Method of controlling the pressure in a heavy water cover gas circulating system for a heavy water moderated reactor

Purpose: To reduce the exhausting and the supplying of a cover gas externally and enable the exhausting of the cover gas into the atmospheric air in low radioactivity level by providing a buffer tank for storing the cover gas only for a purifier in high pressure immediately after a purifying device. Method: Cover gas containing impurities and water is purified and returned to a circulating system, and is partly stored at high pressure in a buffer tank. A pressure regulator is provided in this circulating system, and if the pressure in the circulating system is too high, excess gas is stored in the tank. On the other hand, if the pressure in the circulating system is too, a signal from the pressure regulator causes gas to be supplied from the tank. Since the excess gas is stored, the need for an external supply of expensive helium can thus be reduced, and radioactive discharge into the atmosphere can also be accordingly reduced. (Yoshino, Y.)