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NuclearPlantJournal.com Nuclear Plant Journal, July-August 2014
6. Simplified emergency procedures
for small break LOCAs.
The
original emergency procedures used
two different procedures to transfer
to sump recirculation depending on
sump level. This has been simplified
to a single procedure.
Additional Benefits
In addition to the aforementioned
benefits that have been realized,
the changes from the ECCS Water
Management Project have the potential
to provide additional operational
advantages. Such additional benefits
would require further analyses and
justification to implement. The potential
additional benefits to boron precipitation,
post-LOCA subcriticality, sump debris
transport, and LOCA peak cladding
temperature are summarized below.
Initiation of hot leg recirc at an
earlier point in time following
a LOCA
. Hot leg recirc is the
realignment of one train of
intermediate head safety injection
to two hot legs instead of the cold
legs. The realignment is required to
prevent the core boron concentration
from reaching the level at which
precipitation will occur, and to
preclude the buildup of regions of
demineralized water that pose a
recriticality concern. Hot leg recirc
is aligned following the transition
to sump recirc, and may lead to an
increase in containment pressure
and temperature when it is done. As
a result, current analyses require a
significant delay from the initiation
of the event before starting hot leg
recirc. Revised analyses should
enable earlier transition to hot leg
recirc, producing associated benefits:
1) increased margin to post-LOCA
recriticality, and 2) increased margin
to boron precipitation.
Termination of high head safety
injection flow following transfer
to sump recirc
. The current
Westinghouse ECCs design and
procedures maintain high head
injection flow after a LOCA. With
low head and intermediate head
safety injection pumps providing
ample flow for core cooling, it
should be possible to terminate high
head pump operation without an
indicated subcooling margin as is
done for B&W designed reactors.
Implementing this benefit would be
a first for Westinghouse designed
reactors. This would limit the
exposure of the high head injection
pumps (which have the tightest
clearances) and the associated
throttle valves from the post-LOCA
debris that may be expected during
extended sump recirc operation.
Additional
margin
when
demonstrating compliance with
LOCA peak cladding temperature
requirements.
The margin may
be obtained through analysis by
increasing minimum containment
backpressure and extending the
duration of relatively cold RWST
injection. The increased containment
backpressure is estimated to result
in a 100°F benefit for peak cladding
temperatures.
Transferability
The ECCS Water Management
Initiative Project should be directly
applicable to any ice condenser
containment plant. There are five other
nuclear power reactors in theUnited States
with ice condenser units (DC Cook 1&2,
Sequoyah 1&2, andWatts Bar 1), and one
unit under construction (Watts Bar Unit
2). In addition, the methodologies used in
this work are also applicable to PWR dry
containment plants. The potential benefits
at any plant will depend on plant-specific
factors such as the extent those plants rely
upon containment spray to mitigate the
range of design basis events.
Contact: Eric Henshaw, Duke
Energy, telephone: (704) 382-7420,
email: Michael.henshaw@duke-energy.
com.
ECCSWater...
(
Continued from page 61)
Leveraging
Technology...
(
Continued from page 47)
Nuclear Generating Station to support
the IRT was well received. Palo Verde
Nuclear Generating Station plans to
permanently adopt the IRT process and
technologies used during the fall 2013
refueling outage. Based on the advantages
observed using the network accessible
collaboration software, Palo Verde
Nuclear Generating Station updated
their Unit 2 OCC with this technology
to improve outage communication and
collaboration. Use of the new OCC
technology during the spring 2014
refueling outage was well received and
Palo Verde Nuclear Generating Station
achieved a new station record for outage
duration.
LWRS Program researchers will
continue to monitor and assess the
process of technology implementation,
develop new AOCC capabilities, and
look for industry best practices related
to outage management for incorporation
into the AOCC. The results of this
research will be published in a technical
report for industry-wide implementation
of the AOCC in 2014.
References: St. Germain, Shawn, Ronald
Farris, and Heather Medema, 2013,
Development
of
Methodologies
for
Technology Deployment for Advanced
Outage Control Centers that Improve Outage
Coordination, Problem Resolution, and
Outage Risk Management, INL/EXT-13-
29934, Revision 0, September 2013.
Contact: Shawn St. Germain, Idaho
National Laboratory, telephone: (208)
526-9575, email: shawn.stgermain@inl.
gov.
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