The normal operating temperature range in a reactor lies between 400ºC and 550ºC. K-type thermocouple
with a working range of -200ºC to 1200ºC is suitable to measure temperatures in the reactor. The drift of K-type
thermocouple due to nuclear radiation is also less. When temperature is above 0ºC, the limits of error of K-type
thermocouple is 2.2°C or 2.0% (whichever is greater). Fig. 1 shows the schematic diagram of attachment of a 1 mm
diameter thermocouple to a pressurized capsule. A hole of 1.01mm to 1.02mm diameter is drilled through the sleeve
and end plug portion of the pressurized capsule for insertion of thermocouple. First, the sleeve is attached to the
thermocouple by laser welding. After insertion of the thermocouple with the sleeve, through the hole drilled in the
end plug, the thermocouple sheath is welded to the projected part of the end plug. Finally the sleeve is
circumferentially welded to the end plug. All the welds should withstand a leak tightness of 10-8 std cc/s.