IRUS Total

Finite element modelling of nuclear fuel performance in advanced gas-cooled reactors

File Description SizeFormat 
Haynes-T-2019-PhD-Thesis.pdfThesis17.5 MBAdobe PDFView/Open
Title: Finite element modelling of nuclear fuel performance in advanced gas-cooled reactors
Authors: Haynes, Thomas Anthony
Item Type: Thesis or dissertation
Abstract: This thesis presents a two dimensional (r-θ) finite element model (PELICAN) for pellet-clad interaction in advanced gas-cooled reactors; it can also be applied to light water reactor designs. The model consists of a number of user-defined subroutines, together with a set of finite element models built using the commercial finite element software Abaqus. PELICAN can model cracked fuel pellets; slivers of fuel bonded to the cladding; a cross-pin temperature tilt, due to carbon deposition; and clad bore cracks. Pellet bore closure during power ramps was predicted by this model. Closure of the pellet bore reduces the increase in pellet outer radius during ramps and therefore the intensity of pellet-clad interaction. It was found that radial cracks through the pellet act as significant stress raisers in the cladding. This stress concentration is increased further in the presence of fuel-clad bonding. The stress concentration was however reduced to close to that observed in un-bonded fuel when microscopic ‘ladder cracks’ in the adherent sliver of fuel were modelled as being open. The cracks were modelled by reducing the elastic modulus of the sliver when the hoop stress was tensile. This was achieved by using a non-local approach, which has not previously been applied to nuclear fuel. The same broad trends were seen in the inelastic cladding strains in the models with both cracked and un-cracked fuel pellets. In the upper fuel elements (which have hotter cladding and lower linear rating), the creep strain is highest and the instantaneous plastic strain negligible. In the lower (colder cladding and higher linear rating) fuel elements, instantaneous plastic strains were of more importance. In addition, whilst instantaneous plastic strains were due mostly to increases in power, creep strains were due mostly to continuous full power operation. The impact of a cross-pin temperature tilt was investigated. Despite some stress concentration due to greater pellet fragment motion, the maximum hoop stress and inelastic strains were bounded by models with uniformly deposited and un-deposited thermal boundary conditions.
Content Version: Open Access
Issue Date: Jun-2018
Date Awarded: Mar-2019
URI: http://hdl.handle.net/10044/1/78873
DOI: https://doi.org/10.25560/78873
Copyright Statement: Creative Commons Attribution Non-Commercial NoDerivatives Licence
Supervisor: Wenman, Mark
Davies, Catrin
Sponsor/Funder: EDF Energy
Engineering and Physical Sciences Research Council
Funder's Grant Number: 1402033
Department: Materials
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Materials PhD theses