Drywell
Replica
By Brian O’Grady, Entergy Nuclear.
Brian O’Grady is the former
Vice President and Cheif Nuclear
Officer of Cooper Nuclear
Station, Entergy Nuclear.
Credit:
World Association of
Nuclear Operators “Inside
WANO” newsletter, Volume 21,
Number 1, 2013.
Cooper
Nuclear
Station’s
construction of a replica of a quarter of
the plant’s drywell area helped to save
an estimated 600 man hours of outage
work and reduce radiation dose from
a predicted 44 REM to 31 REM during
work to replace four fan coil units.
“The fan coil replacement – an
infrequently conducted evolution – was
a tremendous success for Cooper,” said
Entergy Nuclear’s Brian O’Grady, former
Vice President and CNO of Cooper.
“We came in under our dose goal and
on schedule, both of which are directly
related to the use of our drywell mockup.”
Construction of the
drywell replica
Cooper, an 810-megawatt boiling
water reactor, is owned by the Nebraska
Public Power District and managed by
Entergy Nuclear. The plant came online
in July 1974. In 2010 the station received
a license renewal from the US Nuclear
Regulatory Commission to operate for
another 20 years. Cooper is located 80
miles from Omaha, Nebraska in the
central United States.
Chris Pelchat, Cooper project
manager, said the work included
contracting local metal fabricators,
carpenters and other specialists to build
the $250,000 replica, which was housed
inside a closed school at a nearby town.
The replica took three months to build.
The replica supported a project
to replace the plant’s four belt-driven
fan coil units with direct-drive units,
an enhancement related to Cooper’s
change from a 12-month fuel cycle to an
18-month cycle.
The drywell replica was built and an
adjoining training facilitywith classrooms
and a workstation for the radiation
simulation tracking was constructed.
A wireless system was set up to
analyze movements in the radiation
area, with location tags worn with the
dose rate metres. The location tags gave
workers information on the best path
while performing work in the replica to
lower the dose. Real-time video added
to the practice work and the video of
the actual drywell work was available to
anyone with access to the plant’s internal
website.
A radiation survey of the actual
drywell in the station, taken during the
last refuelling outage, supplied the data
for the mockup radiation simulation.
Imagery also was taken during the last
outage by a 360-degree laser measuring
of all the elevations of the drywell.
Training and teamwork
Groups of plant employees,
supplemental workers and vendors spent
three weeks at the replica, practicing ways
to limit dose. The coursework was broken
into two-hour rotations of three teams,
who would then evaluate their training
through video playback and discussion.
“We went through the training with
the workers and went from basic to
more complex work,” said Pelchat. “For
example, the drywell mockup is pretty
well lit for the initial training. But then as
training progresses, they have to hang the
temporary lighting, be dressed out and
perform all the tasks that they would have
to do in the actual evolution.”
“The team members have come up
with some incredible ideas – how can we
get around this, how can we make this
better – it’s a questioning attitude that
makes this whole project even better,”
said Pelchat.
Pelchat said ideas solicited from
the workers resulted in an easier way to
move equipment and tools to and from
the drywell mockup, without the hazards
and raised dose from rigging.
A metal box was constructed to roll
on rails of ball bearings to and from the
entrance of the drywell mockup, reducing
dose and saving time.
“That gave us a lot more flexibility to
move something, to get it out of the way,”
said Pelchat.
The mockup was painstakingly
designed from the original plant
blueprints, with details down to small
upward kinks in the metal-grating
floor that workers would step on while
performing the evolution.
The replica fan motor assemblies and
coil assemblies are the precise weights of
the actual plant machinery. The training
also included disassembling pipes in
order for welders to reassemble them.
“Just sharing an identical replica
is beneficial,” said Pelchat. “When the
workers come down here they can see the
challenges other teams or personnel face.
It really makes the teams think about how
to work well together.”
Public engagement
Pelchat said while building the
mockup, nearby residents would come
by the closed school to see what was
going on. He said the interest prompted
a community outreach day sponsored by
Cooper. More than 200 people attended.
“This gave us a chance to tell the
people how we are working to assure
their safety and be transparent about the
changes we’re making to the plant,” said
Pelchat. “There was a lot of community
interest and a great chance for us to tell
our story.”
“I am definitely happy with the
results,” said Pelchat. “The vendors
on the project were all new to nuclear
prior to this. The drywell mockup gave
them the opportunity to develop proper
radiation worker behaviours better than
any classroom training. The project’s
aggregate dose, duration and overall
success can be attributed to their practice
and lessons learned while rehearsing the
mockup.”
Nuclear Plant Journal, July-August 2014 NuclearPlantJournal.com
65
The plan sheet of Cooper’s Drywell
used to build the mockup.
