Speedup of Monte Carlo code MCACE for shielding analysis by parallel computer

In order to study the applicability of a parallel computer to Monte Carlo method, a Monte Carlo radiation shielding analysis code, MCACE, is examined and modified to execute on an experimental highly parallel computer, AP-1000. Despite the simple modifications without changing the original program flow, the MCACE code has achieved a speedup of 52 times on the AP-1000 equipped with 64 cell processors. The main causes of deteriorating the performance are non-parallelizable part of the codes which affects more with the increment of cell processors, and an idle time of cell processors which becomes significant when the number of particles is small. (author)