Note: Descriptions are shown in the official language in which they were submitted.
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Casz 2867
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FUELLI~G MACHINE FI~E HOMI~G SYSTEM
This invention is directed to a refuelling
system for a CANDU M type nuclear reactor, and in
particular to an improved homing system for
controlling the mating of the refuelling machine to an
end fitting of a reactor fuel channel.
In the CANDU system of nuclear reactors the
nuclear reaction takes place within a calandria having
a plurality of elongated pressure tubes within which
the nuclear fuel is positioned, and through which the
heavy water coolant passes, in heat transfer relation
with the fuel. There being several hundred such
tubes, and with the operating requirement to carry out
refuelling during operation of the reactor while
on-load, the need for obtaining optimum operation of
the refuelling system will be clearly recognized,
particularly bearing in mind that the operation is
carried out simultaneously at both ends of the
reactor, with attachment of a refuelling machine to
each end of the tube being refuelled.
Because of the very minor differences in
inclination from a standard position, for the
individual fuel channels, and in view of the close
tolerances necessary in order to achieve a leakproof
seal, alignment of the re~uelling machine with the
respective fitting la vital. The prior refuelling
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systems have provided a coarse homing system to a
predetermined channel location memory, utilizing
fluidic sensors, using fine homing to a stalled
position in front of the selected channel and fitting
and a final homing control using gap sensing provided
by fluidic proximity sensors~
In operation, the prior system located the
selected fuel channel by memory, then brought the
~uelling machine into stalled contacting relation with
the fuel channel end fitting under control of the
coarse homing system, being then backed off, to return
under the fine homing, gap sensing system, using
fluidic proximity sensors.
In accordance with the present invention
there is provided a homing system wherein the homing
sensor system solely comprises magnetic proximity
sensors, preferably of the eddy current type.
There is further provided an arrangement of
magnetic proximity sensors incorporating built-in
redundancy whereby the reliability of the system
within its irradiated environment is beneficially
enhanced.
The present invention thus provides in a
nuclear reactor refuelling system for use in
conjunction with a nuclear reactor having an end face
and a plurality of fuel channels each having an end
fitting extending forwardly of the end face, the
fuelling machine b~ing resiliently mounted to permit
limited tilting and pivoting away from an axis normal
to the reactor face, and having a forward snout means
extending towards the reactor for axial displacement
in receiving relation over a pre-selected one of the
end fittings, a preliminary homing system responsive
to the selection of a predetermined fuel channel for
bringing the fuel machine into coarse, substantially
aligned relation with the selected channel, having the
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fuel channel end fitting positioned in entered
relation with the snout portion, wherein axial
misalignment is accommodated by tilting and pivoting
of the machine about the end fitting, and a single
stage fine ho~ing system having a plurality of
magnetic ~lux proximity sensors mounting in mutually
spaced relation on a ring portion of the snout means
to make individual magnetic flux-llnking connection
with the entered end fitting in response to the
relative proximity of the fitting portion proximate
thereto, and proximity signal responsive means
connecting the sensors with the fine homing drive
means having X-axis and Y-axis drive modes for
displacing the fuelling machine along the respective
axis in a sense responsive to differences between the
proximity signals to minimize such differences and to
bring the snout into engaging sealing relation with
the end fitting.
The present invention provides in one
embodiment an arrangement wherein at least four
magnetic proximeters are arranged in diametrically
opposed pairs located on axes at 45 degrees to the X
and Y axes of the fuelling machine noz~le, in order to
provide both X and Y component readings. In the event
of failure of one of the four proximeters, the
remaining proximeters would still be capable of
providing the necessary accuracy of homing control to
enable continuing operation of the system.
The outputs from the four proximeters are
connected to a microprocessor arranged in controlling
relation with the X-axis and Y-axis servo-motors of
the fuelling machine positioning system.
In the case of the two proximeter
pairs A, C; B, D arranged on 45 axis at the ten
o'clock, four o'clock; two o'clock, eight o'clock
positions the response of the microprocessor to the
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Ca6e 2867
relative dis~ance values provided by the respective
sensors A, B, C, D as steering responses to the
respective servo-motor might be:
when sensing A' ~-~ ~' or D' =-~ C' steer right
A' ~ B' or D' ~_ C' steer left
~' ~> D' or B' ~ C' steer up
A'c~ D' or B' ~ C' steer down
In the event conditions require greater s~stem
sensitivity, or the detection power of the proximeters
is inadequate, it is possible to position the
proximeters on the X and Y axes (i.e. vertically and
hori70ntally). However, while this enhances the
available signals by a factor of ~ ~ , the extent of
protection by se~sor redund~ncy is diminished.
15 The refuelling system of the present
invention operates in conjunction with a sealing ring
fixture and a plurality of jaw members, carried by the
refuelling machine providing a positive mechanical
clamping effect to secure the machine in sealed
relation to the end fitting, as is carried out in
prior art systems.
In the know~prior art system it has been the
practice to maintain the locking jaws and the jaw
nozzle plates in a closed condition while approaching
the respective fuel channel end-fitting under locating
drive using X-coordinate and Y-coordinate memory. The
fuel machine is then driven forward, to stall the
closed nozzle plates against the channel end fitting.
Under fine homing control, using fluidic sensors, the
fuelling machine is s~uared up to the end fitting so
that the nozzle plates are parallel therewith. Upon
the completion of fine homing the machine is backed
off and the locking jaws are then moved to an open
condition and the machine driven forward until it
stalls the snout against the end fitting, using the
fine homing sensors based upon three fluidic proximity
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sensing elements, to check the ~ap, with the jaws in a
closed condition.
In accordance with the present invention it
is now possible to make the initial approach to the
end fitting with the locking jaws already withdrawn
into the open position, thereby obviating the need to
interrupt the procedure in order to open the locking
jaws.
Thus there is provided, in a homing system
for locking a fuelling machine in sealing relation
with a reactor end fitting the steps of opening the
machine locking jaws, positioning a snout portion of
the machine in substantially aligned relation with the
selected end fitting, driving the snout forwardly in
the Z-axis direction to diminish the axial distance
between the end fitting and a plurality of proximity
sensors mounted on the snout, sensing the differences
in readings of the proximity sensors indicating the
extent and sense of tilt and pivot of the machine
relative to the end fitting, and selectively
energizing X-axis and Y-axis servo-motors in machine
position modifying relation in the sense to dlminish
the sensed differences between the sensors, driving
the snout forwardly whilst minimizing the sensed
sensor differences, and locking the machine to the end
fitting on achieving a predetermined homed
relationship.
Thus it will be understood that the present
invention provides a significantly simplified system,
possessing inherent redundancy in certain of its
embodiments, and resulting in an operational sequence
yielding significant savings in the cycle time
necessary to perform a homing and lock on sequence.
Such savings of time can, in turn, significantly
benefit the operational efficiency of a nuclear
reactor, while also enhancing refuelling machine
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utilization. In a multi-reactor such enhanced
utilization may lead to the possibility of using less
refuelling machines with consequent large savings in
capital costs.
Of equal importance i8 the simplification of
the re~uelling system by limiting it to a single fine
homing system, with consequent enhancement of
statistical reliability and potential large savings in
both operation and maintenance time.
Illustrative of the type of high temperature
eddy current transducer suited to the adverse reactor
environment is the Kaman Sciences Corporation
Displacement Transducer such as their KD l901(T.M.).
Certain embodiments of the invention are
lS described, reference being made to the accompanying
drawings, wherein:
Figure 1 is a partial general view, in
section showing the relative positions of the
mechanicaI elements, preparatory to locX-up;
Figure 2 is a partial diametrical section,
illustrating a subject proximity sensor in relation to
the other ele~ents, just prior to lock-up;
Figure 3 is a schematic front view of the
fuelling machine snout, showing sensor locations for
enhanced redundancy, and
Figure 4 is a circuit diagram for the system.
Turning to Figures 1, 2 and 3, the
arrangement 10 shows a portion of an end fitting 12,
of generally tube-like form. A fuelling machine (not
shown) located leftwardly of the end fitting 12 has a
snout ring 14 extending rightwardly therefrom, in
facing relation with the end fitting 12. Also carried
by the machine is an annular sealing ring 16 and a
plurality of sealing ring segments 18. A plurality of
magnetic proximity sensors, such as A, B, C and D of
the type discussed above, or similar, are mounted in
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the snout ring 14, being located in facing relation
with the GAP formed between en~ fitting 12 and the
outer face 20 of the snout ring 14, so as to "rea~"
across the GAP in response to the proximity of the end
face 22 of the end fitting 12.
In operation, owing to manufacturing and
operational variables the end faces 22 of the end
fittings 12 are frequently not truly vertical.
Operating by X and Y coordinate "memory" under remote
control the fuelling machine positions the snout 14
with the end fitting 12 in entered relation therein.
In most instances the fuelling machine cants and
pivots on spring loaded trunnion mounts, (not shown)
so as to enter over the end fitting 12. After
advancing of the machine axially ~Z-axis) the sensors
A, B, C or D give read-outs, the differences between
which indicate the extent and the sense of canting or
pivoting of the fuelling machine snout 14 relative to
the end fitting 12.
Referring to Figure 4, the outputs of
sensors A, B, C and D are connected to conditioner 30
b~ connections 26, 27, 28 and 29, and pass thence to
the micro-processor 32.
The processor 32 has inputs for Alignment
Set Point and Gap Set Point, with outputs to an
X-steering and Y~steering servo-motor, and to a GAP
M~ASUREME~T read-out.
Considering the geometry of the
arrangement, it will be evident that in the
preferred arrangement (hereinafter the
"A-arrangement") of locating the sensors A, B, C and D
at the lO-o'clock, 2-o'clock, 4-o'clock and 8-o'clock
locations, this requires more powerful sensors than
would be required if located at the cardinal
points (12, 3, 6 and 9 o'clock), known hereinafter as
the "C-arrangement". However, failure of one sensor
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still permits the system to operate, with reduced
accuracy.
While the sensitivity of the arrangement is
enhanced if the cardinal point, C-arrangement is
adopted, in the instance of failure of one sensor the
redundancy factor i8 diminished, due to a
significantly greater loss in accuracy.
Adoption of the C-arrangement improves the
signal by multiplying the vector difference by a
factor of r-~~. However, whilst the redundancy
capability is not entirely sacrificed, it is
correspondingly less effective.
