Abstract: The In-vessel retention (IVR) is an important mitigation strategy in severe nuclear accidents. During IVR conditions, the tensile and compressive stress states both exist along the thickness direction of the reactor pressure vessels (RPV). Therefore, the tensile and compressive creep behavior of the SA-508 Gr.3 Cl.1 steel should be discussed to guarantee the structure integrity of the RPV in IVR conditions. Based on this, tensile and compressive creep tests of the SA-508 Gr.3 Cl.1 steel are conducted, and the differences of creep behavior and creep deformation mechanism between tensile and compressive creep are analyzed. Results indicate that the primary and secondary creep regimes of the compressive creep are consistent with that of the tensile creep, while the tertiary creep stage is not observed for compressive creep test. The dominant creep deformation mechanism for tensile creep is dislocation climb within the stress levels studied, while that for the compressive creep changes from dislocation climb to grain boundary sliding or vacancy diffusion with the decrease of the stress. The tensile creep plays a more important role on the evolution of the sub-grain than the compressive creep, which may be induced by the transformation of creep deformation mechanism.

Key words: IVR, tensile creep, compressive creep, creep deformation mechanism, sub-grain