Abstract
In light water reactors the nuclear fuel is in the form
of uranium dioxide pellets stacked inside a thin-walled
tube made from Zirconium alloy. The fuel rods provide the
first barriers to the release of radioactivity as the
isotopes are contained within the fuel matrix and the
cladding tubes. Fuel behaviour analysis investigates the
state of the fuel at given boundary conditions and
irradiation history.
The scope of this thesis consists of two main themes. The
first is the uncertainty and sensitivity in fuel
behaviour modelling and the tools required for its
propagation to the rest of the nuclear reactor
calculation chain. The second is the analysis and
modelling of cladding response to transient stresses.
A nuclear reactor is a strongly coupled system. The
neutronics depend on the fuel and coolant temperature,
the fuel temperature on the neutronics and the heat flux
to coolant and coolant thermal hydraulics on the amount
of heat transferred from the fuel. Propagation of
uncertainties through the nuclear reactor calculation
chain is an international on-going effort, and the
complex interactions in the fuel rods make them
challenging to analyze. In this thesis uncertainty and
sensitivity of fuel behaviour codes is investigated and
the development of a fuel module suitable for propagation
of the uncertainties is detailed.
The creep response of a cladding tube to changing
conditions is conventionally modelled using the strain
hardening rule. The rule assumes accumulated strain to be
invariant during changes in the conditions, and is
relatively simple to utilize. However, the original
experiments which are used to justify the use of the
strain hardening rule show that it applies only to a
restricted set of conditions. In this thesis a simple
methodology for predicting fuel cladding macroscopic
response to stresses and imposed strains is developed by
taking anelastic behaviour into account. The model is
shown to perform well in describing both creep and stress
relaxation experiments.
| Original language | English |
|---|---|
| Qualification | Doctor Degree |
| Awarding Institution |
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| Supervisors/Advisors |
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| Award date | 23 Oct 2015 |
| Place of Publication | Espoo |
| Publisher | |
| Print ISBNs | 978-951-38-8346-1 |
| Electronic ISBNs | 978-951-38-8347-8 |
| Publication status | Published - 2015 |
| MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- nuclear fuel behaviour
- modelling
- uncertainty and sensitivity analysis
- cladding creep
- stress relaxation
- viscoelasticity