Maintaining the soundness of nuclear reactors is a major concern for scientists, engineers, and the general public. Among many factors, “cavitation erosion” of cooling system components is a significant mechanism for long-term degradation in nuclear power plants. Cavitation occurs when a liquid experiences rapid change in pressure that creates low-pressure cavities within the liquid. These cavities, or cavitation bubbles, cause stress when they collapse and hit a solid surface, and therefore cause deterioration of the surfaces of materials.

However, cavitation bubbles also provide benefits.  Nanobubbles are used to prevent Stress Corrosion Cracking (SCC)—the biggest reason the lifetime of nuclear reactors is shortened. When nanobubbles form, they create low-pressure regions, but when they collapse near a solid surface, the result is the creation of high-pressure areas that relieve the tensile stresses that cause SCC in the material.

To get a molecular-level understanding of nanobubble collapse near a solid surface, Priya Vashishta and his colleagues, Rajiv Kalia and Aiichiro Nakano, at the University of Southern California (USC) are using Intrepid, the IBM Blue Gene/P system at the Argonne Leadership Computing Facility (ALCF), to simulate and unravel the complex mechanochemistry problem. The 1-billion-atom simulation is feasible because it runs efficiently on 163,840 cores, the full Intrepid system. The goal of this nanobubble collapse simulation is to understand molecular processes to improve both the safety and longevity of nuclear reactors. The efficiency with which these simulations run on Intrepid is the result of successful work conducted by the USC group using an ALCF Discretionary allocation in 2010.