Chain reactions, nuclear fission

Commercially, there are only two nuclear species that will function in a self-sustaining nuclear fission chain reaction and Pu (plutonium). 

The fission ofor Tu liberates, on average, two to three neutrons. One neutron is required to sustain the nuclear fission chain reaction. In a nuclear breeder reactor, the extra neutrons are used to induce nuclear reactions that lead to the production of Tu. The sequence begins by arranging for... 

This figure illustrates the ongoing reactions characteristic of a nuclear fission chain reaction. 

Coffee Filter Chromatography 312 21.1 A Nuclear Fission Chain Reaction 763... 

A nuclear fission chain reaction in a reprocessing plant is an accident that must be carefully guarded against. Although such a critical reaction is not likely to generate sufficient energy to be mechanically destructive, it emits intense neutron and gamma radiation that can kill nearby plant personnel and may release radioactive fission products outside the plant. 

On December 2, 1942, the first artificial self-sustaining nuclear fission chain reaction was achieved in an abandoned squash court at the University of Chicago. This accomplishment led to the development of the first atomic bomb, at Los Alamos National Laboratory in New Mexico in July 1945 (T FIGURE 21.17). In August 1945 the United States dropped atomic bombs on two Japanese cities, Hiroshima and Nagasaki. The nuclear age had arrived. 

The term neutronic purity as used herein has no necessary relation to chemical purity and merely refers to the absence of foreign material having the characteristic of relatively great neutron absorption. In other words, a substance may be said to have high neutronic purity, if the total amount of other material therein is incapable of absorbing a substantial number of neutrons and is thus ineffective to poison the nuclear fission chain reaction. 

This invention relates to nuclear physics, and mere particularly to a novel method and means for producing power and fissionable material which may be utilized to sustain a nuclear fission chain reaction. 

A primary object of the present invention is to provide a breeder system wherein a nuclear fission chain reaction is utilized to produce fissionable material at a rate 10 greater than the rate of consumption of fissionable material within the chain reacting composition. This is accomplished by neutron bombardment of fertile material adapted to undergo nuclear reaction productive of fissionable material as hereinafter described. Fertile iso-15 topes as herein defined are isotopes such as and U238 which are converted to thermally fissionable isotopes, and Pu 39, respectively, by nuclear reaction under neutron bombardment. These fertile isotopes are fissionable by fast neutrons and substantially nen-fission-20 able by slow neutrons (below about 1000 e.v.) and absorb neutrons fast or slow to undergo the above-mentioned nuclear reactions. 

The nuclear fission chain reaction is regulated by a neutron absorbing control rod 50 reciprocated within a tube 51 formed of a material such as beryllium having a relatively small neutron capture cross section. Ihe rod is actuated by a rack and pinion mechanism 55. Emergency control of the reaction is afforded by a safety rod 54 disposed within a beryllium tube 52, said rod being normally maintained in an elevated position by an electrically... 

The nuclear fission chain reaction within the tank 80 is controlled by a neutron absorbent control rod 98 re- 30 ciprocable within a permeable tube 100 formed of a material such as beryllium having a small neutron capture cross section, and the rod 98 is actuated by a rack and pinion mechanism 102. Emergency control of the reaction is provided by a neutron absorbent control rod 104 35 disposed within a neutron permeable tube 106 and held in the retracted position shown in FIG. 3 by an electrically operated latch 1C8. Under emergency conditions, the latch is released and the rod 104 is drawn into the central portion of the system by means of a weight 110 con- 40 nected to the rod 104 by a line 112 supported by a pulley 114. The neutron density within the system is monitored by a conventional ionization chamber 116 connected in a conventional manner to an electrical circuit (not shown) for measuring the neutron density. 45... 

The rods 106 and 108 are cooled by any suitable coolant such as molten bismuth or a sodium potassium alloy 5q circulated as indicated by the arrows in FIG. 8 by inlet and outlet conduits 109 and 111. The inlet conduit is connected to the outer tank 104 and the coolant flows downwardly therethrough into the tank 102 through ports at the bottom thereof and upwardly therethrough into the 55 outlet conduit 111. Thus, the coolant absorbs the heat of the nuclear fission chain reaction and the energy in the form of heat carried from the reactor by the coolant may be utilized for power or other purposes, if desired. 

This invention relates to an improved apparatus for the measurement of neutron absorption characteristics of materials. More specifically the invention relates to an improved apparatus for measuring the effect of the presence of the sample under measurement on the neutron reproduction factor, and thus the power output, of a neu-tronic reactor capable of sustaining a nuclear fission chain reaction. 

The big difference between a conventional power plant and a nuclear power plant is that the nuclear power plant produces heat through nuclear fission chain reactions. 

The atomic bomb is a fission bomb it operates on the principle of a very fast chain reaction that releases a tremendous amount of energy. An atomic bomb and a nuclear reactor both depend on self-sustaining nuclear fission chain reactions. The essential difference is that in a bomb the fission is wild, or uncontrolled, whereas in a nuclear reactor the fission is moderated and carefully controlled. A minimum critical mass of fissionable material is needed for a bomb otherwise a major explosion will not occur. When a quantity smaller than the critical mass is used, too many neutrons formed in the fission step escape without combining with another nucleus, and a chain reaction does not occur. Therefore the fissionable material of an atomic bomb must be stored as two or more subcritical masses and brought together to form the critical mass at the desired time of explosion. The temperature developed in an atomic bomb is believed to be about 10 million degrees Celsius. 

Key Terms Nuclear fission Chain reaction Critical mass... 

Duderstadt, J. J. and L. J. Hamilton. 1976. Nuclear Reactor Analysis. New Yoik John Wiley Sons. Designed for the nuclear engineering student, this book provides the basic scientific principles of nuclear fission chain reactions and applications in nuclear reactor design. References and problems are included at the end of each chapter along with appendices, which include selected nuclear data, selected mathanatical formulas, and nuclear power reactor data. 

---