LRSS
Clevis Bolt
Replacement
By David Dolby, American Electric
Power.
David Dolby
David Dolby is a project manager
employed by American Electric Power
(AEP) and is working at DC Cook
Nuclear Plant (CNP). Mr. Dolby
has held an active Senior Reactor
Operator’s license at CNP for more
than 20 years. He
was also a member
of the CNP refueling
team. Mr. Dolby’s
interest in project
management
motivated him to
achieve a Project
Management
Professional
Certification (PMP)
in 2010. He later left
operations to pursue
a career in project
management with
AEP.
Nuclear Energy Institute’s Top Industry
Practice (TIP) Awards highlight the
nuclear industry’s most innovative
techniques and ideas.
This innovation won the 2014 AREVA
Vendor Award.
The team members who participated
included: Kevin Kalchik, Mechanical
Design Engineer, American Electric
Power; David Dolby, Project
Manager, American Electric Power;
Randy Villeneuve, Project Engineer,
Component Replacement & Repair,
AREVA Inc.; John Orr, Manager,
Tooling Design, Component
Replacement & Repair, AREVA Inc.;
Steve Hunter, Advisory Engineer,
Component Repair Design, Component
Replacement & Repair, AREVA Inc.
Summary
This article describes an innovative
response to a First-Of-A-Kind (FOAK)
nuclear industry maintenance need
involving the replacement of the Reactor
Vessel (RV) Lower Radial Support
System (LRSS) Clevis Bolts at the
American Electric Power (AEP) DC
Cook Unit 1 plant during the spring 2013
Refuel Outage.
DC Cook experienced an anomaly
within the lower radial support system
clevis inserts during a 10-year In-Service
Inspection of the Unit 1 reactor vessel
during the March 2010 outage. Six sets
of LRSS clevis lugs are welded to the
Inside Diameter of the reactor vessel
just above the lower
shell to spherical
head weld with each
set being equally
spaced around the
RV
circumference.
Each clevis assembly
includes an insert
which is attached to
the clevis lugs with
eight cap screws
and
two
dowel
pins. Degradation
of the clevis insert
cap
screws
was
discovered at seven
(7) of the 48 cap
screw locations. The
compromised bolts were distributed
throughout three of the six clevis inserts.
It was also noted that at five of the seven
locations, cap screw heads had been
dislodged and repositioned. AEP worked
with the reactor vessel OEM to establish
a minimum bolt pattern required for
integrity of the LRSS clevis inserts for
the remaining expected life of the plant.
The minimum bolt pattern required some
bolts be replaced in each of the six clevis
insert assemblies. In all, 28 bolts were
replaced successfully with five of these
being oversized contingency bolts.
Safety Response
AEP and AREVA are committed to
the number one priority in the nuclear
industry – Safety. The bolt replacement
project was completed with no safety
issues. There were no first aid incidents
and no OSHA recordable injuries. The
project team also conducted an exhaustive
risk analysis in order to highlight potential
cost, schedule, and non-quality events
that would adversely impact the project.
One of the critical risks identified was
a stuck bolt event. To mitigate this risk
an innovative oversized bolt contingency
repair was developed. A contingency
was also developed for removal of a bolt
shank where the bolt head was separated
from the shank, either as found or as a
result of the removal process.
Life of plant:
Personnel dose was also a factor that
drove many aspects of this project. From
the design of the tooling to the levels of
staffing, the importance of incorporating
ALARA principles into the bolt
replacement task and minimizing dose to
personnel was adhered to throughout the
project.
Engineering controls were also
implemented to mitigate reactor cavity
water contamination by swarf created
as a part of the electrical discharge
machining (EDM) process. For example,
the water in the cavity was raised as high
as possible to provide worker shielding
and the general area cavity water was
filtered by a tri-nuke filter.
Additionally, the AREVA and AEP
project teams worked together to optimize
removal of the swarf generated during
the EDM process. The radiological
engineering controls used were an
AREVA designed, dedicated particulate
filtration skid and plant equipment.
The teams collaborated to develop an
interface between the AREVA swarf
filtration skid and the spent fuel pool
(SFP) demineralizer plant system. The
interface directed effluent from the swarf
filtration skid to the SFP demineralizer
system and returned the effluent back to
the reactor cavity.
Hydrogen peroxide was added
routinely to the cavity water during this
process.
These controls performed as
expected with the results evident in the
cavity water dose rate reduction. The
reactor cavity general area dose rates
due to the reactor cavity water started at
approximately 1 mr/hr effective dose rate
(EDR) and leveled off in the 0.3 mr/hr
EDR range.
46
NuclearPlantJournal.com Nuclear Plant Journal, May-June 2015
