ECCSWater
Management
Initiative
By Eric Henshaw, Duke Energy.
Eric Henshaw
Eric Henshaw is a Principal Engineer
in the Duke Energy Nuclear Fuels
Engineering Safety Analysis Section,
located in Charlotte NC.
Mr. Henshaw received a Master of
Science in Nuclear Engineering from the
Georgia Institute of Technology and is a
registered professional engineer in North
Carolina and South Carolina.
Since joining Duke Power in 1984, he
has helped develop Duke Energy’s in-
house licensing basis methodologies
for performing Updated Final Safety
Analysis Report (UFSAR) Chapter
15 non-LOCA analyses and UFSAR
Chapter 6 containment response
methods for both large dry and ice
condenser containments.
Nuclear Energy Institute’s Top Industry
Practice (TIP) Awards highlight the
nuclear industry’s most innovative
techniques and ideas.
This innovation won the 2014 Vision,
Leadership and Ingenuity Award.
The team members who participated
included: Eric Henshaw, Principal
Engineer; Mike Weiner, Principal
Engineer; Bryan Meyer, Principal
Engineer; Ari Tuckman, Lead Engineer;
Tom Baumgardner, Senior Technical
Specialist, Duke Energy.
Summary
Duke Energy developed, licensed
and implemented significant changes
in the post-accident operation of
containment spray at the McGuire and
Catawba Nuclear Stations. The changes,
known as the Emergency Core Cooling
System (ECCS) Water Management
Project, produced a marked increase
in safety (reduction in calculated core
damage frequency or CDF) and reduced
operator burden during a postulated
accident. This project is consistent with
the Nuclear Energy Institute (NEI) and
the Pressurized Water Reactor Owners
Group (PWROG) Water Management
initiative.
Duke Energy recognized that
improvements in containment analysis
(coupled
with
other
analytical
improvements and minor plant hardware
changes) could, during certain postulated
events, significantly delay sump recirc
and provide other benefits by postponing
or eliminating the need for containment
spray. Accordingly, Duke Energy initiated
the ECCS Water Management Project to
use in-house methods to modify the plant
design basis for high energy line breaks
inside containment. The project hinged
on the ability to obtain an acceptable
containment pressure response and
acceptable dose consequences following
a large break LOCA with delayed credit
for containment spray.
The project was successful and
resulted in the following plant changes
which have been fully implemented in the
Catawba and McGuire Nuclear Stations.
The containment spray system was
changed from automatic actuation
on high-high containment pressure
to manual initiation following the
transfer to sump recirc.
Only one spray pump is operated
rather than two.
The requirement to take manual
action to align Residual Heat
Removal (RHR) spray was removed.
A narrow range refueling water
storage tank (RWST) level instrument
was installed to reduce RWST level
measurement uncertainty.
The RWST low and low-low level
alarm setpoints were reduced to
maximize injected volume from the
RWST.
The emergency procedures were
revised to transfer the intermediate
head and high-head injection pumps
to high pressure recirc at the RWST
low-low level alarm setpoint (rather
than the low level alarm setpoint).
The
technical
specification
requirement for minimum initial
RWST volume was increased.
Safety
Background Information
The
McGuire
and
Catawba
Nuclear Stations are dual unit four-loop
Westinghouse pressurized water reactors
(PWRs) with ice condenser containments.
Ice condenser containments contain
large quantities of ice through which hot
steam and liquid would flow following a
high energy line break inside the reactor
building. High energy line breaks include
large and small break loss of coolant
accidents (LOCAs), steam line breaks
and main feedwater line breaks. The
steam released from the high energy line
break would condense on the ice, thereby
minimizing the increase in containment
pressure. As a result, it was possible to
construct ice condenser containments
smaller and with a much lower design
pressure (15 psig for McGuire and
Catawba) than conventional PWR
containments.
Ice condenser containments are
equipped with containment spray
systems which were designed to actuate
at the initiation of a high energy line
break, taking suction from the refueling
water storage tank (RWST) and pumping
cold water into the top of containment to
provide additional steam condensation
(pressure reduction) and radioactive
fission product removal. The RWST
is also the source of ECCS injection
water – high head, intermediate head
and low head injection flow into the
reactor coolant system. The ECCS flow
keeps peak cladding temperatures below
regulatory limits and ensures adequate
soluble boron in the reactor coolant in the
event of postulated accidents.
Once the large inventory of the
RWST depletes to the low level alarm
setpoint following an accident (known as
injection phase), the suction source for the
low head injection pumps transfers to the
containment sump (known as the sump
60
NuclearPlantJournal.com Nuclear Plant Journal, July-August 2014
