Determination of 131I Uptake in Fucus Gardneri Using Gamma-Ray Spectroscopy Determination de 1'Accumulation de I dans Fucus Gardneri par Spectroscopie Gamma A thesis submitted to the Division of Graduate Studies of the Royal Military College of Canada By Kristine Margaret Mattson In Partial Fulfillment of the Requirements for the Degree of Master of Applied Science in Nuclear Engineering August 2011 © This thesis may be used within the Department of National Defence, but copyright for open publication remains the property of the author. 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Canada Acknowledgements I wish to express my appreciation to Dr. David Kelly and Dr. Leslie Bennett, my thesis advisers, for their guidance, advice and support during the course of this research. I wish to thank Dr. Louis Druehl for his expert advice with respect to seaweeds and for sampling and shipping excellent specimens of Fucus gardneri from his kelp farm in Bamfield, BC to the Royal Military College of Canada. I would like to thank Ms. Kathy Nielsen, Director of the SLOWPOKE-2 Facility at RMC, for allowing me to use the High Purity Germanium Detectors in the Facility without interruption. I wish to thank Mr. David Ferguson for his help setting up my aquaria and for helping me with the construction of my lead casde and to the Nuclear Emergency Response members and the Navy divers for their assistance in collection of the seaweed samples in Shearwater, NS. Appreciation is extended to Dr. Christopher Lane, Dalhousie University, for his commitment to help me identify the seaweeds and other specimens collected in Shearwater. Thanks go to Kim Bylow and the staff in the Imaging Department, at the Kingston General Hospital, for their help acquiring 131I solutions, and to DGNS who kindly provided funding for this thesis. Finally, I especially wish to thank my family. Collin, you were very loving, supportive, patient and understanding. Your help and commitment to the rest of our daily life together was amazing and I cannot thank you enough. To Blake and Emma, my precious children, thank you for being absolutely wonderful and for letting me take over the computer without ever complaining. It is with my heartfelt gratitude and love that I dedicate my thesis work to my family. 11 Abstract Low level releases of 131I and other fission products in the environment, such as seawater, may be difficult to detect by standard methods Seaweeds have a high iodine concentration and absorb 131I to levels measurable by gamma-ray spectroscopy. A gamma-ray detection system was designed and validated to use for the detection of low level activities The detection limit and minimum detectable activity of 131I for the system were determined to be 0 28 ± 0.07 Bq and 0 09 ± 0.02 Bq, respectively. Samples of seaweeds were collected on the East and West coasts of Canada. Ascophyllum Nodosum and the Sacchanna Latissima were sampled in Shearwater, NS (Eastern Passage) in December 2006 and had 131I average dry weight activity of 30 ± 2 Bq kg1 and 175 ± 7 Bq kg1, respectively Fucus gardnen samples were harvested from the western shoreline of Vancouver Island in Bamfield, Bntish Columbia, at low tide in January, March and November of 2008. The average concentration of iodine in Fucus gardnen determined using INAA was 290 ± 50 fig g' dry weight Assuming an average concentration of iodine in seawater at the sampling location in Bamfield, BC, in the range of 0.03—0.05 |4.g g1 and the average concentration of iodine in the Fucus gardnen, the equilibrium constant for iodine between Fucus gardnen and seawater in this study was 5800-9700 mL g1. The equilibrium of 131I between seawater and Fucus gardnen can be established within hours and can be modelled using first order equilibrium kinetics. The average equilibrium constant, measured experimentally using first order equilibrium kinetics, for Fucus gardnen is 78 ± 46 mL g1 based on wet weight and 480 ± 270 mL g based on dry weight. The average rate constants kf +kb, kf and kb are 0.57 ± 0.22 h1, 0 55 ± 0.21 h1 and 0.012 ± 0.011 h\ respectively. It was found that seaweed samples can be stored for up to one week in temperatures ranging from -17°C to 25°C without any loss of 131I, indicating that samples may be kept for later analysis, as necessary. Fucus gardnen exposed to reactor container water from the SLOWPOKE-2 Facility absorbs the low level fission products within 4 hours The fission products include radioisotopes of iodine, metals and noble gases. in Resume Les methodes de detection standard eprouvent des difficultes a detecter avec precision les faibles relachements de 131I et d'autres produits de fission dans l'environnement comme l'eau de mer. Les plantes marines sont capables d'accumuler de grandes concentrations d'iode et peuvent absorber 1'131I a des niveaux mesurables par spectroscopic gamma. On a concu et valide un systeme de detection par rayonnement gamma afin de l'utiliser pour la detection de faibles niveaux d'activite. On a determine la limite de detection et l'activite minimum detectable de P,MI pour ce systeme a 0.28 ± 0.07 Bq et 0.09 ± 0.02 Bq, respectivement. Des echantillons de plantes marines ont ere recueillis sur les cotes est et ouest du Canada. Ascophyllum Nodosum et Saccharina Latissima ont ete echantillones a Shearwater N.E. (Passage de l'Est) en decembre 2006 et avaient une activite specifique moyenne (a sec) pour F13,I de 30 ± 2 Bq kg1 et 175 ± 7 Bq kg1, respectivement. Des echantillons de Fucus gardneri ont ete recueillis sur la cote ouest de l'ile de Vancouver a Bamfield, Colombie-Britannique, a maree basse en Janvier, mars et novembre 2008. La concentration specifique moyenne d'iode dans Fucus gardneri tut determinee a l'aide de l'Analyse Instrumentale par Activation Neutronique (AIAN) comme etant egale a 290 ± 50 |Jg g1 (de masse a sec). En supposant que la concentration moyenne de l'iode dans l'eau de mer a l'emplacement de rechantillonage a Bamfield C.-B. se trouvait entre 0.03 |Jg g' et 0.05 [Jg g' et en supposant la valeur ci-dessus pour la concentration moyenne d'iode dans Fucus gardneri, on a pu determiner la constante d'equilibre pour l'iode entre Fucus gardneri et l'eau de mer comme etant de 5800-9700 mL g-1 pour cette etude. L'equilibre de 1'131I entre l'eau de mer et Fucus gardneri peut etre etablie en quelques heures et peut etre modelisee a partir d'un modele de cinetique a l'equilibre du premier ordre. La constante d'equilibre moyenne, mesuree experimentalement a l'aide du modele de cinetique du premier ordre pour l'equilibre et pour Fucus gardneri est de 78 ± 46 mL g' , valeur basee sur une masse mouillee, et de 480 ± 270 mL g' pour une masse a sec. Les constantes de taux moyennes 1% 1 1 1 +kb, kf et kb sont de 0.57 ± 0.22 h , 0.55 ± 0.21 h et 0.012 ± 0.011 h , respectivement. On a trouve que les echantillons de plantes marines peuvent etre entreposes pour une semaine a des temperatures entre -17°C et 25°C sans perte de 131I, indiquant que les echantillons peuvent etre gardes pour analyses ulterieures, au besoin. Fucus gardneri, lorsque espose a l'eau du vaisseau du reacteur SLOWPOKE-2, absorbe les produits de fission de faibles niveaux en 4 heures au plus. Ces produits de fission incluent l'iode, certains metaux et des gaz nobles. iv Contents Acknowledgements ii Abstract iii Resume iv Contents v List of Figures ix List of Tables xii Nomenclature xiv Acronyms xvi Chapter 1 Introduction 1 1.1 Project Background 1 1.2 Thesis Objectives 2 1.3 Radiation in the Environment 3 1.3.1 General 3 1.3.2 Radiation from Fission 7 1.3.3 Activation Products 9 1.4 Environmental Radionuclide Monitoring Program 9 1.4.1 Visiting Nuclear Powered Vessel