Elemental distribution in a decommissioned high Ni and Mn reactor pressure vessel weld metal from a boiling water reactor

•Weld metal from a decommissioned BWR was analysed by atom probe tomography.•There were no well-defined nanometre Ni-Mn-Si-Cu clusters.•Early stage of clustering of Ni atoms was indicated by radial distribution functions. In this paper, weld metal from unique material of a decommissioned boiling water reactor pressure vessel is investigated. The reactor was in operation for 23 effective full power years. The elemental distribution of Ni, Mn, Si and Cu in the material is analysed using atom probe tomography. There are no well-defined clusters of these elements in the weld metal. However, some clustering tendencies of Ni was found, and these are interpreted as a high number density of small features. Cu atoms were found to statistically be closer to Ni atoms than in a fully random solid solution. The impact of the non-random elemental distribution on mechanical properties is judged to be limited.