Investigation of 15kh2NMFAA steel and weld after irradiation in the “Korpus” facility on the RBT-6 reactor D. Kozlov, V. Golovanov, V. Raetsky, G. Shevlyakov, V. Lichadeev, M. Tikhonchev

Object: -Determination of radiation embrittlement for weld and base metal through the wall thickness of WWER-1000; - Evaluation of radiation condition influence on the damage and mechanical properties of vessel steel

Materials: Weld, Base metal, Heat Affected Zone, Vessel of WWER-1000/320, the shells after complete treatment. Experimental shell 15kh2NMFAA steel (class 0) with low nickel content (0,75%Ni ) Irradiation condition: The specimens irradiation was carry out in the “Korpus” facility on the RBT-6 reactor. Fluence - up to 11×10 19 cm -2 Irradiation temperature - 290±15 0 C

Chemical composition CSiMnCrNiMoVCuSPCoSbSnAs 15kh2nmfa class kh2nmfa class kh2nmfa class Weld metal

Core Location of capsule in the facility and specimens in the capsule Level Core Central Plane I II III V IV VI Specimens Charpy specimens on the third and fourth level Thickness of the specimens block 60 or 70 mm

Energy ( J) Temperature ( 0 C) deviation changes  T F Analysis results after irradiation of capsule with rotation

Deviations of Charpy tests results from fitting curve. Dependence from irradiation place. а) For Base metal and HAZ b) For weld а) b)b) Deviation ( J) Distance from capsule center, mm

а) b)b) Deviations of Charpy tests results from fitting curve. Dependence from irradiation temperature. а) For Base metal and HAZ b) For weld Deviation ( J) Irr. Temperature ( 0 C)

Dependence  T F from neutron fluence for 15kh2NMFAA steel after irradiation of “thick” assemblies : class 0 (○); class 1 (■); class 1 (×);  T F = A f (F/F 0 ) 1/3 with A f =9 о С ( ); Base metal Fluence

A F =20 A F =16.5 A F =11.5 Fluence ×10 19 см -2 (Е>0.5 МeV) ΔT F, 0 C Dependence  T F from neutron fluence for weld metal after irradiation of “thick” assemblies Weld metal

Figure 3 – Role of Mn in embrittlement of high Ni welds (VVER-1000 surveillance data)

Radiation energy release (а) and flux of thermal neutrons (b) through the specimens block thickness under irradiation with rotation Irr. Heating(W/g) Distance from capsule center, mm Thermal neutron flux(1/cm 2 c)

1. Irradiation of the WWER-1000 vessel materials was carried out using the capabilities of the KORPUS facility. Irradiation of the reactor wall was simulated in the experiment including changes of neutron flux and spectrum. 2.  T F for base metal does not exceed С, for weld metal С at fluence corresponding to years of the WWER-1000 operation. 3. The dependences of radiation embrittlement obtained under the radiation flux attenuation do not correspond to the normative dependence, where  T F depends on neutron fluence with energy more than 0,5 MeV. For base metal there is difference from the surveillance data. The change of the radiation flux characteristics effects the embrittlement degree. 4. One of the possible causes of the embrittlement degree change under irradiation of the “thick” assemblies is the change of thermal neutron flux. However, the determination of the quantitative contribution of each type of ionizing radiation requires additional experiments. Conclusions