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NuclearPlantJournal.com Nuclear Plant Journal, March-April 2016
Solution for...
Fleet-wide Analysis Cost: $300K vs.
$9.0M ($1.5M average industry cost per
unit, to date).
Fleet-wide Hardware Cost: $620K
vs. $9.2M ($400K estimated industry
cost per transformer).
Additional savings are anticipated
for installation and outage costs. This
is because the design scheme utilizes
existing wiring and logic (negates long
cable installations from switchyard to
main control room) and because the
scheme can be installed independent of
refueling outages. Total cost savings are
anticipated at greater than $17M.
Innovation Response
Following the initial open-phase fault
at Byron Nuclear Plant in early 2012,
members of the team took up leadership
roles in various industry working groups,
including the NEI Open-Phase Steering
Committee and Open-Phase Analysis
Working Group. The initial industry
consensus to this issue was to focus on
open-phase detection at the offsite power
transformer, utilize a fast-acting transfer
scheme (within cycles), and abandon
traditional analytical software (e.g.
Electrical Transient Analyzer Program
(ETAP)). As the industry approach
to this new failure mode continued to
evolve over the next two years, the team
leveraged their involvement in the issue
to make industry-wide advancements on
several fronts. The over-arching principle
behind the team’s efforts was to fully
understand the underlying phenomena
associated with an open-phase fault and
then to use the engineering process to
develop the best solution.
Team members worked with the
academic community through a TVA-
sponsored research lab at the University
of Tennessee, Chattanooga to develop
academically sound analytical techniques
and modeling approaches (Ref. 1).
Team members also used their
leadership role in the ETAP Nuclear
Utility User Group to work directly
with the supplier of ETAP software (the
most commonly used software in the
U.S. nuclear industry) to drive changes
to the software which were needed to
allow proper modeling of an open-phase
condition for nuclear plants. Once ETAP
software was modified and validated by
the supplier, the team directed an Open-
Phase Fault Task Force, made up of ETAP
NUUG members, to demonstrate that
the software could be used to model the
effects of an open-phase fault on a typical
nuclear plant. Using the ETAP software
and existing plant models, the team
developed a unique way to characterize
the effects of an open-phase fault by using
a “heat map” to graphically display five
critical parameters on a single plot (see
Graphic 1). This allowed visualization
of the nature of open-phase fault effects.
Thus, the efforts of the team on this front
have led to a first-of-a kind analytical
methodology, all of which has effectively
changed the nuclear industry in this field.
This has been recognized by NRC (Ref 2),
WANO (Ref 3), and World Nuclear News
(Ref 4). In May 2014, TVA partnered
with EPRI to test and validate the EPRI-
developed open-phase detection (OPD)
technology at TVA’s Bellefonte Nuclear
Plant where, for the first time in history,
an open-phase fault was intentionally
created on an offsite power circuit to a
nuclear plant. The successful testing of
EPRI’s OPD system on a station offsite
power transformer proved that nuclear
plants can use the EPRI technology to
detect open-phase faults under all loading
conditions. As part of this validation
test, the team collected electrical data
throughout the plant to provide further
characterization of the effects of open-
phase faults. An industry standard Class
1E voltage balance relay was installed
at the Class 1E boundary during the test
to demonstrate that such a relay may be
used to protect the critical safety-related
power system against the effects of an
open-phase fault. The efforts of the team
on this front has been recognized by both
NRC (Ref 5) and EPRI (Ref 6).
Like the rest of industry, TVA’s
goal was to develop a solution to the
open-phase issue that would provide
complete protection of the safety systems
for any open-phase condition. While
initial industry speculation was that a
Class 1E protection system could not be
developed to remove the vulnerability
of an open-phase fault, the analytical
techniques pioneered by the team (heat
maps) demonstrated that for every type
of open-phase fault that could prevent the
functioning of safety equipment, therewas
an associated voltage unbalance that was
readily measurable by existing protective
Graphic 1.
