Energy amount released from fission

The neutrons released from the fission of first uranium atom can hit other uranium atoms and which again release neutrons, each of which can further hit are uranium atom. In this way, a chain reaction is set up resulting into the liberation of a tremendous amount of energy. 

The energy released by the fission of one uranium-235 nucleus is enormous—about seven million times the energy released by the explosion of one TNT molecule. This energy is mainly in the form of kinetic energy of the fission fragments, which fly apart from one another. A much smaller amount of energy is released as gamma radiation. 

Note that three neutrons are released as product for each single reacting neutron. Each of the three neutrons produced is available to initiate another fission process. Nine neutrons are released from this process. These, in turn, react with other nuclei. The fission process continues and intensifies, producing very large amounts of energy (Figure 10.2). This process of intensification is referred to as a chain reaction. 

From the energy scale in Figure 2.1 it is clear that large amounts of energy are released upon the fission of very heavy nuclei. The action of thermal neutrons on results in a reaction of the general type shown in equation 2.15 where the fission process is variable Figure 2.5 shows a schematic representation of the process. Reaction 2.16 gives a typical example once formed, yttrium-95 and iodine-138... 

This process, shown below, releases 2.1 x 10 joules of energy per mole of aam 52U. Compared with what we get from typical fuels, this is a huge amount of energy. For example, the fission of 1 mol of produces about 26 million times as much energy as the combustion of 1 mol of methane. 

Highly heat-conducting fuel rods - for reducing the maximum operating fuel temperature to T < 1,000°C, which provides a small (less than 7%) fission gas release from fuel and its low pressure on claddings, as well as a relatively small amount of thermal energy in fuel. 

In 1938, Hahn, Strassman, and Meifner proved that they had fissioned the uranium atom using neutrons from an artificial source (a mixture of radium and beryllium). Scientists throughout the world used the values that were then known for the masses of the fission products versus that of the starting atom of uranium and concluded that a tremendous amount of energy is released in the fission process. The fissioning experiment was reproduced in about 100 different universities in the United States within the next year. The conversion of the mass lost in the fission process indicated that the fission of a uranium atom would release approximately 200 MeV (million electron volts). This is in sharp contrast to most chemical processes, such as combustion, which release only about 3-5 eV (electron volts) per combustion of a carbon or hydrogen atom. The ratio on an atom-to-atom basis is the order of 50,000,000 to 1. 

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... 

As long as the amount of fissionable material is less than the critical mass, the rate of fission events does not grow, and the rate of energy release remains low. In contrast, a sample behaves quite differently when the amount of fissionable material is larger than the critical mass. Above the critical mass, more than one neutron, on average, is recaptured for every fission that occurs. Now the number of fission reactions grows rapidly. As an illustration, consider what happens when two neutrons are recaptured from each fission reaction. As shown in figure 22-11 on... 

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. 

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). 

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