Le département des Landes correspondant actuellement au diocèse d'Aire et de Dax, est constitué par le regroupement des anciens diocèses d'Aire et de Dax augmentés de portions de ceux d'Auch, Bazas et Bordeaux. Les édifices religieux de ce département sont fortifiés au cours de la période s'échelonnant du début du conflit franco-anglais, à la fin du XIIIe siècle, puis pendant la guerre de Cent Ans, et, pour certains, jusqu'au milieu du XVIe siècle. La grande majorité d'entre-eux sont de modestes églises destinées à la défense des populations des villages dans une région marquée par la relative rareté des châteaux. Elles sont fortifiées de façon quelquefois très élaborée et souvent très sommaire. Elles sont particulièrement éprouvées lors des guerres de Religion, période pendant laquelle elles sont presque toutes pillées, souvent incendiées et détruites au niveau de leur voûtement. Leur inventaire dans ce département est constitué de plus de soixante-quinze églises. Soixante-huit d'entre-elles font l'objet d'une notice détaillée, avec plan, historique, description architecturale, photos, relevés, description et analyse des fortifications. D'autres édifices religieux des Landes, et certains appartenant à des départements différents, ayant un rapport direct avec ce sujet, sont également mentionnés. Cette recherche a permis de révéler la grande quantité et la diversité des églises fortifiées de cette région et leurs différents modes de mise en défense. Elle a également mis en évidence un type particulier et rare de fortification constitué par des façades ou des porches semi-circulaires édifiés dans la seconde moitié du XVe siècle ou au début du XVIe siècle. L'étude comparative de ces constructions semi-circulaires de façade, à usage militaire, avec les églises à contre-abside, à usage liturgique, existant encore dans les Landes et en Aquitaine, a été faite afin de bien distinguer les deux types d'édifices. / The Landes currently corresponding to the diocese of Aire and Dax, is formed by the combination of the former dioceses of Aire and Dax plus those portions of Auch, Bazas and Bordeaux. Religious buildings of this department are strengthened during the period from the beginning of the Anglo-French conflict in the late thirteenth century, and during the Hundred Years War, and for some, until the mid-sixteenth century. The vast majority of them are small churches for the defense of the village population in a region marked by the relative scarcity of castles. They are fortified so sometimes very elaborate and often very brief. They are particularly affected during the Wars of Religion, during which they are almost all looted, burned and destroyed often in their vault. Their inventory in this department consists of more than seventy-five churches. Sixty-eight of them are subject to detailed instructions, with plan, historical, architectural description, photos, statements, description and analysis of fortifications. Other religious buildings in the Landes, and some belonging to different departments, having a direct bearing on this subject are also mentioned. This research revealed the large amount and variety of fortified churches in this region and their different modes of defense. She also highlighted a particular and rare fortification consists of facades or semicircular porches built in the second half of the fifteenth century or early sixteenth century. The comparative study of these constructions semicircular facade for military use, with the churches against the apse, in liturgical use, still existing in the Landes and Aquitaine, was made to distinguish between the two types of buildings.

Fuels comprised of the element thorium have become increasingly popular with researchers and the public as the next generation fuel due to its ability to produce its own fissile element (U-233) and generate lower concentrations of heavy actinides. The use of thorium can possibly lead to a self-sustaining cycle whereby the addition of fissile material is not required and that the fuel can breed sufficient amounts of U-233 for a continuous supply. Research into thorium use in CANDU reactors has mainly been focused on using driver elements such as U-235 or Pu-239 to initiate the nuclear reaction by taking advantage of bundle design or by mixing the thorium and driver fuel together; however, these methods have added complexities and may not lead to a pure thorium fuel cycle, but extend the life of current nuclear fuels used. This thesis will investigate a simpler means of utilizing thorium for the intent of breeding U-233 through the use of pure thorium bundles in a once-through cycle by the ways of a heterogeneous core loading in a CANDU-6 reactor model. A 3x3 multi-cell model using DRAGON 3.06K will simulate the dual fuel model by having the centre lattice enclosing the thorium bundle and the outer eight lattices enclosing the enriched uranium bundles as the driver fuel. Next, the diffusion code DONJON 3.02E is used to produce time-average, instantaneous, and initial startup full-core simulations. As well, a brief look at the refuelling operations on the thorium channels will be done. The presence of a thorium bundle places a negative reactivity load on the multi-cell, but causes a positive insertion of reactivity for a coolant void and shutdown scenario. In the full-core modelling, the final core configuration chosen shows that thorium channels should be located in the inner core rather than in the most outer channels to produce a flattening effect on the radial profile. Thorium channels will require a combination of SEU and thorium bundles in an attempt to maintain channel power levels. Specifically, the use of 4, 6, or 8 Th bundles were investigated. The most optimal core performance shown has a radial form factor of 0.816, a total average core burnup of 18.32 GWd/t, and operates within designed power limits. It is possible to implement pure thorium bundles into a reactor set in a dual fuel mode. A careful consideration of where thorium bundles should be located in the core can help flatten the radial power distribution and help the reactor operate within the operating licensing parameters without the use of adjuster rods while breeding U-233 for a future thorium fuel cycle. / Thesis / Master of Applied Science (MASc)

<p>Due to the strong interest in thorium fuels in CANDU reactors rooting back to 1970’s and 1980’s, four experiments were done in the ZED-2 critical facility at Chalk River Laboratories to test the properties of (Th,Pu)O­₂ fuel. The fuel was placed in five bundles with a typical CANDU design, stacked vertically in the center of the core (K0 site) and surrounded by natural uranium fuel.</p> <p>The simulation of these experiments using the transport code DRAGON coupled with the diffusion code DONJON is presented. DRAGON is initially used to model two lattices and the full cores in 2D. These models are designed to calculate direct/adjoint flux, k_∞ and k_eff values using the collision probability method. Furthermore, the models determine a set of homogenized and condensed cross sections in two energy groups. Subsequently, DONJON is used to model the full core facility in three dimensions. Using the homogenized and condensed macroscopic cross section libraries obtained from the DRAGON models, DONJON is able to calculate the flux alongside with the k_eff values for the specific cases in two energy groups. The results are then compared to those from the experiments and will further validate the accuracy of the simulations.</p> <p>Sensitivity and uncertainty results for the infinite lattices and the 2D full core model using DRAGON and SUSD3D code are discussed. The direct and adjoint flux values determined by DRAGON for the lattices and the full core model are used by SUSD3D to calculate the sensitivity profiles for specific reactions of the isotopes present. The sensitivity profiles are then used alongside with the covariance matrices to calculate the uncertainty contribution of nuclear data to criticality. The sensitivity and uncertainty (S/U) results of the 2D model for full core, using the DRAGON/SUSD3D code coupling are then compared with the S/U results of a 3D model of the full core using the code TSUNAMI within the SCALE6 package in reference. The comparisons will show an excellent degree of consistency between the two methods, while reasons for possible differences in the results are also presented.</p> / Master of Applied Science (MASc)

In the field of nuclear medicine, radioisotopes are used for applications such as diagnostic imag- ing, treatment, and equipment sterilization. The most commonly used radioisotope in medicine is technetium-99m (Tc-99m). It is used in 80% of all nuclear medicine procedures. Its parent isotope is molybdenum-99 (Mo-99). NRU, which is now closed, formerly produced 40% of the worlds demand for Mo-99. The production capacity of this reactor has been supplemented by a network of cyclotrons and a modified research reactor. This study aims to provide an alternative means of production for Mo-99, as well as other radioisotopes by modifying the center pin of a standard 37-element bundle of a CANDU reactor. The neutron transport code DRAGON, and the neutron diffusion code DONJON were used to model a CANDU-9 reactor. The lowest, median, and highest power channels were chosen as candi- dates for the modified bundles. It was found that the reactor parameters were altered by a negligible amount when any one channel was used to house the modified bundles. Significant quantities of the radioisotope lutetium-177 as well as the generating isotopes of the alpha-emitting radioisotopes lead- 212/bismuth-212, and radium-223 were produced. However, only minute amounts of molybdenum-99, and the generating isotope of bismuth-213 were produced. / Thesis / Master of Applied Science (MASc)

Le niveau de conversion des réacteurs CANDU et REP en cycle thorium a été étudié dans l'optique d'une utilisation en troisième et dernière strate de scénarios symbiotiques. Le plutonium du combustible REP usé serait par exemple utilisé en CANDU Th/Pu pour produire de l'233U, qui alimenterait ces réacteurs à eau et haute conversion. En cas d'augmentation importante de la production d'énergie à partir d'uranium, cette alternative basée sur des réacteurs existants pourrait suppléer une IVe génération trop tardive. Pour évaluer la compétitivité de tels scénarios, des calculs de cycles détaillés ont été effectués selon une méthodologie de simulation de coeur développée pour le CANDU-6 et adaptée au REP de type N4. Le CANDU Th/233U enrichi à 1.30 wt% est régénérateur, avec un burnup court de 7 GWj/t. Augmenter légèrement l'enrichissement allonge considérablement le cycle, au prix d'une sous-génération. Multirecycler conduit également à une perte de conversion, qui peut néanmoins être compensée par un chargement fissile hétérogène. La conversion à puissance standard est moins bonne en REP Th/233U qu'en CANDU (inventaire fissile réduit de moitié après 50 GWj/t) mais peut être améliorée par sous-modération. L'analyse neutronique montre que l'essentiel du gap de conversion entre CANDU et REP vient des conditions opératoires économes en neutrons du CANDU. Des scénarios ont été comparés du point de vue de l'économie d'uranium et de l'aval du cycle dans les deux cas, et ont confi rmé l'intérêt du CANDU. Deux pistes de recherche ont été identi fiées : l'évaluation de la sûreté des CANDUs au thorium par cinétique avec contre-réactions thermiques, et l'étude de coeurs fortement sous-modérés en cuve standard de REP.