Nuclear fuel bundle spacer envelope dimension measuring system and methods

The spacer envelope measurement system includes a generally U-shaped fixture having support plates extensible into positions overlying the spacer for supporting the fixture from the spacer. Extensible heads are carried by the fixture for engaging the spacer, followed by the heads of measurement gauges whereby, upon extending the heads into clamping engagement with the spacer along opposite sides thereof, the measurement gauges accurately determine the lateral dimensions of the irradiated spacer. A spacer bar clamp member is pivotal between positions opening the fixture opposite the base leg of the U-shaped fixture, enabling the bundle to reside within the U-shaped opening and a second position closing the opening for aligning the fixture and the bundle. The measurements are taken under water in a nuclear fuel service pool.

BACKGROUND OF THE INVENTION 
The present invention relates to apparatus and methods for measuring the 
lateral dimensions of irradiated spacers of a nuclear fuel assembly and 
particularly relates to apparatus and methods for measuring the lateral 
dimensional envelope of irradiated spacers in fuel bundles while located 
within a nuclear reactor servicing pool to determine the extent of growth 
or out-of-squareness of the irradiated spacer. 
Spacers are employed at axially spaced locations in fuel bundles to 
maintain the fuel rods separated from one another at well-defined lateral 
distances and permit flow of moderator/coolant from the lower tie plate of 
the nuclear fuel assembly upwardly through the assembly to generate steam 
ultimately used to produce electrical power. The fuel bundle comprising 
the spacers and fuel rods are encased within a generally rectangular fuel 
bundle channel and a plurality of such nuclear fuel assemblies makes up 
the core of a nuclear reactor. During operation in the nuclear reactor, 
the spacers in the nuclear fuel assemblies are subjected to radiation and 
thermomechanical stresses that can cause the overall dimensions of the 
spacers' envelopes to change, e.g., to increase. The term envelope as used 
herein means the lateral dimensions of the spacer, i.e., the X-Y 
dimensions, where the Z axis of the Cartesian coordinate system is in the 
direction of the fuel rods from the lower to the upper ends of the fuel 
bundle. If the envelope dimensions for a given spacer in a bundle increase 
to a significant extent, the ability to remove the fuel bundle from the 
channel and to reinsert the fuel bundle into a channel during servicing of 
the fuel assembly is seriously compromised. Accordingly, there is a need 
for a system for measuring the spacer envelope dimensions for each spacer 
in an irradiated or unirradiated assembled fuel bundle without requiring 
disassembly of the bundle and to enable the measurements to take place in 
situ in the nuclear reactor servicing pool. 
BRIEF SUMMARY OF THE INVENTION 
According to a preferred embodiment of the present invention, apparatus and 
methods are provided to enable measurement of the lateral envelope 
dimensions of fuel bundle spacers while a dechanneled bundle is in the 
fuel bundle inspection or fuel prep station in the nuclear reactor 
servicing pool whereby measurements of the spacer envelopes enable 
prediction of when or if the spacer dimensions exceed the internal 
tolerances of the fuel bundle channel. To accomplish this and in a 
preferred embodiment of the present invention, there is provided a fixture 
for submersion in the service pool. The fixture has reference points which 
are located relative to "bathtubs" on the external sides of the spacers. 
The "bathtubs" comprise lateral outward projections formed on the sides of 
the spacer band forming the peripheral margin of the spacer and which bear 
along an inside surface of the fuel bundle channel. The fixture is 
generally U-shaped and has fuel bundle engaging supports, e.g., fingers 
movable between extended positions overlying the marginal band of the 
spacer and a retracted position laterally outwardly of the spacer. The 
fingers, when the fixture is positioned about the spacer in the pool, are 
extended such that the fixture is wholly supported by the spacer from the 
fuel bundle. 
To ensure the relative positioning of the fixture and fuel bundle, the 
fixture carries a member movable between a position enabling the U-shaped 
fixture to receive the spacer within the fixture and a second position 
adjusting and clamping the fixture and spacer relative to one another. 
More particularly, with the spacer in the fixture and the fixture 
supported by the fingers engaging the marginal band of the spacer, the 
member in a preferred embodiment is pivoted from a first position to a 
second position and applies a force against the side of the spacer 
opposite the base of the U-shaped fixture to locate the fixture and spacer 
relative to one another and to ensure proper alignment. Once the fixture 
and the particular spacer undergoing measurement are located relative to 
one another, the fixture and bundle are releasably secured to one another 
by clamps carried by the fixture. The clamps include clamping heads or 
members which are extendible from opposite legs of the channel-shaped 
fixture to engage the bathtubs on opposite sides of the spacer. Measuring 
gauges follow the movement of the clamping members. Consequently, the 
movement of the gauges from predetermined reference points is used to 
determine the lateral dimension. 
Once a measurement is taken, e.g., in the X-direction of the spacer, the 
fixture and bundle can be relatively moved such that sides of the spacer 
90.degree. relative to the measured sides of the spacer can be disposed in 
the fixture to enable lateral measurement of the spacer dimensions in the 
Y-direction of the spacer. 
Once the dimensions of a particular spacer are ascertained, the fixture and 
fuel bundle are relatively moved to enable lateral envelope measurements 
of additional spacers of the fuel bundle. Preferably, the fuel bundle is 
elevated or lowered by the fuel preparation machine such that the fixture 
and another spacer of the bundle can be positioned relative to one another 
to afford measurements of the envelope of the additional spacer. 
It will be appreciated from the foregoing discussion that the spacer 
envelope measurements are made without requiring disassembly of the bundle 
and that the measuring apparatus is handled and positioned remotely while 
under water in the fuel storage pool. Also, the measuring apparatus 
accurately positions the fixture relative to the fuel bundle spacer to 
enable highly accurate measurements of the lateral spacer dimensions. For 
example, the desired accuracy of the spacer envelope dimensional 
measurement is .+-.0.0005 inches. 
In a preferred embodiment according to the present invention, there is 
provided a method of measuring a lateral dimension of an irradiated spacer 
forming part of an irradiated fuel bundle, comprising the steps of (a) 
engaging a fixture along opposite sides of the fuel bundle, (b) 
positioning at least one measuring element carried by the fixture along 
one side of the spacer and (c) determining the lateral dimension of the 
spacer between one side and an opposite side thereof using the measuring 
element. 
In a further preferred embodiment according to the present invention, there 
is provided apparatus for measuring a lateral dimension of an irradiated 
spacer of a nuclear fuel bundle, comprising a generally U-shaped fixture 
for receiving the fuel bundle within opposite legs of the fixture, a 
measuring element carried by one of the legs in lateral opposition to 
another of the legs, a reference adjacent another leg wherein the element 
and reference are used to measure a lateral dimension of the spacer and a 
member carried by the fixture for movement between a first position 
enabling the fuel bundle for reception within the U-shaped fixture and a 
second position at least in part in an opening opposite a base of the 
U-shaped fixture to clamp the fuel bundle within the fixture. 
In a still further preferred embodiment according to the present invention, 
there is provided apparatus for measuring a lateral dimension of an 
irradiated spacer of a nuclear fuel bundle, comprising a generally 
U-shaped fixture for receiving the fuel bundle within opposite legs of the 
fixture, a measuring element carried by one of the legs in lateral 
opposition to another of the legs, a reference adjacent another leg 
wherein the element and reference are used to measure a lateral dimension 
of the spacer and at least one fixture support movable between a first 
position retracted from the spacer and a second position engaging the 
spacer for supporting the fixture from the spacer. 
In a still further preferred embodiment according to the present invention, 
there is provided apparatus for determining the out-of-squareness of an 
irradiated spacer of a nuclear fuel bundle, comprising a generally 
U-shaped fixture for receiving the spacer of the fuel bundle within 
opposite legs of the fixture and a pair of movable measuring elements 
carried by the fixture and respective datums therefor, the elements being 
movable relative to the datums upon receipt of the spacer within the 
fixture affording an indication of the out-of-squareness of the spacer. 
In a still further preferred embodiment according to the present invention, 
there is provided a method of determining any out-of-squareness of an 
irradiated spacer forming part of an irradiated fuel bundle, comprising 
the steps of (a) engaging a fixture along opposite sides of the fuel 
bundle, (b) engaging a third side of the spacer along a reference carried 
by the fixture, (c) positioning a pair of spaced measuring heads carried 
by the fixture along one side of the spacer and (d) determining the extent 
of out-of-squareness of the spacer with reference to any displacement of 
the measuring heads from predetermined datums.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings and particularly to FIG. 1, there is illustrated 
a spacer envelope measurement system, generally designated 10, comprised 
of a fixture 12 preferably having a U-shaped configuration with a base leg 
14 and opposite legs 16 and 18. The fixture 12 also carries a clamp 
assembly 20 movable between a first position illustrated by the dashed 
lines in FIG. 1 wherein the side of the fixture 12 remote or opposite to 
the base leg 14 is open and a second position as illustrated wherein the 
assembly 20 at least in part closes the open side of the U-shaped fixture. 
Thus, the legs 14, 16 and 18 define a normally open area for receiving the 
spacers of a nuclear fuel bundle. Also illustrated in FIG. 1 is a nuclear 
fuel bundle 22 comprised of a matrix of nuclear fuel rods 24 and one or 
more water rods 26 passing through a plurality of spacers S spaced 
vertically from one another. The spacers typically comprise ferrules for 
maintaining the fuel rods and water rods in accurate lateral spaced 
relation from one another throughout the height of the bundle and are 
typically bounded by a marginal band 28. In this particular arrangement, a 
9.times.9 array of fuel rods is illustrated. 
Referring to FIG. 1, it will be appreciated that the legs 16 and 18 on 
opposite sides of the fixture 12 are identical to one another and a 
description of one will suffice as a description of the other. Referring 
to FIG. 5, the left side leg 16 forms an integral leg of a base frame 30 
of the fixture 12. Depending from leg 16 are a pair of spaced mounting 
bosses 32 for mounting water-dampened, spring returned air actuated clamp 
cylinders 34. Each of the clamp cylinders 34 carries an extensible and 
retractable head 36 for engagement with a bathtub 38 (FIG. 1) on the side 
of the spacer S. The bathtubs 38 are lateral projections adjacent opposite 
ends of each side of the marginal band about the spacer S. The bathtubs 38 
engage along the inside surface of the fuel bundle channel, not shown. 
Thus, it will be appreciated that the heads 36 can be advanced and 
retracted to engage the opposite sides of the spacers at the bathtubs 38. 
Depending below each boss 32 is another boss 40 for mounting a linear scale 
springloaded measuring element, e.g., a gauge 42. The heads 44 of the 
gauges 42 engage along the rear surfaces of the heads 36 carried by the 
clamp cylinders 34. Thus, as the heads 36 advance and retract, the heads 
44 of the measuring gauges 42 follow the movement of the heads 36. 
Mounted on top of each of the legs 16 and 18 is a fixture support, e.g., a 
plate 50 having a plurality of fingers 52 along an inside edge. Preferably 
the fingers 52 are scallop-shaped and correspond in position to the 
position of the fuel rods 24 (FIG. 1) in the 9.times.9 array thereof. 
Plate 50 is mounted on each leg for sliding movement toward and away from 
the fuel bundle. Particularly, guide and hold-down bars 54 and 56 are 
located on the legs 16 and 18 adjacent opposite ends thereof. Bars 54 and 
56 include flanges for overlying the margins of plates 50 whereby plates 
50 are slidable toward and away from the fuel bundle. To slide each plate 
50, there is provided on each leg 16 and 18, an angle bracket 58, a base 
of which is secured to the corresponding legs 16 or 18. The upstanding 
flange of bracket 58 mounts a double-acting air cylinder 60. The 
extensible rod 62 of the air cylinder 60 is connected to a lug 64, in turn 
secured to the plate 50. It will be appreciated that by actuation of the 
air cylinder 60, rod 62 may be extended whereby plate 50 is advanced 
toward the fuel bundle and, upon retraction of the rod 62, the plate 50 is 
retracted relative to the fuel bundle. 
Referring particularly to FIGS. 1, 4 and 6, one of the legs 16 and 18, for 
example, leg 16, includes a depending bracket 70. Bracket 70 mounts an 
air-actuated cylinder 72 having a piston rod 74 connected to a spacer bar 
clamp member 76, all forming part of the clamp assembly 20. By extending 
and retracting the piston 74, the spacer bar clamp member 76 may be moved 
away from and toward the leg 16. Additionally, the rod 74 includes a 
groove 78 engaging a fixed pin 80 carried along the interior surface of a 
cylinder 72 surrounding the piston rod 74. By engaging the pin 80 in the 
groove 78, retraction of the clamp member 76 toward the leg 16 causes the 
bar to pivot about the axis of the cylinder 72 into a second position 
illustrated in full lines in FIG. 1. The clamp member 76 also includes a 
loose-fitting clamping head 84 for bearing engagement against the bathtubs 
38 along the side of the spacer remote from the base leg 14 of fixture 12. 
A pin 86 is mounted on the end of the clamp bar member 76 and engages in a 
slot on the opposite leg 18, assisting to guide the clamp bar member 76 
into a position at least in part closing the open side of the U-shaped 
fixture 12. Thus, the member 76, in an axially extended first position as 
illustrated by the full lines in FIG. 4, permits relative movement of the 
fuel bundle and fixture enabling location of the fuel bundle within the 
fixture 12. In an axially retracted second position, the clamp bar member 
76 bears against the outside surface of the spacer, maintaining the 
interior corners of the spacer bearing against nesting radii 88, thus 
assuring alignment of the bundle within the fixture. 
From the foregoing description, it will be appreciated that once the spacer 
and fixture are relatively located as in FIG. 1, the pairs of measuring 
gauges adjacent opposite sides of the spacer measure the lateral 
dimensions of the spacer adjacent the fixture 12 and clamp bar 76, i.e., 
in an X-direction. Those two measured dimensions can also indicate the 
degree to which, if any, the spacer band is out-of-square. By rotating the 
fixture and bundle 90.degree. relative to one another, the lateral 
dimensions of the spacer in the Y-direction can similarly be ascertained. 
Whether the spacer is out-of-square in that direction can also be 
determined. 
It will be appreciated that the fixture is first calibrated before any 
measurements are taken in order to zero out the measuring gauges. To 
accomplish this, a gauge block is inserted between the legs 16 and 18. 
Preferably, the gauge block corresponds to the desired exact dimensions of 
the spacer. Thus, any deviation of the gauges from the calibrated position 
is indicative of the growth of the spacer. It will also be appreciated 
that the bundle need not be exactly centered between the opposite legs 16 
and 18 in order to effect an accurate measurement of the lateral dimension 
of the spacer. That is, once the gauges are calibrated, the difference in 
the extension and/or retraction of the left and right-hand gauges is 
indicative of the desired length measurement. It is also noted that the 
gauge heads 44 follow the movement of the clamp heads 36 and therefore it 
is only the change in lateral dimension from the measured gauge block 
which is measured. The measurements, of course, are recorded remotely. It 
will also be appreciated that a single measuring gauge can be utilized 
with the head 36 or other abutment opposite the single measuring gauge 
serving as a reference datum for the measurement. Preferably, however, 
oppositely directed pairs of measuring gauges are used, particularly where 
out-of-square measurements are desired. 
To employ the spacer envelope dimension measurement system of the present 
invention, it will be appreciated that the fuel assembly is removed from 
the nuclear core and transported to a fuel assembly service pool, 
generally indicated P in FIG. 7. The bundle is de-channeled, i.e., the 
channel is removed from about the bundle, leaving the bundle, including 
the fuel rods 24, spacers S and lower tie plate LTP intact. The bundle is 
also disposed in a fuel prep machine 90 which supports the bundle. The 
fuel bundle is now in position to employ the measuring system hereof. With 
the clamp assembly 20 in a first position out of registration with the 
opening between legs 16 and 18 and after calibration, the fixture 12 is 
lowered on a support tool, for example, a pole 92, which releasably 
connects with the base leg of the fixture mounting 11. By manipulating one 
or the other, or both, of the fixture and the fuel bundle, the fuel bundle 
can be disposed between the opposite legs 16 and 18 of the fixture 12 and 
at an elevation corresponding to the elevation of the spacer selected for 
measurement. In FIG. 7, the uppermost spacer is being measured. With the 
fixture located adjacent the spacer S, the air-actuated cylinders 60 
carried by the legs 16 and 18 are actuated to extend the plates 50 to 
locate the fingers 52 above the upper margin of the peripheral band of the 
spacer S. The plates 50 are extended such that the scalloped edges 52 
overlie the peripheral band of the spacer along its opposite sides. The 
edges 52, however, need not and preferably do not engage the fuel rods 24. 
With the plates 50 extended, the fixture is lowered relative to the bundle 
such that the fixture is entirely supported by the spacer without support 
by the pole 92. When supported, pole 92 is removed. The air-actuated 
cylinder 72 is then actuated to retract the spacer bar clamp member 76 
toward the outside margin of the spacer. The retraction of the clamp 
member 76 also causes the member 76 to pivot into a position, bringing the 
clamp head 84 against the outer bathtubs of the exposed side of the 
spacer. By engaging clamp head 84 against the outer bathtubs 38 of the 
spacer, the fixture 10 is drawn into alignment with the spacer with the 
inside corners of the spacer engaging against the nesting radii 88. 
Air cylinders 34 are then actuated to engage the clamp heads 36 against the 
bathtubs 38 along opposite sides of the spacer. The heads 44 of the 
measuring gauges follow the movement of the clamp heads 36, the measuring 
elements 42, particularly heads 44 serving as references for one another. 
When the clamp heads 36 are engaged against the spacer, the measurements 
can be taken and compared with baseline dimensions of the spacer to 
determine the extent, if any, of growth of the spacer as a result of 
irradiation. Additionally, by comparing the measurements of the opposed 
measuring gauges adjacent the leg 12 and the spacer bar clamp member 76, 
the degree to which, if any, the spacer is out-of-square can also be 
ascertained. 
Once the measurements in one direction, for example, the X-direction, have 
been taken, measurements in the Y-direction can be taken. To accomplish 
this, the air cylinders 34 are retracted, disengaging the clamp heads 36 
from the spacer. The pole 92 is engaged with the fixture and the air 
cylinders 60 retract the fixture support plates 50 whereby fixture 10 is 
supported by the pole 92. Additionally, the cylinder 72 is extended to 
axially displace the bar clamp member 76 away from the spacer and pivot 
the bar clamp into an out-of-the-way position, for example, as illustrated 
in FIG. 4. The fuel bundle and fixture are then moved relative to one 
another to locate the fuel bundle outside of the fixture. Preferably, the 
fuel prep machine then rotates the fuel bundle 90.degree. such that the Y 
dimension of the spacer can be measured, similarly as described above with 
respect to the X dimension. Upon completion of the measurement in the 
Y-direction, measurements of one or more additional spacers of the bundle 
can be taken by relatively displacing the fuel bundle and fixture in a 
vertical direction to align the next spacer to be measured in the fixture. 
To measure for out-of-squareness, the movement of the measuring heads 44 
from their datums, e.g., zeroed-out positions, can be used to determine 
out-of-squareness of the spacer. For example, and with reference to FIG. 1 
illustrating an inner side of the spacer aligned against the base leg 14 
of the fixture, the movement of the heads 44 adjacent base leg 14 from the 
zeroed-out positions will be to the left or right, i.e., the heads will be 
displaced relative to their respective datums. 
The measuring heads 44 adjacent the distal ends of the legs 16 and 18 will 
likewise move from their respective zeroed-out positions. The extent of 
the movement of the opposed pairs of heads as measured from their 
respective datums provides a measure of the out-of-squareness of the 
spacer in one direction, e.g., an X-direction. Out-of-squareness in the 
opposite Y-direction can similarly be measured upon relative movement of 
the fuel bundle and fixture to locate the spacer in the fixture 90.degree. 
relative to the first measurement in the X-direction. Thus, the combined X 
and Y measurements give a true value to the degree to which the spacer is 
out-of-square. 
While the invention has been described in connection with what is presently 
considered to be the most practical and preferred embodiment, it is to be 
understood that the invention is not to be limited to the disclosed 
embodiment, but on the contrary, is intended to cover various 
modifications and equivalent arrangements included within the spirit and 
scope of the appended claims.