Dislodging
A Fuel
Assembly
By Rob Garver, Dominion.
Rob Garver
Rob Garver is
currently the
Design Engineering
Manager at
Dominion’s
North Anna
Power Station in
Mineral, VA. Since
joining Dominion
in 1985, he has
held a variety
of engineering
positions at North
Anna and at the
fleet corporate
office, and
previously held
a Senior Reactor
Operator’s License. Rob graduated
with a Bachelor of Science in Nuclear
Engineering from The University of
Virginia and was a test engineer at
Newport News Shipbuilding before
joining Dominion.
Nuclear Energy Institute’s Top Industry
Practice (TIP) Awards highlight the
nuclear industry’s most innovative
techniques and ideas.
This innovation was a 2013 NSSS Vendor
Award Winner.
The team members who participated
included:
Rob Garver, Project Manager,
North Anna Power Station (NAPS);
Stewart Morris, Engineering Lead,
NAPS; Donna Rogosky, Project
Manager, Westinghouse; Jayne Boynton,
Design Manager, Westinghouse; Michael
Beddick, Field Project Manager,
Westinghouse.
Summary
On March 18, 2012, during lifting of
the reactor vessel upper internals during
a planned refueling outage, an irradiated
fuel assembly was determined to be
attached to the upper internals. Based
on industry OE, removal of the upper
internals above the reactor vessel flange
is closely monitored by underwater video
for just such an occurrence. The crane
motion was stopped within seconds
leaving the upper internals only about
one foot above the flange. By design, all
of the fuel assemblies are to remain in
the core as the upper
internals are lifted.
The polar crane was
secured in place and
deenergized. Due to
a concern that the
assembly could drop
back into the core
and be damaged,
the
containment
equipment
hatch
was closed and
the
containment
was evacuated as
a
precautionary
measure.
A laser device
was setup on the
upper internals to
detect any movement and a continuous
video feed to the main control room was
established. Only a Fuel Handling Senior
Reactor Operator and a Health Physics
Technician remained in containment
to monitor the fuel. Reactor Coolant
sampling verified that the assembly
had not been breached. An initial video
inspection identified the fuel assembly
and its location on the periphery of the
core. The 14 foot tall assembly had been
withdrawn from the core approximately
12 feet, with the 2 foot lower portion
inserted in the core. The fuel assembly
was suspended from the associated two
guide pins on the bottom of the upper
internals. Following successful capture
and separation of the fuel assembly
from the upper internals, inspection
and measurement determined that the
upper internals guide pins were slightly
bent resulting in sticking within the
fuel assembly top nozzle alignment
holes. This project demonstrated an
overriding commitment to nuclear
safety, employed strong teamwork and
project management, and developed an
innovative, timely, low cost solution to
this complex emergent issue.
Safety
Nuclear, Radiological, and Industrial
safety were ensured throughout the
effort to stabilize and capture the fuel
assembly attached to the upper internals.
Following the initial actions to protect
plant personnel and the public from any
potential radiological release from the
fuel, conservative decision-making, and
standard plant processes and procedures
were put in to action. Prompt review of
INPO Operating Experience (OE) and
contact with industry subject matter
experts, identified the need to ensure that
changing conditions did not disrupt the
stability of the assembly. The Operational
Decision Making process of Dominion
Procedure OP-AA-101 was invoked
to: 1. ensure that operator response and
procedures were identified, should the
assembly drop, and 2. to ensure that
no entries into containment or work
potentially affecting containment or
associated systems would be allowed
without a risk assessment and Plant
Manager approval. This ensured that the
assembly would not be disturbed, and
activities that could affect containment
ventilation alignments, containment
temperature, or reactor coolant/residual
heat removal temperature and flow
would be precluded. The Operational
Decision Making process was revised as
the plan was developed for the eventual
fuel assembly capture. These restrictions
and controls resulted in refueling outage
critical path work being suspended from
containment.
Operational Risk Assessments and
mitigation plans were prepared and
reviewed for every activity in containment
or on systems with the potential for
affecting the fuel assembly. Limited work
in containment was evaluated to resume.
Once the physical work was confirmed to
be low risk, evaluations were required to
safeguard the workers in the event of a fuel
assembly drop and radiological release.
Time motion evaluations and extremely
conservative radiological uptake analyses
were performed by the North Anna
Radiological Protection department to
ensure that workers in containment at the
time of a release would be able to safely
stop their work and exit containment in
38
NuclearPlantJournal.com Nuclear Plant Journal, March-April 2014
