• Title/Summary/Keyword: helium leak

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Methodology of Non-Destructive Examinations on Hydraulic Expansion Region of Steam Generator Tubes (증기발생기 세관 수압확관부 비파괴검사 방법론)

  • Kim, Chang-Soo;Jung, Nam-Du;Lee, Sang-Hoon
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.4 no.2
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    • pp.29-33
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    • 2008
  • As the measures of nuclear power plant utilities and manufacturers to reduce the defects of tube expansion region during manufacturing steam generators, many types of NDEs(Non-Destructive Examinations) are conducted to inspect the expansion region. The expansion region of tube is subject to degrade because of stress concentration induced by tube expansion, sludge pile and high temperature. So the inspections for tube expansion region have been reinforced. Liquid penetrant test, helium leak test, Bobbin profile test and hydraulic test are performed to confirm the integrity of tube expanded by hydraulic expansion method. Liquid penetrant test and helium leak test are used to inspect seal weld region on tubesheet end part. Bobbin Profile test is used to inspect fully the expanded region of steam generator tube. Hydraulic test finally verifies the integrity of seal weld region on tubesheet end part.

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Commissioning result of the KSTAR in-vessel cryo-pump

  • Chang, Y.B.;Lee, H.J.;Park, Y.M.;Lee, Y.J.;Kwag, S.W.;Song, N.H.;Park, D.S.;Joo, J.J.;Moon, K.M.;Kim, N.W.;Yang, H.L.;Oh, Y.K.
    • Progress in Superconductivity and Cryogenics
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    • v.15 no.4
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    • pp.53-58
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    • 2013
  • KSTAR in-vessel cryo-pump has been installed in the vacuum vessel top and bottom side with up-down symmetry for the better plasma density control in the D-shape H-mode. The cryogenic helium lines of the in-vessel cryo-pump are located at the vertical positions from the vacuum vessel torus center 2,000 mm. The inductive electrical potential has been optimized to reduce risk of electrical breakdown during plasma disruption. In-vessel cryo-pump consists of three parts of coaxial circular shape components; cryo-panel, thermal shield and particle shield. The cryo-panel is cooled down to below 4.5 K. The cryo-panel and thermal shields were made by Inconel 625 tube for higher mechanical strength. The thermal shields and their cooling tubes were annealed in air environment to improve the thermal radiation emissivity on the surface. Surface of cryo-panel was electro-polished to minimize the thermal radiation heat load. The in-vessel cryo-pump was pre-assembled on a test bed in 180 degree segment base. The leak test was carried out after the thermal shock between room temperature to $LN_2$ one before installing them into vacuum vessel. Two segments were welded together in the vacuum vessel and final leak test was performed after the thermal shock. Commissioning of the in-vessel cryo-pump was carried out using a temporary liquid helium supply system.

Cool-down test of HWR cryomodule for RAON

  • Kim, Y.;Lee, M.;Jo, Y.W.;Choi, J.W.;Kim, H.;Kim, W.K.;Kim, H.J.
    • Progress in Superconductivity and Cryogenics
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    • v.17 no.4
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    • pp.43-46
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    • 2015
  • The heavy ion accelerator that will be built in Daejeon utilizes four types of superconducting cavities. Cryomodules holding the superconducting cavities in them supply thermal insulation for cavities operating in 4.3 K or 2.1 K. A Prototype of cryomodule which holds two HWR (Half Wave Resonator) cavities was fabricated and tested. Since the operating temperature of the HWR is 2.1 K, the superfluid helium was generated with warm vacuum pumping system. The cyromodule was successfully cooled down below lambda point temperature of helium and any detectable leak was not observed during the test. The static thermal load at 4.2 K was measured. The result and the experience for the cool-down below lambda point of helium are reported in this paper.

Effect of Silane Coupling Treatment on the Joining and Sealing Performance between Polymer and Anodized Aluminum Alloy

  • Lee, Sung-Hyung;Yashiro, Hitoshi;Kure-Chu, Song-Zhu
    • Korean Journal of Materials Research
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    • v.31 no.3
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    • pp.122-131
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    • 2021
  • In the fabrication of joined materials between anodized aluminum alloy and polymer, the performance of the metal-polymer joining is greatly influenced by the chemical properties of the oxide film. In a previous study, the dependence of physical joining strength on the thickness, structure, pore formation, and surface roughness of films formed on aluminum alloys is investigated. In this study, we investigated the effect of silane coupling treatment on the joining strength and sealing performance between aluminum alloy and polymer. After a two-step anodization process with additional treatment by silane, the oxide film with chemically modified nanostructure is strongly bonded to the polymer through physical and chemical reactions. More specifically, after the two-step anodization with silane treatment, the oxide film has a three-dimensional (3D) nanostructure and the silane components are present in combination with hydroxyl groups up to a depth of 150 nm. Accordingly, the joining strength between the polymer and aluminum alloy increases from 29 to 35 MPa, and the helium leak performance increases from 10-2-10-4 to 10-8-10-9 Pa ㎥ s-1.

On-Chip Process and Characterization of the Hermetic MEMS Packaging Using a Closed AuSn Solder-Loop (사각고리형상의 AuSn 합금박막을 이용한 MEMS 밀봉 패키징 및 특성 시험)

  • Seo, Young-Ho;Kim, Seong-A;Cho, Young-Ho;Kim, Geun-Ho;Bu, Jong-Uk
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.4
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    • pp.435-442
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    • 2004
  • This paper presents a hermetic MEMS on-chip package bonded by a closed-loop AuSn solder-line. We design three different package specimens, including a substrate heated specimen without interconnection-line (SHX), a substrate heated specimen with interconnection-line (SHI) and a locally heated specimen with interconnection-line (LHI). Pressurized helium leak test has been carried out for hermetic seal evaluation in addition to the critical pressure test for bonding strength measurement. Substrate heating method (SHX, SHI) requires the bonding time of 40min. at 400min, while local heating method (LHI) requires 4 min. at the heating power of 6.76W. In the hermetic seal test. SHX, SHI and LHI show the leak rates of 5.4$\pm$6.7${\times}$$^{-10}$ mbar-l/s, 13.5$\pm$9.8${\times}$$^{-10}$ mbar-l/s and 18.5$\pm$9.9${\times}$$^{-10}$ mbar-l/s, respectively, for an identical package chamber volume of 6.89$\pm$0.2${\times}$$^{-10}$. In the critical pressure test, no fracture is found in the bonded specimens up to the applied pressure of 1$\pm$0.1MPa, resulting in the minimum bonding strength of 3.53$\pm$0.07MPa. We find that the present on-chip packaging using a closed AuSn solder-line shows strong potential for hermetic MEMS packaging with interconnection-line due to the hermetic seal performance and the shorter bonding time for mass production.

Closed-Loop Cooling System for High Field Mangets (고자기장용 자석을 위한 밀폐순환형 냉각장치)

  • Choi, Y.S.;Kim, D.L.;Lee, B.S.;Yang, H.S.;Painter, T.A.;Miller, J.R.
    • Progress in Superconductivity and Cryogenics
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    • v.8 no.1
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    • pp.59-64
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    • 2006
  • A closed-loop cryogenic cooling system for high field magnets is presented. This design is motivated by our recent development of cooling system for 21 tesla Fourier Transform ion Cyclotron Resonance (FT-ICR) superconducting magnets without any replenishment of cryogen. The low temperature superconducting magnets are immersed in a subcooled 1.8 K bath, which is connected hydraulically to the 4.2 K reservoir through a narrow channel. Saturated liquid helium is cooled by Joule-Thomson heat exchanger and flows through the JT valve, isenthalpically dropping its pressure to approximately 1 6 kPa, corresponding saturation temperature of 1.8 K. Helium gas exhausted from pump is now recondensed by two-stage cryocooler located after vapor purify system. The amount of cryogenic Heat loads and required mass flow rate through closed-loop are estimated by a relevant heat transfer analysis, from which dimensions of JT heat exchanger and He II heat exchanger are determined. The detailed design of cryocooler heat exchanger for helium recondensing is performed. The effect of cryogenic loads, especially superfluid heat leak through the gap of weight load relief valve, on the dimensions of cryogenic system is also investigated.

Containment Evaluation of the KN-12 Transport Cask

  • Chung, Sung-Hwan;Choi, Byung-Il;Lee, Heung-Young;Song, Myung-Jae
    • Journal of Radiation Protection and Research
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    • v.28 no.4
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    • pp.291-298
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    • 2003
  • The KN-12 transport cask has been designed to transport 12 PWR spent nuclear fuel assemblies and to comply with the regulatory requirements for a Type B(U) package. The containment boundary of the cask is defined by a cask body, a cask lid, lid bolts with nuts, O-ring seals and a bolted closure lid. The containment vessel for the cask consists of a forged thick-walled carbon steel cylindrical body with an integrally-welded carbon steel bottom and is closed by a lid made of stainless steel, which is fastened to the cask body by lid bolts with nuts and sealed by double elastomer O-rings. In the cask lid an opening is closed by a plug with an O-ring seal and covered by the bolted closure lid sealed with an O-ring. The cask must maintain a radioactivity release rate of not more than the regulatory limit for normal transport conditions and for hypothetical accident conditions, as required by the related regulations. The containment requirements of the cask are satisfied by maintaining a maximum air reference leak rate of $2.7{\times}10^{-4}ref.cm^3s^{-1}$ or a helium leak rate of $3.3{\times}10^{-4}cm^3s^{-1}$ for normal transport conditions and for hypothetical accident conditions.

A Study on a Quality Characteristics of Pressure Leak Test of Process Piping for Offshore Plant (해양플랜트 프로세스 배관 Pressure Leak Test의 품질 특성에 관한 연구)

  • Park, Chang-Soo;Kim, Hyungwoo
    • Journal of the Korean Society of Industry Convergence
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    • v.21 no.6
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    • pp.429-437
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    • 2018
  • The process gas piping of the offshore plant can cause a massive explosion if the gas leakage occurs during operation. For the purpose of precaution of gas leakage accident, an air pressure test is performed on the process equipment tests using a test pump as much as the power to the piping inner side, mix 99% nitrogen gas and 1% helium gas. The purpose of the air pressure test is to check the work conformity process by handling and regulation for initial piping process, assembly, installation of module, welding, center alignment of the pipes assembling flange gasket in an unrestrained free state. In this paper, the regulation of the problematic air pressure test was analyzed and the solution criteria were established. And leakage tests of existing equipment were performed applying these solution methods. As a result, it was confirmed that there was no problem.

Construction and Assembly of KSTAR Current Leads and the Helium Control System (KSTAR 전류인입선 및 헬륨냉매 제어시스템 제작 및 설치)

  • Song, N.H.;Woo, I.S.;Lee, Y.J.;Kwag, S.W.;Bang, E.N.;Lee, K.S.;Kim, J.S.;Jang, Y.B.;Park, H.T.;Hong, J.S.;Park, Y.M.;Kim, Y.S.;Choi, C.H.
    • Journal of the Korean Vacuum Society
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    • v.16 no.5
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    • pp.388-396
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    • 2007
  • KSTAR (Korea Superconducting Tokamak Advanced Research) current lead system (CLS) has a role to interconnect magnet power supply (MPS) in room temperature (300 K) and superconducting (SC) bus-line, electrically. For the first plasma experiments, it should be assembled 4 current leads (CL) on toroidal field (TF) current lead box (CLB) and 14 leads on poloidal field (PF) CLB. Two current leads, with the design currents 17.5 kA, and SC bus-lines are connected in parallel to supply 35 kA DC currents on TF magnet. Whereas, it could supply $20\;{\sim}\;26\;kA$ to each pairs of PF magnets during more than 350 s. At the cold terminals of the leads, there are joined SC bus-lines and it was constructed helium coolant control system, aside from main tokamak system, to protect heat flux through current leads and enhanced Joule heat due to supplied currents. Throughout the establishment processes, it was tested the high vacuum pumping, helium leak of the helium lines and hardwares mounted between the helium lines, flow controls for CL, and liquid nitrogen cool-down of possible parts (current leads, CL helium lines, and thermal shield helium lines for CLB), for the accomplishment of the required performances.

A Study on the Construction of the Gas Conversion Process System for a Pilot Plant Using a Small-scale Hydrogen Liquefaction System (소규모 수소 액화 시스템을 활용한 파일럿 플랜트의 기체 전환 공정 시스템 구축에 관한 연구)

  • YOUNG MIN SEO;HYUN WOO NOH;TAE HYUNG KOO;ROCK KIL KO;DONG WOO HA
    • Journal of Hydrogen and New Energy
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    • v.35 no.4
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    • pp.353-362
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    • 2024
  • In this study, several studies were conducted on the construction of gas conversion process system for a pilot plant using a small-scale hydrogen liquefaction system. The pilot plant considered in this study includes a liquefier, a storage tank, an evaporator, a gas booster, and a gas storage tank. First, the suspected leak area of the container was checked using the sprayed method of helium gas. The small-scale hydrogen liquefaction system was designed based on the analysis results of the pre-cooling system and the liquefaction system. Additionally, the program was developed to maintain pressure within vessel for an automatic production of liquid hydrogen. The evaporator for liquid hydrogen was manufactured based on the designed analysis data, and the pollution of gas in the vessel was analyzed through a gas recovery line system.