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| NKS Programme Area: | NKS-R | | Research Area: | Plant life management and extension | | Report Number: | NKS-427 | | Report Title: | WRANC, Warm Pre-Stressing – Validation of the relevance of the main mechanisms behind Warm Pre-Stressing in assessment of nuclear components | | Activity Acronym: | WRANC | | Authors: | Tobias Bolinder, Alexander Eriksson, Jonas Faleskog, Irene Linares Arregui, Martin Öberg, Bård Nyhus, | | Abstract: | The embrittlement of the reactor pressure vessel (RPV) due to extended operation can lead to difficulties in demonstrating safe operation beyond 40 years. But by utilizing the warm pre-stressing (WPS) effect in assessments, safe operation for continued operation beyond 40 years of the RPV can be shown. The practise of utilizing the beneficial WPS effect in RPV assessments have already been adopted in several European countries.
The WPS effect is the increase of the apparent brittle fracture toughness for a ferritic component when pre-loaded at a temperature in the ductile upper shelf region and then cooled to the brittle lower shelf region of the material fracture toughness transition curve.
Within this research project the main mechanisms behind WPS and their importance relating to RPV assessments are studied using both experiments and numerical methods. For a realistic load case the most influenceable mechanism behind the WPS effect is shown to be the change in yield strength due to lowering of the temperature. Furthermore, the actual load path can be considered path independent during the unloading/cooling phase assuming that the load is not increased during cooling. The results also clearly show that for a realistic load case the deactivation of initiation sites is an active mechanism. | | Keywords: | Warm pre-stressing, Cleavage fracture, Failure probability, Fracture toughness, Fracture experiments, Non-local probabilistic model | | Publication date: | 07 Oct 2019 | | ISBN: | ISBN 978-87-7893-517-5 | | Number of downloads: | 1669 | | Download: |  NKS-427.pdf |
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