A long journey toward advanced nuclear fuels
By Casey O'Donnell,
for INL Communications & Governmental Affairs
 |
| The
samples were transported inside a cask within this shipping container,
which was then transferred from the ship to an Idaho-bound truck. |
This summer, researchers at the U.S. Department of Energy's Idaho National Laboratory received a long-awaited delivery.
After years of waiting, a trans-Atlantic voyage and a cross-country
trip, a cask containing four experimental irradiated pins of nuclear
fuel arrived at INL's Materials and Fuels Complex in late July. With
shipping facilitated by AREVA TN,
these pins traveled from the Phénix nuclear reactor in France, where
INL researchers had shipped them more than eight years ago.
The four pins contained advanced metallic and nitride fuels
fabricated by INL and Los Alamos National Laboratory, respectively, in
2006. The fuel within the pins holds the final bits of data from an
international experiment called FUTURIX-FTA.
FUTURIX, a collaboration between the U.S. DOE and the French Atomic
Energy Commission (CEA), is an important part of INL's research for
DOE's Fuel Cycle Research & Development program. The "FTA" in the
experiment's name alludes to the French phrase for "Actinide
Transmutation Fuels." In a nuclear sense, transmutation, the act of
turning one thing into another, involves re-using certain components of
used nuclear fuel. This would maximize the energy received from mined
uranium. It would also decrease the quantity of hazardous, extremely
long-lived radionuclides ultimately destined for nuclear repositories.
 |
| Upon arriving at INL, the shipping cask was unloaded into the truck lock at INL's Hot Fuel Examination Facility (HEFE). |
"One
goal of the Transmutation Fuels program is to increase the holding
capacity of a nuclear fuel repository without increasing the
repository's size," INL nuclear engineer Heather Chichester said. "To do
this, we're looking at ways to address limits on holding capacity:
volume, heat (produced by radioactive decay) and radiotoxicity of used
nuclear fuel."
Reusing uranium is one way to drastically reduce the volume of used
nuclear fuel, Chichester explained. Currently, only about 5 percent of
the uranium loaded into a reactor is actually consumed to produce
energy. The remaining uranium goes unused. This is because light water
reactors, the type of reactor found most predominantly in the world
today, can only fission U
235, a less plentiful isotope of uranium.
However, there is a type of reactor that can generate the energy necessary to fission the more abundant U
238 as
well as the other transuranic isotopes produced during irradiation of
nuclear fuel: a fast reactor. About 20 fast reactors exist in the world
today.
"Most of what's left in used light water reactor fuel—the U
238 , Pu
239 and
a few minor actinides—can be reused in a fast reactor," Chichester
said. "This would use our uranium resources more efficiently and reduce
the size and heat of the used fuel that has to be disposed."
 |
| The experiment cask is lifted into the HFEF hot cell through a hatch in its floor. |
Over
the past 10 years, the INL Transmutation Fuels team has tested dozens
of different fuel compositions that mimic what recycled used nuclear
fuel could look like. They are searching for the fuel composition that
offers the best results on both ends: efficient energy production in a
fast reactor and reduced waste disposal in a nuclear repository.
So where does FUTURIX come in?
"These fuels are intended for use in a fast reactor, but we don't
have a fast reactor available for testing in the U.S.," Chichester
explained. "So we've been running experiments under modified conditions
in ATR (INL's Advanced Test Reactor). We believe that the modifications
we've made reproduce most of the important aspects of the environment
inside a fast reactor, but we needed to confirm that."
To validate their ATR experiments, INL researchers sent four
FUTURIX-FTA fuel pins to France to be irradiated in the Phénix Fast
Reactor. The scientists also irradiated four identical pins under the
modified ATR conditions. After irradiation of the FUTURIX-FTA pins in
Phénix was completed, the four pins were stored in a hot cell in France
for several years before being shipped back to INL in July.
 |
| Employees
used manipulators to place the experiment cask in the hot cell, where
the cask will be opened so examination of the fuel samples can begin. |
Now
that they've returned to INL, researchers will perform detailed
examinations of both sets of pins. By comparing the ATR-irradiated pins
with those from the French fast reactor, researchers will be able to
deduce whether ATR experiments can adequately recreate fast reactor fuel
behavior.
Researchers hope the conditions experienced by these fuels in the
French fast reactor will line up with the conditions created for the
identical fuels tested in ATR. This would signify that the ATR
experiments accurately recreate fast reactor fuel behavior. If so, INL
researchers can continue to use their ATR experiments to study new fuels
and advance the goals of the Transmutation Fuels program.
"Hopefully, the FUTURIX-FTA experiment will validate the work we've
been doing with ATR for the Transmutation Fuels program," Chichester
said. "That's why finally getting a chance to examine these fuel pins is
such a big deal."
(Posted Nov. 7, 2014)
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