Nuclear Plant Journal, January-February 2016 NuclearPlantJournal.com
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and to power systems needed to provide
cooling of the nuclear core. We do have
emergency diesel generators and backup
battery systems in the plant, but they are
not required to protect and maintain the
cooling and safety of the core.
2.
How did you achieve unlimited
coping time period?
All commercial nuclear power
plants currently use large banks of DC
batteries as backup power for their
Engineered Safety Feature Actuation
Systems (ESFAS) when all AC power
is lost. Because these batteries serve
a safety function, they must meet the
IEEE standard for classification as a “1E
system.” One of the key functions of the
ESFAS is to start the emergency core
cooling system (ECCS). Because of the
simplicity of the NuScale design, only a
handful of safety-related valves need to
be opened or closed in the event of an
accident to ensure actuation of the ECCS.
These safety-related valves have been
designed to mechanically align to their
pre-set safe condition without the use of
batteries following a loss of all station
power. No AC or DC power is required
for this valve alignment. Similarly, the
inherent, passive cooling capacity has
been designed such that no pumps or
additional water are required to provide
an unlimited period of core cooling.
3.
Did you say that you are not using
DC power?
Neither AC nor DC power is required
to establish a safe, long-term cooling
configuration for the NuScale design. We
do have back-up AC power and a highly
reliable DC power source available as
part of our defense in depth program and
to assure post-accident monitoring for a
minimum of 3 days.
4.
What have you done with the SMR
design so that the instrumentation that
you have will support you during this
unlimited period to get the correct data
and also will sustain the brunt of the
accident?
With regards to post-accident
monitoring needs, the NuScale design
is quite a bit different because of its
simplicity, very low decay heat and
passive safety systems. Because of its
very simple and passive safety systems,
for example no pumps, there are very few
parameters to monitor. We implement
a highly reliable DC power system for
post-accident monitoring for the first 3
days. However that power is not required
to establish or maintain a safe long-term
cooling configuration. After 3 days the
core decay heat in each module is only
800 kW - a factor of 20 less than what was
generated in the reactors at Fukushima.
Natural convection and conduction heat
transfer from the modules to the water in
the pool where they reside are more than
adequate to assure cooling to the core
without instruments or power.
5.
How have you taken advantage of
the technology in the control room, in
the local control panels and auxiliary
electrical equipment room?
I think there’s probably no other place
that has changed as much as the control
room. The digital I&C capabilities today
are just phenomenal. If you look at the
existing fleet of nuclear plants compared
to what can be done with state-of-the-
art digital I&C, it’s a pretty remarkable
change. We built the world’s first SMR
control room simulator in Corvallis with
the goal of controlling 12 modules from
one control room. The control room
simulator has 12 independent work
stations each dedicated to simulating the
operation of a NuScale Power Module.
The first NuScale plant will be
a 12-module plant, controlled from
one control room. The reason we can
do that today is because of all of the
advancements in computer systems and
software in the digital I&C arena.
In terms of the instrumentation that
we’re looking at for the NuScale design,
wherever we found suitable existing
instrumentation, we tried to use it because
it already had the pedigree. These types
of instruments have been used in the
nuclear industry for a while. What we’re
finding that’s a little bit different is that
the accuracy of the instruments has
greatly improved, in terms of what you
can measure, and also, how you access
and connect that instrumentation to your
control room - to your digital controls.
We are taking advantage of things like
fiber optic cables to further improve the
safety of the design.
Wherever we could apply lessons
learned, we’ve done that. We have been
working with different instrumentation
groups. There’s the sensor side, and then
there’s our module protection system
side, where we’re looking at a digital
protection system.
We recently partnered with Ultra
Electronics in the UK, who work with
Rock Creek Technologies, LLC in the
US. They’re one of our strategic partners
now and are the designers of reactor
protection systems.
In terms of things that we’re
measuring, they are pretty much
standard—core inlet temperatures, outlet
temperature, pressures, etc…. But the
types of technology available and the
accuracy of the measurement systems
have really moved forward significantly.
Cross-sectional View of Reactor Building.
