Irradiation-Assisted Stress Corrosion Cracking

Transcription

1 Irradiation-Assisted Stress Corrosion Cracking Elin Toijer 1;2 Pär Olsson 1 Mats Jonsson 2 1 Reactor Physics KTH Stockholm 2 Applied Physical Chemistry KTH Stockholm SKC Symposium, Elin Toijer IASCC / 14

2 Outline 1 Background 2 Factors for IASCC 3 Main focus of the project 4 Surface Chemistry 5 Grain Boundary Segregation 6 Perspectives Elin Toijer IASCC / 14

3 Background Irradiation-Assisted Stress Corrosion Cracking (IASCC) Stress Corrosion Cracking - The premature cracking of an alloy in the presence of a tensil stress and a corrosive environment. Failure has been observed in nuclear reactor core components consisting stainless steel alloys that have received a significant neutron fluence in aggressive environments. The process is strongly accelerated by the irradiation and has thus been termed Irradiation-Assisted Stress Corrosion Cracking Gary S. Was Fundamentals of Radiation Material Science (2007) Elin Toijer IASCC / 14

4 Background IASCC Factors Loading - Stress intensity, Loading rate Material properties - Microstructure, Composition, Segregation characteristics, Stacking fault energy, Precipitation, Metallurgical condition, Yield strength Irradiation - Dose, Temperature, Flux NRC RIC Conf Water Chemistry - Radiolysis of water leading to the formation of free radicals Elin Toijer IASCC / 14

5 Background IASCC Factors Gary S. Was Fundamentals of Radiation Material Science (2007) Simultaneous effects of radiation, stress and high temperature water environment Elin Toijer IASCC / 14

6 Background Main Focus of this Project Surface Chemistry Grain Boundary Segregation NRC RIC Conf Elin Toijer IASCC / 14

7 Surface Chemistry Water Coolant Radiolysis M. Yang 2015 Highly reactive free radicals are formed as a consequence of the water radiolysis. Elin Toijer IASCC / 14

8 Surface Chemistry Processes at the Solid-Liquid Interface H 2 O 2 is one of the key reactants since it is one of the more long-lived products of radiolysis of water. At solid-liquid interfaces it reacts via: Non-catalytic processes Redox reactions will lead to corrosion and dissolution of the material Catalytic process Diffusion of H 2 O 2 to the metal surface will lead to surface reactions and its decomposition into OH and HO 2 The stability of the material is affected by the strongly oxidizing OH at the surface. Elin Toijer IASCC / 14

9 Surface Chemistry Catalytic decomposition of H 2 O 2 on stainless steel oxide surfaces Reactivity studies of H 2 O 2 towards the 304-L stainless steel alloy Elin Toijer IASCC / 14

10 Surface Chemistry Catalytic decomposition of H 2 O 2 on stainless steel oxide surfaces Quantification of the amount of OH formed through the reaction with Tris(hydroxymethyl)aminomethane and formation of formaldehyde Elin Toijer IASCC / 14

11 Radiation Induced Segregation at Grain Boundaries Radiation Modification of Stainless Steel Microstructure Any preferential association of defects with a particular component in defect diffusion will couple a net flux of the alloying element. Elin Toijer IASCC / 14

12 Radiation Induced Segregation at Grain Boundaries Change in Grain Boundary Concentration due to RIS Gary S. Was Fundamentals of Radiation Material Science (2007) Solute element profile across grain boundary in SS irradiated in a reactor to a dose of several dpa at about 300 o C Elin Toijer IASCC / 14

13 Perspectives Radiation induced corrosion studies - Experiments are to be preformed using a Cs-137 gamma source in order to investigate the overall mechanism of radiation induced corrosion of the steel in question. Modeling of crack tip growth - The effect of radiation induced defects on crack tip growth can thus be addressed using hybrid atomistic models, and provide input parameters to the fracture mechanics modelling code under development. Elin Toijer IASCC / 14

14 Thank you for your attention! Elin Toijer IASCC / 14