REDISTRIBUTION OF RESIDUAL WELDING STRESSES IN IN-VESSEL CORE BARREL OF WWER-1000 REACTOR DURING OPERATION O.V. MAKHNENKO, E.A. VELIKOIVANENKO and I.V. MIRZOV E.O. Paton Electric Welding Institute, NASU 11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: office@paton.kiev.ua Reactor baffle is subjected to high radiation doses that results in its swelling and change of form in operation. Inside pressure of baffle on core barrel creates additional stresses in zone of contact. Residual welding stresses can also significantly effect a level of stressed state of core barrel wall, that should be considered in estimation of working capacity of vessel internals for extension of WWER-1000 reactor service life. Thus, a relevant task is an estimation of stressed state of in-vessel core barrel in area of its contact with baffle, in particular, when place of contact coincides with welded joint zone. Aim of present work is an investigation of stressed state in zone of welds of in-vessel core barrel of WWER-1000 reactor during operation considering radiation swelling and contact interaction of baffle and core barrel. A problem was solved by 2D finite element method using current mathematical models of radiation swelling and change of mechanical properties of 08Kh18N10T steel. Calculations show that effect of only temperature deformation does not promote high stresses in the core barrel wall, but degree of stress redistribution in it due to radiation swelling depends on residual welding stresses. Circumferential and axial stresses, caused by contact interaction of core barrel with baffle, have the largest impact on stressed state of the in-vessel core barrel wall in course of 60 years of operation. Stresses in the in-vessel core barrel welds at the end of extended operation period (60 years) are close to the values of yield strength of irradiated material. Residual welding stresses can significantly effect the level of stressed state of the core barrel wall, that should be considered in estimation of working capacity of vessel internals at extension of service life of WWER-1000 reactor. 4 Ref., 2 Tables, 11 Figures. Keywords: in-vessel core barrel, WWER-1000 re- actor, vessel internals, residual welding stresses, irradia- tion, 08Kh18N10T steel, life extension In-vessel core barrel of WWER-1000 reactor is a welded cylinder structure manufactured from austenite steel 08Kh18N10T. Location of the core barrel in reactor vessel and its drawing are given in Figure 1. In-vessel core barrel has external radius 1805 mm and wall thickness 60 mm at the level of setting of core baffle. Reactor baffle is subjected to high radiation doses, that results in its swelling and change of form in operation. Gap between baffle rings and core barrel makes 2.5 mm under initial condition. Contact of baffle and in-vessel core barrel during operation should be taken into account based on calculation results [1]. Inside pressure of baffle on core barrel creates additional stresses in zone of contact. Residual welding stresses can also significantly effect a level of stressed state of a core barrel wall, that should be considered in estimation of working capacity of vessel internals (VI) for extension of WWER-1000 reactor serv- ice life. Thus, estimation of stressed state of the in-vessel core barrel in area of its contact with baffle, in particular, when place of contact co- incides with welded joint zone, is a relevant task. It is necessary to note that the core barrel wall is also subjected to radiation swelling, however, damaging dose is an order of magnitude less than that in the baffle. Aim of present work is investigation of stressed state in zone of the welds of in-vessel core barrel of WWER-1000 reactor during op- eration considering radiation swelling and con- tact interaction of baffle and core barrel. Initially, this problem was studied in work [2]. Present study improves mathematical models of radiation swelling and mechanical properties of VI material, specifies values of volumetric heat generation and damaging dose in the core barrel, develops numerical model for calculation of stress-strain state in contact of baffle and core barrel as well as simulates residual welding stresses in the welds of in-vessel core barrel. Procedure of investigations. Series of prob- lems was solved for achievement of stated aim. Initially, the core barrel was considered in a free state without consideration of its contact with baffle. It was done in order to understand in what way operating temperature fields and ra- © O.V. MAKHNENKO, E.A. VELIKOIVANENKO and I.V. MIRZOV, 2014 8 11/2014