Annual Report

density polyethylene (HPDE) pipes, which EDF
Energy is currently using in an increasing number
of their existing and planned nuclear power
stations to replace cast iron pipework that
is susceptible to high levels of corrosion and
other forms of degradation and fouling. In contrast,
HDPE is not subject to such degradation.
Ultrasonic inspection is of great importance in
this area as HDPE pipe welds can sometimes
become contaminated with defects during the
welding process. The welds can also be produced
under suboptimal conditions, leading
to areas where the pipe ends have not correctly
fused together. These defects and others considered
can reduce the strength of the weld and
therefore provide unwanted uncertainty in the
operational lifetime of the pipe, which is not
acceptable in the nuclear sector where safety
is of primary concern. A major focus of this project
is on simulation of ultrasound produced by
ultrasonic transducers in NDE of the pipe welds
so that experimental data can be better understood
and supported by the findings. Coupled
with this, current work involves the accurate determination
of phase velocity and attenuation
of HDPE over a range of frequencies, temperatures,
and other parameters relevant to ultrasonic
NDE. These data will be used within the
simulations to ensure accuracy and reliability.
Finite Element Methods for MHD Modelling
with Application to Fusion Blankets
Researcher: Ji Soo Ahn
Supervisor: Dr Mike Bluck
Sponsor: Imperial College PhD Scholarship
Finite element methods for Magneto Hydro-
Dynamic (MHD) modelling are being applied to
fusion blanket. Developing an accurate and efficient
numerical solver for MHD is desired in
fusion engineering because of the limitations
of testing facilities. The boundary layers near
the Hartmann walls and side walls can have
significant impact on flow behaviour and heat
transfer capabilities in the presence of a strong
magnetic field. Analysing the flow behaviour
in these layers is thus crucial when designing
the fusion blanket. This process can be costly
because the smallest thickness of the layer is
in the order of Ha-1 and the Hartmann number
(Ha) is often greater than 104 under fusion conditions.
Thermohydraulics of DRACS Passive Safety
System in Fluoride High-Temperature Nuclear
Reactor
Researcher: Niccolo Le Brun
Supervisors: Dr Christos Markides and Prof Geoff Hewitt
Sponsor: Centre for Nuclear Engineering
Molten salt reactors are currently being scrutinised
as an alternative to conventional nuclear
power plants because of their inherent safety.
In a molten salt reactor passive safety systems,
which do not rely on human intervention
and/or supply of power, can be used to assure
the removal of decay heat under various critical
scenarios. DRACS (Direct Reactor Auxiliary
Cooling System) is a passive safety system currently
being considered as a viable design component.
The aim of this project is to assess the
feasibility of DRACS from a thermo-hydraulic
point of view. In particular several aspects of
molten salts as coolants need to be considered
for a safe design. One of the most critical point
which was recognised in the current study is
the possible catastrophic freezing of the coolant
during DRACS operation.
47 http://www.imperial.ac.uk/nuclear-engineering