Oxidation and hydrogen pick-up of titanium alloys in primary coolant of pressurized water reactors: mechanisms, kinetics and impact on the mechanical behavior
Description
Titanium alloys have a low neutron activation, good mechanical properties and good corrosion resistance in common environment. They could be good candidates for nuclear Pressurised Water Reactor (PWR) primary circuit structure components. This study deal with their durability in primary water. Samples of three titanium alloys α (Ti CP), α +β (Ti 64) and metastable β (Ti10-2-3) were exposed to primary water at 300 C and 350 C for maximum durations of 11000 h and 1750 h, respectively. Based on SEM observations as well as XPS, XRD, GD-OES, MET-ASTAR and photo-electrochemistry analysis, a corrosion mechanism was proposed. It involves the inward growth of a dense TiO2 layer and its simultaneous dissolution into primary water as well as TiO2 and FeTiO3 oxide crystallites precipitation. Image analysis and mass uptake modelling indicated a maximum resulting metal matrix corrosion rate of 2.9 μm.year-1 at 300 C and of 18 μm.year-1 at 350 C. An abrupt decrease of the corrosion rate was noticed as FeTiO3 oxide crystallites surface covering fraction reached 100 %. Materials exposure to primary water also led to a hydrogen uptake which increased with both temperature and β phase ratio. Room temperature tensile tests were performed on primary water exposed specimens, hydrogen charged specimens and heat treated specimens. These tests highlighted a loss of ductility of Ti10-2-3 samples linked to their exposure to primary water. It could be due to the combined effects of both thermal ageing and hydride presence at α/β interfaces. Primary water exposure performed in laboratory had little effect on T40 and TA6V mechanical properties because hydrogen uptake was low in comparison with hydrogen concentration leading to the ductile-to-brittle transition. Long duration use of titanium alloys in primary water seems reasonable, provided that β phase is stable and that the surface/volume ratio of the considered component is low enough. (author)
Abstract (French)
Les alliages de titane possedent une faible activation neutronique, une bonne tenue mecanique et une bonne resistance a la corrosion de maniere generale. Ils sont susceptibles d'etre utilises comme materiau de structure de composants du circuit primaire des reacteurs nucleaires a eau pressurisee. Cette etude s'interesse a leur durabilite dans ce milieu. Des echantillons de trois alliages de titane α (T40), α +β (TA6V) et β metastable (Ti10-2-3) ont ete exposes au milieu primaire a 300 C et a 350 C pour des durees maximales de 11000 h et 1750 h respectivement. Des observations MEB et des analyses XPS, DRX, SDL, MET-ASTAR et de photoelectrochimie ont permis de proposer un mecanisme de corrosion impliquant simultanement la croissance interne et la dissolution dans le milieu d'une fine couche dense de TiO2 accompagnees de la precipitation de cristallites d'oxydes TiO2 et FeTiO3 liee a la saturation du milieu en hydroxydes. Il en resulte une consommation du metal estimee grace a des analyses d'images et a la modelisation des prises de masse en fonction du temps de 2,9 μm.an-1 a 300 C et de 18 μm.an-1 a 350 C au maximum. Cette cinetique de corrosion est fortement ralentie lorsque les cristallites de FeTiO3 recouvrent la totalite de la surface des echantillons. L'exposition au milieu primaire des materiaux implique aussi une prise d'hydrogene d'autant plus importante que la temperature et le taux de phase β sont eleves. Des essais de traction a temperature ambiante ont ete realises sur des eprouvettes exposees au milieu primaire et sur des eprouvettes chargees en hydrogene ou traitees thermiquement. Ces essais ont mis en evidence une baisse de ductilite du Ti10-2-3 liee a son exposition au milieu primaire. Cette baisse de ductilite semble resulter de l'effet couple du vieillissement thermique et de la presence d'hydrures aux interfaces α/β. L'exposition au milieu primaire realisee au laboratoire du T40 et du TA6V ne modifie que tres peu leurs proprietes mecaniques etant donne que les prises d'hydrogene sont faibles devant les concentrations en hydrogene de transition ductile/fragile. L'utilisation des alliages de titane en milieu primaire parait donc possible sur de longues durees sous reserve que leur phase β soit stable et que les pieces possedent un rapport surface/volume suffisamment faible pour limiter leur teneur en hydrogene.
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Additional details
Additional titles
- Original title (French)
- Oxydation et prise d'hydrogene d'alliages de titane en milieu primaire de reacteur a eau pressurisee: mecanismes, cinetiques et effet sur le comportement mecanique
Publishing Information
- Imprint Pagination
- 247 p.
- Report number
- FRCEA-TH--11315
INIS
- Country of Publication
- France
- Country of Input or Organization
- France
- INIS RN
- 51025461
- Subject category
- S36: MATERIALS SCIENCE;
- Resource subtype / Literary indicator
- Thesis
- Descriptors DEI
- AGING; CORROSION; DISSOLUTION; DUCTILITY; HYDRIDES; HYDROGEN; IRON COMPOUNDS; MECHANICAL PROPERTIES; PRECIPITATION; PRIMARY COOLANT CIRCUITS; PWR TYPE REACTORS; TENSILE PROPERTIES; TITANATES; TITANIUM ALLOYS; TITANIUM OXIDES
- Descriptors DEC
- ALLOYS; CHALCOGENIDES; CHEMICAL REACTIONS; COOLING SYSTEMS; ELEMENTS; ENERGY SYSTEMS; ENRICHED URANIUM REACTORS; HYDROGEN COMPOUNDS; MECHANICAL PROPERTIES; NONMETALS; OXIDES; OXYGEN COMPOUNDS; POWER REACTORS; REACTOR COMPONENTS; REACTOR COOLING SYSTEMS; REACTORS; SEPARATION PROCESSES; TENSILE PROPERTIES; THERMAL REACTORS; TITANIUM COMPOUNDS; TRANSITION ELEMENT ALLOYS; TRANSITION ELEMENT COMPOUNDS; WATER COOLED REACTORS; WATER MODERATED REACTORS
Optional Information
- Notes
- 186 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Also available from Bibliotheque universitaire de Sciences 915 avenue centrale Domaine universitaire 38400 Saint-Martin-d'Heres (France)