POWER October 2014 - 46

OPERATIONS & MAINTENANCE
2. Readiness upgrades. Byron finished refurbishing its natural
draft cooling towers in 2013, including the extension of a metal barrier
along the bottom of the towers to help prevent icing and improve winter
readiness. Courtesy: Exelon Corp.
■ INPO Just-In-Time Operating Experience Report, " Cold Weather
Preparations. "
■ INPO Significant Operating Experience Report (SOER) 82-15,
" Freezing of Safety Related Equipment. "
■ INPO SOER 07-2, " Intake Cooling Water Blockage. "
A corporate procedure and many other internal Exelon procedures
drive all aspects of seasonal readiness and include various attachments
and checklists to complete. The procedure details the roles and
responsibilities for the winter readiness coordinator, and the other disciplines,
along with spring, summer, and fall milestones. It culminates
with a site certification letter stating that the plant is ready for the
upcoming winter season (Figure 2).
tems are evaluated by engineering and operations to identify maintenance
needs for pumps, valves, and heating coils. In addition, a
winter surveillance is performed by operations to ensure that insulation
is installed on selected outside louvers and to validate readiness
of tank heating systems.
To provide clear direction on this subject, a corporate seasonal
readiness procedure was created from past industry experiences and
NRC notices. It specifically references the following Institute of Nuclear
Power Operations (INPO) documents addressing winterization:
Don't Get Frazzled
An unusual phenomenon that some power plants must be alert to
is the formation of " frazil ice. " The ice forms below the surface
of a body of turbulent water when the sustained air temperature
is 18F or lower. Frazil ice crystals appear as elongated disks.
These disks gradually stick together to form large ice floes and
jams. Frazil ice can be drawn into cooling water intakes, where
it blocks flow by adhering to screens designed to prevent trash
from entering the intakes.
The Byron station has experienced issues with frazil ice in the past.
To correct this issue, a 4-inch warming line was installed off the 10inch
gravity-fed circulating water blowdown line. Blowdown water is
discharged on the outer bar grate, where the makeup pumps take suction
from the Rock River. This warm water increases the temperature
of the intake water to prevent frazil ice.
Although D.C. Cook's corrective action program has not recorded
instances of frazil ice blocking the cooling water intakes, as a preventative
measure, it uses the following factors to determine when it is
necessary to switch its circulating water system to de-ice mode:
■ Circulating water temperature is less than 35F.
■ There is greater than 1 foot of water drawdown in the forebay,
which is not caused by starting a circulating water pump. (The
forebay sits below the screenhouse and is the source of water for
the circulating water pumps and essential/non-essential service
water pumps.)
■ Traveling screens' high, or extreme high, differential pressure
alarms are annunciating with little or no trash collection in the
screen wash trash baskets.
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Effective Results
The successful Byron and D.C. Cook winterization programs utilize
team approaches. They also provide a framework for maintaining
plant reliability while preventing cold weather disruptions.
Despite snowstorms and frigid temperatures dominating the first
month of 2014, Exelon's nuclear fleet produced electricity around the
clock and was unaffected by ice. Exelon's 10 nuclear power plants
in Illinois, Pennsylvania, and New Jersey operated continuously
throughout January to help meet the region's electricity demand,
which peaked in the PJM transmission system on Jan. 7 at 141,312
MW-a wintertime demand record at the time. Its plants continued
to operate with the same reliability through a second blast of polar air
that began Jan. 21.
The D.C. Cook seasonal readiness program also proved its value
during the 2013-2014 winter season as southwest Michigan experienced
one of its coldest winters. Both units operated successfully
without any de-rates or unit trips, and they maintained 100% power
throughout AEP's winterization period. ■
-James M. Hylko is a POWER contributing editor.
http://www.hawkmeasure.com http://www.powermag.com
POWER October 2014

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