POWER February 2015 - 16

Robotic Inspections of
Nuclear Power Plant
Storage Tanks
Nuclear power station water storage tanks,
located above ground or underground, are
constructed of aluminum, stainless steel,
or carbon steel. All have naturally occurring
electro-chemical processes that can
eventually deteriorate the metal, resulting
in leaks. Defects that develop on the underside
of tank floors are particularly difficult
to detect and measure.
The Nuclear Energy Institute (NEI) has
recommended that nuclear plant storage
tanks, among other infrastructure, undergo
periodic inspection. The guidelines
for tank inspection were laid out in the
publication NEI 09-14 (Rev 1), issued in
December 2010. Historically, plant managers
have utilized divers or drained the
tanks and sent personnel inside to conduct
manual surveys and non-destructive
examination (NDE) inspections, but that
process is often costly, time consuming,
and can restrict operation.
An Automated Solution
Newton Research Labs and IHI Southwest
Technologies Inc. responded to the industry
need by developing and implementing
automated NDE phased-array ultrasonic
and eddy-current array techniques and
qualified procedures. The simultaneous acquisition
of these data for analysis was accomplished
utilizing the Inspector robotic
delivery system (Figure 1).
The Inspector is a semi-autonomous
underwater robotic delivery platform designed
to precisely position a variety of
sensors, measuring instruments, or repair
tools that are used in the evaluation and
maintenance of water storage tanks at
nuclear power generating stations. There
are four major elements to the Inspector
system: the robot, the global observation
device, the navigation and operation software,
and the NDE systems.
The Newton-developed Inspector performs
NDE tank floor surveys and inspections
without the need for draining or removing
the tank from service. It is a unique tool
that can position NDE probes and sensors
at designated locations in order to perform
the NDE inspections on all accessible areas
of the tank floor surface. Additionally, data
for analysis may be acquired on the wall
and near the wall-to-floor interface. The
Inspector precisely maps the tank floor, as
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POWER | February 2015
well as obstacles, and is capable of returning
to within one-eighth inch of locations
identified for further evaluation.
Versatile and Maneuverable
As a delivery platform, the Inspector is
exceptionally maneuverable thanks to an
independent, steerable drive wheel system
and a split, pivoting chassis design. Wheel
pods can rotate 193 degrees, and each
wheel drive motor is independently variable.
Steering and drive motors are software
coordinated, thus giving the Inspector a
full range of motion: forward and backward,
side-to-side, spin on central axis, diagonal
" crabbing, " and radius turns.
Inspector robots are designed to fit
through narrow tank entrances or manways
(minimum diameter of 19 inches). Lower
tank manway entry can also be used if the
site can drain the tank just below the bottom
entry. The top speed of the Inspector is
in excess of six inches per second. The split
chassis design allows the Inspector to maintain
four-wheel ground contact while moving
across surfaces of different elevations.
During deployment, a 72-in-tall mast is
attached to the top of the robot. At the
peak of the mast are five light-emitting
diode (LED) lights, which allow the robot
to be tracked by the navigation software.
The mast keeps the lights above any sediment
or turbidity that may be present in
the bottom of a tank.
The robot chassis contains five onboard
video cameras, which provide 360degree,
plus down-looking, live video.
Additionally, there are laser range finders
on all four sides to aid in positioning the
unit near the wall of a tank. A built-in
1. The " Inspector. " This underwater robot can be used to examine water storage tanks as
an alternative to draining the tank or using divers. Courtesy: Newton Labs
http://www.powermag.com
POWER February 2015

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