Retrospective dosimetry based on niobium extraction and counting:VTT 's contribution to the RETROSPEC project

Within the European Commission 5th Framework RETROSPEC project several irradiated VVER-440 pressure vessel materials have been investigated in order to determine the feasibility of "retrospective" neutron dosimetry based on the analysis of 93mNb induced in structural reactor materials containing small amounts of niobium (about 50 ppm to 1 %). Methods for chemical separation of niobium and activity measurements, previously developed at VTT, were tested and refined and found accurate and reliable for typical cladding materials. For base material containing niobium only as an impurity the methods were not successful. The measured specific 93mNb activities were in good agreement with both calculated activities and other induced activities in the same materials and in dedicated dosimetry materials irradiated together with the investigated materials. The results of the three participants (NRG Petten, VTT and SCKoCEN) will be compared and summarised in a final report published by NRG Petten. The feasibility of different chemical separation and activity determination methods will be evaluated in a Code of Practice