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CONF-6650604-/
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'APR 27 1965

-LEGAL NOTICE -
Two ropory mu prepared n na socontent of Dovanumit mpound vort. Noldhar the Undert
fate, mar the communion, mar w porno nothing a bowall of the Countnedali
A. Marsh waynurtnaty or masualaton, appeared or impued, wd rospect to the ICC
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mol employee or contractor of the Canadianban, or employe o mica contractor properes,
dururaw, or prordne m u to, un taformation surmulto No aplognal or contract
wiu de Constanton, or Me employment with such contractor.
NONDESTRUCTIVE TESTING OF IRRADIATED MATERIALS IN THE UNITED STATES*
PATENT CLEARANCE OOTAINED. RELEASE TO
THE PUBLIC IS APPROVED. PROOEDURES
ARE ON FILE IN THE RE:DIVING SUCTION,
Robert W. McClung and Donald A. Douglas, Jr.
Oak Ridge National Laboratory, U.S.A.
*Research sponsored by the U. S. Atomic Energy Commission under
contract with the Union Carbide Corporation.
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Areny
NONDESTRUCTIVE TESTING OF IRRADIATED MATERIALS IN THE UNITED STATES
Robert W. McClung and Donald A. Douglas, Jr.
Abstract - Resume'
NONDESTRUCTIVE TESTING OF IRRADIATED MATERIALS IN THE UNITED
STATES. New demands for nondestructive evaluation of radioactive
specimens in high-activity hot laboratories have required extensive
development of new techniques. Several methods using external
radiation sources have needed greuter development beyond that
necessary for cold laboratory operation. Radiation techniques
which are discussed include neutron radiography, x-radiography,
gamma attenuation and the use of x-ray sensitive television. Many
other methods such as ultrasonics, eddy currents, liquid penetrants,
and leak testing have been possible by making mechanical modifica-
tions to allow the test to be performed remotely.
ESSAIS NON DESTRUCTIFS DE MATERT.AUX IRRADIES AUX ETATS UNIS.
L'accroissement de la demande pour les essais non destructifs
d'echantillons radioactifs dans des laboratoires chauds à haute
activite' a exige' un developpement considerable de techniques
nouvelles. En particulier plusieurs methodes utilisant des sources
exterieures de radiation ont exige' une extension importante de la
technique utiliseé dans les laboratoires à très faible activite'.
Les methodes à radiation qui sont decrites comprennent la radio-
graphie neutronique, à rayons X et à gamma attenue et la production
d'images de television à portir de rayons X. L'application des
methodes à penetrants liquides a ete' rendue possible grâce à des
modifications mecaniques qui permettent de faire les essais à distance.
L
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INTRODUCTION
Con
Many specimens such as in-pile capsules which are subjects for
examination in high-activity hot laboratories are intended for further
service after examination. This requires that the tests be performed
nondestructively. On other specimens such as fuel elements nondestruc-
tive examination of the interior of the object for observation of the
assembly details, and detection of internal flaws can be desirable or
necessary. This is important not only to provide more interrogations
to learn about the condition of the specimen after irradiation service
but also to enhance the intelligent application of the destrictive tests
for os tim'm results. These new demands on nondestructive testing have
required extensive development to achieve the desired end. Many of the
methods which have been developed and applied in highly radioactive
environs are quite similar to those used in conventional laboratories.
For example, with ultrasonics and eddy currents the principal difference
is the mechanical modifications or developments necessary to perform
the test remotely. Some methods (radiography for example) require
extensive modification before useful application can be made. Except
for the radiographic methous, the radiation background has very little
effect on most of the tests.
Several of the current techniques are discussed in this paper with
the major emphasis being on those which are different from those commonly
practiced under cold laboratory conditions. Among those techniques des-
cribed are neutron and x-radiography, gamma-ray attenuation, television
viewing of x-ray images, ultrasonic detection of nonbond and other flaws,
and eddy-current applications for the detection of sodium nonbonding
and the measurement of coolant channel spacing in fuel elements. Other
techniques which are also nondestructive in nature but are more related
to visual observation, metrology, and detection of self-emitted radiation
are described at this symposium in the paper, "Remote Metrology and
Examination Techniques on Irradiated Fuel Materials As Practiced in the
United States," by F. L. Brown et al.
PENETRATING RADIATION METHODS
A number of the nondestructive testing applications use external
sources of penetrating radiation such as x rays, gamma rays, or neutrons
despite the high levels of background radiation associated with activated
materials. Most of the methods use a Photosensitive emulsion as the
final recording medium but some work has been cone using scintillation
detection or television imaging devices using semi-conductor detectors.
X-ray machines are preferred over gamma sources for film radiography
because of the higher beam intensities which are readily available.
Only a few of the methods will be discussed in detail.
Neutron Radiography
Thermal neutron beams are now being used routinely to examine
irradiated reactor fuel specimens. (1,2) The inspection method makes
use of thin metallic foils of materials such as silver, dysprosium,
rhodium, gold, and indium. These foils are rendered radioactive by a
beam of neutrons. After a neutron beam has passed through an inspection
object, its intenc:ty will be modified by variations in the attenuation
caused by the specimen. These variations in neutron beam intensity this
cause variations in the radioactivity in the metal foil used as a
detector. This is analogous to the x-radiographic process in which
attenuation of x rays through a specimen produces a latent image on a
photosensitive detector. The neutron-induced radioactive image can be
replicated or made visible by allowing it to decay for a few half lives
in close contact with photographic film. The gamma radiation from the
inspection object will not influence the radioactivity of the detecting
screen and therefore will not influence the final radiograph. The
radioactivity of the screen is sufficiently low so that the transfer
of the image to photographic film does not need to be done reinotely.
Most of the neutron radiographic work has been accomplished using
beams emergent from nuclear reactors. Specially designed shielded
facilities have been built adjacent to the reactor wall. One such site
has a neutron intensity on the order of 10? neutrons cm-2 secºl and the
cr
beam cross section 18 6.35 x 10 cm (2 1/2 X 4 in.). The exposure time
to the neutron beam varies according to the half life of the screen
material as well as the speed of the film emulsion on which the auto-
radiograph of the screen is recorded. Typical exposure for irradiated
fuel capsules are 5 to 7 min in the neutron beam and a transfer time of
three half-live3 decay. In practice a preliminary alignment radiograph
is made to determine the proper orientation of the capsule. A rhodium
screen is used with a 15 sec neutron exposure and the decay transfer is
made to Polaroid X3000 film. After proper alignment is attained, the
high quality radiograph is made using fine-grained x-ray film. The
gamma activity of the radiographed irradiation capsules has been measured
and shown to be greater thar. 5 x 103 r/hr at 30.5 cm (1 ft). The sensi-
tivity has been adequate to detect thickness changes of approximately
I to 2 percent and the resolution is better than 0.12 mm (0.005 in.)
Figure 1 shows a pinhole autoradiograph and a neutron radio-
graph (both positive prints) of a radioactive, unopened fuel capsule
compared with a photograph of the opened capsule.
Another interesting application of this technique is the determi-
nation of high burnup in reactor control materials. (3) Neutron radio-
graphs of a cadmium shim-safety rod indicated an abrupt change from an
effective thickness of 0.625 mm to less than 0.025 mm in highly irra-
diated areas.
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X-Radiography
X-ray film radiography has found application despite the formidable
conditions of background gamma radiation. The requirement is to minimize
the total exposure and response of the film to the incoherent, background
radiation while enhancing the response to image-forming radiation. Steps
which have been used are: (1) shielding of the film at all times other
than the intended exposure, (2) reduction of the image-forming exposure:
time with intense x-ray sources, (3) separation of the specimen from the
film, (4) shielding of the non-radiographed portion of the specimen,
and (5) use of film which has been manufactured to have an enhanced
sensitivity for the softer x rays. (4)
Recent studies (5) under mockup conditions have been conducted to
determine the amount of non-image-forming radiation which can be toler-
ated without excessive degradation of the radiograph. A further stage
of the study developed techniques for salvaging film which had received
an excessive amount of background radiation. A series of radiographs
of an aluminum step wedge were double-exposed before processing to
varying amounts of 50-, 100-, and 300-kvcp (kilovolts constant potential)
x rays and 1.2-Mev gamma rays. The film was then processed and evaluated
to determine the radiographic sensitivity. That which was exposed to a
background of x rays accepted an accumulated dose up to 2 r with no sig-
nificant degradation. Up to 32 r of the 1.2-Mev gamma rays were toler-
ated without serious problem. The best results were obtained if the
original image-forming exposure would have produced a film density from
1 to 2 in the absence of background radiation. Since these radiation
values are accumulated doses and not dosc ratus, a calculation with the
exposure time is necessary before the tolerance to a radiation field can
be estimated. For instance, if exposure time can be limited to 1 min,
the tolerable radiation field could be 1.2 x 102 r/hr of low energy
gamma and 1.8 x 103 r/hr of l-Mev gamma. These and subsequent values,
of course, pertain to the particular fine-grained film which was used
and tests should be run for others.
Photographic reduction witir Farmer's reducer (6) was performed on
those radiographs which had received so much fogging background that
they were uninterpretable. This salvaging operation greatly increased
the allowable tolerance. For instance, an accumulation of 16 r of the
50-, 100-, and 300-kvcp x rays was acceptable and an accumulation of
380 r of the 1.2-Mev gamma ruys was not excessive. The best results
were obtained if the original image-forming exposure would have pro-
duced a film density in the range from 2 to 3 in the absence of back-
ground radiation. As noted before, if an exposure time of 1 min is
applicable, the tolerable radiation field could be 103 r/hr of low-
energy gamma and 3 x 10* r/hr of l-Mev gamma. As a demonstration of
the validity of these tests, un excellent radiograph was taken of a
4.45-cm (1 3/4 in.) diam housing containing a 5 curie 6°co source as
ma.
shown in Fig. 2. The radiation field at the film surface was approxi-
mately 1.2 x 104 r/hr. Of course, without the reduction step the film
was completely black and the details could not be seen.
Non-Film Techniques
Scintillation Detection
A growing application has been the use of high-energy gamma
attemation coupled with scintillation detectors to measure fuel homo-
geneity. The radiation beam from a radiation source such as 6oCo is
transmitted through the specimen. The thickness, density, or chemical
composition in the specimen will affect the relative beam intensity
whi.ch is monitored by the scintillation detector. In a typical appli-
cation in a recycle pilot plant, (7,8) a fuel rod containing vibratorily-
compacted uranium oxide powder is translated axially through a tightly-
collimated beam from a 6°co source. Variation in fuel loading
(homogeneity) change the transmitted intensity which is detected and
recorded. Figure 3 shows this equipment. Calibration with known stan-
dards establishes the relationship between transmitted-beam Intensity
and fuel content. The detector must be adequately shielded so that the
major portion of the detected radiation is that which has passed through
the inspected rod. Sensitivity and accuracy for fuel content has been
better than 1%.
Ccuro
X-Ray Sensitive Television
Another non-film device which is finding application in hot recycle
facilities is the x-ray sensitive closed-circuit television (9,10) for
examination of closure welds and assembly features. An x-ray machine is
used as the source of radiation for the Inspection. The difference
between this technique and film radiography is the substitution of a
special television camera tube in place of the film. The camera tube
contains a very thin layer of a semiconductor material which serves as
a target or detec or. Thus variations in x-ray beam intensity produce
an image on the camera tube which can be processed electronically and
and displayed just as an optical image is processed and displayed in
a conventional television system. dvantages of this method of inspection
include the lower sensitivity to high-energy gamma rays of the very thin
semiconductor layer, excellent resolution, immediate viewing of speci-
mens, and the ability to observe detail while the object moves. Among
the limitations are the need for high f.ntensity x-ray beams impinging
on the detecior (limiting the specimen thickness), the small detector
area of 0.95 x 1.25 cm (3/8 x 1/2 in.) and the requirement for main-
taining the target face at a temperature below about 29.5°C.
ULTRASONIC METHODS
Ultrasonic techniques ure also finding an increased application
in high-activity environments. In general the approach is similar to
that used in a cold laboratory although the performance may be more
difficult or require more mechanization. The method 18 insensitive to
radiation except for the accumulated damage to the in-cell components.
It has been found that the ceramic piezoelectric transducer elements
such as lead zirconate-titanate have a higher resistance than quartz
to change in characteristics due to radiation damage.
Nonbond Detection
Many of the uses of ultrasonics have been for the detection of
nonbonding in fuel plates and pins and control rod plates. The simplest
test uses a resonance technique, elementary mechanical guides and manip-
ulator movement of the probe. Nonbonds with a size approximately 1/4
of the probe area can be detected at core-clad interfaces on either side
of the fuel or absorber plates. More complex systems have been assembled
to make completie mechanical scans of plates or pins. For example, mechan-
ical equipment has been set under about twelve feet of water to evaluate
a cylindrical uranium fuel element tiaving both inner and outer surface
Zircaloy cladding. (11) Bond testing is conducted at both bonded inter-
faces using a pulse-echo, longitudinal.-wave "ringing" technique; i.e.,
an impinging pulse of the proper frequency ultrasound will induce
resonant vibrations in nonbonded clad.
This ringing can be detected
as an elongation in time of the received echo. In addition to the
bond testing, the same scanner is used to measure clad-thickness with
a high resolution, short pulse, untuned instrumentation system and to
detect flaws in the core using both longitudinal and shear mode techniques.
General Scanning Equipment
ASS
Ultrasonic equipment has been assembled for in-cell testing of
irradiated fuel rods for cladding defects. (12) The equipment includes
an immersion tank with features for clamping and rotating the rod and
positioning and adjusting the test head which contains the ultrasonic
transducer. The system has proven to be capable of finding radial
cracks 0.32 cm (1/8 in.) long with depths of 5-10% of the wall thickness.
An all-purpose scanning tank has been developed for in-cell per-
formance of ultrasonic examination of specimens with cylindrical, flat,
or other shapes. (13) The system has remote control on the transducers
in 3 linear and two angular directions. For scanning of rectangular
objects the search tube can automatically be moved in repetitive longi-
tudinal scans with indices of a preset amount in the transverse direction
between each longitudinal movement, thus providing complete XmY coverage.
Rotary motion can be applied to cylindrical objects and, when coupled
with transducer movement in the longitudinal direction, this will pro-
duce helical scanning. Thus almost any ultrasonic technique which can
be performed by immersion testing in a cold laboratory should be possible
in-cell. The device has been used thus far only in a mockup facility.
EDDY CURRENT METHODS
Flaw Detection
The eddy-current techniques, like ultrasonics, can be performed
without concern for high-intensity background radiation. Again the tech-
niques can be similar to those used in cold laboratories with the
principal difference being the mechanization required for remote opera.-
tion. One such application was for detection of flaws in sodium bonding
Was
in a fuel pin after fabrication in a fuel recycle facility. The
equipment translates the fuel pin from a magazine (heated to maintain
the sodium in a liquid state during inspection) up through an encircling
inspection coil and allows its return. The inspection coil was wound on
aluminum silicate for heat resistance. It is operated as part of a
pulsed eddy-current system. (14,15) The device, when used and inter-
preted by an experienced operator, can be used to detect most of the
flaws characteristic of the casting operation. For instance, it can
determine the sodium level with an accuracy of 10.39 nim
and is able to detect and show the difference between surface defects
at the sodium interface and voids in the sodium bonding as small as
1.5 + 0.25 mm (1/16 + 0.010 in.). (17)
Space Measurement
A new series of eddy-current probes using the "lift-off" effect*
have been developed for the measurement of spacing in coolant channels
and other restricted areas. (13,19) One type has been made small enough
to fit into 0.875-mm (0.035 in.) channels between fuel plates. Others
have been made to perform similar measurements between fuel rods and in
annular spaces in rods with concentric configuration. Hot-cell measure-
ments have been made manually. Also by attaching a notorized drive
system such as the bed of a milling machine, continuous scanning and
recording of channel prorlles can be performed. Accuracies have been
0.025 mm (0.001 in.) or better.
om
OTHER METHODS
Liquid penetrant and magnetic particle examination have been used
to detect surface flaws at several sites. (20,21) Speaker-driven sonic
methods (22) to measure elastic moduli in small machined specimens have
also found application. Several types of leak testing have been per-
formed for the detection of leaks through a container such as a fuel
*The "lift-off" ef'fect may be defined as the change in the elec-
trical impedance of an eddy-current coil due to a change in the distance
between the coil and a neart; electrically conducting material.
10
element cladding. These include helium leak detection employing mass
spectrometers (23) and the observation of gas bubble formation on the
surface of internally pressurized containers. ( The latter can be
accomplished by immersion in a liquid bath such as oil or by coating
the surface with a liquid film. Another system uses pressure decay in
a miniature pressure chamber as a measure of closure weld leakage for
fuel rods. (24) Analysis of pressure decay rate permits determination
of leak size up to a sensitivity of approximately 5 x 10-6 std cm He/ sec.
These various test methods in general differ from out-of-cell techniques
only in the more difficult manipulation of material and viewing of results.
CONCLUSIONS
A number of nondestructive testing techniques have been developed
and applied in the United States for postirradiation examination in hot
cells. Some of the methods have been basically the same as those in
cold-laboratories except for the requirement for mechanization necessary
for remote performance. Others have necessitated extensive modification
and ingenuity. Although it is recognized that the technology is still
in its Infancy, great strides have been made and the cited methods and
others yet to come will find even greater usefulness in the future.
ANL-1047002


DB

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*
Gamma Autoradiograph
of Unopened Capsule
Neuiron Radiograph of
Unopened Capsule
Optical Photograph of
Clad Fuel Specimens
after Capsule Was
Opened
Fig. 1. An Autograph and a Neutron Radiograph of a Radioactive,
Unopened Fuel Capsule Compared with a Photograph of the Opened Capsule.
1. Berger, "A Summary Report on Neutron Radiography," US AEC Report
ANL-6846, Argonne National Laboratory, July, 1964.

Y.55921
i
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Fig. 2. Chemically Reduced Radiograph of a Housing containing a
5 Curie Source of 6°co.
PHOTO 59404

PHOTOMULTIPLIER
TUBE
TROLLEY
FUEL ROD
COLLIMATOR
2
mo
LEAD PIG CONTAINING
1 C060 SOURCE
..!
Fig. 3. Equipment for Measuring Fuel Inhomogeneity by Through-
Transmission Gamma Attenuation.
14
REFERENCES
1. . Berger and W. N. Beck, "Neutron Radiographic Inspection of
Radioactive Irradiated Reactor Fuel Specimens," Nucl. Sci. Eng.
411-14 (1963).
2. W. N. Beck, "Recent Advances in Nondestructive Examination of
Irradio:ced Fuel Capsules," USAEC Report TID-7697, Technical Information
Division, pp. 2.22.1-11.
3. H. Berger, "A Summary Report on Neutron Radiography," US AEC
Report ANL-6846, Argonne National Laboratory, July, 1964.
4. G. H. Tenney, Los Alamos Scientific Laboratory, personal
communication, 1964.
5. R. W. McClung, "Radiography in the Presence of Background
Radiation," Mater. Evaluation (to be published).
6. C. B. Neblette, Photography, Its Principles and Practice,
D. Van Nostrand Co., Inc. New York, 1942.
7. J. D. Seuse, A. L. Lotte, and F. C. Davis, "Thorium-Uranium-233
Oxide (Kilorod) Facility-Rod Fabrication Process and Equipment," US AEC
Report ORNL-3539, Oak Ridge National Laboratory, April 1964.
8. B. E. Foster, S. D. Snyder, and R. W. McClung, "Measurement
and Application of X- and Gamma-Ray Attenuation to Reactor Materials
Evaluation," paper presented at the Fourth International Conference on
Nondestructive Testing, London, England, Sept. 9-13, 1963. To be
published in Proceedings.
9. J. W. Allen and R. W. McClung, "An Electronic, High Resolution,
X-Ray Imaging System," USAEC Report ORNL-2671, Oak Ridge National
Laboratory, May 1959.
10. J. P. Mitchell, M. Rhoten, and R. C. McMaster, "X-Ray Image
System for Nondestructive Testing of Solid Propellent Missile Case
Walls and Weldments," U. S. Army Report WAL 142.5/1-5, Watertown
Arsenal Laboratory, August 1962.
11. D. 0. Hunter, "Ultrasonic Testing of Irradiated NPR Fuels,"
Paper No. CP 63-715 presented at the Institute of Electrical and
Electronics Engineers Electronuclear Conference, Richland, Washington,
April 29–30, 1963.
12. T. G. Lambert, "Ultrasonic Inspection of Irradiated Fuel Rods,"
pp. 255-265 in Proceedings of the llth Conference on Hot Laboratories and
Equipment, ANS Winter Meeting, New York, December 28-31, 1963, American
Nuclear Society, New York, 1963.
15
13. Technical Function and Operation of the High Radiatior. Level
Examination Laboratory, Building 3525, USAEC Report ORNL CF-61-1-75,
Oak Ridge National Laboratory, January 1961.

14. C. J. Renken, R. G. Myers, and W. J. McGonnegle, "Status
Report in Eddy Current Theory and Application," USAEC Report ANL-5861,
Argonne National Laboratory, November 1958.
15. K. Ono and W. J. McGonnagle, "Pulsed Eddy-Current Instrument
for Measuring Sodium Levels of EBR-II Fuel Rods," USAEC Report ANL-6278,
Argonne National Laboratory, July 1961.
16. T. C. Cameron and II. M. McCall, Jr., "Development and Evalua-
tion of Prototype Remote-Controlled Sodium-Bonding and Bond-Inspection
Processes for EBR-II Fuel Cycle Facility," US AEC Report ANL-6724,
Argonne National Laboratory, May 1963.
17. M. J. Feldman, Argonne National Laboratory, personal
communication, February 1965.
18. C. V. Dodd, and R. W. McClung, "Fuel Element Coolant Channel
and Other Spacing Measurements by Eddy-Current Techniques," US AEC Report
ORNL-TM-129, Oak Ridge National Laboratory, March 1962.
19. C. V. Dodd, "Design and Construction of Eddy-Current Coolant
Channel Spacing Probes," (First part) Microtecnic, 18(5) 286-289
(Oct. 1964). Second part in issue 6.
20. G. H. Tenney, Los Alamos Scientific Laboratory, personal
communication, 1964.
21. K. K. Klindt, A. E. Richt, and W. C. Thurber, "Postirradiation
on of 17-4 PH Stainless Steel Control Rod Drive Rack from SM-1
Reactor," USAEC Report ORNL-3218, Oak Ridge National Laboratory,
November 1961.
22. R. E. Womack, "Modulus of Elasticity Equipment for Hot Cell
Application," US AEC Report UCRL-7173, University of California
Radiation Laboratory, January 1963.
23. $. E. Dismuke, Oak Ridge National Laboratory, personal
communication, February 1965.
24. A. P. Grunwald, "Leak Testing of EBR-II Fuel Rods," Nucl.
Sci. Eng. 12 419 423 (1962).
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DATE FILMED
16 / 8 /65







LEGAL NOTICE –

This report was prepared as an account of Government sponsored work. Neithor the United
Statos, aor the Coliinission, nor any person acting on behalf of the Commission:
A. Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completeness, or usefulness of the information contained in this report, or that the use
of any information, apparatus, method, or process disclosed in this report may not infringe
privately owned rights; or
B. Assumes any liabilities with respect to the use of, or for damages resulting from the
use of any information, apparatus, method, or process disclosed in this report,
As used in the above, “person acting on behalf of the Commission” includes any em-
ployee or contractor of the Commission, or employee of such contractor, to the extent that
such employee or contractor of the Commission, or employee of such contractor prepares,
disseminates, or provides access to, any information pursuant to his employment or contract
with the Commission, or his employment with such contractor.
7
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END