Pages: 325-333

Authors: Dileep Blangat, Ravi Pazhayathu Mana, Karunakara Naregundi, Sangameshwar Managanvi, and Raj Mangal Tripathi

Abstract

In pressurized heavy water reactors, leaks from D₂O primary coolant and moderator to H₂O secondary coolant and other light-water systems in heat exchangers cannot be completely ruled out. High cost of D₂O demands that its loss should be prevented to maximum extent possible. Traditionally D₂O leak detection and identification of leaky heat exchanger is carried out by measurement of tritium activity in H₂O. Since tritium emits low energy beta radiation, its concentration in H2O is measured by mixing it with liquid scintillation solution in a definite proportion in counting vial and counted in a Liquid Scintillation Analyzer. It is very sensitive method for leak detection, but identification of leaky heat exchanger is time consuming and may require low power operation or reactor shut down. In the new method, high energy beta emitting fission products, which emit Cherenkov photons in H₂O, were used as the tracer. H₂O was poured in 20 mL plastic vials without scintillator and counted on Liquid Scintillation Analyzer.
D₂O leak was identified by comparing the Cherenkov photon count rate with that of the blank. A discrimination ratio significantly higher than average Cherenkov photon count rate for all heat exchangers was used to identify the leaky one. The technique has advantageous over existing method of D₂O leak detection, such as, (1) scintillation chemicals are not required (2) low power operation or reactor shut down is not required for identifying the leaky heat exchanger (3) no generation of radioactive chemical waste (4) on-power leak identification reduces generation of radioactive liquid waste. .

Key words: pressurized heavy water reactor, D₂O to H₂O leak, Cherenkov photon counting

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