Microstructural Characterization of Irradiated Baffle Bolts Removed from a Finnish VVER and a French PWR

Janne Pakarinen, Ulla Ehrnstén, Heikki Keinänen, Wade Karlsen

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

Abstract

Two baffle bolts, one from a Finnish VVER and one from a French PWR, were examined by using analytical transmission electron microscopy (TEM). The examined VVER bolt was removed from the plant due to indications found in non-destructive examinations (NDE). During the removal of the bolt, it was found that the bolt washer had been inappropriately spot welded to the shielding plate during assembly. Destructive investigations showed that the VVER bolt had two large intergranular cracks, and the TEM samples were prepared from the material adjacent to those cracks. The PWR bolt had not failed, although cracks in similar bolts had been found previously. The VVER bolt was made of solution annealed titanium stabilized 0X18H10T (corresponding to Type AISI 321) and had accumulated a maximum fluence of about 2.9 dpa. The fluence for the cold-worked AISI 316 PWR bolt was estimated to be about 15 dpa. Both the examined bolts showed a clear radiation induced segregation of alloying elements at the grain boundaries (GB-RIS), presence of dislocation loops, formation of precipitates, and linear deformation microstructures. Additionally, voids were found from the PWR bolt and a high density of dislocations in the VVER bolt. Finite element modeling (FEM) was performed for the VVER bolt to examine the stress state of this particular bolt. Most importantly, the results indicate that it is not possible to set a limit for IASCC based solely on the fluence as the stress state of the bolt and gradients in local chemistry also play a critical role.
Original languageEnglish
Title of host publicationProceeding of the 16th International Conference on Environmental Degradation of Materials in Nuclear power Systems
Subtitle of host publicationWater Reactors 2013
PublisherNational Association of Corrosion Engineers (NACE)
Pages994-1007
Volume1
ISBN (Print)978-1-5108-1923-8
Publication statusPublished - 2013
MoE publication typeA4 Article in a conference publication
Event16th International Conference on Environmental Degradation of Materials in Nuclear power Systems - Water Reactors - Asheville, North Caroline, United States
Duration: 11 Aug 201315 Aug 2013

Conference

Conference16th International Conference on Environmental Degradation of Materials in Nuclear power Systems - Water Reactors
Country/TerritoryUnited States
CityAsheville, North Caroline
Period11/08/1315/08/13

Keywords

  • baffle bolts
  • IASCC
  • transmission electron microscopy
  • finite element modeling

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