High Quality Content by WIKIPEDIA articles! RELAP5-3D is a simulation tool that allows users to model the coupled behavior of the reactor coolant system and the core for various operational transients and postulated accidents that might occur in a nuclear reactor. RELAP5-3D (Reactor Excursion and Leak Analysis Program) can be used for reactor safety analysis, reactor design, simulator training of operators, and as an educational tool by universities. RELAP5-3D was developed at Idaho National Laboratory to address the pressing need for reactor safety analysis and continues to be developed through the Department Of Energy and the International RELAP5 Users Group (IRUG) with over $3 million invested annually. The code is distributed through INL`s Technology Deployment Office and is licensed to numerous universities, governments, and corporations worldwide.