Date of Award

2011

Degree Type

Report

Degree Name

Master of Science (MS)

Department

Mechanical and Aerospace Engineering

First Advisor

Heng Ban

Abstract

The knowledge of in-reactor thermophysical properties of nuclear fuel rods, which are usually composed of uranium dioxide (UO2) ceramics, is important for the safe design and operation of nuclear power plants. A two thermocouple method can be utilized to determine the thermal conductivity within the fuel rods by measuring rod centerline temperature and cladding temperature. Using this technique, Halden Reactor Project (HRP) has developed a correlation for thermal conductivity of UO2 as a function of temperature and burnup. This correlation for thermal conductivity was extracted from experimental data based on a constant thermal conductivity assumption of the fuel rod. However, there are no studies to quantify the error in temperature or thermal conductivity due to the constant thermal conductivity assumption, which will help define the error level of the HRP correlation. Therefore, the first objective for this study was to develop a working model to identify the error associated with constant thermal conductivity of UO2 compared to the variable conductivity mode using the correlation determined by HRP. The second objective was to develop an approach for data processing that could be used to obtain the correct temperature dependent thermal conductivity. These objectives were achieved by finding analytical solutions of the governing equations with constant and variable thermal conductivity. Two models were developed to characterize the error between the two assumptions of thermal conductivity. The first model generates the temperature profiles and associated errors of the two assumptions by using constant values for burnup, heat generation, and radius of the fuel rods. The second model is used to determine the dependence of error on heat generation and radius values. Discussion on various solution methods is provided. A hypothetical data set was produced in order to show how the HRP data set can be reprocessed to produce a higher order correlation for thermal conductivity. The result shows that there is as much as 12% error in the temperature profile by assuming constant thermal conductivity. Furthermore, the result shows that the HRP correlation contains an error of about 6%. The higher order data processing method developed in this study can be used in processing HRP or future data from reactor experiments. This study quantified the error of the constant thermal conductivity assumption for UO2 nuclear fuel rods, and provided a useful tool for data processing.

Comments

Publication made available electronically February 2, 2012.

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