Development of Sensor Material for Application in Temperature ...

ENGINEERING-4
ADDITIONAL INFORMATION
The calibration data relating the chemical composition to Curie temperature of the arc melted samples (few grams) was
generated. However, for same composition, it was found that the Curie temperature of vacuum induction melted ingots (5
kg batch size) was lower (about 25°C). Therefore the vacuum induction ingots were prepared with cobalt in the range 12 to
15% (Ni – 51% and Fe – balance) to identify the exact chemical composition.
GENERAL EXPLANATION RELATED TO THE DESCRIPTION
The Diverse Safety Rod employs a driving mechanism,
called DSRDM that incorporates a temperature sensitive
electromagnetic switch (TSMS), the function of which is
to cut off the energising current supplied to the
electromagnet of DSRDM, once the sodium temperature
crosses the Curie temperature. The de-energisation of the
magnet results in the drop of the Diverse Safety Rod
(DSR) into the reactor core. In this regard, the choice of
the candidate material for the electromagnetic switch is
rather crucial as well as limited, from the point of view of
o
ensuring a Curie temperature in the range 620 to 630 C,
which is set by design considerations. The Curie point of
this sensor material depends on the chemical
composition and it is necessary to optimise the chemical
composition and thermo-mechanical processing to
achieve the required Curie temperature. Based on
extensive melting trials and characterisation, the Curie
temperature of the alloy with Ni51Fe36Co13
compositions
resulted in required Curie temperature in the range 620 –
o
630 C. This alloy with the required Curie temperature is
forged based on the optimised thermomechanical
processing and the sensor components fabricated are
shown in Fig. 3. The performance of these components in
furnace is found to be satisfactory.
Fig. 3 : The sensor components of about 38 mm diameter and 40 mm
height fabricated from the forged alloy
BRIEF DESCRIPTION OF THEORETICAL BACKGROUND
Based on the requirement of the Curie temperature in the range 620-630°C, and the data available in literature, Fe-Ni-Co
alloy is decided as sensor material. The Curie temperature depends on the chemical composition of Fe-Ni-Co alloys.
Various compositions of Fe-Ni-Co were prepared using arc melting at IIT, Madras and the Curie temperatures of as melted
buttons were obtained in the temperature range 637 to 725°C.
ACHIEVEMENT
o
The chemical composition of the sensor material that possesses Curie temperature in the range 620 – 630 C is identified
as Ni51Fe36Co 13. Thermo-mechanical processing of this alloy is optimized for avoiding cracking during hot forging. The
temperature sensitive magnetic switch is successfully fabricated and tested for its performance.
Further inquiries:
Dr. P.V. Sivaprasad, Materials Technology Division
Metallurgy and Materials Group, IGCAR, e-mail:prasad@igcar.gov.in
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