Reactor
Inspection
System
By Jae-Hee Kim, Korea Atomic Energy
Research Institute.
Jae-Hee Kim
Jae-Hee Kim has been working in the
area of computer controlled system of
nuclear power plant at Korea Atomic
Energy Research
Institute (KAERI)
since 1983. He
has led a variety
of nuclear
projects during
his professional
carrier and
developed many
nuclear inspection
robots. Mr. Kim has
also served as an
adjunct professor
at Korea University
and Chungnam
National University
in Korea, and
as a visiting scholar at University of
California, Irvine. He received the B.S.
degrees in Mechanical Engineering
from Seoul National University, Korea,
and the Ph.D. degree in Production
Engineering from Korea Advanced
Institute of Science and Technology
(KAIST).
Introduction
The reactor pressure vessels are
usually constructed by welding large
rolled plates, forged sections or nozzle
pipes together. These welds should be
periodically inspected using sensors such
as ultrasonic transducers or visual cameras
to assure the integrity of the vessel.
Such inspections are usually conducted
underwater to minimize an exposure to
the radioactively contaminated vessel
walls. The reactor vessel inspection has
been performed using a conventional
inspection machine with a big column.
This machine, however, is so huge and
heavy that its maintenance and handling
is extremely difficult.
In order to re-
solve these prob-
lems, KAERI has
developed an under-
water mobile robot,
which is guided by
a laser pointing de-
vice, and has per-
formed a series of
experiments
both
in the mockup and
in the real reactor
vessel. The sys-
tem is so small and
compact that it will
reduce the critical
path process for a
pre-service
inspec-
tion of pressurized water reactors. By
deploying two robots simultaneously in
the vessel, the overall inspection time can
be greatly reduced. This article describes
the outline of the robotic inspection sys-
tem developed in KAERI’s laboratory.
System Configuration
Our reactor inspection system, called
RISYS, consists of a reactor inspection
robot, a laser pointing device, a main
control computer, a sonic data acquisition
and analysis system.
The Reactor Inspection Robot
(RIROB) is a submarine type mobile
robot whose weight is approximately
50 kg in air and becomes zero in water
by the aid of floats. Most of the reactor
pressure vessel in a PWR is composed
of carbon steel and lined inside with
austenitic stainless steel. In order to
climb the vertical wall of the vessel, the
RIROB has four magnetic wheels: two
are caster wheels and the other two are
driven by DC servo motors so that the
robot can move in any direction on the
vertical inner wall of the reactor vessel.
The robot can control its linear velocity
and angular velocity by the sum and
difference of the velocities of the left and
right driving wheels. Both the front and
rear caster wheels are mounted on the
parallelogram links with the robot body
plate, so that the robot body can always
be parallel to the wall, even though the
wall is cylindrical.
The robot also has a light and long
manipulator, and the ultrasonic probes
are attached to its end effector. The ma-
nipulator has five degrees of freedom
which are slide forward, twist, rotation,
telescopic stretch, and a probe rotation.
The manipulator can reach up to 120 cm
using 4 consecutive translation links. The
camera and lamp are mounted on the ro-
bot and the visual image from the camera
is transmitted to the main control station.
The robot has an inclinometer to measure
the inclination of the mobile robot and to
control the robot posture. The depth sen-
sor is also mounted on the robot body to
measure the water pressure and to calcu-
late the current vertical depth of the robot.
A conventional inspection machine
with a huge manipulator can easily
place its end effector equipped with an
ultrasonic probe to the desired weld
position. However, the inspection system
using an underwater mobile robot guided
by a laser pointing device, needs a lot of
calculations and geometric analysis. In
order to inspect the welds accurately, the
robot should move exactly to the given
position.
The laser pointing device induces
the robot to the next position. The laser
pointing device is fixed in the middle of
the crossbeam across the reactor upper
flange. The laser pointing device emits
a laser beam to the next position for
the robot to move to. The robot, with
the position sensitive detector (PSD)
on its back, detects the deviation of the
laser beam spot from the center of the
position sensitive detector, and moves
in the appropriate direction to make this
deviation zero. The laser pointing device
is a kind of pan-tilt device on which the
diode laser is mounted. The device is
accurately driven by the servo motors of
which the resolution is less than 0.01 deg/
step.
40
NuclearPlantJournal.com Nuclear Plant Journal, May-June 2014
