|
|
| |
| |
|
| |
|
A neutron radiography facility(NRF) for non-destructive
testing was installed at the NR port, one of the eight
tangential beam ports of HANARO, a 30MW high flux research
reactor on 1997. It was developed in compliancewith
the nuclear fuel development program in KAERI for one
of the post-irradiated fuel test methods. In variety
of inspections in hot-cell laboratory, the fuel soundness
and dimensional assessment of fuel elements and tubes
were tested. As for non-nuclear applications, many diverse
tests and trials on explosives, detonators, metallic
molds and corrosions detection, archeological objects,
were conducted etc. together with regular students education.
As industry in Korea is requiring more advanced
technologies to be developed, neutron radiography techniques
were applied and expanded for general industry in addition
to nuclear field. Among the recent results in this trend
include measurements of boron distribution and the analysis
of it's quantitative content in alloy steels, defect
finding in turbine blades, some tests from defense industry,
and test of lithium-ion density of the cellular phone
batteries, archeological objects and fuel cell.
As
part of quality assurance in these of inspections, KAERI's
neutron radiography laboratory has prepared not only
for accrediating in KOLAS, but also the development
of tomography and dynamic radiogrpahy since 2000.
There
are two exposure units along the beam- line. The size
of the first exposure unit is 120(w)185(l)190(h) cm
and that of the second exposure unit is 120(w)185(l)190(h)
cm. There is a beam window of 3040 cm between units
through which the beam passes. The exposure time is
controlled by the main beam shutter of 90 cm thickness
located just behind the collimator exit. Currently,
it takes about 15 seconds to open or close the main
beam shutter. A quick beam shutter that spends less
than 2 seconds is installed. The first exposure unit
located behind the main beam shutter was designed to
test the highly radioactive specimen of nuclear fuel
pins using transfer method with a Dy screen converter.
There is a hole of 30cm diameter, with a depth of 200cm
below the floor and A cask will be moved through the
ceiling so that a nuclear fuel pin up to 330cm can be
scanned. The second exposure unit was designed to test
the low activity or general specimens by the direct
method using the combination of a 25m thick Gd converter
screen and SRX-ray film. When we utilize the direct
method, a typical irradiation time of 5 minutes is required
to get a darkness film density of 2.5 to Kodak SR X-ray
film by using a 25 mm gadolinium screen at 17 to 24MW
reactor power. Gd converter is manufactured. Flaw in
turbine blades, the fill-in of explosives from defense
industry, the lithium-ion density of the cellular phone
batteries and archeological objects are being tested
In addition, an image processing system has been
installed to obtain real-time images in the second exposure
unit. A commercial NE426(6LiF-ZnS(Ag)) scintillator
screen and a high sensitivity SIT(silicon intensifier
target) camera are being temporarily used. A digital
image of 5124808bits is collected at a rate of 30 frames/sec
through a commercial frame grabber. The input image
frames are processed by using software we developed
to perform dynamic studies.
The experiments in
autoradiography require a somewhat high neutron intensity
of ~ 1013 n/cm2 in order to make the clear tracks on
a solid state nuclear track detectors(SSNTD) like Kodak
CN-85 and LR 115. Since the neutron flux of NR beam
port is not enough to reach this fluence in a reasonable
time condition, a autoradiography system was set up
at the vertical hole of HANARO. In principle, when 10B
nuclei captures a thermal neutron, it emits alpha and
recoils 7Li. These two particles make the tracks on
the surface of the SSNTD detector. Total intensity
needed to make a clear image on a commercial SSNTD depend
upon boron distribution in a sample. In the case of
the HANARO autoradiography system, thermal neutron flux
at the autoradiography beam port at the vertical hole
of NAA1, NAA2, NAA3 with a diameter of 60mm is 2.671013
n/cm2/sec. An exposure time of less than 10 seconds
is required for a metallic alloy having a boron content
greater than 30 ppm when Kodak CN-85 is used.[4] Autoradiography
of boron distribution of 130 ppm in carbon steel
The
development of tomography and dynamic radiography is
also in progress.
Since the HANARO NRF system has
been set up, some NDT for industries and institutes
has successfully been performed using film method. In
addition, an image processing system has been set up
for the study of dynamic observations. Development
of tomography 3D usinf cooled CCD camera is on the commissions.
Along with these techniques, the HANARO neutron radiography
program can be used in a wide range of user applications
coming from industries and others. |
|
|
|
|
