Experimental study of the boron and air effects on lodine transport in the primary circuit during a severe nuclear accident

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Abstract

In case of a severe accident on a nuclear reactor, radioactive iodine may be released into the environment, impacting significantly the source term. Determination of the amount released, and of the physical state of iodine (gaseous form or solid aerosol form), is thus a major issue, regarding the improvement of the accident management and mitigation measures. An experimental study has been launched at VTT investigating the behaviour of iodine on primary circuit surfaces during a severe nuclear accident. From the caesium iodide, used as precursor material, studies were conducted in order to highlight the effects of carrier gas composition (varying H2/H2O molar ratio), especially the behaviour under presence of air, and the presence of boron and/or caesium hydroxide. The study investigated, first, the influence of boron presence on the caesium iodide behaviour at 650°C under three atmospheres: Ar/H2O, Ar/H2O/H2 and Ar/Air. Experiments showed that the transport of gaseous iodine is enhanced by the presence of boron, because of the formation of a glassy caesium borate compound in the crucible, suggesting that a reaction between condensed caesium iodide and boron is possible at the surface of primary circuit in these conditions. The amount of steam present in the carrier gas, more than the air, seems to have an influence on the caesium borate formation. Then, experiments were performed with a mixture of CsI, CsOH and B2O3, in the aim to have an initial molar Cs/I ratio higher than 1. Preliminary results have shown that the amount of gaseous iodine is higher than the iodine particles. Presence of boron still tends to favour the formation of gaseous iodine however; the competitive reaction with caesium hydroxide may result in the formation of a diffusional barrier that prevents contacts between boric acid and the caesium iodide.
Original languageEnglish
Title of host publication2016 International Congress on Advances in Nuclear Power Plants (ICAPP 2016)
PublisherAmerican Nuclear Society ANS
Pages752-758
ISBN (Print)978-0-89448-725-5
Publication statusPublished - 2016
MoE publication typeA4 Article in a conference publication
EventInternational Congress on Advances in Nuclear Power Plants, ICAPP 2016 - Hyatt Regency San Francisco, San Francisco, United States
Duration: 17 Apr 201620 Apr 2016

Conference

ConferenceInternational Congress on Advances in Nuclear Power Plants, ICAPP 2016
Abbreviated titleICAPP 2016
CountryUnited States
CitySan Francisco
Period17/04/1620/04/16

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  • Cite this

    Gouëllo, M., Hokkinen, J., Kärkelä, T., & Auvinen, A. (2016). Experimental study of the boron and air effects on lodine transport in the primary circuit during a severe nuclear accident. In 2016 International Congress on Advances in Nuclear Power Plants (ICAPP 2016) (pp. 752-758). American Nuclear Society ANS.