POWER February 2017 - 38

FUELS
Mixed Oxide Fuel
Mixed oxide fuel (MOX) is a blend of plutonium
dioxide and depleted uranium dioxide
that can be used as fuel in commercial
nuclear power plants. MOX fuel has been fabricated
and used in Europe for many years.
There, plutonium and uranium separated
from commercial spent fuel is recycled to
produce MOX fuel.
In the U.S., the Department of Energy
(DOE) proposed irradiating surplus plutonium
from dismantled nuclear weapons to
produce MOX fuel. CB&I AREVA MOX Services
is under contract with DOE's National
Nuclear Security Administration to design,
build, and operate a MOX Fuel Fabrication
Facility (MFFF) at the Savannah River site
in Aiken, South Carolina. Construction was
authorized to begin in 2007 (Figure 3),
but progress has been slow due to funding
shortfalls.
Even so, MFFF construction activities
have advanced with admirable nuclear
safety and quality records. Summary reports
released by the Nuclear Regulatory Commission
have identified no areas needing
improvement for six consecutive years. According
to AREVA, the rework rate during
construction has been less than 1%.
In February 2016, AREVA said that about
cooled to its solid state. The cylinders are
then shipped to an enrichment plant.
Enrichment. Although a number of
uranium enrichment processes have been
demonstrated, only two have operated on a
commercial scale: the gaseous diffusion process
and the gaseous centrifuge process. As
recently as 2000, half of all enriched uranium
was produced using the gaseous diffusion
technique; however, today the centrifuge process
has completely replaced gaseous diffusion.
The
gas centrifuge enrichment process
uses several rotating cylinders in series and
parallel formations. The machines are interconnected
to form trains and cascades.
When rotated at high speeds-from 50,000
revolutions per minute (rpm) to 70,000
rpm-the heavier UF6
gas molecules, which
include the most common uranium isotope
found in nature (U-238), move toward the
outside of the cylinder, while the lighter
molecules, containing U-235, remain closer
to the center.
Streams of slightly enriched uranium are
withdrawn from the centrifuge and sent to the
next-higher stage, while streams of slightly
depleted uranium are recycled back to the
38
3. New fuel fab facility. When finished,
the Mixed Oxide Fuel Fabrication
Facility will support the U.S. government's
nonproliferation program by converting nuclear
weapons-grade plutonium into reactor
fuel for commercial power plants. Courtesy:
CB&I AREVA MOX Services
Abundant Resources, Difficult
Decisions
Today, Kazakhstan is the world's leading
uranium producer (Table 1). And while Australia
leads the world by a wide margin in
reasonably assured recoverable uranium resources
(Table 2), Canada has the most tierone
(best-margin) assets.
The Temrezli project in Turkey offers one
$5 billion had been spent on construction.
Although most of the project procurements
were complete, it still expected about $3
billion more would be needed to finish the
job-mostly allocated to labor expenses. As
of July 2016, progress included 93% of concrete
and 96% of rebar installed; 325 glove
boxes on contract with 129 installed; 27 of
28 long lead glove boxes tested; 72 of 73
tanks installed; and 22 of 31 active gallery
modules installed.
next-lower stage, until eventually the desired
enrichment level is obtained. The enriched
UF6
is then packaged in cylinders for shipment
to a fuel fabrication plant.
Fabrication. There are various types of
fuel fabricated for different reactors around
the world (see sidebar), but the most common
fuel is low-enriched uranium (LEU)
fuel for light-water reactors. The fabrication
process begins by heating the solid UF6
) powder.
example of the difficult situation faced by
uranium mining companies under current
market conditions. The project, located near
the town of Sorgun, approximately 125 miles
east of the capital city of Ankara, is central
Turkey's largest identified uranium deposit.
Uranium Resources Inc. (URI) acquired the
project in 2015 when the company merged
with Anatolia Energy Ltd.
According to URI's 2016 annual report,
an independent pre-feasibility study (PFS)
was completed in February 2015. The PFS
assumed the project would produce an average
of 825,000 pounds of U3
O8 per year during
an initial 12-year mine lifetime. Under
such conditions, the study projected the allin
sustaining production costs for the project
would be $30.12/lb of U3
With the price of U3
O8
O8
.
less than $18/lb,
to
return it to its gaseous form. The gas is then
chemically processed to form LEU uranium
oxide (UO2
The powder is pressed into pellets, sintered
into ceramic form, and loaded into
zirconium alloy tubes. The alloy typically
contains about 95% zirconium combined
with various other metals designed to enhance
mechanical properties and resist corrosion.
Zirconium is a good choice due to its
low cross section for absorption of thermal
neutrons, effectively making it transparent
to the fission process in the reactor core.
The tubes, known as fuel rods, are constructed
into fuel assemblies containing up
to 264 rods. Some of the more common assemblies
have a 5-inch to 9-inch cross section
and measure about 12 feet long.
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the decision to move forward is a difficult
one. However, as one of AREVA's experts
explained to POWER, mining projects such
as Temrezli often take 10 years to go from
discovery into production, so putting them
on hold because of market price fluctuations
isn't always practical. Often, companies have
to move forward with the hope that prices
will recover sufficiently to make the project
successful in the long run.
Tim Gitzel, president and CEO of Cameco
Corp., one of the world's largest uranium
producers, with headquarters in Saskatoon,
Saskatchewan, expects prices to rebound. " It
is a question of 'when', not 'if' more uranium
is needed, " Gitzel wrote in the company's
most recent annual report. " There is still going
to be a need for more uranium-perhaps
even more so now that many projects have
been delayed or cancelled in the wake of low
uranium prices. "
Cameco follows a unique stage-gate process
when developing its projects. The process
includes several defined decision points
during the assessment and development stages.
According to the company, it reevaluates
each project based on current economic, competitive,
social, legal, political, and environmental
considerations, and it only proceeds to
the next stage if the project continues to meets
the company's criteria. Cameco has scaled
back development of its Yeelirrie and Kintyre
properties in Australia and at its Millennium
deposit in the Athabasca Basin of Saskatchewan,
based on this methodology.
POWER | February 2017
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POWER February 2017

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