Reflector neutron moderation

Beryllium is added to copper to produce an alloy with greatly increased wear resistance it is used for current-carrying springs and non-sparking safety tools. It is also used as a neutron moderator and reflector in nuclear reactors. Much magnesium is used to prepare light nieial allo>s. other uses include the extraction of titanium (p. 370) and in the removal of oxygen and sulphur from steels calcium finds a similar use. 

Beryllium is used in nuclear reactors as a reflector or moderator for it has a low thermal neutron absorption cross section. 

The overwhelming majority of carbon utilized in nuclear reactors is in the form of graphite for the neutron moderator and reflector. However, several other applications of carbon are noteworthy, and are briefly discussed here. 

Sintered beryllia. This material exhibits an extraordinarily high thermal conductivity, only surpassed by graphite and metals — hence the high resistance to thermal shock which together with high chemical inertness is its main practically utilized property. In the application of sintered BeO in nuclear reactors, use is made of its low absorption cross section and of high scattering cross section of neutrons (moderators, reflectors). 

Beryllium oxide is used as a reflector and moderator in nuclear reactors. In addition to its low neutron-capture cross section, BeO has physical, mechanical, and chemical properties that allow its use at elevated temperatures, but its high cost and propensity to damage under irradation have limited its applications " ... 

USE Source of neutrons when bombarded with alpha particles according to the equation jBe + JHe J C + jn This yields about 30 neutrons per million alpha particles. Also as neutron reflector and neutron moderator in nuclear reactors. In beryllium copper and beryllium aluminum alloys (by direct reduction of beryllium oxide with carbon in the presence of Cu nr Al). In radio tube parts. In aerospace structures. In inertial guidance systems. 

Beryllium is used in nuclear reactors as a reflector or moderator for it has a low thermal neutron absorption cross section. It is used in gyroscopes, computer parts, and instruments where lightness, stiffness, and dimensional stability are required. The oxide has a very high melting point and is also used in nuclear work and ceramic applications. Beryllium and its salts are toxic and should be handled with the greatest of care. Beryllium and its compounds should not be tasted to verify the sweetish nature of beryllium (as did early experimenters). The metal, its alloys, and its salts can be handled safely if certain work codes are observed, but no attempt should be made to work with beryllium before becoming familiar with proper safeguards. Beryllium metal is available at a cost of about 5/g (99.5% pure). 

It is known that a self-sustaining chain reaction can be obtained in devices known as neutronic reactors utilizing natural uranium, as a result of slow neutron fission of the content of the natural uranium. In such reactors, discrete bodies of natural uranium of high purity are disposed, usually in the form of a lattice arrangement of spheres or rods, in a neutron moderator such as graphite, baryllium or heavy water of high purity, surrounded by a neutron reflector. Neutron absorption in the U s content of the natural uranium during the reaction leads to the production of the transuranic isotope 94, known as plutonium (symbol Pu), which is fissionable in much the same manner as 94 3 or Pu 3 is formed in... 

According to the present invention the novel breeder system comprises a neutronic reactor wherein and 25 heavy water (D2O) neutron moderator are combined in a chain reacting composition surrounded by a neutron reflector of heavy water containing a fertile isotope or isotopes in solunon or in suspension. The fertile material absorbs neutrons emanating from the chain reacting 30 composition and is thus converted to thermally fissionable material. 

Neutron-physical parameters of the salt coolants make it possible to use them effectively both as neutron moderators and reflectors thermo-physical and neutron-physical properties of NaF-BeF2 salt are slightly worse than those of LiF-BeF2, but tritium production using this salt in the reactor is considerably smaller to improve the neutron balance and reduce the tritium production, the initial enrichment by Xi shall be at least 99.999%. 

Criticality Precautions. The presence of a critical mass of Pu ia a container can result ia a fission chain reaction. Lethal amounts of gamma and neutron radiation are emitted, and a large amount of heat is produced. The assembly can simmer near critical or can make repeated critical excursions. The generation of heat results eventually ia an explosion which destroys the assembly. The quantity of Pu required for a critical mass depends on several factors the form and concentration of the Pu, the geometry of the system, the presence of moderators (water, hydrogen-rich compounds such as polyethylene, cadmium, etc), the proximity of neutron reflectors, the presence of nuclear poisons, and the potential iateraction with neighboring fissile systems (188). As Httle as 509 g of Pu(N02)4 solution at a concentration Pu of 33 g/L ia a spherical container, reflected by an infinite amount of water, is a critical mass (189,190). Evaluation of criticaUty controls is available (32,190). 

Beryllium has a high x-ray permeabiUty approximately seventeen times greater than that of aluminum. Natural beryUium contains 100% of the Be isotope. The principal isotopes and respective half-life are Be, 0.4 s Be, 53 d Be, 10 5 Be, stable Be, 2.5 x 10 yr. Beryllium can serve as a neutron source through either the (Oi,n) or (n,2n) reactions. Beryllium has alow (9 x 10 ° m°) absorption cross-section and a high (6 x 10 ° m°) scatter cross-section for thermal neutrons making it useful as a moderator and reflector in nuclear reactors (qv). Such appHcation has been limited, however, because of gas-producing reactions and the reactivity of beryUium toward high temperature water. 

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