All DAE

DAE

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.

 

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:

  1. 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 220 mm 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.

     


    Cross-sectional view of the reactor

     

    Table-1: Salient Features Of Kamini

     

    Nature of reactor system Tank type
    Nominal power 30 kW
    Fuel U 233 (20 Wt %)-Al alloy
    Number of fuel per subassemblies 9
    Number of fuel plates per subassembly 8
    Reflector material 200 mm thick BeO encased in Zircaloy
    Moderator/Coolant/Shield material Demineralized water
    Core cooling mode By natural convention
    Absorber Cadmium
    Beam tubes 3
    Flux at outer end of beam tube 106 to 107 n cm2 s-1
    Flux at irradiation sites 1011 to 1012 n cm2 s-1
    Core flux 1012 n cm2 s-1
  2. 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.

     


    Cassette Drive Mechanism designed and fabricated indigenously

     


    Location of rabbit position in the reactor core

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 characterizing the highly irradiated fuel pins of FBTR after a burnup of 25,000 MWD/T (megawatt day per tonne) and 50,000 MWD/T.

 


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:-

 


Neutron radiographic image of irradiated fuel pin

  1. 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.
  2. 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 198 Au 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.

     


    (a)

     


    (b)
    A typical pin pusher (a) Digitised radiographic image (b)

     


    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 organizations 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 radio isotopes 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.