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A comprehensive re-evaluation of all neutron dosimetry results for the Loviisa reactors (WER-440, 2 units) started in 1992.
Revised and better validated neutron spectra, a refined semiem pirical approach utilizing the computer program PREVIEW , unified and up-dated nuclear data and refined and extended calibrations of the applied Liquid Scintillation Counter (LSC) for 93mNb activity measurements are applied. The kernel-based computer program PREVIEW makes it possible to take into account the detailed local irradiation history e.g. the influence of the calculated time-dependent axial flux changes during a cycle.
The main features of this re-evaluation are reported together with updated results for two IAEA-CRP surveillance chains (SC) denoted “4K” and “5K”.
The fluence (>1 MeV) estimates increased by +16 to +20% and the dpa estimates by +24 to +27% as compared to previous results. The largest changes, about +20% in the >1 MeV fluences, arose from the revised and better validated neutron spectra. The refined treatment in PREVIEW of time-dependent variations fin the axial flux distribution accounted for 0 to −5% in the fluence estimates based on 54Fe (0 to −16% for 58Co).
Nb, Fe, Ni, Ti and Cu dosimeters were used for validations of the calculated neutron spectra built into the PREVIEW kernel library.
The quality of the neutron fluence estimates could be signifi cantly improved by applying revised and better validated neutron spectrum shapes and by applying a refined semiempirical approach taking into account calculated axial flux changes during an operating cycle. The remaining significant uncertainties in the neutron spec trum shapes and cross sections emphasise the development and applica tion of additional and more reliable dosimeters for the lower fast neutron energies.
neutron spectrum, kernel methods, Nb dosimetry, power distribution, irradiation history, surveillance dosimetry
Senior research scientist, Technical Research Centre of Finland (VTT), Reactor Laboratory, ESPOO,
Research scientist, Technical Research Centre of Finland (VTT), Reactor Laboratory, ESPOO,