Lunar 3He estimations and related parameters analyses

Abstract

As a potential nuclear fuel, 3 He element is significant for both the solution of impending human energy crisis and the conservation of natural environment. Lunar regolith contains abundant and easily extracted 3 He. Based on the analyses of the impact factors of 3 He abundance, here we have compared a few key assessment parameters and approaches used in lunar regolith 3 He reserve estimation and some representative estimation results, and discussed the issues concerned in 3 He abundance variation and 3 He reserve estimation. Our studies suggest that in a range of at least meters deep, 3 He abundance in lunar regolith is homogeneously distributed and generally does not depend on the depth; lunar regolith has long been in a saturation state of 3 He trapped by minerals through chemical bonds, and the temperature fluctuation on the lunar surface exerts little influence on the lattice 3 He abundance. In terms of above conclusions and the newest lunar regolith depth data from the microwave brightness temperature retrieval of the "ChangE-1" Lunar Microwave Sounder, a new 3 He reserve estimation has been presented.The fast population expanding, elevated standards of living, and ever-increasing industrialization of the developing nations make world energy consumption grow rapidly, thus put unprecedented pressures on the Earth's resources and environment. Scientists predict that the Earth's energy supplies will have to increase by a factor 3 to 6 in the 21st century, and the 21st century will be the last century in which fossil fuels play a dominant role [1]. One of the effective solutions of this energy resource crisis is the utilization of nuclear energy released by nuclear fission and fusion. However, nuclear fission usually produces many radioactive wastes potentially threatening the security of human kind. Compared to the "traditional" nuclear fuel reaction process releasing 80% neutrons, the reaction between 3 He and Deuterium only generates a few percent of neutrons, which is characterized by enormous reduction of radioactivity, even without nuclear wastes, greatly lowered radiation damage to reactor, safe operation, very high overall operation efficiency, lower cost of electricity, and shorter time to commercial electrical power plants [2,3]. Especially, the 3 He-3 He reaction does not release neutrons, completely without the radioactive wastes and radioactivity worried by people [1,4], and can provide mankind with environment-friendly and inexhaustible electric energy [5]. 3 He, therefore, is the type of nuclear fusion fuel that can be long used, safe, highly efficient, and controllable, with vast developing potential.The Earth is deficient in 3 He resources. Kulcinski [2] believes that the 3 He available on the Earth is from two sources. One is from underground natural gases, with a total reserve of some 200 kg; the other from decaying tritium in thermonuclear weapons and heavy water CANDU fission plants, about 300 kg. Murali and Jordan [6] hold that the known 3 He in terrestrial natural gas deposits could not e...

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“…From the results shown in Figure 7, distributions of the thickness of lunar surface regolith as well as 3 He were estimated [34][35][36][37]. According to the results, the lunar regolith varies from ~1 m to 14 m - more reasonable than the results based on the Apollo data.…”

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“…Such a decision would normally be made on the basis of previous studies that have either directly or indirectly assessed the quality of each site. In our case, however, there are no maps available that directly characterize He distribution, although in recent works, authors, such as Li et al [ 7 ], Slyuta et al [ 13 ], WenZhe and YaQiu [ 14 ] and Zheng et al [ 15 ], agree that there might be a direct correlation between TiO and He abundance. In Section 5.1 of the paper, we therefore consider a two-dimensional target area in which non-uniform mapping of TiO indicates the suitability of each site for He characterization.…”

“…The compilation of all of these variables in a system model makes He estimation an extremely complex task. Indeed, existing He distribution and reserves models are marked by critical discrepancies due to imprecise or insufficient lunar data [ 7 ]. More accurate estimations would require large-scale, more detailed on-site surveying.…”

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“…As a result, 3 He carried by the solar wind gather together at a depth of 5-10 meters in the regolith on the lunar surface. 136 It is estimated that the reserves of 3 He within the lunar regolith range from a few hundred thousand tons to a few million tons, [137][138][139][140] presenting an energy potential ten times greater than the recoverable fossil fuels on Earth. 141 The abundance of 3 He on the Moon is primarily governed by three factors: the flux of solar wind, the maturity of lunar soil, and the presence of titanium dioxide (TiO 2 ).…”