The Paton Welding Journal, 2022, №08



2022 №08 (06)

DOI of Article 10.37434/tpwj2022.08.07

2022 №08 (01)

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The Paton Welding Journal, 2022, #8, 46-54 pages

Evaluation of brittle fracture resistance of WWER-1000 reactor enclosure during long-term service, taking into account the residual technological stresses

O.V. Makhnenko, S.M. Kandala

E.O. Paton Electric Welding Institute of the NAS of Ukraine 11 Kazymyr Malevych Str., 03150, Kyiv, Ukraine. E-mail: office@paton.kiev.ua

Abstract
The need to take into account the residual technological stresses (RTS) in the material of the enclosure of reactor internals (RI) of NPP power units of WWER-1000 type, resulting from technological processes of welding and postweld heat treatment at extension of safe service period beyond the design life is substantiated. The influence of RTS on the stress-strain state of the enclosure, as well as brittle fracture resistance (BFR) of the material in service was determined. It is shown that an essential redistribution of axial and hoop stresses in the enclosure is observed due to allowing for RTS, namely of the zone of high tensile stresses, which under normal operation conditions (NOC) move into the internal volume of the enclosure from its outer surface, while the area of these zone becomes larger. Such a redistribution of stresses has an essential influence on the level of stress intensity coefficient on the contour of the cracklike defects. The most critical areas, in terms of brittle strength, form in thei nner volume of the enclosure, whereas the dimensions of subsurface elliptical crack, which is postulated, can be increased due to widening of the tensile stress zone, thus promoting greater conservatism of BFR assessment. Moreover, taking RTS into account allows a significant lowering of conservatism at assessment of enclosure BFR under NOC for surface semielliptic cracks, located on the enclosure outer surface, where residual compressive stresses arise during manufacture. Obtained results allow more precise determination of enclosure zones, prone to brittle fracture of the material under NOC that is important for improvement of the approaches to determination of RI of WWER-1000 type reactor. Ref. 9, Tabl. 2, Fig. 9.
Keywords: WWER-1000, reactor internals, enclosure, residual technological stresses, brittle fracture resistance, postulated cracks, stress intensity coefficient, normal operating conditions

Received: 30.05.2022
Accepted: 17.10.2022

References

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