In the event of a postulated severe accident, fission products may leak into the reactor building through the containment wall, exerting a radiological impact on the emergency response team as they are tasked with performing mitigative missions. It is thus important to estimate the potential radiological consequences of the mission before taking action so that an optimized plan can be devised to avoid putting the team in harm’s way unintentionally. Some of the most well-known accident simulation codes were attempted to do the estimation, but were found to be too time consuming to get the results, making them not suitable for emergency use. The problem evidently arises from the fact that there are too many (about 200) compartments in a typical reactor building.

In this study, the software REMADA is developed to simulate fission product dispersion in a reactor building (with about 200 compartments) within a reasonable timeframe, and to estimate the radiation doses to those who are carrying out mitigative missions in the reactor building. The results show that the software is not only fast, but also informative, to provide support for well-informed emergency decision making.