The new "thru-wall" look at Sellafield - Mirion Technologies

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INSPECTION & ROBOTICS ROUND-UP
The new "thru-wall" look at Sellafield
BNFL and IST-rees have been
working together to develop high
performance optical inspection systems
for viewing through shield walls of active cells
for many years. The latest version, a "thru-wall"
(and roof) endoscope camera system, will be fitted
into the Sellafield Drypack Plant (SDP). The
system optically relays a view of the inside of a
cell to a ccd cameral on the cold side of the wall,
eliminating the cumbersome process of withdrawing
the camera assembly and its associated
shield plug from the wall for maintenance. This
significantly reduces maintenance costs and staff
dose uptake. The system offers standard and wide
angle fields of view with 6:1 zoom range.
The endoscope provides shielding against the
radiation shine path by placing fused silica blocks
in the viewing path allowing standard ccd cameras
to be used rather than radiation tolerant cameras.
This enables the system to be simply upgraded
as ccd technology advances.
The design of the new modular endoscope
system benefited from the experience of the first
two endoscope projects at Sellafield, for the vitrification
plant (VIT Line 3) and the Silo Emptying
Plant (SEP). The first used the first modular
design to generate through-wall endoscope
systems for wall thickness of 1000 mm and 1550
mm incorporating double prism technology in a
viewing head for image correction. The SEP
project called for developing a wider angle of
view and through-roof variant using the same
endoscope assembly. This required the second
image correcting prism to be located within the
endoscope and not part of the viewing head.
The latest modular version was inspired by
SDP which has a number of different wall thicknesses
and through roof variants. It combines the
technologies developed on VIT 3 and SEP.
The system provides an operator with full
hemisphere viewing through a single non-browning
glass viewing dome located inside the cell,
taking up very little space and providing a biological
shield. This is achieved using a rotating
and tilting prism located in a viewing assembly,
32
Non-browning
Glass Dome
Silo Emptying Plant (SEP) Endoscope on a transport trolley
Thru-wall endoscope
Optical Head Filler Liner Alpha Liner Endoscope
Diagram of the IST-Rees 'thru-wall' endoscope
tested for 30 year operation, at the front of the
system. This prism is driven from control electronics
on the cold side via drive shafts.
The endoscope is located behind this front
prism in order to relay the image to a ccd camera
on the cold side. This endoscope contains a
second rotating prism for image correction which
is driven off the same rotate drive shaft as the
front prism. The difference between through wall
and roof systems is simply the rotational speed
relationship between the two prisms, which can
be changed via a gearbox.
At the rear of the system, on cold side, is an
electronics enclosure containing the ccd camera,
telemetry receiver card and all the drive electronics.
In the case of a through wall system, an
addition control card is fitted, developed by
BNFL Product development Centre at
Capenhurst, which enables the system to emulate
a standard pan
and tilt system.
This important feature
ensures that
the system can be
controlled intuitively
by the operator
making the
system user
friendly and reducing
training times.
The endoscopes
are made up
of a combination of
standard modules,
which enable the
Electronics
Enclosure
system to cater for wall/roof thicknesses from
750 mm to 2000 mm in steps of 250 mm. There
is a choice of front module between wide and
standard fields of view.
The viewing head, endoscope, drive shafts
and electronics enclosure form one assembly
which is fitted into an Alpha liner (on which is
mounted the non-browning glass dome). This
enables the operational parts of the system to be
removed, without breaking biological containment,
should any maintenance be required. The
whole system will fit into a minimum of 150 mm
encast liner, thus removing the civil engineering
issues associated with larger encast liners. Large
encast liners can be catered for using filler liners
within the system.
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