При выполнении работ по продлению ресурса внутрикорпусных устройств реактора ВВЭр-1000 на втором энергоблоке Южноукраинской аЭс возник вопрос о влиянии остаточных сварочных напряжений в выгородке на величину радиационного распухания. В институте электросварки им. е.о. Патона НаНУ, г. Киев, разработана и реализована математическая модель определения остаточного напряженно-деформированного состояния выгородки реактора ВВЭр-1000 при электрошлаковой сварке с последующей термообработкой, а также модель расчета радиационного распухания выгородки с учетом радиационной ползучести. По результатам математического моделирования можно сказать, что напряженное состояние выгородки после 60 лет эксплуатации, посчитанное с учетом остаточных сварочных напряжений, близко к результатам, полученным по модели без учета сварки. В данной работе рассматривается релаксация остаточных сварочных напряжений в выгородке ВВЭр-1000 под действием радиационного облучения и выводится зависимость их величины от времени в процессе эксплуатации. библиогр. 15, табл. 3, рис. 11.
Reactor pressure vessel internals have a multipurpose task that is mainly to ensure optimal coolant flow, to form and support the active core, and to shield, guide, and support the in-core instrumentation. The VVER-1000 reactor internal components are in an environment with high radiation doses, boric (H3BO3) acid dissolved in water, high temperatures, and gamma heating. These effects, together with the high moderator flow rate, form strongly inhomogeneous temperature fields in vessel internal components and induced internal stresses. In the case of the VVER-1000 reactor baffle, the main potential limiting factor for prolongation of the reactor operational lifetime is a void swelling of the Russian-type titanium stabilized stainless 08Cr18Ni10Ti steel used to construct the baffle surrounding the active core. This paper presents a VVER-1000 mock-up model validation for the thermal neutron and gamma fluence in the region of the baffle and a precise gamma heating as well as a displacement-per-atom estimation in a one-sixth section of the reactor baffle. Obtained results on the mock-up are scaled to the VVER-1000 nominal power and used in ABAQUS code for void swelling estimation.
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.
The question of effect of baffle residual welding stresses on radiation swelling value has appeared in course of works on life extension of WWER-1000 reactor internals at the second power generating unit of the South-Ukrainian NPP. The E.O. Paton Electric Welding Institute has developed and realized a mathematical model for determination of residual stress-strain state of WWER-1000 reactor baffle in electroslag welding with further heat treatment as well as a model for calculation of baffle radiation swelling taking into account radiation creep. It can be stated based on the results of mathematical modelling that the baffle stressed state after 60 years of operation, calculated taking into account residual welding stresses, is close to the results received using the model without welding. This work studies relaxation of residual welding stresses in the WWER-1000 baffle under effect of irradiation and works out their in-service value-to-time dependence. 15 Ref., 3 Tables, 11 Figures.
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