Optimum
Power
Coastdown
Strategy
By James Tusar, ExelonGenaration.
James Tusar
James Tusar is a graduate of
Pennsylvania State University with a BS
in Nuclear Engineering, from Drexel
University with an MS in Environmental
Engineering, and
has a Professional
Engineer’s License in
Nuclear Engineering.
He is currently
Senior Manager
of Boiling Water
Reactor Design for
Exelon Generation
which includes
responsibility for
nuclear fuel design,
reactor core design,
core management,
core monitoring
systems, and reload coordination for 8
reactors in 4 states.
James has been recognized for his
nuclear industry accomplishments with
ten (10) Nuclear Energy Institute (NEI)
Top Industry Practice (TIP) Awards.
Nuclear Energy Institute’s Top Industry
Practice (TIP) Awards highlight the
nuclear industry’s most innovative
techniques and ideas.
This innovation won the 2015 Nuclear
Fuel Award.
The team members who participated
included: James Tusar, Senior Manager,
Nuclear Fuels, Exelon; Dale Bradish,
Engineer, Nuclear Fuels, Exelon;
Richard McCord, Principal Engineer,
Global Nuclear Fuel; Adam Donell,
Reactor Engineer, Peach Bottom Atomic
Power Station, Exelon; Rob Lee, Nuclear
Fuel Buyer, Nuclear Fuels, Exelon.
Summary
Exelon’s optimum power coast-
down strategy is a top industry practice
in the Fuels category because it directly
addresses one of the key issues in the
nuclear power industry today – challeng-
ing economic conditions. The economic
challenge is primarily low electricity
prices, largely driven by the natural-gas
fracking boom and also the new renew-
able energy projects such as wind power.
Plants at four U.S. nuclear power stations
have recently shut down: San Onofre,
Kewaunee, Crystal River and Vermont
Yankee. Those closures have largely
been the result of falling power prices and
rising costs (main-
tenance,
repairs).
The optimum power
coastdown strategy
addresses the eco-
nomic challenges by
realizing significant
net cost savings for
every fuel cycle.
Power coastdown
is the planned reactor
operating condition at
the end of a fuel cycle
where
maximum
thermal power can no
longer be maintained due to fissionable
isotope depletion. This results in a
gradual decrease in core thermal power
(Graphic 1 on page 58). The optimum
power coastdown strategy uses an
automated method to determine the
optimum coastdown length (measured
in days) and maximum net cost savings
based on many economic and plant-
specific factors. Optimum coastdown
is ultimately achieved by balancing
the incremental fuel cost associated
with maintaining full power against
the generation cost associated with lost
generation during the coastdown.
On the surface, the optimum
power coastdown strategy may seem
counterintuitive. If a power plant is not
operating to maximum capacity at all
times, it is clear that maximum revenue
is not being generated. However, by
utilizing power coastdown, additional
energy is being produced after the reactor
has lost its ability to maintain full power.
This strategy essentially extends the cycle
length and produces additional power
(albeit at a de-rated condition) without the
necessity to purchase additional fuel. By
planning coastdown into the fuel cycle,
generation losses are offset by fewer new
fuel assemblies (or a lower enrichment)
which need to be purchased, resulting
in significant cost savings. Graphic 2 on
page 59 shows the net fuel cycle savings
as a function of planned coastdown
lengths. In this example, the maximum
net fuel cycle savings is $1.6 million
for a 24 day coastdown. On an Exelon
fleet basis, this conservatively results in
savings of at least $8 million annually.
This strategy maximizes the earnings and
cash flow from our assets.
Exelon’s optimum power coastdown
strategy is sophisticated, accounting
for the time cost of money (new fuel is
purchased two years in advance of the
power coastdown for a two year fuel cycle)
and multi-cycle energy carryover impacts
on future cycles due to the reload fuel
batch size reduction. The Exelon strategy
of optimum coastdown is embodied in
a software quality-assured spreadsheet
model, accounting for many plant and
cycle specific factors including the cost
of new fuel, replacement power costs
during the coastdown period, coastdown
rate, fuel cycle length, power level,
interest rates, and the energy capability of
the new fuel. The coastdown strategy is
applicable to both BWR and PWR units,
at all power levels and cycle lengths.
Safety Response
The optimum power coastdown
strategy enhances nuclear safety. This
strategy results in a decrease in the
number of reload fuel assemblies that
need to be purchased and loaded into the
core. On average, a 5% reduction in the
number of new fuel assemblies required is
realized. Therefore, fewer fuel moves are
necessary during a refueling outage and
generally less handling of fuel assemblies
is necessary (receipt, inspection and
storage). Nuclear safety is enhanced due
to a reduction in handling of new nuclear
fuel assemblies which reduces the risk of
accidents and human performance errors.
Also, full core discharge capability to
the spent fuel pool is being challenged
at some of our stations. The optimum
power coastdown strategy reduces the
total number of fuel assemblies purchased
56
NuclearPlantJournal.com Nuclear Plant Journal, July-August 2015
