Heavy water moderator surrounding each fuel channel is one of the important safety features in CANDU reactors since it provides an in-situ passive heat sink for the fuel in situations where other engineered means of heat removal from fuel channels have failed. In a critical break LOCA scenario, fuel cooling becomes severely degraded due to rapid flow reduction in the affected flow pass of the heat transport system. This can result in pressure tubes experiencing significant heat-up during early stages of the accident when coolant pressure is still high, thereby causing uniform thermal creep strain (ballooning) of the pressure tube (PT) into contact with its calandria tube (CT). The contact of the hot PT with the CT causes rapid redistribution of stored heat from the PT to CT and a large heat flux spike from the CT to the moderator fluid. For conditions where subcooling of the moderator fluid is low, this heat flux spike can cause dryout of the CT. This can detrimentally affect channel integrity if the CT post-dryout temperature becomes sufficiently high to result in continued thermal creep strain deformation of both the PT and the CT. A comprehensive mechanistic model is developed to predict the critical heat flux (CHF) variations along the downward facing outer surface of calandria tube. The model is based on the hydrodynamic model of \cite{Cheung/Haddad1997} which considers a liquid macrolayer beneath an elongated vapor slug on the heated surface. Local dryout is postulated to occur whenever the fresh liquid supply to the macrolayer is not sufficient to compensate for the liquid depletion within the macrolayer due to boiling on the heating surface. A boundary layer analysis is performed, treating the two phase motion as an external buoyancy driven flow, to determine the liquid supply rate and the local CHF. The model takes into account different types of flow regime or slip ratio. It is applicable for a calandria vessel as well, under a sever accident condition where a thermal creep failure is postulated to occur if sustained CHF is instigated in the surrounding shield tank water. Model shows good agreement with the available experimental CHF data. The model has been modified to take into account the effect of subcooling and has been validated against the empirical correction factors. / Dissertation / Doctor of Philosophy (PhD)

<p> This thesis is principally concerned with the performance of the phase-locked FM demodulator under conditions of interference in comparison to the conventional FM demodulator. The linear no interference performance of the phase-locked oscillator is well known, however this aspect is included in the interests of completeness and reference.</p> <p> Mechanisms tor threshold effects in the phase-locked and conventional FM demodulator are discussed and compared. It is shown theoretically and experimentally that the noise threshold is reduced in the phase-locked FM demodulator by virtue of the limits of Ψi (t) being restricted by the noise bandwidth of' the feedback loop. Fall off in baseband signal level in the presence of noise was seen to be a function of θ(t) and (S/N)IF.</p> / Thesis / Master of Engineering (MEngr)

<p> This work is concerned with the calculation by means of many-particle perturbation theory of the lowest order corrections to the Random Phase Approximation (RPA) description of an interacting electron gas in its ground state. Expressions in terms of the dynamically screened coulomb interaction are obtained for the electron proper self-energy, the electron momentum distribution function, and the screening function. Techniques, which reduce computational labour to a manageable level, are developed for the practical evaluation of the required corrections. The numerical results are not conclusive but they indicate that when all corrections of the same order (in the screened interaction) are included, the expansion converges sufficiently rapidly that the results are valid in the range of metallic densities.</p> / Thesis / Doctor of Philosophy (PhD)

<p> This thesis presents a derivation of a method to obtain two-body, diagonal and non-diagonal, reaction matrix elements for central and tensor forces respectively directly from nucleon-nucleon scattering phase shifts. This procedure eliminates the necessity for constructing a nuclear potential.</p> / Thesis / Master of Science (MSc)

<p> The use of gamma radiation to initiate the iodination of methane in liquid phase was studied using a semi-batch technique whereby the methane was bubbling through a column of iodine solution in a reactor. Yields of CH3I and CH2I2 lower than 10% and G < 500 were obtained as contrasted with the 60% yield and G=7xl0^7 reported in the gas-phase reaction. In view of the propensity of the iodine as a radical scavenger and the endothermic nature of the reaction, various attempts to improve the low yields were carried out. Results are eiven that indicate the chances of achieving a laree G value for liquid-phase reaction are very low even if the operating conditions are optimized. </p> / Thesis / Master of Engineering (MEngr)

<p> The a-β phase transformation was studied in hydrothermally grown crystals of A1PO4 by measuring the spin-Hamiltonian parameters of Fe^3+ as a function of temperature. </p> <p> The theory of the Blume-Orbach mechanism for the zero-field splitting of s-state ions was generalized and used to calculate the D-tensor of the spin-Hamiltonian. The experimentally observed temperature variation of the spin-Hamiltonian was interpreted in terms of a temperature-dependent point-multipole model of the charge distribution in the crystal lattice. </p> <p> A similar study of the a-S phase transformation in quartz was attempted but E.P.R. measurements could only be taken up to 450°C (123°C below the transformation temperature) because of the instability of the Fe^3+ center at higher temperatures. </p> / Thesis / Doctor of Philosophy (PhD)

no abstract provided. / Thesis / Master of Science (MSc)

<p> It is well known that complex coacervates can be prepared by combining aqueous solutions of oppositely charged biopolymers, such as gelatin and gum arabic. There are few examples of synthetic polyelectrolytes that produce complex coacervates, however. Two series of anionic copolymers capable of forming complex coacervates with branched polyethylenimine (PEI) in water have been prepared. One series consists of binary copolymers containing methacrylic acid (MAA) and poly(ethylene glycol) monomethyl ether monomethacrylate (PEGMA) in molar ratios ranging from 20:80 to 80:20, as well as the two homopolymers, poly(MAA) and poly(PEGMA). Another series contains an equimolar amount of MAA and PEGMA, together with between one and ten percent of a third, hydrophobic monomer, butyl methacrylate (BMA).</p> <p> Both binary and ternary copolymers show lower critical solution temperatures, LCST's, ranging from 60.8°C to 1.5°C depending on composition. Furthermore, complex coacervation occurs upon addition of aqueous PEI to aqueous solutions of these copolymers. The percent volume of the liquid coacervate phase is independent of copolymer composition. However, with increasing MAA to PEGMA ratio in the binary copolymer, the concentration of the coacervate increases, reflecting an increased coacervation efficiency. The coacervate composition was not significantly affected by the BMA in the ternary copolymer series.</p> / Thesis / Master of Science (MSc)

<p> Self-consistent field theory (SCFT) is a well established theoretical framework for describing the thermodynamics of block copolymer melts and blends. Combined with numerical methods, the SCFT can give useful and accurate predictions regarding the phase behavior of polymer blends. </p> <p> We have applied SCFT to study the phase behavior of blends composed of diblock copolymers (AB) and homopolymers (C). Two cases are studied in detail. In the first case the homopolymers have a repulsive interaction to the diblock copolymers. We found an interesting feature in the phase diagram that there exists a bump of the phase boundary line when A is the majority-component. In the second case, the homopolymers have an attractive interaction to one of the blocks of the diblock copolymers. A closed-loop of microphase separation region forms for strong interactions. For both cases, we have investigated the effects of homopolymer concentration, homopolymer chain length, and monomer-monomer interactions, on the phase behavior of the system. </p> <p> We also investigated micelle formation in polymer blends. Diblock copolymers (AB) blended with homopolymers (A) can self-assemble into lamellar, cylindrical and spherical micelles. The critical micelle concentrations for different geometries are determined using self-consistent field theory. The effect of varying copolymer block asymmetry, homopolymer molecular weight and monomer-monomer interactions on micelle morphology are examined. \\Then the blends are confined between two flat surfaces, the shape of the micelles may differ from that of the bulk micelles. We study the shape variation of a. spherical micelle under confinement and its dependence on the film thickness and surface selectivity. </p> / Thesis / Doctor of Philosophy (PhD)

The present apparatus was used to obtain rate data for the absorption of oxygen in a catalysed liquid phase reaction with acetaldehyde. The effects of several system parameters, namely, acetaldehyde concentration, catalyst concentration, partial pressure of oxygen and temperature on the rate of absorption were studied. An attempt was made to correlate absorption rates and product distribution with mathematical models based on the film theory and existing kinetic models proposed by Bolland and Bawn. Absorption rates predicted by these semi-empirical correlations are compared with experimental values. The differential equations involving diffusion with chemical reaction were solved on the digital computer IBM 7040 and the analog computer PACE TRlO. / Thesis / Master of Engineering (MEngr)