Sodium
Cooled
Fast
Reactor
By Yoon Il Chang, Argonne National
Laboratory.
Yoon Il Chang
Dr. Chang joined Argonne National
Laboratory in 1974 and has been
responsible for leadership of advanced
reactor design and
fuel cycle technology
development
activities in position
of increasing
responsibility
including: Director
of Large Pool Plant
Project, General
Manager of the
Integral Fast Reactor
Program, Associate
Laboratory Director
for Engineering
Research, and
Interim Laboratory
Director.
He has a Ph.D. in
nuclear science
from University of
Michigan.
Responses to questions by Newal
Agnihotri, Editor of Nuclear Plant
Journal.
1.
Does the PGSFR have any affiliation
to the International Generation Four
project coordinated by the Nuclear
Energy agency/OECD?
Although Prototype Generation-IV
Sodium-cooled Fast Reactor (PGSFR)
is so designated to represent a prototype
of Generation-IV reactors, the project
is not affiliated with the Generation-IV
International Forum.
2.
Who will fund the cost for prototype
development?
The South Korean government is
responsible for funding the project.
3.
Describe the inherent safety
characteristics of the metal fuel design?
During an unpro-
tected
loss-of-flow
event, which can be
initiated by a station
blackout, the cool-
ant temperature rises
rapidly. The rising
temperature causes
thermal expansion of
fuel assemblies which
introduces negative
reactivity, prompting
the automatic shut-
down of the reactor
without operator ac-
tion. Such inherent
safety potential was
demonstrated in land-
mark tests conducted
at the U.S. Depart-
ment of Energy’s Experimental Breeder
Reactor-II (EBR-II) in April 1986. The
key factors making this possible are: 1)
sodium coolant with large margins to
boiling temperature, 2) pool configura-
tion with large thermal inertia, and 3)
metal fuel with low stored Doppler reac-
tivity.
Another important characteristic
stems from the fact that sodium’s
boiling temperature is very high, 881
degrees Celsius. The coolant system
does not need to be pressurized and can
be operated near atmospheric pressure.
Instead of a pressure vessel, a large pool
configuration is possible. The reactor
vessel is large enough to accommodate
primary system components -- the core
itself, primary piping, sodium pumps,
and intermediate heat exchangers, which
are all submerged in the sodium pool.
In such an arrangement, a passive decay
heat removal system based on natural
convection can be easily implemented.
These two features combined allow
PGSFR to survive and maintain safe
conditions, even after a station blackouts,
for several days without operator
intervention.
4.
Where will the PGSFR be located?
United States or South Korea?
PGSFR will be constructed in South
Korea.
5.
Why was the metal fuel technology
not applied to current reactor designs
after its success in April 1986?
As a matter of fact, GE Hitachi
Nuclear Energy changed its PRISM
Generation IV sodium-cooled reactor
fuel system from oxide to metal following
EBR-II’s inherent safety tests. Toshiba’s
4S (Super Safe, Small and Simple) reactor
and TerraPower’s TWR (Traveling Wave
Reactor) also use metal fuel. Why others
haven’t yet? A European colleague once
commented, “Our horse is in the middle
of a river. We will sink or swim with it.
We cannot switch horses in mid-stream.”
They have so much invested in the
conventional technologies -- on the order
of tens of billions dollars -- and cannot
afford to abandon their infrastructure
and start from scratch to develop a new
technology base.
6.
Describe the, “innovative design
features” of PGSFR
.
Obviously metal fuel and its inherent
safety potential are the most important
design features. With such inherent safety
features, the designers can emphasize
prevention of severe accidents rather than
adding mitigation features to deal with
the consequences of severe accidents.
In addition, PGSFR’s innovative design
features include advanced cladding
material to achieve high core outlet
temperature (545°C), diversity and
redundancy in passive decay heat
removal systems, electromagnetic pumps
for higher reliability, a pantograph in-
vessel fuel handling system to eliminate
the double rotating plug hence reducing
the reactor vessel diameter, failed fuel
40
NuclearPlantJournal.com Nuclear Plant Journal, September-October 2014
