Modelling grain boundary cavity growth in irradiated Nimonic PE16

Experimental evidence for the growth and coalescence of cavities nucleated at grain boundary helium bubbles in Nimonic PE16 is presented. A model for creep constrained cavity growth in this alloy is developed and applied over a range of stresses covering in-reactor applications and post-irradiation test conditions. It is shown that low failure strains are the direct result of cavity nucleation at closely spaced helium bubbles. Both the strain and time to failure decrease as the grain size increases. The high creep strength of PE16 is of benefit in restricting cavity growth rates. (orig.)