Fuel cycle cost of sodium cooled fast reactors is strongly dependent on the performance of core structural materials, i.e., clad and wrapper materials of the fuel subassembly, which are subjected to intense neutron irradiation during service, that leads to unique materials problems like void swelling, irradiation creep and helium embrittlement. In order to increase the burnup of the fuel and thereby reduce the fuel cycle cost, it is necessary to employ materials which have high resistance to void swelling as well as better high temperature mechanical properties. The Indian fast reactor program began with the commissioning of the 40 MW_t Fast Breeder Test Reactors (FBTR). The core structural material of FBTR is 20% cold worked 316 austenitic stainless steel (SS). For the 1250 MW_t Prototype Fast Breeder Reactor which is nearing completion of construction, 20% cold-worked alloy D9 (15Cr-15Ni-Ti) has been selected as the clad and wrapper material. The target burnup is 100 GWd/t. Advanced austenitic stainless steel called as IFAC-1 SS and oxide dispersion strengthened martensitic steels have been developed as future materials for achieving higher burnup. Type 316 SS and its modified versions are used as the major high temperature structural materials for out-of-core permanent components. Ferritic-martensitic steels are selected for steam generator applications. This paper reviews the unique problems in fast reactors and illustrates the global progress in developing advanced structural materials for fast reactors in the context of the Indian nuclear programme.

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The contact gasket stress distribution and the hub stress of pipe flange connection under external bending moment and internal pressure are analyzed using three dimensional elasto-plastic FEM. The effect of external bending moment on the sealing performance is evaluated and the amount of the leakage is predicted using the contact gasket stress distribution. From the obtained FE analyses, it is found that a large decrease in the contact gasket stress at the tension side occurs and a small increase at the compression side occurs. The difference in the change in the contact gasket stress occurs due to the non-linear hysteresis characteristics of stress-contract curve of the gasket (spiral wound gasket) used in the study. The FE analyses also suggest that the loading order, that is, the following two cases are analyzed, 1) an internal pressure is applied at first and then the external bending moment is applied to the connection, 2) the external bending moment is applied to the connection and then the internal pressure is applied, also affects the sealing performance due to the non-linear contract characteristic of the gasket. The sealing performance when the external bending moment is applied prior to the internal pressure is degraded more than that when the internal pressure is applied prior to the external bending moment. The leakage tests using helium (He) gas and the measurement of the hub stress were carried out, and then the amount of the leakage was measured. The amount of leakage from the connection is predicted using the contact gasket stress distribution obtained from FE analyses and the results are in a fairly good agreement with the measured results. It is found that the effect of the external bending moment is substantial on the sealing performance of the connections. Also, the calculated hub stresses are fairly consistent with the measured results.

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An experimental model has been developed to characterize the effect of lateral radius of curvature to the wear rate of a disc. This is to simulate the wheel-rail contact wear phenomenon in railway transportation where excessive rail wear commonly occurs at the curve, and eventually this will cause accidents such as derailment, etc. The experiment was conducted using two stainless steel discs, ST37 (0.132% C) and ST60 (0.458% C), with different lateral radius of curvature. One disc has the radius of 13 mm while the other disc has several variations of the radius i.e. 16 mm, 18 mm, 20 mm, 22 mm, and 24 mm. The lowest wear rate was observed for the disc with 22 mm radius while the highest wear rate was observed for the disc with 16 mm radius.

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This paper describes about the joint strength and their improvement of a type 5052 aluminum alloy (A5052) autocompleting friction welded joint, that welding method was developed by authors. When the joint was made at a friction pressure of 60 MPa, it had approximately 75% joint efficiency at a groove bottom thickness of 1.1 mm with an overhanging length of the weld faying surface part (overhanging length) for the fixed workpieces of 15 mm. Those joints had the flexural deformation of the fixed workpiece during the welding, although those had the circumferential shear fracture by the increasing insert thickness with reliability. To reduce the flexural deformation of the fixed workpiece, the joint was made with an overhanging length for the fixed workpieces of 5.0 mm. The joint had 100% joint efficiency with the base metal fracture at a groove bottom thickness of 1.4 mm which was made at a friction pressure of 80 MPa, although that did not achieve 100% joint efficiency at a friction pressure of 60 MPa. In addition, the joint with a groove bottom thickness of 1.3 mm or thin did not achieve 100% joint efficiency, and that with 1.5 mm or thick did not have the circumferential shear fracture. To obtain the generating of the circumferential shear fracture with reliability during the friction process and 100% joint efficiency with the base metal fracture, the joint should be made with thick insert piece, opportune groove bottom thickness of the insert piece, short overhanging length for the fixed workpieces, and relatively high friction pressure.

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