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Title: Intergranular fracture in irradiated Inconel X-750 containing very high concentrations of helium and hydrogen

In recent years, it has been determined that Inconel X-750 CANDU spacers have lost strength and material ductility following irradiation in reactor. The irradiated fracture behaviour of ex-service material was also found to be entirely intergranular. The heavily thermalized flux spectrum in a CANDU reactor results in transmutation of 58Ni to 59Ni. The 59Ni itself has unusually high thermal neutron reaction cross-sections of the type: (n, γ), (n, p), and (n,α). The latter two reactions, in particular, contribute to a significant enhancement of the atomic displacements in addition to creating high concentrations of hydrogen and helium within the material. Metallographic examinations by transmission electron microscopy (TEM) have confirmed the presence of helium bubbles in the matrix and aligned along grain boundaries and matrix-precipitate interfaces. He bubble size and density are found to be highly dependent on the irradiation temperature and material microstructure; the bubbles are larger within grain boundary precipitates. TEM specimens extracted from fracture surfaces and crack tips give direct evidence linking crack propagation with grain boundary He bubbles.
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [3] ;  [3] ;  [2] ;  [1]
  1. Atomic Energy of Canada, Limited, Chalk River, ON (Canada)
  2. McMaster Univ., Hamilton, ON (Canada)
  3. Idaho National Lab. (INL), Idaho Falls, ID (United States)
Publication Date:
OSTI Identifier:
1177655
DOE Contract Number:
AC07-05ID14517
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Nuclear Materials; Journal Volume: 457; Journal Issue: C
Publisher:
Elsevier
Research Org:
Idaho National Laboratory (INL), Idaho Falls, ID (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 Materials Science; Inconel Alloys; SPACERS; CANDU TYPE REACTORS; IRRADIATION; THERMAL NEUTRONS; Neutron Flux; Fracture Properties; DUCTILITY; GRAIN BOUNDARIES; Neutron Reactions; CROSS SECTIONS; TRANSMUTATION; NICKEL 58; NICKEL 59; Gamma Decay; Alpha Decay; HELIUM; Helium Embrittlement; HYDROGEN; Hydrogen Embrittlement; CONCENTRATION RATIO; TRANSMISSION ELECTRON MICROSCOPY; METALLOGRAPHY; Energy-Loss Spectroscopy; BUBBLES; PRECIPITATION; Interfaces; FRACTURES; CRACK PROPAGATION; CRACKS CANDU; EELS; EMBRITTLEMENT; INCOMEL X-750