Reflector moderator materials

The moderator material and optimum sizes, the extraction channel configuration, as well as the converter and reflector material and sizes, were determined using the MCNP-4B code and the steepest descent method to attain a maximum flux density of thenual neutrons at the position of an object to be studied. The calculated data were experimentally verified, which showed good agreement. 

The effects in graphite and beryllium (reflector and moderator materials)... 

HANSEN, G. E., et aL, Reflector Savings of Moderating Materials on Large Diameter U(93.2) Slabs, ... 

Twenty critical experiments using. the plastic and concrete reflectors had 9,2-, 12.4->, or 24j-mm-thick plastic moderator material between cans. These arrays achieved criticality without the necessity of a driver. Some experiments also had oly vinyl chloride mild-steel neutron absorber material tetween. cans. Critical parameters are given in table I. The critical cpre separation varied between 2.3 and 18,4 mm. Critical oxide weights varied from 603.5 to 1508.8 kg. 

The neutron leakage In a reactor is a function of the reactor else and the neutron migration area it is strongly influenced by the presence of a reflector of pure moderator material surrounding the active core. For a uniform homogeneous loading the effective and Infinite lattice multiplication factors are related by the equation ... 

The average cross sections and results for a typical multigroup calculation are shown in Figs. 8.31 through 8.39. The particular assembly chosen is a spherically symmetric system consisting of core and reflector. The fuel is and the principal moderating material in both the core... 

The result (10.255) may also be used to obtain the criticality condition for the reactor with finite fuel lattice but with infinite reflector (composed of the same moderator material). It is necessary to impose the latter condition because otherwise expression (10.243) for the slowing-down density would no longer be valid and new functions satisfying boundary conditions at the surface of the reflector would be required. The appropriate neutron-balance relation in terms of the flux at the various fuel-rod locations is then given by... 

Compare the influence which the value of the atomic weight of a particular material has on how good a moderator it is with its influence or how good a reflector the materials is. Explain. 

Table 1 (4,5) lists some useful properties of several graphites used for moderators or reflectors in nuclear reactors. Reactor designers have taken advantage of graphite s properties in applying the material to other than moderator and reflector components, usually in conjunction with some other material. 

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). 

Preparation of Nuclear Ceramic Materials 17.3.12.2. Moderators and Reflectors 17.3.12.2.1. Beryllium Oxide. 

Use Structural material in space technology moderator and reflector of neutrons in nuclear reactors source of neutrons when bombarded with a-parti-cles special windows for X ray tubes in gyroscopes, computer parts, inertial guidance systems additive in solid-propellant rocket fuels beryllium-copper alloys. 

Four general methods have been used or proposed for changing the power or neutron flux in a nuclear reactor each involves the temporary addition or removal of (a) fuel, (b) moderator, (c) reflector, or (d) a neutron absorber or poison. This chapter discusses the materials used as poisons in a reactor plcmt. 

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