Patent Number: 
Section: claims

1. A system for collecting 3He, the system comprising:a) a nuclear reactor having a vessel containing heavy water and having a cover gas head space containing a cover gas above the heavy water and a gas outlet in communication with the cover gas head space, whereby operation of the nuclear reactor results in thermal neutron activation of deuterium in the heavy water to produce tritium (3H) and at least some of the tritium undergoes β− decay to produce 3He gas that mixes with the cover gas;b) a gas extraction passage fluidly connected to the gas outlet of the vessel to extract a gas outlet stream through the gas outlet, the gas outlet stream comprising the cover gas and the 3He gas mixed with the cover gas;c) a 3He separation apparatus fluidly connected to the gas extraction passage downstream gas outlet and operable to receive the gas outlet stream and separate the 3He gas from the cover gas wherein the 3He separation apparatus comprises at least one of a thermal diffusion apparatus, a fractional diffusion apparatus, a heat flush apparatus, a superleak apparatus and a differential absorption apparatus. 2. The system of claim 1, further comprising a gas inlet provided in the vessel and in communication with the cover gas head space, and a cover gas supply passage coupled to the gas inlet of the vessel to supply the cover gas to the cover gas head space. 3. The system of claim 2, wherein the 3He separation apparatus comprises a 3He outlet to output a separated 3He gas stream and a separate treated cover gas outlet to output a treated cover gas stream. 4. The system of claim 2, wherein the treated cover gas outlet of the 3He separation apparatus is fluidly connected to the cover gas supply passage to re-introduce at least a portion of the treated cover gas stream into the cover gas head space. 5. The system of claim 1, wherein the gas outlet stream is extractable as a generally continuous gas stream while the nuclear reactor is in operation. 6. The system of claim 1, wherein the cover gas provided above the heavy water consists essentially of 4He. 7. A moderator cover gas system for use with a nuclear reactor having a vessel containing heavy water, the cover gas system comprising:a) a cover gas supply passage having a gas outlet connectable to a gas inlet on the vessel to supply a cover gas into the vessel,b) a gas extraction passage having a gas inlet connectable to a gas outlet on the vessel to extract an outlet gas stream from within the vessel, the outlet gas stream comprising a mixture of at least the cover gas and 3He gas;c) a gas separation apparatus connected to the cover gas flow passage downstream from the gas outlet on the vessel and operable to separate the 3He gas from the outlet gas stream, wherein the 3He separation apparatus comprises at least one of a thermal diffusion apparatus, a fractional diffusion apparatus, a heat flush apparatus, a superleak apparatus and a differential absorption apparatus. 8. The system of claim 7, further comprising a fresh cover gas source fluidly connected to the cover gas supply passage to introduce cover gas consisting essentially of 4He into the interior of the vessel. 9. The system of claim 7, wherein the gas separation apparatus comprises a first outlet to output the separated 3He gas and a second outlet to output a treated cover gas stream. 10. The system of claim 9, wherein the second outlet is fluidly connected to the cover gas supply passage to feed at least a portion of the treated cover gas stream into the cover gas supply passage.