Many historic nuclear facilities have reached the end of their lifetimes and are now being decontaminated and dismantled. Our institute has been working on innovative solutions for these huge and complex decommissioning projects. These include remote handling tools, in situ characterization, and the simulation of intervention scenarios. The latter is a valuable means of visualizing and gathering information on highly radioactive environments that humans cannot enter. Various treatment techniques can be compared and workers can be trained before operating on site. For the past 10 years, our institute has been developing a virtual reality tool that simulates all the key elements of a dismantling project, including the remote handling, and the accessibility of the site for humans, and the dose assessment associated. This tool allows all these parameters to be computed in a single interactive environment, allowing pre-defined scenarios to be verified and alternative solutions to be designed. This software is presented in the following paper; we here illustrate that it is particularly well-suited to dismantling projects. We also describe a first application of the tool to investigate radiological exposure scenarios; the STEL (a contaminated effluents treatment facility) decommissioning project is presented and the data preparation, configuration of the simulation, and results are described. The advantages of this software include its user-friendliness, responsiveness, speed, and usefulness for the preparation of complex dismantling operations. The perspectives of this project include the simulation in Virtual Reality of human interventions.