Thesis Abstracts 2005
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Materials Chemical Compatibility for the Fabrication of Small Inherently Safe Nuclear Reactors
By: Abdul-Samed Seidu MSc (Chem. Eng.) Candidate
Supervisor: Dr. H.W. Bonin
Abstract
Aqueous nuclear fuels offer a unique set of characteristics for homogeneous reactor nuclear applications. Their advantages include high nuclear stability and inherent safety, high power density, high burn-up, simple preparation and reprocessing, easy fuel handling, high neutron economy, and simple control system leading to simple mechanical designs. The major disadvantages are corrosion, limited uranium concentration, and radiation decomposition of water. Likewise, organic coolants offer certain properties that are conducive for small reactor applications. These include reduced corrosion and activation, and low vapour pressures with good heat-transfer capabilities. Their major disadvantages are decomposition, fouling and flammability. A particular organic coolant, HB-40, has been extensively studied in Canada and was used for nineteen years in the 60-MWt organic-cooled WR-1 reactor at the Whiteshell Nuclear Research Establishment (WNRE) of Atomic Energy of Canada Limited (AECL). Proper attention to design and coolant chemistry in the nineteen years of operation in the WR-1 reactor kept the coolant aspects related to decomposition, fouling and flammability to acceptable levels. For small reactor applications, organic coolants are potentially superior to heavy water in terms of overall cost.
The purpose of this thesis work was, through a literature review, to select the most suitable aqueous fuel and materials of construction for two proposed small inherently safe reactors, the QH-1 reactor and the homogeneous SLOWPOKE reactor under design at the Royal Military College of Canada. In addition to these, organic coolants particularly HB-40 were investigated for their suitability in QH-1 applications. The bibliographical work was supplemented by the experimental work involving measurements of xenon solubility in water and 0.05M sulphuric acid in the temperature range 25.0 – 75.0˚C.
For the QH-1 and homogeneous SLOWPOKE applications, aqueous uranyl sulphate was found to be the most suitable fluid fuel with respect to thermal and radiation stability, solubility, and tolerable corrosion properties. In addition, HB-40 was found to be a suitable organic coolant for the proposed QH-1 application. The literature review revealed that Type 347 stainless steel and Zircaloy-2 were both appropriate materials for the fabrication of both reactor cores and/or fuel channels. The corrosion rates of Type 347 stainless steel and Zircaloy-2 in uranyl sulphate solutions are low; moreover, both alloys are compatible with the HB-40 coolant.
Based on experimental results, a thermodynamic model was developed for estimating the molal xenon solubility in water as a function of temperature and xenon partial pressure. The experimental part of the thesis research aimed at providing information on the behaviour of xenon, in particular 135Xe, in homogeneous liquid fuels as this strong thermal neutron absorber accumulates in the fuel. Uranyl sulphate-fuelled reactor cores consist of a mixture of uranyl sulphate, sulphuric acid and cupric sulphate. Therefore, a semi-empirical model was developed for estimating the solubility of xenon in electrolyte and mixed electrolyte solutions.
