Oxide films in high temperature aqueous environments

Timo Laitinen, Kari Mäkelä, Timo Saario, Martin Bojinov

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

    Abstract

    The evaluation of modified water chemistries as well as of the effects of increased power output in nuclear power plants is associated with a need to understand their effect on occupational dose rates and on environmentally assisted cracking as well as other types of corrosion of structural materials. Occupational dose rates are due to activity build-up on the primary circuit components, which in turn depends on the dissolution, transport, deposition and incorporation of the activated corrosion products in the oxide films formed on material surfaces. Accordingly, activity build-up is influenced by the electrochemical and electric properties of the oxide films and by the water chemistry of the coolant. Concerning different types of corrosion, it can with good reason be assumed that both the oxidation reaction related to corrosion (e.g. crack growth) as well as the coupled cathodic reaction involve steps in which charged species are transported through the oxide films formed on material surfaces either within the crack or on surfaces exposed to the bulk coolant. In spite of the significant work of Robertson [1] and others, it can be stated that a sufficient characterisation and a satisfactory model for the electrochemical behaviour and electric properties of the oxide films formed in nuclear power plants are not available. More experimental support is needed concerning especially the preferential paths and driving forces for ion transport as well as the nature of mobile species or defects. The lack of sufficient understanding has complicated the assessment of the applicability and possible side-effects of e.g. noble metal water chemistry and the injection of zinc as a means to prevent the uptake of activated corrosion products into corrosion films. The long-term aim of the work perfomed within the present research program is to minimise the risk of activity build-up, environmentally assisted cracking (EAC) and other types of corrosion, as well as to be prepared for the evaluation and introduction of modified water chemistries in Finnish power plants. To achieve this, the focus of this project is on understanding the mechanism of the incorporation of radioactive species into the different layers of the oxide film, as well as the transport phenomena contributing to stress corrosion cracking and other corrosion phenomena. This requires modelling the electrochemical behaviour and electrochemical and electric properties of oxide films formed on iron- and nickel-based alloys in relevant conditions. The project is divided into four sub-projects as follows: · Behaviour of oxide films in plant conditions · Oxide films in simulated plant conditions · Modelling the processes in oxide films on metal surfaces · Development of electrochemical techniques for high-temperature measurements
    Original languageEnglish
    Title of host publicationRATU2: The Finnish Research Programme on the Structural Integrity of Nuclear Power Plants
    Subtitle of host publicationSynthesis of achievements 1995-1998
    Place of PublicationEspoo
    PublisherVTT Technical Research Centre of Finland
    Pages145-176
    ISBN (Electronic)951-38-5264-4
    ISBN (Print)951-38-5263-6
    Publication statusPublished - 1998
    MoE publication typeA4 Article in a conference publication
    EventRATU2: The Finnish Research Programme on the Structural Integrity of Nuclear Power Plants: Synthesis of achievements 1995−1998 - Espoo, Finland
    Duration: 7 Dec 19987 Dec 1998

    Publication series

    SeriesVTT Symposium
    Number190
    ISSN0357-9387

    Conference

    ConferenceRATU2: The Finnish Research Programme on the Structural Integrity of Nuclear Power Plants
    CountryFinland
    CityEspoo
    Period7/12/987/12/98

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    Laitinen, T., Mäkelä, K., Saario, T., & Bojinov, M. (1998). Oxide films in high temperature aqueous environments. In RATU2: The Finnish Research Programme on the Structural Integrity of Nuclear Power Plants: Synthesis of achievements 1995-1998 (pp. 145-176). VTT Technical Research Centre of Finland. VTT Symposium, No. 190 http://www.vtt.fi/inf/pdf/symposiums/1998/S190.pdf