Heat and mass transfer analysis for crud coated PWR fuel
Author(s)
Haq, Inam Ul
Type
Thesis
Abstract
In water-cooled nuclear reactors, various species are present in the coolant, either
in ionic solution, or entrained as very fine particles. Most arise from corrosion of
primary circuit surfaces, or from chemicals, such as boric acid, lithium
hydroxide, zinc and hydrogen, deliberately added to the coolant. These materials
deposit on the surfaces of fuel pins, typically in the upper regions of the core,
forming what is generally termed “crud”. This thesis reports a study of the
thermal-hydraulic consequences of this deposit. These crud deposits are
generally found to contain a large population of through-thickness chimneys,
and it is believed that this gives rise to a wick-boiling mechanism of heat transfer.
A coupled two-dimensional model of the processes of heat conduction, advection
and species diffusion in the crud has been developed. An iterative scheme has
been employed to solve the set of coupled equations of each process. The wick
boiling process has been found to be an efficient heat transfer mode, taking away
about 80% of the heat generated.
It has also been found that consideration of heat transfer in the clad can increase
the predicted solute concentration in the crud. The effects of some important
parameters, such as chimney density, chimney radius, porosity of the crud, crud
thickness, clad heat flux and boron concentration in the coolant have been
investigated. The fuel thermal performance has been characterized in terms of an
effective crud thermal conductivity, and the non-linear dependence this has on
parameters such as crud thickness and chimney density had been determined.
Lastly, it is observed that plausible pore sizes of the crud, coupled with higher
temperatures in the crud, may be such that a film of vapour is generated at the
base of the crud. Initial estimates are presented of the cladding temperatures and
solute concentration that may be generated as a consequence of this vapour
layer.
in ionic solution, or entrained as very fine particles. Most arise from corrosion of
primary circuit surfaces, or from chemicals, such as boric acid, lithium
hydroxide, zinc and hydrogen, deliberately added to the coolant. These materials
deposit on the surfaces of fuel pins, typically in the upper regions of the core,
forming what is generally termed “crud”. This thesis reports a study of the
thermal-hydraulic consequences of this deposit. These crud deposits are
generally found to contain a large population of through-thickness chimneys,
and it is believed that this gives rise to a wick-boiling mechanism of heat transfer.
A coupled two-dimensional model of the processes of heat conduction, advection
and species diffusion in the crud has been developed. An iterative scheme has
been employed to solve the set of coupled equations of each process. The wick
boiling process has been found to be an efficient heat transfer mode, taking away
about 80% of the heat generated.
It has also been found that consideration of heat transfer in the clad can increase
the predicted solute concentration in the crud. The effects of some important
parameters, such as chimney density, chimney radius, porosity of the crud, crud
thickness, clad heat flux and boron concentration in the coolant have been
investigated. The fuel thermal performance has been characterized in terms of an
effective crud thermal conductivity, and the non-linear dependence this has on
parameters such as crud thickness and chimney density had been determined.
Lastly, it is observed that plausible pore sizes of the crud, coupled with higher
temperatures in the crud, may be such that a film of vapour is generated at the
base of the crud. Initial estimates are presented of the cladding temperatures and
solute concentration that may be generated as a consequence of this vapour
layer.
Date Issued
2011-01
Date Awarded
2011-02
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Walker, Simon
Hewitt, G. F.
Richardson, Stephen
Sponsor
Higher Education Commission of Pakistan, PIEAS, KNOO Project, EPSRC, Dr Wali Trust
Creator
Haq, Inam Ul
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)