Electrical resistivity response to annealing of VVER440-type weld material in irradiated, post-irradiation annealed and re-irradiated conditions

In the work resistivity response to annealing of weld 501 materials in various irradiationannealing-reirradiation conditions was measured by using isothermal annealing. Annealing temperature of 420°C was chosen in order to get relatively slow annealing response and to be able to follow also short time behaviour. Resistivity changes are relatively small and hence relatively much time was allocated to electronic measuring technique. Resistivity gets the response from deformation of the lattice, which in the current work originates from foreign atoms dissolved in the matrix. The irradiated materials with irradiation as the final state (-AI) show increase of resistivity by 1% after the first 5 minutes and the resistivity value remains constant up to an annealing time of 25 minutes, where after it starts to grow relatively fast. Resistivity of the annealed conditions (U, lA, IAIA) increase by 0.3% during the first 5 minutes, which may not be a real effect. Resistivity of the annealed conditions remains constant up to an annealing time of 100 minutes, where after resistivity starts to grow but clearly slower than in the irradiated conditions (-AI). This early behaviour is related to dissolution of small size copper rich precipitates (CRP). The subsequent long term increase of resistivity is assumed to be related to dissolution of larger CRPs. The irradiatedannealed condition materials have a wide size spectrum of CRPs, which allows further increase of resistivity. The long term increase of resistivity up to annealing time of 9800 minutes may be an experimental artefact, because also resistivity of the un-irradiated condition increases, which is not expected. The cause for the artefact is assumed to be the electrolytic plating of the wire contact, which oxidizes during long term annealing.