[en] To develop the creep capsule to be used for the irradiation test of various nuclear materials, it is necessary to examine the compatibility of the capsule with HANARO and the structural integrity as well as the thermal behavior due to a thermal gradient of the capsule. The stress level under free-drop impact load is satisfied with the allowable stress of the capsule material. The mechanical stresses occurred by the pressure difference at the inner and outer surface of external tube and by the coolant pressure at the surface of external tube were 5.39MPa and 18.93MPa, respectively. The temperature on the outer surface of the external tube was 80.35 .deg. C, and this temperature is lower than the temperature criterion(<125 .deg. C) of Onset of Nucleate Boiling(ONB) in HANARO. The maximum stress intensity in the external tube due to thermal gradient was 6.63MPa. The maximum stress intensity at the contact part of bottom plug and external tube was 25.4MPa. Through the mechanical and thermal analysis, it was ensured that the creep capsule for nuclear material irradiation test meets the strength criterion in ASME boiler and pressure vessel code during the irradiation test in HANARO. Based on the results of thermal deformation analysis, it is known that there is no interference or failure between the components of the creep capsule during the irradiation tests