Direct Harvesting of Helium-3 (3He) From Heavy Water Nuclear Reactors

The thermal neutron activation of deuterium inside a heavy-water-moderated or -cooled nuclear reactor produces a build-up of tritium in the heavy water. The in situ decay of tritium can, for certain reactor types and operating conditions, produce potentially useable amounts of 3He, which can be directly extracted via the heavy-water cover gas without first separating, collecting and storing tritium outside the reactor. It is estimated that the amount of 3He available for recovery from the moderator cover gas of a 700 MWe class Pressurized Heavy Water Reactor (PHWR) ranges from 0.1 to 0.7 m3 (STP) per annum, varying with the tritium activity buildup in the moderator. The harvesting of 3He would generate approximately 12.7 m3 (STP) of 3He, worth more than $30M at current market rates, over a typical 25-year operating cycle of the PHWR. This paper discusses the production of 3He in the moderator of a PHWR and its extraction from the 4He moderator cover gas system using conventional methods.