISO-coated fuel particle with $ZrO_2$ kernel Instead of $%UO_2$ kernel was measured by using micro-focus X-ray radiography with micro-focus X-ray generator and flat panel detector The radiographic image was also enhanced by image processing technique to acquire clear boundary lines between coating layers. The coaling thickness wat effectively measured by applying the micro-focus X-ray radiography The inspection process for the TRISO-coated fuel particles will be improved by the developed micro-focus X-ray radiography and digital image processing technology.