The Unique
Safety
Attributes
of the
NuScale
Power
Module
By Jose Reyes, NuScale.
Jose Reyes
Dr. Reyes is the co-founder of NuScale
Power and co-designer of the NuScale
passively-cooled small nuclear reactor.
He is an internationally recognized
expert on passive
safety system
design, testing
and operations
for nuclear
power plants. He
has served as a
United Nations
International Atomic
Energy Agency
(IAEA) technical
expert on passive
safety systems. He
is a co-inventor
on over 60 patents
granted or pending
in 17 countries. He
recently received
two national awards;
the 2013 Nuclear Energy Advocate
Award and the 2014 American Nuclear
Society Thermal Hydraulic Division
Technical Achievement Award.
He holds Ph.D. and M.S. degrees in
Nuclear Engineering from the University
of Maryland and a B.S. degree in Nuclear
Engineering from the University of Florida.
An interview by Newal Agnihotri,
Editor of Nuclear Plant Journal, at
the American Nuclear Society Winter
Meeting in Washington, D.C. on
November 10, 2015.
1.
How does the NuScale design ensure
that the reactor keeps cooling in a beyond
design basis accident?
First, we need to have a basic
understanding of the NuScale plant.
NuScale Power Modules are comprised
of an integrated reactor vessel which
houses the fuel, steam generators and
pressurizer, which sits inside of a
cylindrical containment vessel. So our
containment is a steel vessel, factory
manufactured, and rated at 1000 psi.
Typical PWR containments operating
today are less than 20 psi. Our design
does not have Reactor Coolant Pumps.
Instead, the driving force for primary
system reactor coolant is natural
circulation, using convection, conduction
and gravity, within the unique system
geometry, to provide coolant flow.
NuScale Power Modules reside be-
low grade in a common concrete pool with
a stainless steel liner that provides stable
cooling for an unlimited period of time
following any ac-
tuation of the emer-
gency core cooling
system
(ECCS).
During normal plant
operations,
heat
is removed from
the pool through a
closed loop cooling
system and ultimate-
ly rejected into the
atmosphere through
a cooling tower or
other external heat
sink. In the event AC
power is lost, core
decay heat is trans-
ferred to the reactor
pool by the passive
safety systems previously mentioned and
the pool will gradually heat up and be-
gin to boil. Water inventory in the reactor
pool is over 7 million gallons and is large
enough to remove core decay heat from
all the NuScale Power Modules for an
unlimited period of time without adding
water. In the evolution of a design-basis
accident scenario the reactor core never
becomes uncovered with water.
The events of Fukushima highlighted
the importance that traditional reactors
have of needing back-up sources of
electricity to power the essential valves
and pumps needed for long-term cooling
of their nuclear power plants. The
complete station black-out caused by
the earthquake and subsequent tsunami
eventually led to extensive damage to
the Daiichi nuclear units because of their
inability to power their safety systems.
Their final lines of defense were banks of
DC batteries with a limited life.
Two years after the Fukushima
event, we introduced a safety system for
our NuScale Power Module that does not
require DC batteries to place the plant
in a safe cool-down condition following
an extreme event. This is a revolutionary
solution to one of the biggest technical
challenges for the current fleet of nuclear
energy facilities. Because of our unique
design, it allows the NuScale plant to
achieve a ‘
Triple Crown for nuclear
plant safety
’—to safely shut down and
self-cool,
indefinitely
, with no operator
action, no AC or DC Power and no
additional water. The patent pending
breakthrough eliminates all of the DC
batteries usually needed to align valves
Cutaway of the NuScale PowerModule.
26
NuclearPlantJournal.com Nuclear Plant Journal, January-February 2016
