Neutrons fission and

See Molten salt extraction Slow neutron fission and isotopes... 

Figure 11.7 Schematic diagram of neutron, fission, and 7-ray widths of a typical nucleus with a neutron binding energy slightly less than 6 MeV. The inset shows the predicted fission excitation function for a nucleus with Bf — Bn = 0.75 MeV together with more recent data.

Fig. 9. Relation between the amount of neutron fission and uranium concentration in a uranium mineral or ore concentrate (126).

The nuclear chain reaction can be modeled mathematically by considering the probable fates of a typical fast neutron released in the system. This neutron may make one or more coUisions, which result in scattering or absorption, either in fuel or nonfuel materials. If the neutron is absorbed in fuel and fission occurs, new neutrons are produced. A neutron may also escape from the core in free flight, a process called leakage. The state of the reactor can be defined by the multiplication factor, k, the net number of neutrons produced in one cycle. If k is exactly 1, the reactor is said to be critical if / < 1, it is subcritical if / > 1, it is supercritical. The neutron population and the reactor power depend on the difference between k and 1, ie, bk = k — K closely related quantity is the reactivity, p = bk jk. i the reactivity is negative, the number of neutrons declines with time if p = 0, the number remains constant if p is positive, there is a growth in population. 

Control of the core is affected by movable control rods which contain neutron absorbers soluble neutron absorbers ia the coolant, called chemical shim fixed burnable neutron absorbers and the intrinsic feature of negative reactivity coefficients. Gross changes ia fission reaction rates, as well as start-up and shutdown of the fission reactions, are effected by the control rods. In a typical PWR, ca 90 control rods are used. These, iaserted from the top of the core, contain strong neutron absorbers such as boron, cadmium, or hafnium, and are made up of a cadmium—iadium—silver alloy, clad ia stainless steel. The movement of the control rods is governed remotely by an operator ia the control room. Safety circuitry automatically iaserts the rods ia the event of an abnormal power or reactivity transient. 

Graphite will creep imder neutron irradiation and stress at temperatures where thermal creep is normally negligible. The phenomenon of irradiation creep has been widely studied because of its significance to the operation of graphite moderated fission reactors. Indeed, if irradiation induced stresses in graphite moderators could not relax via radiation creep, rapid core disintegration would result. The observed creep strain has traditionally been separated into a primary reversible component ( ,) and a secondary irreversible component (Ej), both proportional to stress and to the appropriate unirradiated elastic compliance (inverse modulus) [69]. The total irradiation-induced creep strain (ej is thus ... 

Neutron radiation is emitted in fission and generally not spontaneously, although a few heavy radionueleides, e.g. plutonium, undergo spontaneous fission. More often it results from bombarding beryllium atoms with an a-emitter. Neutron radiation deeays into protons and eleetrons with a half-life of about 12 min and is extremely penetrating. 

Some heavy nuclei will fission spontaneously. Others can be induced to fission through interaction with a neutron. In both spontaneous nuclear fission and induced nuclear fission the pool of neutrons and protons is conseiwed. For example, the nucleus "" Cf (Californium) fissions spontaneously. The 98 protons and 154 neutrons in the nucleus of Cf are reconfigured into other nuclei. Usually a few neu-... 

Our research at Berkeley has resulted in the discovery of element 94, demonstration of the slow neutron fissiona-bility of its isotope 94239, discovery and demonstration of the slow neutron fissionability of U23 3, spontaneous fission measurements on these isotopes, discovery of 93237, isolation of and nuclear measurements on U23, study of the chemical properties and methods of chemical separation of element 94, demonstration of the presence of small concentrations of 94 in nature and much related information. 

In a nuclear power plant, heat must be transferred from the core to the turbines without any transfer of matter. This is because fission and neutron capture generate lethal radioactive products that cannot be allowed to escape from the core. A heat-transfer fluid such as liquid sodium metal flows around the core, absorbing the heat produced by nuclear fission. This hot fluid then flows through a steam generator, where its heat energy is used to vaporize... 

Nuclear and magneto-hydrodynamic electric power generation systems have been produced on a scale which could lead to industrial production, but to-date technical problems, mainly connected with corrosion of the containing materials, has hampered full-scale development. In the case of nuclear power, the proposed fast reactor, which uses fast neutron fission in a small nuclear fuel element, by comparison with fuel rods in thermal neutron reactors, requires a more rapid heat removal than is possible by water cooling, and a liquid sodium-potassium alloy has been used in the development of a near-industrial generator. The fuel container is a vanadium sheath with a niobium outer cladding, since this has a low fast neutron capture cross-section and a low rate of corrosion by the liquid metal coolant. The liquid metal coolant is transported from the fuel to the turbine generating the electric power in stainless steel... 

Nuclear detection approaches that use radioactive isotojjic sources (e.g., Cf for spontaneous fission and asociated neutron emission or ° Co for gamma emission) will have to obtain state and federal hcenses to field the equipment and abide by apphcable health and safety regulations. The Hcensing process takes some time to put into place and may restrict the easy movement of the detection equipment to new locations. This impacts the abffity to rapidly re-locate equipment based up inteUigence estimates of the behavior of smugglers. The use of fixed pre-licensed sites can help to some extent. 

Neon is also used in scintillation counters, neutron fission counters, proportional counters, and ionization chambers for detection of charged particles. Its mixtures with bromine vapors or chlorine are used in Geiger tubes for counting nuclear particles. Helium-neon mixture is used in gas lasers. Some other applications of neon are in antifog devices, electrical current detectors, and lightning arrestors. The gas is also used in welding and preparative reactions. In preparative reactions it provides an inert atmosphere to shield the reaction from air contact. 

The element was discovered in the pitchblende ores by the German chemist M.S. Klaproth in 1789. He named this new element uranium after the planet Uranus which had just been discovered eight years earlier in 1781. The metal was isolated first in 1841 by Pehgot by reducing the anhydrous chloride with potassium. Its radioactivity was discovered by Henry Becquerel in 1896. Then in the 1930 s and 40 s there were several revolutionary discoveries of nuclear properties of uranium. In 1934, Enrico Fermi and co-workers observed the beta radioactivity of uranium, following neutron bombardment and in 1939, Lise Meitner, Otto Hahn, and Fritz Strassmann discovered fission of uranium nucleus when bombarded with thermal neutrons to produce radioactive iso-... 

---