This thesis contains both Parts A and B. / <p> Xenon induced flux oscillations are possible in large thermal reactors operating at high powers because of the inter-play between the xenon concentration, reactivity, and thermal flux, and the fact that xenon is produced mainly by radioactive decay of I-135, which has a half-life of 6.7 hours. Due to these nuclear characteristics along with size and operating conditions of the Pickering and Bruce cores, these oscillations in flux are inherently unstable with respect to xenon. That is, a local perturbation in reactivity will result in a divergent and cyclic time and space variation in the thermal flux distribution in the core.</p> <p> One group diffusion theory and a simple perturbation analysis yield for a bare thermal reactor, a threshold in the average flux level ∅ which satisfies (1) M^2λij^2 / αxe - αT/αxe ∅ = 1/1+λxe/σxe∅ - μxe / 1+(λxe + λ1)/σxe∅ for oscillations in ijth mode of the flux distribution (see Figure 1) M^2 is the migration area in cm^2, αxe is the reactivity load of Xe-135 at high flux levels; αT is the fuel temperature coefficient expressed in terms of reactivity change per unit flux. The function f(∅) depends only upon the decay constants λxe of Xe-135 and λ1 of I-135; μxe is the fraction of Xe-135 produced directly from the fission of the fuel rather than through iodine decay (which fraction is denoted by μ1). The dimensionless parameter λij^2 depends only upon the shape of the flux distribution and is equal to the difference between the bulking of the ijth mode and the fundamental model.</p> <p> The Bruce and Pickering reactors are used as models in this study to determine the threshold power level at which xenon instability is possible and in which mode this instability occurs.</p> <p> Bruce is found to be unstable in the fundamental and first azimuthal mode for fresh and equilibrium fuel conditions, and stable for the radial, axial and higher azimuthal modes.</p> <p> Pickering, on the other hand, is unstable for the equilibrium fuel condition in the fundamental and first azimuthal modes only and is stable in every mode except the fundamental in the fresh fuel condition.</p> (Part A of Thesis)-------------------------------------------------------------------------------------------------------(Part B of Thesis) </p> Trimming of thin-film resistor components by an electrical arc is investigated in this report as an inexpensive and simple alternative to the laser trim and mechanical scribe methods. A multitude of tests were effected on Garrett Manufacturing Limited production circuits containing nichrome thin film resistors. These tests included Temperature Coefficient of Resistivity, resistance stability, substrate damage, noise performance, dynamic trim with active devices operating, width of cut as compared to mechanical scribe and laser trim techniques, and optimum parameters for trimming. In all cases the trimmed circuits were within the design specifications of the resistor properties under test. It is the conclusion of the author that the obvious attributes of the arc-trim method as well as its outstanding performance in the above tests, warrants its serious
consideration as a viable alternative to the laser trim and mechanical scribe methods of altering resistance levels.</p> / Thesis / Master of Engineering (MEngr)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20194 |
| Date | January 1970 |
| Creators | Simmons, J. V. B. |
| Contributors | Trojan, O. A., Shewchun, J., None |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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