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Harnessing thorium power TRENDS |
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Harnessing thorium power
AS the US Congress debates the Indo-US agreement on nuclear cooperation, a key “justification” from the American viewpoint being presented to US lawmakers is that India has certain inherent strengths in the area of nuclear technology, which would enable India to forge ahead, albeit slowly, even without US cooperation. Central to this argument is the availability of huge reserves of thorium in India. Thorium reserves have been estimated to be between 3,60,000 and 5,18,000 tonnes. The US estimates the “economically extractable” reserves to be 2,90,000 tonnes, one of the largest in the world. Our uranium reserves, by contrast, are estimated to be at a maximum of around 70,000 tonnes. We currently have 14 reactors, most of which are pressurised heavy water reactors (PHWR) which use natural uranium. The Tarapur reactors are boiling water reactors which need enriched uranium, which has to be imported. Together they generate about 2770 MWe (Mega Watt Electrical) of power, just 3.7 per cent of that generated from all sources. Another six PHWRs are in construction, and along with the two “VVER” Russian built 1000 MWe reactors which also use enriched uranium, they would add about 3960 MWe by 2008. The goal is to reach at least 20,000 MWe by 2020. Our uranium reserves are meagre. Obtaining enriched uranium for the Tarapur reactors and any new VVER type reactors require Nuclear Suppliers Groups countries, including Russia, to relax norms. This is where the agreement with the US is expected to be beneficial to India. Also central to our success in achieving these goals, is the harnessing of thorium, for which India has developed a three-stage nuclear programme. India has already developed and tested the technologies needed to extract energy from Thorium, but large scale execution has not yet been possible, mainly because of limited availability of Plutonium. Stage one is the use of PHWRs. Natural uranium is the primary fuel. Heavy water (deuterium oxide, D20) is used as moderator and coolant. The composition of natural uranium is 0.7 percent U-235, which is fissile, and the rest is U-238. This low fissile component explains why certain other types of reactors require the uranium to be “enriched” i.e. the fissile component increased. In the second stage, the spent fuel from stage one is reprocessed in a reprocessing facility, where Plutonium-239 is separated. Plutonium, of course, is a weapons material, which goes towards creating India’s nuclear deterrent. Pu-239 then becomes the main fissile element, the fuel core, in what are known as fast breeder reactors (FBR). A test FBR is in operation in Kalpakkam, and the construction for a 500 MWe prototype FBR was launched recently by Prime Minister Dr Manmohan Singh. These are known as breeder reactors because the U-238 “blanket” surrounding the fuel core will undergo nuclear transmutation to produce more PU-239, which in turn will be used to create energy. The stage also envisages the use of Thorium (Th-232) as another blanket. Th-232 also undergoes neutron capture reactions, creating another uranium isotope, U-233. It is this isotope which will be used in the third stage of the programme. Thorium by itself is not a fissile material, and cannot be used directly to produce nuclear energy. The Kamini 40 MWe reactor at Kalpakkam has demonstrated some of these technologies. India is currently developing a prototype advanced heavy water reactor (AHWR) of 300 MWe capacity. The AHWRs, which use plutonium based fuel, are to be used to shorten the period of reaching full scale utilisation of our thorium reserves. The AHWR is thus the first element of the third stage. AHWR design is complete but further R and D work is required, especially on safety. It is expected to be unveiled soon and construction launched. In the third phase, in addition to the U-233 created from the second phase, breeder reactors fuelled by U-233, with Th-232 blankets, will be used to generate more U-233. The Bhabha Atomic Research Centre has estimated that our thorium reserves can amount to a staggering 3,58,000 GWe-yr (Giga Watt Electrical - Year) of energy, enough for the next century and beyond! BARC scientists are also looking at other designs, like an advanced thorium breeder reactor (ATBR) which requires plutonium only as a seed to start off the reaction, and then use only thorium and U-233. Here the plutonium is completely consumed and this reactor is thus considered “proliferation resistant”. Success in harnessing thorium’s potential is thus critical for the India’s future energy security. |
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TRENDS Scientists have proposed a way to control the distribution of contaminants in silicon, potentially opening up the use of cheaper, “dirtier” starting materials for making solar cells. In a study published in the September Nature Materials, the researchers predict that the strategy could lower production costs of solar cells. Silicon is the second most abundant element in Earth’s crust, but nature’s primary sources of silicon — sand and quartz — are tainted with metals. Converting silicon from these sources into superpure crystals is an expensive and time-consuming process.
Rage of the bees At least two species of honeybees there, the native Apis cerana and the introduced European honeybee, Apis mellifera, engulf a wasp in a living ball of defenders and heat the predator to death. A new study of heat balling has described a margin of safety for the defending bees, says Tan Ken of Yunnan Agricultural University in Kunming, China. He and his team also report in an upcoming issue of Naturwissenschaften that the native bees have heat-balling tricks that the European bees don’t. That makes sense, the researchers say, since the Asian bees have long shared their range with the attacker wasp Vespa
velutina. |
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This Universe
How are the distances and diameters of heavenly bodies like Mercury, Venus etc. measured or calculated? After Johannes Kepler gave his laws of planetary motion, relative distances of all the planets from the Sun could be fixed just by comparing their orbital periods. Specifically, Kepler’s law states that the square of the orbital period of a planet is proportional to the cube of the distance from the sun. It was soon appreciated that Newton’s laws of motion could explain the Kepler’s orbits. Though this was a monumental advance one still did not know the scale of the planetary system — we still did not know how big was the solar system! By comparing the periods of revolution around the sun we could make a table of distances of all the planets from the sun in units of the earth-sun distance, for example. This distance unit came to be known as the “Astronomical Unit”. This was the situation till the middle of the 18th century. The astronomers of the world struggled to think of a way of measuring any one of the planetary distances, because then the value of the Astronomical Unit and hence all the planetary distances would become known. The famous astronomer Halley suggested one method of solving this problem; he charged the succeeding generation of astronomers to observe and measure the transit of the planet Venus across the sun that was to occur several years after his death! (Without going into the detail of the reason for this method it is easy to realise the time of the transit would depend not only on the known ratio of the distances of the earth and the Venus from the sun but also on their absolute values). Since then this transit has been observed a few times. But the real advance came through other advances in science and astronomy. A useful means was to measure the distance of the planet Venus using a high power radar involving a large radio telescope. Since the velocity of radio waves in vacuum is well known the timing of the radar return was an accurate determination of the earth-Venus distance. Indeed the radar not only measured this distance but also the direction of rotation of the planet Venus. But that is yet another story. It is easy to understand that once we know the distance to a planet its diameter can be found by multiplying that value by its angular diameter as measured using a telescope. It can also be understood that knowing the diameter of the earth orbit it should be possible to measure the distances to nearby stars by observing their direction from opposite sides of the earth orbit. On the basis of Paul Dirac theory you have well defined the distinction between matter and antimatter. Tell me what does antimatter look like it? Is it possible to store antimatter? Antimatter in isolation would “look” exactly the same as matter. It is true that its protons would be negatively charged and the electrons would be positive. But anti hydrogen would emit the same type of light when excited, as would hydrogen. Indeed if we were made of antimatter and lived in an anti universe we would not be able to tell the difference. The chemistry and biology of an anti universe populated by anti people would not be any different from ours. The anti people and we, both have to make sure that we do not come in close contact with each other because that would result in an enormous fireball in which both of us would be annihilated in a burst of energy. We can, and do, produce antimatter in high-energy collisions. Beams of high-energy electrons and positrons can be accelerated and stored in magnetic rings and manoeuvered to collide with each other to study the consequences of such collisions. This can also be done with beams of high-energy protons and antiprotons. But we cannot bring home a box full of antimatter unless the box itself is made of antimatter, in which case we dare not touch it! |
Honeybees that defend their colonies by killing wasps with body heat come within 5°C of cooking themselves in the process, according to a study in China.