Isotopic separation of (sup 3)He/(sup 4)He from solar wind gases evolved from the lunar regolith

摘要

The potential benefits of (sup 3)He when utilized in a nuclear fusion reactor to provide clean, safe electricity in the 21st century for the world's inhabitants has been documented. Unfortunately, He is scarce on earth. Large quantities of (sup 3)He, perhaps a million tonnes, are embedded in the lunar regolith, presumably implanted by the solar wind together with other elements, notably (sup 4)He, H, C and N. Several studies have suggested processing the lunar regolith and recovering these valuable solar wind gases. Once released, these gases can be separated for use. The separation of helium isotopes is described in this paper. (sup 3)He constitutes only 400 at(center dot)ppm of lunar He, too dilute to separate economically by distillation alone. A ''superfluid'' separator is being considered to preconcentrate the (sup 3)He. The superfluid separator consists of a porous filter in a tube maintained at a temperature of 2.17 K or less. Although the (sup 4)He, which is superfluid below 2.17 K, flows readily through the filter, the He is blocked by the filter, and becomes enriched at the feed end. He can be enriched to about 10% in such a system. The enriched product from the superfluid separation serves as a feed to a distillation apparatus operating at a pressure of 9 kPa, with a boiler temperature of 2.4 K, and a condenser temperature of 1.6 K. Under constant flow conditions, a 99.9% enriched He product can be produced in this apparatus. The heat rejection load of the refrigeration equipment necessary to cool the separation operations would be conducted during the lunar nights.