Sustainable,
Safe
Used Fuel
Management
– It’s not
Waste until
It’s Wasted
By Michael McMahon, AREVA TN.
Michael McMahon
Dr. Michael McMahon is Senior Vice
President of Columbia, Md. based
AREVA TN Americas (a division of
AREVA Inc.), the
U.S. market leader
in providing
innovative total
systems solutions
for used nuclear
fuel and radioactive
waste storage and
transportation. He
was previously
based in France
and served as
the U.S. director
of international
projects for
AREVA’s Back End
Business Group,
which includes
the group’s used fuel management,
recycling, transportation and
decommissioning activities.
Before joining DE&S, Dr. McMahon
was an associate at the management
consulting firm McKinsey & Company.
He is a graduate of the United States
Naval Academy and has also earned a
doctorate in nuclear engineering and an
MBA from the Massachusetts Institute of
Technology.
An interview by Newal Agnihotri, Editor
of Nuclear Plant Journal at the NRC
Regulatory Information Conference
on March 12, 2014 in North Bethesda,
Maryland.
1.
What research and development is
being conducted by AREVA or by the
industry in fuel cladding degradation
during dry fuel storage?
The nuclear energy industry focuses
on safety and incorporates “defense in
depth” into the design of dry fuel storage
systems. The integrity of the fuel cladding
is important, but it is only the first line of
defense. The second line of defense is the
dry shielded canister (DSC). The DSC is
a stainless steel shell with a basket inside
that safely and securely holds fuel. It
contains materials to make sure that the
heat gets out, and it contains neutron
poison materials to ensure it stays
subcritical. Once the fuel is loaded into
the DSC, the water is drained out and it
is back-filled with dry helium. Then it is
welded shut with two lids and transferred
to the independent spent fuel storage
installation (ISFSI). With AREVA’s
technology, the DSC is then placed in a
horizontal storage
module
(HSM),
which is then bolted
shut. This module
serves as physical
protection for the
DSC and is a very
safe, stable system.
When it comes
to the fuel, the ma-
terial – in this case,
the zirconium alloy
cladding – is impor-
tant. Our team eval-
uates how it behaves
under radiation, heat
and stress, and a lot
of people are work-
ing with advanced cladding materials to
see if they can reduce hydrogen pickup.
As the fuel sits in the reactor, the clad-
ding starts to absorb hydrogen, which can
make the material more brittle. We need
to make sure the material is strong enough
so that it can be transported safely.
On the operating fuel side, we’re
working to keep the hydrogen uptake
in the cladding low, which makes the
material stronger and more durable. As
long as the fuel cladding stays intact, it is
a very safe system.
The research we’re doing is
innovating new technologies to improve
safety, quality and cost and to ensure
that the cladding is very robust and stays
intact, that it can be transported safely,
and that we understand the changes it will
undergo over time in dry storage.
2.
How is aging management of fuel in
dry fuel storage accomplished?
We are working directly with
the Electric Power Research Institute
(EPRI) and the U.S. Department of
Energy (DOE) on the high burnup fuel
demonstration project. This project aims
to take a dry cask with a bolted system,
called a TN-32, and test it. We’ll put
high burnup fuel into the canister and
monitor the key parameters over a period
of 10 or even 20 years. We want better
long-term data for the behavior high
burnup fuel in dry storage. For example,
we want to study high burnup fuel with
greater than 45 gigawatt-days per metric
ton of uranium of burnup. As part of this
project, we will take fuel samples from
the canisters at specified times and send
them to a laboratory to determine how
the fuel responded to temperature and
radiation.
We’re also working on innovative
projects related to gas monitoring. If
the fuel in the canister develops a leak,
it will emit a detectable gas. Our goal is
to collect data to better understand what’s
happening to the fuel as it ages in place in
dry fuel storage.
The fuel sitting in dry storage is in a
fairly benign environment. All the water
and moisture have been removed from
the canister and it is filled with an inert
atmosphere of dry helium to prevent
corrosion. When it is transported, we
have to account for vibratory stress and
DOE is doing some analysis to see how
the fuel responds. To address the behavior
of fuel inside the canister, we have long-
term monitoring and vibratory testing.
We’re also evaluating the behavior
of the canister itself for long-term aging
management. We’re conducting research
on chloride-induced stress corrosion
cracking, which is cracking in metal
that can occur under certain conditions,
including the presence of chlorides and
residual stresses in the material. For
our canisters, we are looking at closure
welds that seal the canisters, which
can be a source of residual stresses,
because different parts of the weld heat
up at different rates. To relieve stress
in a fabrication facility, canisters are
placed in large ovens and heated slowly,
which relieves the stress. However when
24
NuclearPlantJournal.com Nuclear Plant Journal, May-June 2014
