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

The irradiation sensitivity and the annealing behaviour were studied on seven different heats from VVER 440 and VVER 1000-type reactor pressure vessel steels. The specimens were irradiated at the Rheinsberg prototype VVER 2 reactor 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 structure was analysed using the small angle neutron scattering (SANS) technique. There is an obvious correlation between the irradiation-induced changes of transition temperature, hardness and volume fraction of microstructural features of radii up to 2 mn. The main parameters of influence are the neutron fluence and the nickel content. The nickel-containing V-VER 1000-type 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. Annealing at 475 degreesC (100 h) reduces the irradiation effect but not completely in every case. (C) 2001 Elsevier Science B.V. All rights reserved.