Thermonuclear Energy And Modern World

By DR. AB THAPA

It is an accepted fact that the mankind is in the midst of a crisis of energy. On a short time scale, we are faced with a shortage of natural gas and petroleum products. On a some what longer time scale we would be facing the problem of exhaustion of the fossil fuels. Thermonuclear energy to be obtained from the fusion of atoms could fulfill our demand for energy almost forever. More importantly, there would be at least a hundred-fold reduction in the radioactive waste problems. It can also be expected that the generation of this type of energy would be free from the threat of accidents.

It is a common knowledge to all that the former Soviet Union had pioneered the works to send men into the space but only very few might know that the former Soviet Union has also been playing the lead role in development of technology to harness the fission and fusion energy for the use of mankind. Former Soviet Union was the first in the world to build atomic electric-power station . The worldwide accepted principle to harness the fusion power is based on the technology developed in the former Soviet Union . Tokamak is the type of fusion reactor, which has now been considered the most appropriate for harnessing the fusion energy. The name tokamak (to-torodial, ka- chamber, mak- magnet) is made of a combination of Russian words.

Fission and Fusion Reactions

Fission and fusion based nuclear energy can be released in two different ways: by fission (splitting) of a heavy nucleus, or by fusion (combining) of two light nuclei. In both cases energy is released. Fusion reactions are difficult to maintain because the nuclei repel each other, but unlike fission reactions, fusion does not create radioactive products.

In the fission reactions the neutron, which has no electric charge, can easily approach and react with a fissionable nucleus—for example, Uranium-235. In the typical fusion reaction, however, the reacting nuclei both have a positive electric charge, and the natural repulsion between them, called Coulomb repulsion, must be overcome before they can join. This occurs when the temperature of the reacting gas is sufficiently high— above 1000 million ° K. In a gas of the heavy hydrogen isotopes, deuterium and tritium at such temperature, the fusion reaction occurs releasing extraordinary amount of energy. The energy appears first as kinetic energy of the helium-4 nucleus and the neutron, but is soon transformed into heat in the gas and surrounding materials.

If the density of the gas is sufficient the energetic helium-4 nucleus can transfer its energy to the surrounding hydrogen gas, thereby maintaining the high temperature and allowing subsequent fusion reactions, or a fusion chain reaction, to take place. Under these conditions, “nuclear ignition” is said to have occurred.

Controlled Nuclear Fusion

Nuclear binding energy is the amount of energy required to remove a single proton or neutron from an atomic nucleus which varies with the mass of the nucleus. The release of nuclear energy can occur through the fusion of two light nuclei into a heavier one. The energy radiated by stars, including the Sun, is produced from such fusion reactions deep in their interiors, where hydrogen nuclei combine at enormous pressure and at temperatures above 1000 million ° K by releasing extraordinary amount of energy.

Nuclear fusion was first achieved on earth in the early 1930s by bombarding a target containing deuterium, the mass-2 isotope of hydrogen, with high-energy deuterons in a cyclotron. To accelerate the deuteron beam a great deal of energy is required, most of which appeared as heat in the target. In the 1950s the first large-scale but uncontrolled release of fusion energy was demonstrated in the tests of thermonuclear bombs. This was such a brief and uncontrolled release that it could not be used for the production of electric power.

The basic problems in attaining useful nuclear fusion conditions are (1) to heat the gas to these very high temperatures and (2) to confine a sufficient quantity of the reacting nuclei for a long enough time to permit the release of more energy than is needed to heat and confine the gas. A subsequent major problem is the capture of this energy and its conversion into electricity.

History of Fusion Technology in Former Soviet Union

I. V. Kurchatov was the chief nuclear physicist who guided the development of the first atomic bomb, the world's first thermonuclear bomb and first atomic electric-power station in the former Soviet Union .

After graduation (1923) from the Crimean University in Simferopol , Kurchatov joined (1927) the staff of the Physico-Technical Institute of the Academy of Sciences in Leningrad . His initial studies concerned ferro-electricity, but by 1933 he was concentrating on nuclear physics. As director of the nuclear physics laboratory at the Physico-Technical Institute, he supervised the construction of the first Soviet cyclotron. In 1939 he and his associates published studies of nuclear chain reactions, and in 1940 he reported the spontaneous fission of Uranium, previously reported only a year earlier by Otto Hahn and Fritz Strassmann in Germany . During the World War II, Kurchatov's nuclear research was suspended in favour of defense research concerning methods of protecting ships from magnetic mines.

Kurchatov directed the construction of the first Soviet cyclotron (1944) and, after the war,the first atomic reactor in Europe (1946). His team produced the first Soviet atomic bomb in 1949, four years after the United States . In 1953 the team detonated a thermonuclear (hydrogen) bomb, six months before the first U.S. thermonuclear bomb. The nonmilitary applications of atomic power explored and developed under Kurchatov's leadership included the world’s first electric-power stations (which began operation in 1954), the nuclear-powered icebreaker Lenin. Kurchatov also directed research on the “ultimate power source,” fusion energy, centering on a means of containment of the extremely high temperatures that are needed to initiate the fusion process.

The Role of the USA

In the fall of 1945, after the success of the atomic bomb and the end of World War II, the future of the Manhattan Project, including Los Alamos and the other facilities, was unclear. Government funding was severely reduced, many scientists returned to universities and to their careers, and contractor companies turned to other pursuits. The Atomic Energy Act, signed by President Truman on Aug. 1, 1946, established the Atomic Energy Commission (AEC) and gave it civilian authority over all aspects of atomic energy, including oversight of nuclear warhead research, development, testing, and production.

On Sept. 23, 1949, Truman announced that “we have evidence that within recent weeks an atomic explosion occurred in the U.S.S.R.” This first Soviet test stimulated an intense, four-month, secret debate about whether to proceed with the hydrogen bomb project. One of the strongest statements of opposition against proceeding with a hydrogen bomb program came from the General Advisory Committee (GAC) of the AEC, chaired by Oppenheimer. In their report of Oct. 30, 1949, the majority recommended “strongly against” initiating an all-out effort, believing “that extreme dangers to mankind inherent in the proposal wholly outweigh any military advantages that could come from this development.” “A super bomb,” they went on to say, “might become a weapon of genocide.” They believed that “a super bomb should never be produced.” Nevertheless, the Joint Chiefs of Staff, the State and Defense departments, the Joint Committee on Atomic Energy, and a special subcommittee of the National Security Council all recommended proceeding with the hydrogen bomb. Truman announced on Jan. 31, 1950, that he had directed the AEC to continue its work on all forms of atomic weapons, including hydrogen bombs.

Teller and Ulam presented a report on March 9, 1951 to elaborate on how a thermonuclear bomb could be constructed. The two-stage radiation implosion design proposed by these reports, which led to the modern concept of thermonuclear weapons, became known as the Teller–Ulam configuration.

The major figures in the breakthroughs was Ulam and Teller configuration. In December 1950 Ulam had proposed a new fission weapon design, using the mechanical shock of an ordinary fission bomb to compress to a very high density a second fissile core. (This two-stage fission device was conceived entirely independently of the thermonuclear program and its aim being to use fissionable materials more economically.) Early in 1951 Ulam went to see Teller and proposed that the two-stage approach be used to compress and ignite a thermonuclear secondary. Teller suggested that radiation implosion, rather than mechanical shock, as the mechanism for compressing the thermonuclear fuel in the second stage.

At present the scientists in the USA are engaged in research works to generate fusion energy by applying the Soviet Union developed technology. In 1993 the scientists at the Princeton University ’s plasma physics laboratory in New Jersey , produced a controlled fusion reaction by using the Tokamak Fusion Test Reactor. During the testing the temperature in the reactor surpassed three times that of the core of the sun. In a tokamak reactor, massive magnets confine hydrogen plasma under extremely high temperatures and pressures, forcing the hydrogen nuclei to fuse. When atomic nuclei are forced together in nuclear fusion, the reaction releases an extraordinary amount of energy.

A plasma hot enough for fusion cannot be contained by ordinary materials. The plasma would cool very rapidly, and the vessel walls would be destroyed by the extreme heat. However, since the plasma in the Tokamak Fusion Reactor consists of charged nuclei and electrons which move in tight spirals around the lines of force of strong magnetic fields, the plasma can be contained in a properly shaped magnetic field region without reacting with material walls.

In Conclusion

Substantial research is still needed to achieve commercial fusion power, which is not expected to be realized earlier than the middle of the 21st century. A primary motivation for research in this field lies in the fact that fusion is environmentally clean, generating no pollutants or greenhouse gases and little radioactivity by comparison with fission-reaction nuclear power plants. A fusion reactor would also be safe, with no analog to the fission meltdown. If one of the reactor control systems fails, the plasma simply cools down and the reactions cease. And because deuterium is abundant in the oceans and tritium can be bred in the reactor, fusion reactors could prove a virtually inexhaustible source of energy for humanity.

(Dr. Thapa writes on water resources)