Irradiation Testing of Structural Materials in Fast Breeder Test Reactor

Fast Breeder Test Reactor (FBTR) at Kalpakkam, India is a sodium cooled fast reactor with neutron flux level of the order of 10 15 n/cm 2/s and temperature of coolant in the range of 600-720K (330-450°C), which is being used for the development of fuel and structural materials required for Indian Fast Reactor Programme. Irradiation performance testing on structural materials is being carried out by subjecting prefabricated specimens to desired experimental conditions as part of planned irradiation experiments, and by testing of material samples sourced from actual fuel clad tubes / fuel assembly wrapper tubes irradiated to various fuel burn up levels in FBTR. Pressurised capsules of Zirconium alloys and D9 alloy (modified stainless steel type 316 with controlled additions of titanium and silicon) have been developed to determine the in-reactor creep performance of indigenously developed zirconium alloys and D9 alloy. Pressurised capsules made of zirconium alloys were subjected to fluence levels up to 1.1 x 10 21 n/cm 2 (E> 1 MeV) in FBTR at temperatures of 579 to 592K and diameter measurements were carried out in the hot cell facility to determine the irradiation creep rate. Pressurised capsules of D9 alloy are currently undergoing irradiation at a temperature of 623K in FBTR along with small size tensile test specimens and shear punch test specimens of D9. Non-instrumented gas-gap type irradiation capsule has been developed to achieve higher irradiation temperatures (673 to 873K) of structural material specimens. The irradiation induced mechanical property changes in cold worked AISI Type SS316 fuel cladding of FBTR have been determined from tensile testing of portions of irradiated fuel clad tubes in the hot cells. Tests were carried out on clad tubes with dpa ranging from 13 to 83 at various test temperatures from ambient (300K) to irradiation temperature (790K). Shear punch tests have been used for characterizing the tensile property changes in cold worked AISI Type SS 316 wrapper material of FBTR fuel assemblies. From the results of shear punch tests on irradiated specimens, using correlation equations, the tensile properties of the wrapper material irradiated to various dpa ranging from 30 to 83 have been estimated. A considerable increase in the strength and decrease in the ductility of the wrapper material with increasing dpa was observed from the results. This paper discusses the salient features of irradiation facilities available at FBTR, irradiation experiments carried out on structural materials, and some of the important results obtained from tests on irradiated structural materials.