RC106 MayJune2023 - Magazine - Page 15
DGR: NWMO, CONTAINERS: JOHN TENPENNY
L TO R: A 3D rendering of Canada’s
proposed deep geological repository.
Made from steel and copper,
used nuclear fuel containers are
designed to contain and isolate used
nuclear fuel in a deep geological
repository, essentially indefinitely.
carbon steel for strength and coated with corrosion-resistant copper—encased in a buffer box of bentonite clay
before being transferred to the main shaft for underground
placement. The clay provides an effective barrier to both
water flow and microbial growth giving an added layer of
protection against corrosion or degradation.
The repository underground will be accessed through
three shafts, which will be located within a single centralized and secure services area. This services area will
also include an underground demonstration facility for
initial testing of the future engineered barrier emplacement equipment. The layout also includes multiple access
tunnels that enable the placement rooms to be situated in
areas with the most suitable host rock. The buffer boxes,
with the used fuel containers inside, will be arranged in
the horizontal placement rooms, and any spaces left over
will be backfilled with granular bentonite pellets or chips.
In 2022, the NWMO’s engineering team successfully
completed a full-scale technical demonstration, where
technical teams built a life-size model of one of the
repository’s underground storage rooms at the NWMO
proof test facility, with the exact dimensions and interior
walls lined with simulated rock tiling. Over several days,
highly customized heavy machinery moved containers
designed for used nuclear fuel into the room and filled
the remaining space with protective material that will
ensure the containers retain their strength and durability
for many thousands of years.
“Our successful demonstration was the result of
made-in-Canada innovation and collaboration,” stated
Chris Boyle, vice president and chief engineer at the
NWMO after the demonstration. “Every step of the
process was undertaken using sophisticated prototype
equipment that was designed and fabricated in partnership with Canadian engineering companies.”
Currently, there are approximately 3.1 million bundles
of used nuclear fuel in Canada that are managed at nuclear sites in Ontario, Quebec, and New Brunswick, as well
as at Atomic Energy of Canada Limited’s sites in Manitoba and Chalk River Laboratories in Ontario.
Although the used fuel’s radioactivity decreases with
time, chemical toxicity persists and will remain a poten-
tial health risk for many hundreds of thousands of years,
“Once a used nuclear fuel bundle is removed from a
reactor they are placed in a water-filled pool where their
heat and radioactivity decrease. After 10 years, the bundles are placed in dry storage containers.”
Used since the 1980s, dry storage containers are made
of reinforced high-density concrete about 510 millimetres
(20 inches) thick and are lined inside and outside with
12.7-millimetre-thick (half-inch) steel plate. The thickness
of concrete provides an effective barrier against radiation.
The dry storage containers have a minimum design life
of 50 years. They are actively monitored, and studies indicate that with ongoing maintenance and inspections these
containers can be safely used for much longer periods
of time. After 50 years the life of the container could be
extended, or the used fuel could be repackaged.
Canada’s plan for safely managing used nuclear fuel
has come a long way over the past two decades, but pales
in comparison to the legacy a deep geological repository
could leave for generations to come.
“The hundreds of metres of rock that will surround the
repository will work with the engineered barrier system
and will help protect the repository from inadvertent
future human intrusion and disruptive events like future
ice ages and glaciations,” says Baker.
MAY/JUNE 2023 – RENEW CANADA 15