Tipus de documentProjecte/Treball Final de Carrera
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The increase in the energy consumption and the expected growth in the nuclear capacity make
it necessary to look for alternative fuels to replace uranium. The fuel chosen, which was also
considered in the early stages of nuclear energy, is thorium. Thorium has some characteristics
that make it valuable as a fuel, like its abundance, the low radiotoxicity of the waste generated,
the higher economy regarding its larger absorption cross-section and higher burnups and the
proliferation resistance as compared to uranium. Despite these benefits it also raises some
questions relating its safe operation in the reactor.
The aim of this work is to offer an overview about the use of thorium as a fuel element in a
power reactor and the critical issues that the cladding faces. The programs run in different
countries to use thorium, the benefits and challenges that presents and the physical
configurations inside the reactor are explained. This work focuses in the configuration proposed
by A.Radkowsky which is to have thorium (blanket) and enriched uranium (seed) in different
assemblies. The physical schemes in the reactor core are the seed-blanket unit and the wholeassembly
seed and blanket core.
The increased power density, higher burnup and longer residence time in the reactor of
thorium fuel enhance some potential failure mechanisms which are presented in this work. This
thesis also seeks to give a general idea about the materials used in the reactor, focusing on the
cladding that is the first barrier and the element subjected to toughest operating conditions.
A modeling program called FEMAXI is used to simulate the interaction between the fuel
element and the cladding in the high burnup region. Two physical phenomena are modeled,
inner pressure and cladding corrosion, showing that the limiting factor would be corrosion due
to the long residence time in the reactor.
In order to understand the difficulties to reach the operating conditions of thorium fuel, an
overlook at the licensing process is done. It shows the strict safety conditions which have to be
accomplished, especially with postulated accidents.
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