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Performance testing and Bayesian Reliability Analysis of small diameter, high power electric heaters for the simulation of nuclear fuel rod temperatures
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The conversion of plutonium from a nuclear weapon to nuclear reactor fuel requires an evaluation of the residual gallium as a potential corrosive material within an operating nuclear fuel element. Homogeneous trace levels of gallium may remain following conversion and have the potential to migrate along the thermal gradient within the fuel and concentrate at the cladding-fuel contact zone. A system to investigate this material transport phenomenon was constructed using small diameter (0.18 inch), indirect electric heaters to simulate the centerline temperatures of operating nuclear fuel in a pressurized water reactor. The heater was inserted into annular surrogate fuel pellets containing depleted uranium, cerium oxide and trace quantities (10 ppm) of gallium to perform an initial study of the gallium migration using non-plutonium fuels and evaluate the performance of the simulation system. Heat was removed from the operating heaters by using an innovative liquid metal heat exchanger. The heaters were of a new design and were required to operate at a nominal temperature of 1000⁰C and for a minimum of 5000 hours. An evaluation of the expected heater lifetime and the thermal simulation system was needed in order to justify the high expense of a proposed full test using prototypic mixed-oxide fuel (MOX) containing plutonium from converted nuclear weapons. Bayesian reliability analysis methods were used to determine the expected heater failure rate because of the expected short test duration and the small sample size. Results from the operation of the simulation system and lifetime data indicate the current heater design is capable of producing the required temperatures and thermal gradients normally found in operating nuclear fuels. However, a design weakness in the heaters resulted in an unacceptably high failure rate of the heaters. The heaters were determined to have a reliability of 0.83 % at 5000 hours of operation with a Mean Time to Failure (MTTF) of 485 hours. The current heater design would require some modification and further testing prior to beginning a full scale test using prototypic MOX fuel pellets.
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Includes bibliographical references (leaves 119-123).
Issued also on microfiche from Lange Micrographics.
O'Kelly, David Sean (2000). Performance testing and Bayesian Reliability Analysis of small diameter, high power electric heaters for the simulation of nuclear fuel rod temperatures. Master's thesis, Texas A&M University. Available electronically from
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