POWER September 2023 - 16

FOCUS ON O&M
implement the processes associated
with preparing for and executing nuclear
refueling outages. "
3. Daily U.S. nuclear capacity outage. Source: U.S. Energy Information Administration
In recent years, the average refueling
outage duration has been about
32 days. That's a marked improvement
from earlier times. In 1997, for example,
the average length of nuclear refueling
outages in the U.S. was more than 80
days. A keen focus on continuous improvement
helped bring the average duration
down in subsequent years until in
2002 an average duration of about 33
days was achieved. Durations have fluctuated
since then, but have remained
constantly in the 30- to 46-day range
over the past two decades, according
to Statista, a market data provider.
EPRI Guidance on Refueling
Outages
Sound planning is essential to a smooth
refueling outage, which is why it's no
surprise that a great deal of time has
been spent optimizing outage planning
techniques. For example, in 1993,
the Electric Power Research Institute
(EPRI) issued a technical report titled
" Effective Refueling Outage Preparation
and Execution Guidance. " The
guidance was specifically developed
to provide the nuclear industry with a
comprehensive resource for improving
the planning, preparation, and execution
of nuclear power plant refueling
outages. The document aimed to help
power plant operators optimize outage
schedules, minimize downtime,
enhance safety, and improve overall efficiency
during the refueling process.
Subsequent versions and updates of
this guidance have been released by
EPRI to reflect evolving industry best
practices and technological advancements.
The most-recent update was
published in November 2022.
The latest abstract for
the
report
notes, " Excellence in nuclear refueling
outage nuclear safety, outage performance,
optimization of outage duration,
and management of costs is an ongoing
industry effort. " It says the report pro16
vides
guidance to assist personnel in the
preparation and execution of a nuclear
refueling outage, including:
■ Transitioning the plant from online and
maintenance activities into an outage
mode.
■ Returning the plant safely and effectively
from outage mode to operating
mode.
■ Information on how outage activities
support station or fleet long-range and
strategic planning.
■ Collection of human performance information
related to the preparation
and execution of a nuclear refueling
outage, including techniques and good
practices used by EPRI members.
EPRI says the information presented
in the report is " a single reference for
outage team members to consistently
ChemWorks Shutdown Calculator
Another useful outage planning tool
developed by EPRI is its ChemWorks
Tools. ChemWorks is a computer program
that includes several modules for
evaluating chemistry in a nuclear power
plant. One of the modules in ChemWorks
is a shutdown calculator (SDC)
tool to model the shutdown chemistry
evolution and predict cleanup times in
pressurized water reactors (PWRs).
Recently, a team of researchers from
Korea Hydro and Nuclear Power's (KHNP's)
Central Research Institute studied
the utilization of EPRI's ChemWorks
Tools for PWR shutdown chemistry evolution
modeling. Results were published
in June 2023 in Nuclear Engineering and
Technology, an international journal of
the Korean Nuclear Society.
The article notes that a shutdown
chemistry evolution is performed in
nuclear power plants at each refueling
outage to establish safe conditions to
open the system and minimize the inventory
of corrosion products in the reactor
coolant system (RCS). It explains
that after hydrogen peroxide is added
to the RCS during the shutdown chemistry
evolution, corrosion products are
released and are removed by filters and
ion exchange resins in the chemical volume
control system.
The researchers note that the shutdown
chemistry evolution, including RCS
cleanup time to remove the released corrosion
products, impacts the critical path
schedule during outages. The estimation
of cleanup time prior to the outage can
provide more reliable actions for RCS
cleanup operations and transients to
operators during shutdown chemistry.
EPRI's SDC tool estimates the cleanup
time using operational data from the nuclear
power plant, specifically, cobalt-58
peak activity.
The team evaluated the SDC tool us4.
The High Flux Isotope Reactor (HFIR)
at Oak Ridge National Laboratory (ORNL)
is shown here undergoing a routine refueling.
While submersed, the spent fuel emits
a luminescent blue glow due to Cherenkov
radiation, in which shedding electrons move
through the water faster than the speed of
light. Source: Jason Richards/ORNL
www.powermag.com
ing actual plant data from two refueling
outages. In summary, the results
showed that EPRI's SDC provided reliable
estimates of cleanup time and modeling
can be used to predict shutdown
chemistry plans more accurately. The
researchers said this could contribute
to improving the efficiency and safety of
future shutdown chemistry evolutions in
nuclear power plants. ■
-Aaron Larson is POWER's
executive editor.
POWER | September 2023
http://www.powermag.com
POWER September 2023

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