Annual Report

lution to the planet’s growing energy demand.
Research interests include the processing and
characterisation of non-oxides for use in Generation
IV nuclear reactors with main interest
focused on the gas cooled fast reactor (GFR).
Several reference fuel concepts exist for the
GFR one being Inert Matrix Fuels which consist
of a dispersion of a non-oxide fissile phase
(such as uranium carbide or uranium nitride)
in a non-fissile material in the form of a pellet.
Zirconium carbide and zirconium nitride are
both promising candidates for use as the inert
phase due to their high hardness, high melting
point and good electrical and thermal conductivities.
The carbothermal reduction-nitridation
process was used to fabricate powders of ZrC
and ZrN from ZrO 2 to firstly investigate this processing
route to non-oxide fuel matrices but
with the additional benefit that Zr could act as
a simulant for uranium or plutonium, in addition
the effects that impurities, such as oxygen
and carbon and vacancy defects may have on
the thermophysical properties of ZrN has been
examined. Electrical and thermal conductivities
of several zirconium carbonitrides have all
exceeded those of commercially available ZrC
and ZrN. Finally this project aims to examine
the effects of proton irradiation on microstructural
and thermophysical properties by collaboration
with the Dalton Institute at the University
of Manchester.
Processing and Microstructural
Characterisation of UO2-based Simulated
Spent Nuclear Fuel Ceramics for the UK’s
Advanced Gas-cooled Reactors
Researcher: Zoltan Hiezl
Supervisor: Prof Bill Lee
Sponsor: EPSRC and NDA.
As the planet’s demand for energy increases,
one solution is to extend the number and the
life time of current nuclear power plants and
build new ones. As a result more radioactive
nuclear waste will be generated making its
management crucial. As part of the UK Spent
Fuel Research Group, with members from Imperial,
Cambridge University and Lancaster University,
the work at Imperial involves fabricating
UO2 based simulant (SIMFuel) samples of
spent Advanced Gas-cooled Reactor fuel.
The aim is to develop a ceramic that reproduces
both core and rim microstructures of spent AGR
fuels at various times after discharge from reactor
(100, 1000, 10000 and 100000 years) containing
nuclides predicted to be present. Initially
the type and amount of fission products have
been calculated using the FISPIN programme.
These fission products are then grouped and
their atomic percentages are calculated within
the spent AGR fuel. SIMFuel samples have
been made in which inactive surrogate metal
oxides are mixed with depleted uranium dioxide
before sintering at 1700°C for 5 hours in H 2
atmosphere then grinding and polishing the
dense samples. Such samples are being characterised
using optical microscopy, SEM, TEM
and XRD and have been supplied to the other
universities for further study. To date, SEM-EDX
analysis revealed metallic and oxide precipitate
(grey phase) formation. The main components
of the metallic precipitates are Mo, Rh, Ru and
Pd, whereas in the grey-phase Ba, Zr and Sr can
be found. Several fission product surrogates
are dissolved in the UO2 matrix, such as Ce and
Nd. These results are in good agreement with
atomistic modelling using empirical pair potentials
calculated by Michael Cooper in the Centre
for Nuclear Engineering at Imperial. With the
help of SIMFuel, different properties, such as:
thermal conductivity, oxidation, dissolution,
51 http://www.imperial.ac.uk/nuclear-engineering