Development of oxide model for activity build-up in LWRs: Plant data review

Klas Lundgren, Iva Betova, Martin Bojinov, Petri Kinnunen

    Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientific

    Abstract

    A total of 16 Scandinavian LWRs, 11 BWRs, 3 PWRs and 2 WWERs, have been included in a data review where the interaction between the reactor coolant and the activity uptake in the primary system oxides formed have been studied. The data are intended to be used in the validation of an oxide model developed within the ANTIOXI project. The data evaluation of activity buildup during reactor operation is performed with a simplified model assuming an adsorption step on outer layer of the oxide followed by a diffusion process into the layer. An alternate model for PWRs and WWERs has also been applied for certain nuclides assuming that the shutdown activity transient in the coolant is the main contributor to the activity buildup. The following main conclusions were obtained: ? The activity buildup for most activated corrosion products, e.g. the cobalt isotopes, is occurring during reactor operation, i.e. with an adsorption step followed by a diffusion process into the oxide. The diffusion process is supposed to quite similar between different reactor environments and the considerable differences seen in different reactor environments are likely to be due to different adsorption rates. ? The highest adsorption rates are seen in PWR and WWERs environments. The analyses shows that a considerable consumption of certain radionuclides, e.g. Co-58, occurs in long, hot stainless steel sampling lines in such reactors, and reactor water activity measurements are recommended to be performed via cold sampling lines. ? BWR plants show lower adsorption rates, likely due to operation at lower pH than the PWRs and WWERs. The BWR adsorption rates are affected by operation conditions; the highest rates are seen in HWC plants without zinc injection, and the lowest rates in NWC plants that are very low in feedwater iron. Zinc has a reducing effect on adsorption rate in all types of reactors. ? The activity build-up in PWRs and WWERs of some other nuclides, Sb-122, Sb-124 and possibly Ag-110m, seems to be controlled by the shutdown transient rather than normal operation conditions. Some differences in this type of activity buildup between plants, as well as year-by-year variations, are observed, e.g. the adsorption in the WWER plants is significantly higher than in the PWR plants.
    Original languageEnglish
    Title of host publicationInternational Conference on Water Chemistry in Nuclear Reactor Systems
    Number of pages8
    Publication statusPublished - 2008
    MoE publication typeB3 Non-refereed article in conference proceedings
    EventInternational Conference on water chemistry of nuclear reactor systems - Berlin, Germany
    Duration: 15 Sep 200818 Sep 2008

    Conference

    ConferenceInternational Conference on water chemistry of nuclear reactor systems
    CountryGermany
    CityBerlin
    Period15/09/0818/09/08

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    Lundgren, K., Betova, I., Bojinov, M., & Kinnunen, P. (2008). Development of oxide model for activity build-up in LWRs: Plant data review. In International Conference on Water Chemistry in Nuclear Reactor Systems