Indian Welding Journal

P. K. Chaurasia ¹, S. Murugan ¹, S. Venugopal ¹, K. V. Kasiviswanathan ¹

Affiliations
1 Group for Remote Handling, Robotics, Irradiation. Experiments and Post Irradiation Examination (GRIP), Metallurgy and Materials Group (MMG), Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam- 603 102, Tamilnadu, IN

Abstract

Fabrication of instrumented capsule for irradiation experiments for evaluating the irradiation performance of fuel and structural materials in a nuclear reactor requires development of thin-walled joints capable of withstanding high temperature and internal pressure. Instrumented capsules are being developed in IGCAR for irradiation of fuel and structural material specimens in Fast Breeder Test Reactor (FBTR). Instrumented capsule for irradiation of fuel pin specimen will have thermocouple of diameter 1 to 1.5 mm passing through the end plug of the fuel pin in a leak tight manner to prevent the release of fission gases generated in the fuel pin that may reach a pressure upto 10 MPa at 550°C during reactor operation. Out of the various joining methods, development of high temperature brazed joint method is found to be beneficial with respect to sealing the thermocouple passing through the end plug of the fuel pin and the intermediate plug of the irradiation capsule. Furnace and induction brazing methods have been tried and induction brazing method is seen to be more suitable for the present application. A procedure has been established to properly orient and braze the thermocouples in stainless steel plugs representing end plug and intermediate plug. Brazing parameters like temperature, time, vacuum level, and the brazing gap width are important factors in achieving good quality brazing joints. The trials carried out and the results obtained are discussed in this paper.

Keywords

Instrumented Fuel Irradiation Capsule, High Temperature Brazing, Induction Heating.

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K. A. Gopal ¹, S. Murugan ¹, S. Venugopal ¹, K. V. Kasiviswanathan ¹

Affiliations
1 Group for Remote Handling, Robotics, Irradiation Experiments and Post Irradiation Examination (GRIP), Metallurgy and Materials Group (MMG), Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam- 603 102, IN

Abstract

Laser beam welding (LBW) with its high power density produces narrow and deep welds with a small heat-affected zone. Nd-YAG laser has been used extensively in the fabrication of small precision components at Indira Gandhi Centre for Atomic Research (IGCAR). Some important laser welding works carried out are related to Eddy Current based Position Sensor (ECPS) and Sodium Leak Detector (SLD) in Diverse Safety Rod Drive Mechanism (DSRDM) of Prototype Fast Breeder Reactor (PFBR), and components for Ir-192 High Dose Rate (HDR) source for Board o f Radiation and Isotope Technology (BRIT). ECPS is being designed to incorporate in the DSRDM to provide a measurement on signal which indicates that all the safety rods are dropped in case of a reactor scram signal. Mineral insulated (MI) cable of 1 mm diameter used as the eddy current coil in the ECPS has been terminated with suitable end configuration using laser welding. SLD is housed inside the electromagnet assembly of DSRDM to indicate if there is any leakage of sodium into the electromagnet. The fabrication of SLD requires precision laser welding of a few of its components. For the indigenous development of Ir-192 source assembly for use in HDR Branchy therapy, the feasibility study has been carried out for the fabrication of the miniature source holder by laser welding process. This paper discusses the techniques followed in the successful fabrication of above mentioned variety of intricate components used in critical applications.

Keywords

Nd-YAG Laser Welding, Precision Components, PFBR, ECPS, DSRDM, Sodium Leak Detector, HDR Source.

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S. L. Mannan ¹, S. Venugopal ¹, A. Veeramani ¹

Affiliations
1 Indira Gandhi Centre for Atomic Research, KALPAKKAM, IN

Abstract

Structural components such as in bridges, cranes, engines, pressure vessels and offshore structures are often subjected to cyclic loading Fatigue failures generally occur at stress concentration sites in the components The geometrical and metallurgical states of welds make them prone to fatigue failures owing to stress concentrations caused by weld shape and discontinuities. Moreover, welding introduces unfavourable tensile residual stresses, often of yield magnitude, which increases the severity of the applied fatigue loading. As a result, both applied compressive and tensile stresses can be equally damaging. In addition, the existence of defects in weld eliminates the fatigue crack initiation stage, and hence, the life IS predominantly governed by fatigue crack propagation.

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