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: firstname.lastname@example.org
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.
WWER-1000, reactor internals, enclosure, residual technological stresses, brittle fracture resistance, postulated
cracks, stress intensity coefficient, normal operating conditions
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