The European Commission Joint Research Centre (JRC) site in Ispra (Italy) hosts eight nuclear installations, including two research reactors and a cyclotron, which are currently under decommissioning. Having performed research on digital tools best suitable to support decommissioning, EC/JRC has developed the tool 3D Information Management System (3DIMS) to assist all the phases of the decommissioning on the site. Its main purpose is to keep the description of a large complex facility updated, which has several decades of active duty and it is not always guaranteed to maintain up-to-date CAD drawings especially as the nuclear facilities were commissioned in the pre-computer era. In essence, the software bundle reconstructs a 3D environment of the site, allowing users to track the tasks progression, update the status of resources and virtually explore critical areas reducing hazardous expositions. The core of the 3DIMS is the digital virtualization of a site thanks to integration of multiple 3D laser scans and resulting point cloud with high-resolution spherical photographic images. Similarly to a BIM system, additional data relevant for decommissioning or items of particular importance, regions of interest (ROIs), dose/contamination maps and relevant documents are mapped onto the environment. Many additional capacities have been developed to facilitate various aspects of the activity, such as virtual visualization of the site using VR-goggles, 3D data extraction and scene change detection. 3DIMS is composed of two software components: Dashboard and Viewer. The Viewer software allows the user to visualize, navigate, add document tags, track objects and to take dimensional measurements in the reconstructed site. The Dashboard software provides a technician with all the tools to maintain the site, add new data and manage items and tags that are instantly made available for the Viewer Software using the common database. The paper presents in detail the 3DIMS software and how the tool is able to facilitate the overall decommissioning activity including use-cases from the JRC/Ispra site.