Homogeneous fuel-moderator mixtures

Homogeneity or heterogeneity of fuel-moderator-poison mixture... 

Wigner initiated and supervised the examination of as many combinations of fuel and moderator as the group could manage. By the end of 1945 he had explored lattices moderated with H2O, D2O, CO2, Be, BeO, and C, as well as homogenous mixtures of U, D2O and H2O. The constants such as diffusion length, resonance absorption, and cross-sections used in this exploration were based on experiments at Columbia, Princeton, and, later, on the exponential experiments in Chicago. 

The neutronic effectiveness of a moderator material can be expressed in terms of the conversion potential of a mixture of fuel and moderators in an infinite medium. This approach has been used in a relative comparison of HjO, BeO, and C with fuel which has appeared in a progress report on BeO reactor studies (26). In this evaluation, the excess production of neutrons per neutron absorbed in the fuel has been calculated for homogeneous mixtures of fuel and moderator having different moderator/ atom ratios, i.e.,... 

The core consists of 37 fuel rods of 3.18 cm diameter combining the functions of neutron-induced fission and moderation. Fuel rods are made of a homogeneous mixture of enriched uranium and zirconium hydride. They are tightly packed into a cylinder vessel of 22.7 cm diameter and 40 cm height. A beryllium reflector and tiltable semi-cylindrical controls being the part of the reflector are located at the vessel outer side. 

Ghermay Y, Mantzaras J, Bombach R Effects of hydrogen preconversion on the homogeneous ignition of fuel-lean H2/O2/N2/CO2 mixtures over platinum at moderate pressures, Combust Flame 157 1942-1958, 2010. 

Consider a homogeneous infinite medium consisting of a mixture of a fuel material and a moderator material into which neutrons are introduced with a high energy Eq. Suppose that each of the macroscopic cross sections 2a(-E), and... 

For the homogeneous natural uranium reactor, a is close to unity. Taking rj = 1.34, it follows that for a critical system, the product pf must be equal to 0.75. It turns out that, for a homogeneous mixture of uranium and a moderator such as graphite, the resonance escape probability is too low to permit this condition to be met. It will be shown later that lumping the fuel results in an increase in p which enables a critical uranium-graphite system to be attained. The other alternative is the enrichment of the isotope in the fuel, which increases rj and f to the point where the four-factor product can reach unity. 

These advantages stem partly from the fluid nature of the fuel and partly from the homogeneous mixture of the fuel and moderator i.e., an aqueous homogeneous reactor combines the attributes of liquid-fuel heterogeneous reactors with those of water-moderated heterogeneous reactors. If practical methods for handling a radioactive aqueous fuel system are developed, the inherent simplicity of this type of reactor should result in considerable economic gains in the production of nuclear power and fissionable material. 

---