A fast responding tritium in air monitor for use in operational areas of heavy water power reactors

A fast responding and sensitive tritium-in-air monitor, suitable for monitoring in heavy water-based nuclear power reactors has been described. The detector is a flowcell of 6.3 ml volume, made of stainless steel body and Teflon window and packed with 600 mg of 5 μm thick dry plastic scintillator films. It is coupled to a matched pair of photomultipliers and measurement is made in the coincidence mode of counting. Tritium counting efficiency for direct passage of sample air through the detector is 65%. The sampling rate is 1 to 10 1/min. For an uncontaminated detector, in the absence of any background activity, the instrument records only 2 counts/min as background which is equivalent to the passage of 8000 Bq/m3 (0.01 DAC) of tritium in air. Microprocessor based electronic compensation has been provided for gaseous radionuclide and gamma background interference. Trial runs of the monitor in our nuclear power plants have shown that the monitor can function on a continuous basis in presence of large levels of gamma background and gaseous radionuclide interference.