Nuclear Plant Journal, May-June 2016 NuclearPlantJournal.com
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Submersion method is the most
favorable approach from the standpoint
of minimizing radioactive exposure to
workers. To realize this method, water
leakage from the PCV needs to be found
and stopped. Although the point to be
investigated on the PCV is very hard to
access with usual vehicle, we have to have
developed various remotely controlled
robots for water leakage investigation.
As the most recent example, we have
developed a shape changing robot that can
go through a penetration to investigate
the PCV to grasp the damage situation
inside the PCV and also the location
and condition of the fuel debris. We also
developed a technology for detection of
fuel debris in the reactor. Remote sensing
technology utilizing cosmic ray muon is
one of the methods to identify location of
fuel debris.
The important process by the final
stage of robot development prior to the
application to Fukushima Daiichi is the
evaluation in the mock-up facilities equal
to the environment of the application
place in the PCV. Not only examining
the performance of the robot, but also
training the workers to carry out the
mission safely and certainly is executed
sufficiently.
In the development of technologies
for fuel debris retrieval, in addition to the
method in which PCV is submerged, we
are evaluating retrieval in the air, partial
or full in air, as an applicable method.
Because the status differs from unit to
unit, we should consider the applicability
of each method.
As the result of our R&D activities,
IRID has acquired some useful outcome,
but at the same time, technical challenges
toward decommissioning have also
becoming clearer. Based on these
achievements and challenges, IRID will
keep working on technology development
necessary to decide the method for fuel
debris retrieval in 2018 and contributing
to completion of decommissioning at the
earliest time.
Radiological Work at
OPG
By Josp Zic, Christopher Glover, Julie
Thrasher, Lindsay Greenland, Tony
Hamilton, and Angie Andrade.
Ontario Power Generation (OPG)
has implemented a series of robots that
it uses to reduce risk and dose associated
with radiological work at its stations. In
particular, a series of four custom made
robots were utilized to remove high
activity debris from boiler drain lines at
the Pickering Nuclear Generating station.
During an outage on Unit 4, Radiation
Protection staff identified elevated dose
rates, in an Access Controlled Area
under Boiler 6, of 500 rem/h (5 Sv/h) at a
distance of 12" (30 cm).
Further inspections identified that
the primary component of the high
activities debris within the drain lines was
35 Ci of Cobalt-60. A locked restricted
high radiation area was set up to control
access until a plan could be developed
to remove the source of the elevated
dose rates. Robotics were designed and
implemented to capture the high activity
debris and deposit it into a shielded flask
for transfer and disposal. The functions of
the primary robot was to apply an ice plug
on the line, cut out the portion containing
the debris and then take a section of the
pipe to a transfer container to be placed
into a shielded flask.
The primary robot was supported by a
robot for performing radiological surveys
and visual inspections, another robot for
cutting off cladding that held insulation
in place and a final multipurpose robot
that assisted with insulation removal. A
full scale mock-up of the high activity
debris removal was performed prior
to work execution. Dual 10,000 rem/h
(100 Sv/h) high range detectors on the
inspection robot triangulated the debris
location at 2.6" (65 mm) from the bend
in the drain line. The robots allowed the
full execution of this work to take place
remotely and with minimal dose to the
robot operators and support staff.
Similar robotics have been deployed
to perform high risk activities like leak
searches in Access Controlled Areas of
on-power units, with general dose rates
in excess of 40 rem/h (0.4 Sv/h). These
robots have the ability to climb stairs and
are fitted with gamma detectors, PTZ
inspection cameras and thermal cameras.
OPG has also deployed Unmanned
Aerial Vehicles (UAVs) for performing
inspections of containment structures.
Upcoming 2016 UAV projects include
emergency response radiological surveys
of the site near boundary and performing
automated reactor face radiological
surveys.
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