CERT researchers have already computed the distribution of neutron radiation using our massively parallel transport computer code, running it with high efficiency on 400,000 processor cores. We ran our code on the NNSA’s Sequoia supercomputer at Lawrence Livermore National Laboratory, which was the second fastest supercomputer in the world at that time (that machine is currently ranked 3rd on the Top 500 list of the world’s fastest supercomputers).Exascale computers are planned for the future and will consist of many millions of processors and be capable of executing on the order of 1018 floating point operations per second. The fastest computers currently in existence execute roughly 1016 floating point operations per second and use enormous amounts of power.