GLOBAL MODEL FOR IODINE BEKAVIOUR FN REACTOR CONTAaYMENT Anandhi Narayanan A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Graduate Department of Chemical Engineering and Applied Chemistry University of Toronto @ Copyright by Anandhi Narayanan 2000 National iibrary Bibliothèque nationale I*I of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services seivices bibliographiques 395 Wellington Sheet 395. rue Wellington Ottawa ON K1A ON4 Ottawa ON K1A ON4 Canada Canada The author has granted a non- L'auteur a accordé une Licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distn'bute or sell reproduire, prêter, distribuer ou copies of ths thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/tilm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts kom it Ni la thèse ni des extraits substantiels may be printed or othenirise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Global Model for Iodine Behaviour in Reactor Containment Master of Applied Science, May 2000 Anandhi Narayanan Graduate Department of Chernical Engineering and Applied Chemistry University of Toronto ABSTRACT The objective of this thesis was io develop a mechanistic model to simulate iodine behaviour within the containment structure of a nuclear generating station. The model included both aqueous and gas phase radiolysis and interfacial mass transfer. Validation of the model was conducted for each phase separately and the combined model was applied to a few reactor accident scenarios. The aqueous model successfùlly reflected various experimental data over a wide range in pH, iodide concentration, temperature, and dose rate. The incorporation of gas phase chemistry served to determine the dominant chemical forms of gaseous iodine. In addition, it was observed that hydrogen, likely to be present in the containment atmosphere, would hinder the elimination of molecular iodine. Finally, the interaction of iodine with nitrogen oxides was signincant when compared to reactions with ozone. Hence, the deposition of ozone onto surfaces did not impact iodine behaviour. The development of this model will serve as a usefbl tool for reactor safety assessments. The people acknowledged in this section assisted by either providing technical assistance or emotional support while completing this thesis. 1 am very grateful to them. Professor G.J. Evans for his supervision, patience and guidance throughout the course of my research. I tmly appreciated your critical review of my thesis document. You enabled me to learn a great deal. NSERC for fbnding my research. Professon M.J. Philiips and C.A. Mims for their participation in my defence cornittee and reviewing my thesis document. The entire nuclear and aerosol research group for their friendship; in particuiar Tutun for his constant assistance throughout, Fariborz for helping me get started and Lis for critiquing my presentation. Paul, Samar and Vani for the coffees, lunches and chats: a much needed break. My mother, father, Desi, Anin and Rudy for their unconditional love and support. Finally God, without whom I would not be. 1.0 INTRODUCTION.... ..w...w..m.I*000.8*a... ...............8...e...........................................8....... f 2.0 LITERATURE REVIEW .......................... ... ......................................................4 2 .L Severe Reactor Accidents .................................................................................. 4 2.2 Aqueous Phase Radiolysis ........................................................................................ 6 2.2.1 Statw cf Iodine Models ...................................................................................... 6 2.2.2 Aquesous Phase Chemistry .............................................................................. 11 2.2.2.1 Effect of pH ............................................................................................. 11 2.2.2.2 Effect of Temperature ............................................................................. 12 2.2.2.3 Effect of Total Iodide Concentration .......................... ...... ....................... 12 2.2.2.4 Effect of Dose Rate ................................................................................... 13 2.2.2.5 Effect of Dissolved Gases ........................................................................ 13 2.3 Gas Phase Radiolysis ............................................................................................. 15 2.3.1 Status of Models ............................................................................................... 15 2.3.2 Gus Phase Chernistry ....................................................................................... 17 3.1 Introduction to Radiation Chernisûy ...................................................................... 22 3.2 Aqueous Phase Radiolysis .................................................................................. 22 3.2.1 Water Radiolysis ............................................................................................. 23 3.2.2 Aqueous Iodine Chemistry ............................................................................... 24 3.3 Gas Phase Radiolysis .............................................................................................. 26 3.3.1 Primav Yields ................................................................................................. 27 3.3.2 Radiation Chemistry of Moist and Dry Air ...................................................... 29 3.3.3 Gas Phase lodine Chemistry............................................................................ 31 3.3.4 Ozone Deposition ............................................................................................. 32 3.4 interfacial Mass Transfer ........................................................................................ 36 4.0 MOOEL DEVELOPMENT .......e...............~~oe.~...................................................... 38 4.1 Facsimile Code ........................................................................................................ 38 4.2 Basis for Aqueous Mode1...................... .. .......................................................... 38 4.3 Basis for Gas Mode1............................................................................................ 39 4.4 Combined Mode1 .................................................................................................... 40 5.0 RESULTS AND DISCUSSION ...................................m. ............ 41 5.1 Aqueous Mode1 Analysis .................................................................................... 4 1 5.1. I Water Radiolysis .............................................................................................. 41 5.1.2 ludine Volatility ............................................................................................. 48 5.1.2.1 Impact of pH and Iodide Concentration............................................... 48 5.1.2.1.1 Flow Experiment................................................................................ 49 5.1 .2. L .2 Sparging Apparatus Experiment ........................................................ 50 5.1.2.1.3 Effect of pH for High Iodine Concentration ...................................... 53 5.1.2.1.4 Effect of pH for Low Ioduie Concentration ....................................... 54 5.1.2.2 impact of Dose Rate .................................................................................. 55 5.1.2.3 Impact of Temperature............................................................................. 58 5. 1.2.4 Impact of Organics.................................................................................. 61 5.1.3 Summary of Mode l.. ......................................................................................... 64 5.2 Gas Model .b slysis ................................................................................................ 67 5.2.1 Air Radiolysis ................................................................................................. 67 5.2.1.1 Ozone Yield: Theoreticai Estimation in Dry Air ...................................... 67 5.2.1.2 Ozone Yield: Theoretical Estimation in Moist Air ................................... 69 5.2.1.3 Ozone. Formation: Experimental Cornparison .......................................... 71 5.2.1.4 Nitnc Acid Formation ............................................................................... 75 5.2.2 Iodine Elimination ......................................................................................... 75 5.2.2.1 Mechanisin for Iodine Elirnination ........................................................... 76 5.2.2.2 Effect of Steam ......................................................................................... 79 5.2.2.3 Effect of Dose Rate ................................................................................... 80 5.2.2.4 Effect of Temperature .............................................................................. 80 5.2.2.5 Effect of Ozone ........................................................................................