Nuclear fission weapons

After this section covering the principles of chain reactions and of reactor operation, the following sections will be dedicated to the concepts of existing reactors. Since nuclear fission weapons are in principle fast reactors, they will also be briefly covered. 

Much of the world s separated plutonium has been used for nuclear weapons (Table 1). It is probable that 5 kg or less of Pu is used in most of the fission, fusion, and thermonuclear-boosted fission weapons (2). Weapons-grade plutonium requires a content of >95 wt% Pu for maximum efficiency. Much plutonium does not have this purity. 

Frisch then demonstrated in his laboratory the tremendous release of energy accompanying fission, and a short paper by Meitner and Frisch in the British journal Natnrcin 1939 revealed the moinelitous concept of nuclear fission to the scientific world. It provided a new source of energy for the Earth, while at the same time introducing the possibility of a new weapon capable of tinbelicr able destructive power. 

Nuclear fission is also involved in nuclear weapons. To create a bomb, the concentration of the isotope uranium-235 must be increased to at least 85 percent from its natural concenti ation of only 0.7 percent. This increase ot concentration is difficult and expensive. In a typical nuclear reactor the uranium-235 concentration in the fuel is only 3 to 4 percent, and hence a nuclear reactor cannot explode like a bomb. In a nuclear bomb... 

The process of nuclear fission was discovered more than half a century ago in 1938 by Lise Meitner (1878-1968) and Otto Hahn (1879-1968) in Germany. With the outbreak of World War II a year later, interest focused on the enormous amount of energy released in the process. At Los Alamos, in the mountains of New Mexico, a group of scientists led by J. Robert Oppenheimer (1904-1967) worked feverishly to produce the fission, or atomic, bomb. Many of the members of this group were exiles from Nazi Germany. They were spurred on by the fear that Hitler would obtain the bomb first Their work led to the explosion of the first atomic bomb in the New Mexico desert at 5 30 a.m. on July 16,1945. Less than a month later (August 6,1945), the world learned of this new weapon when another bomb was exploded... 

The potential of nuclear fission was first realized in the atomic bomb. In 1945, the United States dropped two bombs of unprecedented power, one on Hiroshima and the other on Nagasaki, Japan. Both were fission weapons. 

Shortly after Japan s December 7,1941 attack on Pearl Harbor, the U.S. became more driven to expedite its timetable for developing the first fission weapon because of fear that the U.S. lagged behind Nazi Germany in efforts to create the first atomic bomb. On December 2, 1942 at 3 49 p.m., Enrico Fermi and Samuel K. Allison achieved the world s first controlled, self-sustained nuclear chain reaction in an experimental reactor using natural uranium and graphite. 

Nuclear weapons are broadly divided into two classes -Fission weapons and fusion weapons depending on the dominant source of the weapon s energy. 

Fission weapons or bombs They derive their power from nuclear fission when heavy nuclei such as uranium (U) or plutonium (Pu) are bombarded by neutrons and split into lighter elements, more neutrons and energy. The newly generated neutrons then bombard other nuclei which then split and bombard other nuclei and so on. This process continues and leads to a nuclear chain reaction which releases large amount of energy. These are also historically called atomic bombs or atom bombs or A-bombs. 

Further, the light weight of the elements used in fusion makes it possible to build extremely high yield weapons which are still portable enough to deliver. Compared with large fission weapons, fusion weapons are cheaper and much less at risk of accidental nuclear explosion. 

Atomic (or Nuclear) Bomb. A weapon invented during WWII and developed in the United States as a joint effort with the British and Canadian governments. It utilizes for its destructive effect the energy of an Atomic or Nuclear Explosion (qv). Since atomic explosions are of two types, fission and fusion, atomic bombs are of. corresponding types. However, it has been necessary to first initiate an atomic explosion with a nuclear fission reaction in order to bring about the conditions under which a nuclear fusion(thermonuclear) reaction can occur. 

A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate. Nuclear reactors are used for many purposes, but the most significant current uses are for the generation of electrical power and for the production of plutonium for use in nuclear weapons. Currently, all commercial nuclear reactors are based on nuclear fission. The amount of energy released by one kg 235U is equal to the energy from the combustion of 3000 tons of coal or the energy from an explosion of 20,000 tons of TNT (Trinitrotoluene, called commonly dynamite). 

The first man-made nuclear fission reaction was achieved in 1938, unlocking atomic power both for destructive and creative purposes. In 1951, the first usable electricity was created via the energy produced by a nuclear reactor, thanks largely to research conducted in the Manhattan Project that developed the first atomic weapons during World Warll. 

In some tests carried out at the Nevada Test Site in 1956-8, fission was incomplete and some plutonium was dispersed. Also some weapons were exploded chemically without nuclear fission in safety tests. Analysis of soil from an area extending about 500 km north-eastwards from the N.T.S. into the neighbouring state of Utah showed excess Pu over the amounts expected from global fallout (Hardy, 1976). The Pu from these low-level, low-yield tests was distinguished from global fallout by two criteria ... 

Explosions can be used for constructive purposes, such as mining and road building for entertainment, such as fireworks or for destructive purposes, such as military weapons and terrorist bombs. They may be either deliberate or accidental. Explosive materials must always be handled with extreme care to prevent accidents. Such caution must be exercised with not only industrial explosives, but also commonly encountered materials such as fireworks, laboratory and industrial chemicals, and flammable gases, see also Fire, Fuels, Power Plants Fireworks Kinetics Nuclear Fission Nuclear Fusion Thermodynamics. 

Nuclear Explosions Although conventional explosives have become the weapons of choice of terrorist groups, a joint report issued in 2008 by Harvard s Kennedy School of Government and the Nuclear Threat Initiative reminds us that there is a real danger that terrorists could get and use a nuclear weapon.16 In order to understand what this would mean, we return to the atomic nucleus. A nuclear fission reaction releases far more energy than any ordinary chemical process. The Oklahoma City bomb was equivalent to the explosion of approximately 40001b of TNT.17 In contrast, the atomic bomb dropped on... 

All the components of the nuclear-fission power system are fully operational except for ultimate waste disposal. However, spent fuel is not reprocessed in the United States because there is currently an adequate supply of natural uranium and enrichment services availab 1 e domestically and from other countries at a 1 ower cost than that of the recovered fissionable material from spent fuel. Also, the United States unilaterally declared a moratorium on reprocessing in the early 1980s in an attempt to reduce the spread of nuclear weapons. Current economics do not favor a return to reprocessing and fuel recycling in the United States at this time in as much as it does dramatically increase the amount of interim and final waste storage capacity that is required. 

Major concern about rapidly increasing levels of radioactive fallout in the environment and in foods developed as a result of the extensive testing of nuclear weapons by the United States and the Soviet Union in the 1950s. Nuclear fission generates more than 200 radioisotopes of some 60 different elements. Many of these radioisotopes are harmful to humans because they may be incorporated into body tissues. Several of these radioactive isotopes are absorbed efficiently by the organism because they are related chemically to important nutrients for example, strontium-90 is related to calcium and cesium-137 to potassium. These radioactive elements are produced by the following nuclear reactions, in which the half-life is given in parentheses ... 

It may be noted that Sr is one of the most toxic radionuclides formed in nuclear fission of 235U and 239Pu. It has been widely distributed by nuclear weapons testing and marginally increased by the Chernobyl accident. Analytical problems have been studied in detail1 as have attempts to find extraction procedures using crown and other polyethers, polyethyleneglycols, etc.2... 

Nuclear power is any method of doing work that makes use of nuclear fission or nuclear fusion reactions. hi its broadest sense, the term refers to both the uncontrolled release of nuclear energy, as in fission or fusion weapons, and to the controlled release of energy, as in nuclear power plants. Most commonly, however, the expression nuclear power is reserved for the latter. Approximately 430 nuclear reactors devoted to the manufacture of electricity are operating worldwide. 

These first nuclear weapons were atomic bombs or A-bombs. They depended on the energy produced by nuclear fission for their destructive power. However, scientists like U.S. physicist Edward Teller (1908-) knew even before the first atomic bomb exploded that the fission weapons... 

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