[en] The National Research Universal (NRU) Reactor permanently shut down on March 31, 2018 after over 60 years of service. The NRU reactor and its ancillary buildings are now being readied for decommissioning. The preparation for decommissioning will begin with the deactivation of NRU systems and the ancillary buildings. The focus of this paper will be to document some of the experiences of deactivating the Effluent Heat Recovery System (EHRS) and Building 440 which houses the Emergency Cooling Water Supply system for NRU. Both the EHRS and Building 440 are legacy and obsolete. The deactivation of the EHRS and Building 440 encountered a number of operational challenges such as lapses in maintenance and housekeeping, loss of motivation, and issues with work plans. Organizational challenges, lack of knowledge and expertise, lack of support, and conflicting intra-organizational priorities, are believed to influence the operational challenges. The impact of challenges encountered on the project is reviewed with an emphasis on Project Management and people. 'Lessons learned' based on the experiences of the authors is provided detailing, amongst other things, the importance of people in the success of deactivating the NRU reactor and its ancillary buildings. (authors)