APPLICATIONS
OF KAMINI
Dr. Baldev
Raj, B. Venkataraman and K.V. Kasiviswanathan
Materials, Chemical and
Reprocessing Group
Indira Gandhi Centre for
Atomic Research
The Reactor
The reactor fuel is an alloy of
uranium-233 and aluminium in the form of flat plates and assembled in an
aluminum, casing to form the fuel subassemblies. The reflector is beryllium
oxide encased in zircaloy sheath. Demineralized light water is used as
moderator, coolant as well as shield. Cooling of the reactor core is by natural
convection. Start up and regulation of the reactor is done by adjusting the
positions of two safety control plates made of cadmium, which is sandwiched in
aluminum. These plates are provided with gravity drop mechanism for rapid shut
down of the reactor. All reactor operations are carried out from a central
control panel.
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KAMINI (Kalpakkam Mini reactor) is a Uranium-233 fueled,
low power (30 kW) research reactor
designed and built jointly by the Bhabha Atomic Research Centre (BARC) and
Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam. This reactor functions as a neutron
source with a flux of 1012 neutrons/sqcm/second
at core centre and facilitates carrying out neutron radiography of
radioactive and non-radioactive objects and neutron activation analysis. This
article highlights the various applications of neutron radiography and activation analysis, and
utilization of the reactor as a national facility. |
KAMINI reactor at Kalpakkam |
Facilities in Kamini
Radiography
Of the three collimators provided,
two are for neutron radiography. The length/diameter ratio of the collimators
is about 160 and the aperture size is 220mm x 70 mm. Flux at the outer end of
the beam tube is ~ 106 - 107 neutron/sqcm/second (n cm2 s-1). The south end beam tube
is for the radiography of radioactive objects while the north end beam tube is
for inactive objects. The radioactive subassembly with 61 fuel pins is lowered
from the top of the cell through a guide tube by a carriage-and-drive system
into the beam path. A precise stepper motor controlled indexing system enables
positioning of the object in front of the beam with an accuracy of ±0.5 mm. The
system is also provided with a precise stepper motor based rotation facility
which can index the object in front of the beam in steps of 0.5 degrees
enabling neutron tomography of fuel pins and subassembly. Apart from
subassembly, fuel pin radiography is also possible. Both film and real time
radiography is possible. For film radiography, a cassette drive mechanism with
10 cassettes and remote indexing has
been designed and fabricated. Real time radiography is accomplished using an
image intensifier based system.
Table
-1 : Salient Features Of Kamini
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Nature of reactor system
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Tank type
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Nominal power |
30kW |
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Fuel |
U 233 (20 Wt %)-Al alloy |
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Number of fuel per subassemblies |
9 |
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Number of fuel plates per subassembly |
8 |
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Reflector material |
200 mm thick BeO encased in Zircaloy |
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Moderator/ Coolant/Shield material |
Demineralized water |
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Core cooling mode |
By natural convention |
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Absorber |
Cadmium |
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Beam tubes |
3 |
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Flux at outer end of beam tube |
106 to 107 n cm2 s-1 |
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Flux at irradiation sites |
1011 to 1012 n cm2 s-1 |
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Core flux |
1012 n cm2 s-1 |
Activation Analysis
The facility for activation
analysis consists of a fast pneumatic transfer system with microprocessor based
control for sending and retrieving the samples. Polypropylene sampler holders –
the rabbits – having a diameter of 20 mm and a length of 30 mm, are used for
shooting the samples in and out of the reactor. The sample ends up between the
reactor core and the reflector (BeO
encased in Zircaloy).
The rabbit can accommodate samples with a maximum
weight of 3g. The activation analysis laboratory also contains a fumehood for
wet chemical operations and a high resolution gamma spectrometry system for
assay of short lived nuclei. Nuclei with longer half lives are assayed in the
Radiochemistry Laboratory. Samples of larger dimensions or higher weights can
be irradiated in the two thimble locations in the north and south side of the
core.
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Cassette Drive Mechanism designed and fabricated indigenously |
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Application of Kamini for Neutron Radiography and Activation
Analysis
Post Irradiation
Examination of fuel pins
One of the
purposes for which KAMINI was setup, is for the examination of the irradiated
fuel pins from FBTR. Due to the high levels of radiation from irradiated fuel
pins, conventional X-radiography is difficult because of the problems of gamma
fogging. Neutron Radiography is the best technique for the examination of
highly radioactive objects such as irradiated fuel pins. Neutron Radiography has
been successfully applied for characterising the highly irradiated fuel pins of
FBTR after a burnup of 25,000 MWD/T (megawatt day per tonne) and 50,000 MWD/T.
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Calibration
fuel pin -- rogue pellet crack in the pellet can be seen |
Image
of the pin after contrast stretching and edge enhancement |
Neutron
Radiography of Pyros
Pyro technique devices are
extensively used in space industry. More than 1200 pyro devices are used in any
space launch vehicle. The criticality of the pyros can be judged by the fact
that missions earlier had been aborted due to improper functioning of the
pyros.
Pyros for the Polar
Satellite Launch Vehicle (PSLV – C3, C4), and also for the INSAT – 3C satellite
were referred to IGCAR for Neutron Radiography by Vikram Sarabhai Space Centre
(VSSC), Thiruvananthapuram.
Neutron Activation Analysis
Since the neutron spectrum and the
neutron flux are important parameters which influence the sensitivity of the technique,
one of the first activities taken up after the establishment of the activation
analysis laboratory at KAMINI was to determine the flux and the cadmium ratio
(an indication of the thermal to epithermal reaction rates) at the irradiation
positions. Typical applications of Neutron Activation Analysis (NAA) using KAMIN include:
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Neutron radiographic image of irradiated fuel
pin |
Analysis of forensic samples
Neutron activation analysis
being a sensitive, non-destructive and multielemental technique, it is ideally
suited for the analysis of forensic samples. Analysis of forensic samples has
therefore been a regular programme, which has employed NAA. Over the last three
years, a number of samples received from the Forensic Science Laboratory of the
Government of Tamilnadu have been analysed at KAMINI.
Fire
retardation paints/compounds for Madras Atomic Power Station
One of the ways for spread
of fire is through the electrical cables and to avoid this the cables in the
Madras Atomic Power Station were recently coated with fire retardation paint
and some types of fire retardation compounds were also used. In due course of
time, with reactor operation radioactive isotopes of bromine and chlorine have
been observed in the emission from the stack. Conventional chemical analysis
did not reveal the presence of these elements. The samples were then subjected
to activation analysis using KAMINI.
One of the most popular
uses of INAA is the assay of ore samples for gold and then the other platinum
group elements. The relatively high cross section of gold, the convenient half
life and gamma ray energy of 198Au coupled with the ability of analysing powder or solid
samples makes Instrumented Neutron Activation Analysis (INAA) one of the most
effective technique for this purpose. Samples received from the Ore Dressing Section of BARC located
at AMD, Hyderabad have been assayed for gold.
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(a) |
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(b)
A typical pin pusher(a)
Digitised radiographic image (b) |
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Digitized radiographic image of detonating
catridges. Excellent radiographic contrast and sensitivity was obtained which
enabled clear delineation of the pyro charges, presence/absence of potting
compound, O-ring etc. |
Apart from various
governmental organisations currently using KAMINI, a lot of interest has been
shown by educational institutions. Assay of iodine in leaf samples as well as assay
of rock samples for rare earths and other elements were carried out for
environmental studies.
Another use of KAMINI is
the in-house production of radioisotopes for use in different studies in RCL.
Isotopes of interest are generated by the irradiation of pure foils of the element. Presently irradiation period in
KAMINI is restricted to a maximum of about 10 hrs at full power continuously.
Conclusions
KAMINI is a very versatile
and rich source of neutrons. The L/D ratio of about 160 makes it possible to
have very good contrast neutron radiographs. The reactor has been utilized for radiography of irradiated fuel
pins – one of the objectives of setting up the reactor. It has been in use and
will continue to be used as a national facility for the radiographic
examination and activation analysis of components from strategic departments
like space, forensic science and from educational institutions.