Development of Brazed Joints Using Induction Heating System for High Temperature Nuclear Applications

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.