In the nuclearreactor environment, due to irradiation, the mechanical properties of thematerial are degraded. For the safe and long-time operation of the nuclearreactor, the material properties should be known to us. The non-instrumentedirradiation gas-gap capsule in the research reactor, fast breeder test reactor(FBTR) in INDIA has used the evaluation and prediction of the irradiationbehavior of the material in the reactor core and the development of new nuclearmaterials for the next-generation reactor. An irradiation capsule is loadedwith the tubular and disc types of test specimens. In the reactor, mainly dueto the gamma rays and neutrons irradiation the capsule and specimens work as aheat source. The design of the irradiationcapsule has a main body 1045mm long, and 20 mm diameter which contains four (4)irradiation sub-capsules of diameter 14.5 mm and length 167 mm in a cylindricalshape.
The irradiation capsule consists of an end plug, sub-capsule holderalong with the specimens, insulator gas gap region. A schematic view of thecapsule main body considered in this study is shown in figure 1. The testspecimens are in two shapes. A. Disc shape-which diameter is 8mm and width is 0.5 mm and there are 28 numbers.
B. Tubularshape- 6.6mm outer diameter and 5.7mm inner diameter and there are 2 twonumbers. A schematic view of the irradiation sub-capsule shown in figure 2.After the specimens kept in the sub-capsule and irradiation capsule areirradiated into the reactor core, the heat generation due to the gamma andneutrons flux in the irradiation capsule. This gives in a different temperaturedistribution among the specimens. The nuclear reaction profile in the reactorcore is known that in the middle of the core is higher than the top and bottomof the core .
In the irradiation sub-capsule specimens are kept in a mixtureof helium and argon gas environment for controlling the particular temperaturerange 4500C-6000C. In the study, the thermal analysisof the instrumented capsule for the irradiation test of the specimens materialsare studies in the COMSOL Multiphysics Computer Code. The temperaturedistribution in the irradiation capsule is evaluated and found the percentageof gas mixture of helium and argon for the particular specimen’s temperature.