Page 27 - Nuclear Plant Journal - March April 2013
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Nuclear Plant Journal, March-April 2013
27
protected from tornado missiles or other
debris. Consequently, the U.S. EPR
TM
plant would have sufficient on-site
resources to shutdown and cool the core
for more than two weeks without any
outside assistance.
The U.S. EPR emergency power and
cooling systems are already designed to
address “beyond design basis events”.
The Near Term Task Force (NTTF)
recommendations do not account for
plants with increased levels of safety
and redundancy in emergency cooling
supplies. As a result, to make the U.S.
EPR design even safer, AREVA made
some additions to the design to address
the NTTF recommendations. The NTTF
focused on operating plants that typically
have two seismically qualified emergency
diesel generators that are augmented
by an alternate A/C power source to
accommodate the Station Blackout Rule.
So, the NTTF applied an Extended Loss
of A/C Power event to be addressed by
these units. The U.S. EPR
TM
goes beyond
this approach by incorporating four
emergency diesels that are in seismically
qualified structures that are also located
above the floodplain and are leak tight.
Fuel and cooling sources are likewise
protected from any harm and electrical
connections, air intakes and air exhausts
are locatedmore than 60-feet above grade,
making them impervious to flooding.
Adequate core cooling can easily
be maintained for 24 hours after a loss
of offsite power, even with no credit
for installed emergency or station
blackout diesel generators, by shedding
unnecessary loads from the station
batteries and the use of a hard piping
connection between the firewater system
and the secondary coolant loop. Long-
term cooling in accordance with the task
force recommendations can be provided
via connections from firewater or portable
pumps to allow cooling water to be
delivered to both the secondary coolant
loop and the primary circuit (direct core
cooling).
9.
What fuel design, fuel monitoring,
and fuel storage enhancements have been
made in EPR?
To provide the most reliable fuel
performance possible, AREVA based the
EPR
TM
fuel design on existing AREVA
products with long performance histories.
We retained our advanced M5
TM
cladding
that is extremely resistant to oxidation,
and assembled the fuel pins in our
robust HTP
TM
grids that provide superior
structural support to the fuel. Direct in-
core monitoring is the most advanced of
its type, as fixed in-core neutron detectors
measure power in 72 core locations so
the on-line digital protections system
can calculate the approach to any core
thermal limits and trip the reactor. The
EPR
TM
spent fuel pool can store up to 10
years of irradiated fuel with an additional
full core offload into the pool. The pool is
designed to allow easy transport of spent
fuel from the pool to dry storage.
10.
What provisions have been made in
EPR to exclude the possibility of hydrogen
explosions similar to Three Mile Island
and Fukushima Daiichi?
In case of degraded conditions that
could lead to the production of hydrogen,
operators of EPR
TM
plants will open large
depressurization valves that vent steam
and hydrogen to the containment building.
Passive autocatalytic recombiners (PARs)
located within the containment building
remove hydrogen from the containment
building atmosphere by combining the
hydrogen with oxygen to create water.
This process occurs in the presence of a
catalyst, with no power required. Along
with passive mixing dampers located
throughout the containment building that
promote atmospheric mixing; the PARs
prevent buildup, or “pockets,” of hydrogen
at any location inside containment. The
number and capacity of the PARs are
selected to handle more hydrogen than
can be created from all sources following
any beyond design basis event.
Contact: KellyCousineau, telephone;
(202) 680-2469, email:
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