Nuclear Plant Journal, March-April 2014 NuclearPlantJournal.com
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There is a reduction on challenges to
operators for forced outages.
Failure degradation can result in very
high background activities and the
need of a possible mid-cycle outage,
(such as GGNS Cycle-15).
This is the dose from the Grand Gulf
mid-cycle outage that could have been
saved if a mid-cycle outage would have
been avoided due to early detection of fuel
failure:
~16.0 REM of exposure, total
13.5 REM dose on the refueling floor
~2.5 REM additional dose associated
with other maintenance work while
the unit was down in cold shutdown
and to start the plant back up.
The mid-cycle outage during Grand
Gulf Cycle-15 lasted 7.9 days.
A mid-cycle outage will cost about
$1M/day of outage plus other costs: on
average, $10M.
The Entergy correlation model
predicted a fuel failure at Exelon’s Quad
Cities which was later actually found.
The Entergy correlation was in
agreement with a later fuel failure declared
for Exelon’s LaSalle-2.
Preventing mid-cycle outages saves
$10 million for a utility operator.
Innovation
The innovation of this top industry
practice comes in the form of taking the
initiative to research existing data.
The beginning of the analysis by
David Smith was the first step. After weeks
of deep-dive research, the data began
emerging in a pattern for very minute
levels of off-gas data.
A large data base was assembled using
fleet and data from Exelon’s La Salle-2
and Quad Cities-1 units. Then “NEEDED
ACTIONS” were outlined for the team
along with monitoring recommendations
and charting cycle data. The correlation
took shape following the analysis of Xe-
133 responses power changes and Xe-138/
Xe-133 Ratio responses to power changes.
Productivity/Efficiency
Classic identifiers such as the Xe-
138/Xe-133 ratio were not always reliable
in detecting small, tight fuel failures.
The development of a new correlation
model has proven to be a more accurate
way to look at the data particularly when
radiation levels are complicated by tramp
activity holdup, curd/tramp relocation
and measurement uncertainties. Early
detection of such fuel failures is critical
in that the failure can be quickly identified
and effectively managed to prevent further
degradation and significantly reduce
the probability of a mid-cycle outage to
remove a degraded failure.
1. The correlation model is applied
to ambiguous data gathered to evaluate it.
This is a more efficient way for site and
fleet personnel to conduct analysis on the
collected data.
2. New sampling methods were
recommended by the research for off-gas
sampling within designated hours to the
start of the shutdown of power then at
periodic increments of full power and for
coolant sampling. By obtaining specific
data within the chemistry database, the
correlation model is efficiently applied at
sites across the Entergy fleet.
Transferability
The new model has been incorporated
into the Entergy fleet process for fuel
failure detection applicable to all BWRs.
It will be employed for any questionable
chemistry data and during refueling
shutdowns to ensure any failures are
detected and removed prior to starting up
a new cycle.
Contact: Entergy Nuclear, 1340
Echelon Parkway, Jackson, Mississippi
39213; telephone: (601) 368-5412.
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