Irradiation effects on toughness behaviour and microstructure of VVER-typepressure vessel steels

The irradiation sensitivity and the annealing behaviour were studied on sev en different heats from VVER 440 and VVER 1000-type reactor pressure vessel steels. The specimens were irradiated at the Rheinsberg prototype VVER 2 r eactor to mean neutron fluences between 43 and 127.6 x 10(18) n/cm(2) [E > 0.5 MeV]. Toughness and strength properties were determined and the micro s tructure was analysed using the small angle neutron scattering (SANS) techn ique. There is an obvious correlation between the irradiation-induced chang es of transition temperature, hardness and volume fraction of microstructur al features of radii up to 2 mn. The main parameters of influence are the n eutron fluence and the nickel content. The nickel-containing V-VER 1000-typ e pressure vessel steel is more sensitive to irradiation than the VVER 440- type steel which has a low nickel content. For the latter, the sensitivity to radiation embrittlement depends on the copper and phosphorus contents. A nnealing at 475 degreesC (100 h) reduces the irradiation effect but not com pletely in every case. (C) 2001 Elsevier Science B.V. All rights reserved.