Conceptual Design of Dual Cooled Fuel Rod Components and Fabrication of the Fuel Rod Specimens for Irradiation Test

In the work scope of the development of dual-cooled fuel structural components, the conceptual and fundamental design of a dual-cooled fuel rod components are also included. This is because the structural stability of a dual-cooled fuel rod of a considerably increased diameter and an additional internal coolant passage becomes an important technical issue together with its nuclear performance. The issues are: a cladding tube thickness corresponding to the increased diameter, a supportless inner cladding tube and a spring and spacers in the plenum region of a fuel rod. To determine the cladding tube thickness, conventional design formulae as well as the classical theory of elastic buckling were consulted and relevant experiments were carried out by using PHWR fuel claddings. As a result, a safety margin of 2.76 was obtained if the cladding thickness of 15.9 mm diameter was 0.87 mm. In the preliminary analysis of fuel rod's dynamic stability, it was predicted that the critical velocity that caused an fluidelastic instability would be less than that of the conventional fuel rod case by 20∼30%. However, it was expected that relative stability margin could be increased when compared with the conventional case. The criteria for pellet stability was considered to be 7g, increased from current 6g, and a coil spring which had 12.45 mm mean diameter, 1.9 mm wire diameter and number of turn of 5 was designed for a plenum spring to satisfy it. A plenum spacer having holes was also suggested to accommodate a fission gas as well as decreased plenum volume. Fuel rod specimen was designed and fabricated with developing a micro TIG welder and relevant technology for irradiation test at the Hanaro research reactor