This publication reports on the DACCORD project, which supports Member States in preparing preliminary cost estimates for the decommissioning of research reactors. The report is of particular benefit to programmes with limited decommissioning experience. Costing projects for the decommissioning of research reactors can be broad in scope with many possible inputs and influences that require due consideration in developing the estimate. The publication provides information on unit factors for research reactor decommissioning and a basis for estimating uncertainties and contingencies and for assessing the impact of decommissioning planning and characterization activities. It also addresses the use of the CERREX?D2 (Cost Estimate for Research Reactors in Excel) software code, developed by the IAEA to enable non?specialist users to develop preliminary cost estimates for decommissioning.