helium-3: new fuel for humans

Helium-3 (He-3) is a light, non-radioactive isotope of helium with two protons and one neutron, rare on Earth, sought for use in nuclear fusion research. The abundance of helium-3 is thought to be greater on the Moon (embedded in the upper layer of regolith by the solar wind over billions of years) and the solar system's gas giants (left over from the original solar nebula), though still low in quantity (28 ppm of lunar regolith is helium-4 and 0.01 ppm is helium-3).[1] It is proposed to be used as a second-generation fusion power source.

The helion, the nucleus of a helium-3 atom, consists of two protons but only one neutron, in contrast to two neutrons in ordinary helium. Its existence was first proposed in 1934 by the Australian nuclear physicist Mark Oliphant while based at Cambridge University's Cavendish Laboratory, in an experiment in which fast deuterons were reacted with other deuteron targets (the first demonstration of nuclear fusion). Helium-3, as an isotope, was postulated to be radioactive, until helions from it were accidentally identified as a trace "contaminant" in a sample of natural helium (which is mostly helium-4) from a gas well, by Luis W. Alvarez and Robert Cornog in a cyclotron experiment at the Lawrence Berkeley National Laboratory, in 1939. [2]
Contents
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* 1 Physical properties
* 2 Thermodynamic properties
* 3 Fusion reactions
* 4 Neutron detection
* 5 Cryogenics
* 6 Manufacturing
* 7 Terrestrial occurrence
* 8 Medical lung imaging
* 9 Extraterrestrial supplies
* 10 Power generation
* 11 See also
* 12 Notes and references
* 13 External links

[edit] Physical properties

Helium-3's atomic mass of 3.0160293, being significantly lower than Helium-4's 4.0026, causes it to have significantly different properties. Helium-3 boils at 3.19 kelvins compared to helium-4's 4.23 K, and its critical point is also lower at 3.35 K, compared to helium-4's 5.19 K. It has less than half the density when liquid at its boiling point: 0.059 g/ml compared to helium-4's 0.12473 g/ml at one atmosphere. Its latent heat of vaporization is also considerably lower at 0.026 kJ/mol compared to helium-4's 0.0829 kJ/mol.[3]

[edit] Thermodynamic properties

Equations of state for 3He are available along the vapor-liquid equilibrium line [4][5], the liquid-solid equilibrium line [6] and the normal compressed liquid and gas phases [7].

[edit] Fusion reactions
Fusion reactions involving Helium-3[8][9][10][11][12] Reactants Products Q
First Generation Fuels
21H + 21H → 32He + 10n 3.268 MeV
21H + 21H → 31H + 11p 4.032 MeV
21H + 31H → 42He + 10n 17.571 MeV
Second Generation Fuel
21H + 32He → 42He + 11p 18.354 MeV
Third Generation Fuel
32He + 32He → 42He+ 211p 12.86 MeV

Some fusion processes produce highly energetic neutrons which render reactor components radioactive through the continuous bombardment of the reactor's components with emitted neutrons. Because of this bombardment and irradiation, power generation must occur indirectly through thermal means, as in a fission reactor. However, the appeal of helium-3 fusion stems from the nature of its reaction products. Helium-3 itself is non-radioactive. The lone high-energy by-product, the proton can be contained using electric and magnetic fields. The momentum energy of this proton (created in the fusion process), will interact with the containing electromagnetic field; resulting in direct net electricity generation.[13]

However, since both reactants need to be mixed together to fuse, side reactions (21H + 21H and 32He+ 32He) will occur, the first of which is not aneutronic. Therefore in practice this reaction is unlikely to ever be completely 'clean', thus negating some of its attraction. Also, due to the higher Coulomb barrier, the temperatures required for 21H + 32He fusion are much higher than those of conventional 2H + 31H (deuterium + tritium) fusion.

The amounts of helium-3 needed as a replacement for conventional fuels should not be underestimated. The total amount of energy produced in the 21H + 32He reaction is 18.4 MeV, which corresponds to some 493 megawatt-hours (4.93x108 Wh) per three grams (one mole) of ³He. Even if that total amount of energy could be converted to electrical power with 100% efficiency (a physical impossibility), it would correspond to about 30 minutes of output of a thousand-megawatt electrical plant; a year's production by the same plant would require some 17.5 kilograms of helium-3.

The amount of fuel needed for large-scale applications can also be put in terms of total consumption: According to the US Energy Information Administration, "Electricity consumption by 107 million U.S. households in 2001 totaled 1,140 billion kWh" (1.114x1015 Wh). Again assuming 100% conversion efficiency, 6.7 tons of helium-3 would be required just for that segment of one country's energy demand, 15 to 20 tonnes given a more realistic end-to-end conversion efficiency.[citation needed]

[edit] Neutron detection

Helium-3 is a most important isotope in instrumentation for neutron detection. It has a high absorption cross section for thermal neutron beams and is used as a converter gas in neutron detectors. The neutron is converted through the nuclear reaction

n + 3He → 3H + 1H + 0.764 MeV

into charged particles tritium (T, 3H) and proton (p, 1H) which then are detected by creating a charge cloud in the stopping gas of a proportional counter or a Geiger-Müller tube. [14]

Furthermore, the absorption process is strongly spin-dependent, which allows a spin-polarized helium-3 volume to transmit neutrons with one spin component while absorbing the other. This effect is employed in neutron polarization analysis, a technique which probes for magnetic properties of matter.[15] [16]

[edit] Cryogenics

A helium-3 refrigerator uses helium-3 to achieve temperatures of 0.2 to 0.3 kelvin. A dilution refrigerator uses a mixture of helium-3 and helium-4 to reach cryogenic temperatures as low as a few thousandths of a kelvin. [17]

An important property of helium-3, which distinguishes it from the more common helium-4, is that its nucleus is a fermion since it contains an odd number of spin 1/2 particles. Helium-4 nuclei are bosons, containing an even number of spin 1/2 particles. This is a direct result of the addition rules for quantized angular momentum. At low temperatures (about 2.17 K), helium-4 undergoes a phase transition: A fraction of it enters a superfluid phase that can be roughly understood as a type of Bose-Einstein condensate. Such a mechanism is not available for helium-3 atoms, which are fermions. However, it was widely speculated that helium-3 could also become a superfluid at much lower temperatures, if the atoms formed into pairs analogous to Cooper pairs in the BCS theory of superconductivity. Each Cooper pair, having integer spin, can be thought of as a boson. During the 1970s, David Morris Lee, Douglas Osheroff and Robert Coleman Richardson discovered two phase transitions along the melting curve, which was soon realized to be the two superfluid phases of helium-3.[18][19] The transition to a superfluid occurs at 2.491 millikelvins on the melting curve. They were awarded the 1996 Nobel Prize in Physics for their discovery. Tony Leggett won the 2003 Nobel Prize in Physics for his work on refining understanding of the superfluid phase of helium-3.[20]

In zero magnetic field, there are two distinct superfluid phases of 3He, the A-phase and the B-phase. The B-phase is the low-temperature, low-pressure phase which has an isotropic energy gap. The A-phase is the higher temperature, higher pressure phase that is further stabilized by a magnetic field and has two point nodes in its gap. The presence of two phases is a clear indication that 3He is an unconventional superfluid (superconductor), since the presence of two phases requires an additional symmetry, other than gauge symmetry, to be broken. In fact, it is a p-wave superfluid, with spin one, S=1, and angular momentum one, L=1. The ground state corresponds to total angular momentum zero, J=S+L=0 (vector addition). Excited states are possible with non-zero total angular momentum, J>0, which are excited pair collective modes. Because of the extreme purity of superfluid 3He (since all materials except 4He have solidified and sunk to the bottom of the liquid 3He and any 4He has phase separated entirely, this is the most pure condensed matter state), these collective modes have been studied with much greater precision than in any other unconventional pairing system.

[edit] Manufacturing

Due to the rarity of helium-3 on Earth, it is typically manufactured instead of recovered from natural deposits. Helium-3 is a byproduct of tritium decay, and tritium can be produced through neutron bombardment of lithium, boron, or nitrogen targets. Current supplies of helium-3 come, in part, from the dismantling of nuclear weapons where it accumulates[21]; approximately 150 kilograms of it have resulted from decay of US tritium production since 1955, most of which was for warheads[22]. However, the production and storage of huge amounts of the gas tritium is probably uneconomical, as roughly eighteen tons of tritium stock are required for each ton of helium-3 produced annually by decay (production rate dN/dt from number of moles or other unit mass of tritium N is N γ = N * [ln2/t½] where the value of t½/(ln2) is about 18 years; see radioactive decay). If commercial fusion reactors were to use helium-3 as a fuel, they would require tens of tons of helium-3 each year to produce a fraction of the world's power.[23] Breeding tritium with lithium-6 consumes the neutron, while breeding with lithium-7 produces a low energy neutron as a replacement for the consumed fast neutron. Note that any breeding of tritium on Earth requires the use of a high neutron flux, which proponents of helium-3 nuclear reactors hope to avoid.[citation needed]

[edit] Terrestrial occurrence

Main article: isotope geochemistry

3He is a primordial substance in the Earth's mantle, considered to have become entrapped within the Earth during planetary formation. The ratio of 3He to 4He within the Earth's crust and mantle is less than that for assumptions of solar disk composition as obtained from meteorite and lunar samples, with terrestrial materials generally containing lower 3He/4He ratios due to ingrowth of 4He from radioactive decay.

3He is present within the mantle, in the ratio of 200-300 parts of 3He to a million parts of 4He. Ratios of 3He/4He in excess of atmospheric are indicative of a contribution of 3He from the mantle. Crustal sources are dominated by the 4He which is produced by the decay of radioactive elements in the crust and mantle.

The ratio of Helium-3 to Helium-4 in natural Earth-bound sources varies greatly.[24][25] Samples of the ore Spodumene from Edison Mine, South Dakota were found to contain 12 parts of He-3 to a million parts of Helium-4. Samples from other mines showed 2 parts per million.[24]

Helium is also present as up to 7% of some natural gas sources,[26] and large sources have over 0.5 percent (above 0.2 percent makes it viable to extract).[27]Algeria's annual gas production is assumed to contain 100 million Nm3[27] and this would contain between 5 and 50 Nm3 of Helium-3 (about 1 to 10 kilograms) using the normal abundance range of 0.5 to 5 ppm. Similarly the US 2002 stockpile of 1 billion Nm3[27] would have contained about 10 to 100 kilograms of He-3.

3He is also present in the Earth's atmosphere. The natural abundance of 3He in naturally occurring helium gas is 1.38×10-6. The partial pressure of helium in the Earth's atmosphere is about 4 millitorr, and thus 5.2 parts per million[clarification needed] of helium. It has been proven that the Earth's atmosphere contains approximately 4000 tons of 3He.[citation needed]

3He is produced on Earth from three sources: lithium spallation, cosmic rays, and decay of tritium (3H). The contribution from cosmic rays is negligible within all except the oldest regolith materials, and lithium spallation reactions are a lesser contributor than the production of 4He by alpha particle emissions.
This section contains information which may be of unclear or questionable importance or relevance to the article's subject matter.
Please help improve this article by clarifying or removing superfluous information. (July 2008)

The total amount of helium-3 in the mantle may be in the range of 100 thousand to a million tonnes. However, this mantle helium is not directly accessible.[clarification needed] Some of it leaks up through deep-sourced hotspot volcanoes such as those of the Hawaiian islands, but only 300 grams per year is emitted to the atmosphere. Mid-ocean ridges emit another 3 kilogram per year. Around subduction zones, various sources produce helium-3 in natural gas deposits which possibly contain a thousand tonnes of helium-3 (although there may be 25 thousand tonnes if all ancient subduction zones have such deposits). Wittenberg estimated that United States crustal natural gas sources may have only half a tonne total.[28] Wittenberg cited Anderson's estimate of another 1200 metric tonnes in interplanetary dust particles on the ocean floors.[29] Extracting helium-3 from these sources consumes more energy than fusion would release.[30] Wittenberg also writes that extraction from US crustal natural gas, consumes ten times the energy available from fusion reactions.[31][clarification needed]
[edit] Medical lung imaging

Polarized helium-3 may be produced directly with lasers of the appropriate power, and with a thin layer of protective Cs metal on the inside of cylinders, the magnetized gas may be stored at pressures of 10 atm for up to 100 hours. When inhaled, mixtures containing the gas can be imaged with an MRI-like scanner which produces breath by breath images of lung ventilation, in real-time. Applications of this experimental technique are just beginning to be explored[32].

[edit] Extraterrestrial supplies

The Moon's surface contains helium-3 at concentrations on the order of 0.01 ppm.[33][34] A number of people, starting with Gerald Kulcinski in 1986,[35] have proposed to explore the moon, mine lunar regolith and using the helium-3 for fusion. Because of the low concentrations of helium-3, any mining equipment would need to process large amounts of regolith,[36] and some proposals have suggested that helium-3 extraction be piggybacked onto a larger mining and development operation.[citation needed]

The primary objective of Indian Space Research Organization's first lunar probe called Chandrayaan-I, launched on October 22, 2008, was reported in some sources to be mapping the Moon's surface for helium-3-containing minerals.[37] However, this is debatable; no such objective is mentioned in the project's official list of goals, while at the same time, many of its scientific payloads have noted helium-3-related applications.[38] [39]

Cosmochemist and geochemist Ouyang Ziyuan from the Chinese Academy of Sciences who is now in charge of the Chinese Lunar Exploration Program has already stated on many occasions that one of the main goals of the program would be the mining of helium-3, from which operation "each year three space shuttle missions could bring enough fuel for all human beings across the world."[40]

In January 2006, the Russian space company RKK Energiya announced that it considers lunar helium-3 a potential economic resource to be mined by 2020,[41] if funding can be found.[42][43]

Mining gas giants for helium-3 has also been proposed.[44] The British Interplanetary Society's hypothetical Project Daedalus interstellar probe design was fueled by helium-3 mines on the planet Jupiter, for example. Jupiter's high gravity makes this a less energetically favorable operation than extracting helium-3 from the other gas giants of the solar system, however.

[edit] Power generation

A second-generation approach to controlled fusion power involves combining helium-3 (32He) and deuterium (21H). This reaction produces an helium-4 ion (42He) (like an alpha particle, but of different origin) and a high-energy proton (positively charged hydrogen ion) (11p). The most important potential advantage of this fusion reaction for power production as well as other applications lies in its compatibility with the use of electrostatic fields to control fuel ions and the fusion protons. Protons, as positively charged particles, can be converted directly into electricity, through use of solid-state conversion materials as well as other techniques. Potential conversion efficiencies of 70 percent may be possible, as there is no need to convert proton energy to heat in order to drive turbine-powered generators.

There have been many claims about the capabilities of Helium-3 power plants. According to proponents, fusion power plants operating on deuterium and helium-3 would offer lower capital and operating costs than their competitors due to less technical complexity, higher conversion efficiency, smaller size, the absence of radioactive fuel, no air or water pollution, and only low-level radioactive waste disposal requirements. Recent estimates suggest that about $6 billion in investment capital will be required to develop and construct the first helium-3 fusion power plant. Financial breakeven at today's wholesale electricity prices (5 US cents per kilowatt-hour) would occur after five 1000-megawatt plants were on line, replacing old conventional plants or meeting new demand.[45]

The reality is not so clean-cut. The most advanced fusion programs in the world are inertial confinement fusion (such as National Ignition Facility) and magnetic confinement fusion (such as ITER and other tokamaks). In the case of the former, there is no solid roadmap to power generation. In the case of the latter, commercial power generation is not expected until around 2050[46]. In both cases, the type of fusion discussed is the simplest: D-T fusion. The reason for this is the very low Coulomb barrier for this reaction; for D+He-3, the barrier is much higher, and He-3–He-3 higher still. The immense cost of reactors like ITER and National Ignition Facility are largely due to their immense size, yet to scale up to higher plasma temperatures would require reactors far larger still. The 14.7 MeV proton and 3.6 MeV alpha particle from D–He-3 fusion, plus the higher conversion efficiency, means that more electricity is obtained per kilogram than with D-T fusion (17.6 MeV), but not that much more. As a further downside, the rates of reaction for He-3 fusion reactions are not particularly high, requiring a reactor that is larger still or more reactors to produce the same amount of electricity.

To attempt to work around this problem of massively large power plants that may not even be economical with D-T fusion, let alone the far more challenging D–He-3 fusion, a number of other reactors have been proposed -- the Fusor, Polywell, Focus fusion, and many more. These generally attempt to achieve fusion in thermal disequilibrium, something that could potentially prove impossible[47], and consequently, these long-shot programs tend to have trouble garnering funding despite their low budgets. Unlike the "big", "hot" fusion systems, however, if such systems were to work, they could scale to the higher barrier "aneutronic" fuels. However, these systems would scale well enough that their proponents tend to promote p-B fusion, which requires no exotic fuels like He-3.

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NUCLEAR POWER: IS IT HELPFUL REALLY?????????

“Nuclear power is the best alternative to fossil fuels”

After many trials and tribulations, the historic Indo-US nuclear deal is through. And while some on the Left cry foul, experts say that India stands to gain both at a political and economic level. They claim that India is at the forefront in recognising the distinct advantages of using thorium in the nuclear fuel cycle and will become a significant player on the international nuclear market, given the number of highly skilled nuclear engineers and scientists. The US-India Business Council thinks that the deal could open a wide vista of opportunity for US-India collaboration in commerce, civil nuclear research, technology transfer and essential inputs to power India’s dynamic and fast-moving economy.

On the other side we see that today across the world there are 440 land-based nuclear power reactors that produce around 370 gigawatts of electricity, amounting to 16% of the world’s electricity. But that is barely two percent of the share of total world energy consumption. With depletion of the fossil fuel reserves and global warming becoming a major concern, massive campaigns are being undertaken by governments across the globe to teach their citizens about the importance of conservation and renewable sources of energy, which is often taken to include nuclear power. However, critics contend that nuclear power is neither a renewable nor a clean source of energy.

The nuclear power debate in context:

India's power needs

The world’s largest democracy is in dire need of power. To understand India's hunger for energy, one simply needs to look at the numbers. India is the world’s sixth largest consumer of oil, using an estimated 2,450,000 barrels per day in 2005. That demand is expected to grow rapidly until 2030. Today, India imports about 70% of its oil; and as its demand for natural gas is also expected to grow, most of that would have to be imported too.

The nuclear solution

To curb this dependence, the nuclear option looks viable. However, at present nuclear energy in India accounts for a measly 3% of the total generation of 120,000 MW. As of 2008, India has 17 nuclear power plants in operation generating 4,120 MW, while six others are under construction and are expected to generate an additional 3,160 MW. Large-scale nuclear power production would also mean less dependence on traditional sources of non-renewable fuel such as coal, oil and petroleum. Abundant nuclear power production would lead to a fall in fuel and electricity prices. It especially holds relevance as a promising new alternative in the face of price rise and fall in oil output. India has also done a great amount of work in the development of a thorium-centred fuel cycle. While uranium deposits in the nation are limited there are much greater reserves of thorium, and it could provide hundreds of times the energy with the same mass of fuel. A prototype reactor that would burn uranium-plutonium fuel while irradiating a thorium blanket is under construction at the Kalpakkam Atomic Power Station.

Civil nuclear co-operation and the power politics

India, being a non-signatory of the Nuclear Non-Proliferation Treaty, has been subjected to a de facto nuclear embargo from members of the Nuclear Suppliers Group (NSG) cartel. This had prevented India from obtaining commercial nuclear fuel, nuclear power plant components and services from the international market, thereby forcing India to develop its own fuel, components and services for nuclear power generation. It has been argued that the embargo had both negative and positive consequences for India's nuclear industry. On the one hand it has constrained the country’s ability to move towards its goal of expanding its nuclear power generation capacity to at least 20,000 MW by 2020. On the other hand, the NSG embargo has forced the Indian government to support and actively fund the development of Indian nuclear technologies.

India is a member of the International Atomic Energy Agency (IAEA), and four of its 13 nuclear reactors are subject to IAEA safeguards. However, India has not signed the Comprehensive Test Ban Treaty (CTBT) or the Non-Proliferation Treaty (NPT). With India’s desire to emerge as a global superpower, the status of being one of the countries who will be in civil nuclear cooperation with NSG countries without signing the CTBT or NPT will help further its cause. However critics of the deal are quick to point that the American military-industrial complex has its own calculations to ponder. The enforcement of nuclear non-proliferation is a handy weapon to maintain American nuclear hegemony, and is a policy supplemented with a further stratagem of offering vulnerable countries around the world, under strictest safeguards, driblets of nuclear fuel and technology for civilian use.

Renewable sources - the cleaner yet costlier alternatives to fossil fuel ?

There are many renewable energy options available to India. With a huge coastline, wind power is a viable option. India was one of the pioneering states in establishing hydro-electric power plants. The hydro-power plant at Darjeeling was established in 1898 and is one of the first in Asia. The current installed base of hydro power is 36,033.76 MW, which comes to 24.7% of total installed base. Being a primarily agricultural country, biomass power is under consideration by the government, as well as the conversion of urban and industrial waste into energy. This tropical country is also exploring the option of solar energy. The current installed base of renewable power is 12,194.57 MW, which comes to 7.7% of total installed base and is estimated to increase in the future. But in spite of the steps taken, critics argue that the renewable sources, while cleaner, will be a costlier option and will fail to be the substitute for fossil fuel.

Is nuclear power superior?

Fossil fuels like coal will continue to play a role in meeting our energy needs, and new techniques like carbon capture and storage will make them cleaner and more efficient. However, much of the debate pits nuclear power against renewable energy, particularly hydroelectric and wind power. Critics see government targets for the increase in renewables as pure wishful thinking and see alternative sources like wind power and biomass fuel as expensive and intermittent. But supporters contest that not only is wind power reliable, it is the future of energy: the subsidies for wind power are small by nuclear standards, and cost reductions will continue in the future. However, critics of the nuclear option like Arthur Scargill, former president of the UK National Union of Mineworkers, claim that nuclear-power generated electricity is the most expensive form of energy - 400% more expensive than coal, having received £6bn in subsidies, with £70bn to be paid by UK taxpayers in decommissioning costs. Besides the cost scenario, there are the added problems of nuclear waste disposal and the risk of nuclear disasters; and reminders of the disasters at Windscale (UK, 1957), Three Mile Island (USA, 1979) and Chernobyl (Russia, 1986) still feature prominently in this discussion.

The arguments against nuclear power

Opponents of nuclear power argue that an assessment of potential benefits must take into account the entire life cycle of a nuclear power station. Factoring in the costs of construction, insurance, waste disposal and decommissioning undermines the economic case for nuclear. The question of cost is a complex one and both sides agree that we will only really know how much a nuclear power station costs by building one. It is also argued that the carbon dioxide emitted in the mining and refinement of uranium makes the case that nuclear is clean look more doubtful. There is also concern about the link between nuclear power and weapons proliferation and about vulnerability to terrorism. Critics say that extending civil nuclear cooperation to India, a non-signatory of CTBT and NPT, will escalate the nuclear race in the subcontinent. However India has a declared nuclear no-first-use policy and is in the process of developing a nuclear doctrine based on ‘credible minimum deterrence.’ In August 1999, the Indian government released a draft of the doctrine which asserts that nuclear weapons are solely for deterrence and that India will pursue a policy of ‘retaliation only.’