Soo-Sung Kim

Design and Fabrication of Remote Welding Equipment in a Hot-Cell

The remote welding equipment for nuclear fuel bundle fabrication in a hot-cell was designed and developed. To achieve this, a preliminary investigation of hands-on fuel fabrication outside a hot-cell was conducted with a consideration of the constraints caused by the welding in a hot-cell. Some basic experiments were also carried out to improve the end-plate welding process for nuclear fuel bundle fabrication. The resistance welding equipment using end-plate welding was also improved. It was found that the remote resistance welding was more suitable for joining an end-plate to end caps in a hot-cell. This paper presents an outline of the developed welding equipment for nuclear fuel bundle fabrication and reviews a conceptual design of remote welding equipment using a master-slave manipulator. Furthermore, the mechanical considerations and a mock-up simulation test were described. Finally, its performance test results were presented for a mock-up of the remote resistance welding equipment for nuclear fuel bundle fabrication.

Development of Zircaloy-4 Endplate Welding Technology for a DUPIC Fuel Bundle Assembly

This study was carried out to establish the remote resistance welding technology for a hot cell environment for Direct Use of spent PWR fuel In CANDU reactors (DUPIC) fuel fabrication. A preliminary investigation for a hands-on fuel fabrication outside a hot cell was conducted with consideration of the constraints caused by a welding in a hot cell. The optimum resistance welding parameters for the endplate welding process were obtained in terms of the welding current, electrode pressure, and welding time. The welds made on the basis of optimum welding parameters showed higher torque strength than those made by laser beam welding. The integrity of the welds fabricated by resistance welding was confirmed by the results of the torque test, an examination of the microstructure, and the fracture surface of the welds.

Development of Electronic Radiation Dosimeter Using Commercial Power pMOSFET

When a metal oxide field effect transistor (MOSFET) is exposed to ionizing radiation, electron/hole pairs are generated in its oxide layer. The slow moving holes are trapped in the oxide layer of pMOSFET and appear as extra charges that change the characteristics of the transistor. The radiation-induced charges directly impact the threshold (turn-on) voltage of the transistor. This paper describes the use of the radiation-induced threshold voltage change of commercial power pMOSFETs as an accumulated radiation dose monitoring method. Two kinds of commercial p-type power MOSFETs were tested in a Co-60 gamma irradiation facility to see their capabilities as a radiation dosimeter. We found that the transistors showed good linearity in their threshold voltage shift characteristics with radiation dose. According to these results, a electronic radiation dosimeter using inexpensive commercial power pMOSFETs was developed for the first time. And these power pMOSFETs show good linearity in dose rate effect, room temperature annealing, and 100 iÉ thermal annealing for 48 hours.

Irradiation Behavior of Reactor Pressure Vessel SA508 class 3 Steel Weld Metals

Abstract Irradiation behavior of the reactor pressure vessel SA508 class 3 steel weld metals was examined by Charpy V Notch impact specimens. The specimens were exposed to a fluence of 2.8x1019 neutrons(n)/cm 2 (E>1 MeV) at 288℃. The irradiation damage of weld metal was evaluated by comparison between unirradiated and irradiated specimens in terms of absorbed energy and lateral expansion. The specimens for neutron irradiation were welded by submerged arc welding process at a heat input of 3.2 kJ/mm which showed good toughness in terms of weld microstructure, absorbed energy and lateral expansion. The post-irradiation Charpy V notch 41J and 68J transition temperature elevation were 65℃ and 70℃, respectively. This elevation was accompanied by a 20% reduction in Charpy V notch upper shelf energy level. The lateral expansion at 0.9㎜ irradiated Charpy specimens showed temperature elevation of 65℃ and was greatly decreased due to radiation damage. Key Words : Radiation damage, SA508 class 3, Submerged arc welding, Impact test, Absorbed energy, lateral expansion, Transition temperature elevation

Effect of Heat on the Soundness of Zircaloy-4 End Cap Closure Using a Resistance Upset Welding

The objective of this study is to investigate the effect of main heat on the soundness of Zircaloy-4 end cap welds and the process of weld line elimination in resistance upset welding for a Direct Use of spent PWR fuel In CANDU reactor (DUPIC) fuel fabrication. The weld current and amount of upset increased linearly with the main heat, from which two relations between them were derived. It was found that the threshold to obtain sound welds was 50% of the main heat in terms of upset size, mechanical strength, and weld line elimination. A microstructure of resistance upset welds of Zircaloy-4 comprised basketweave, Widmanstätten, and martensite depending on the alteration of the main heats. Dimples on the uniaxially fractured surface at the weld line in Zircaloy-4 welds were larger and deeper than those on a biaxially fractured surface. It was also found that the process of weld line elimination in the resistance upset weld of Zircaloy-4 could be divided into three stages in terms of the presence of many pores, their shrinkage and elimination, and the shrinkage of the original weld interface with increasing weld current.

Development of a Remote Welding Machine for a DUPIC Fuel Bundle Fabrication

A remote welding machine for a DUPIC (Direct Use of spent PWR fuel In CANDU reactors) bundle fabrication was designed to establish the optimum welding processes in a hot cell environment. An initial investigation for hands-on fabrication outside the hot cell was performed in the consideration of the constraints of welding machine in the hot cell conditions. Gas tungsten arc welding (GTAW), laser beam welding (LBW), friction welding (FW), and resistance welding (RW) process were assessed as candidates for this application. A preliminary welding investigation to improve the RW process was also performed. The RW process was determined to be the most suitable process in a hot cell environment for joining an endplate to an endcap. An advantage of RW would be a qualified process for overlapped plates welding for which there is extensive production experience were available. A preliminary investigation for a hands-on fuel fabrication outside the hot cell was conducted in the consideration of the constraints caused by a welding in a hot cell. The optimum resistance welding parameters for the endplate welding process were obtained in terms of the current, electrode pressure and welding cycle. This paper presents an outline of the developed RW machine for a DUPIC bundle fabrication and reviews the conceptual design of a remote RW welder by using a master-slave manipulator. The design of RW machine by using the 3D modeling method was also designed. Furthermore the integrity of the welds by the resistance welding was confirmed by the results of the torque test, an examination of the microstructure and the fracture surfaces of the welds.Copyright

Investigation of LBW characteristics using Ta thermocouple wire for instrumented fuel irradiation test

Laser beam welding technology is widely used to fabricate some parts of nuclear fuel in the nuclear industry. In particular, laser welding has become one of the key technologies not only for the fabrication of precise products in nuclear fuel but also for the fuel irradiation test. It is also important for us to secure laser welding technology to perform various instrumentations for the fuel irradiation test.Laser beam welding technology is widely used to fabricate some parts of nuclear fuel in the nuclear industry. In particular, laser welding has become one of the key technologies not only for the fabrication of precise products in nuclear fuel but also for the fuel irradiation test. It is also important for us to secure laser welding technology to perform various instrumentations for the fuel irradiation test.

Investigation of Electron Beam Welding Characteristics Using AA6061-T6 for Nuclear Plate-Type Fuel Assembly

This study was carried out to establish an electron beam welding process for nuclear plate-type fuel assembly fabrication. A preliminary investigation for plate fuel fabrication was conducted with a consideration of the weld performance using AA6061-T6 aluminum alloy made through the EBW (Electron Beam Welding) process. The optimum welding parameters for the plate-type fuel assembly were obtained in terms of the accelerating voltage, beam current and welding time. The welds made by the optimum parameters showed slightly lower tensile strengths than those of the un-welded specimens. The integrity of the welds by the EBW process was confirmed by the results of the tensile test, an examination of the macro-cross sections and the fracture surfaces of the welded specimens.Copyright

Heat Treatment Effect on Super Duplex Stainless Steel UNS S32750 FCA Multipass Welds

Abstract This study was carried out to investigate the effect of postweld heat treatment(PWHT, 930, 1080, 1230℃)on the microstructure, phase formation, pitting corrosion and mechanical properties such as hardness, tensile strength and impact values of super duplex stainless steel(UNS S32750) multipass welds. Based on the microstructural examination and X-ray diffraction analysis, it was found that the σ phase was formed in the welds heat treated at 930℃ in which the ferrite content greatly decreased into 5~10% in the welds. The secondary austenite was formed in the reheated zone of welds and redissolved into ferrite with increasing heat treatment temperatures. The tensile strength and impact values of welds heat treated at 930℃were the lowest and revealed the brittle fracture surface. The weight loss by pitting corrosion increased with test temperatures. It was confirmed that pitting corrosion occurred mainly in secondary austenite of reheated zones. The postweld heat treatment temperature is recommended to be in the range of 1050~1150℃.Key Words : Super Duplex Stainless Steel, FCA multipass, PWHT, Pitting corrosicon, Mechanical properties

Development of Electron Beam Welding Technology Using AA6061-T6 Aluminum Alloy for Nuclear Fuel Plate Assembly

This study was carried out to establish the electron beam welding process for a nuclear fuel plate assembly fabrication. A preliminary investigation for plate fuel fabrication was conducted with a consideration of weld performance using AA6061-T6 aluminum alloy made by the EBW (Electron Beam Welding) process. The optimum welding parameters for the fuel plate assembly were obtained in terms of the accelerating voltage, beam current and welding time. The welds made by the optimum parameters showed slightly lower tensile strengths than those of the un-welded specimens. The integrity of the welds by the EBW process was confirmed by the results of the tensile test, an examination of the macro-cross sections and the fracture surfaces of the welded specimens.Copyright