Atomic fuel particles

Zirconium carbide is a highly refractory compound with excellent properties but, unlike titanium carbide, it has found only limited industrial importance except as coating for atomic-fuel particles (thoria and urania) for nuclear-fission power plants.l " ] This lack of applications may be due to its high price and difficulty in obtaining it free of impurities. 

Zirconium-carbide CVD coatings are used extensively on atomic fuel particles such as thoria and urania. These coatings are applied by thermal CVD in a fluidized bed reactor. 

If a fuel is in the liquid state, such as fuel oil, most of it must be vaporized to the gaseous state before combustion occurs. This vaporization can be accomplished by supplying heat from an outside source, but usually the liquid fuel is first atomized and then the finely divided fuel particles are sprayed into a hot combustion chamber to accomplish the gasification. 

Konoplev A. V. and Bulgakov A. A. (1999) Kinetics of the leaching of Sr-90 from fuel particles in soil in the near zone of the Chernobyl power plant. Atomic Energy 86(2), 136-141. 

A key feature of LEADIR-PS, shared with the Modular High Temperature Gas-Cooled Reactor (MHTGR) under development by General Atomics, is that radionuclide releases are prevented by retention of the radionuclides within the fuel particles under all design basis events without operator action or the use of active systems. Thus, the control of radionuclide releases is achieved primarily by reliance on the inherent characteristics of the coolant, core materials, and fuel. Specifically, the geometry and size of the reactor core, its power density, coolant, and reactor vessel have been selected to allow for decay heat removal from the core to the ultimate heat sink through the natural processes of radiation, conduction and convection, while the negative temperature coefficients of the fuel and moderator assure reactor shutdown. 

Most CFD providers track particles in the reactive flow field by solving the pertinent equations for the trajectory of a sfafisfically significant sample of individual particles that represents a number of the real particles with the same properties. For example, following the Rosin-Rammler size distribution (Figure 6.6), coal particles are tracked using a statistical trajectory model followed by the modeling of the kinetics of devolatilization and subsequent volatile and char combustion as discussed previously in this chapter (Figure 6.9). Models similar to the law presented earlier are used for droplet combustion of atomized fuel oil. 

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

Radioactivity occurs naturally in earth minerals containing uranium and thorium. It also results from two principal processes arising from bombardment of atomic nuclei by particles such as neutrons, ie, activation and fission. Activation involves the absorption of a neutron by a stable nucleus to form an unstable nucleus. An example is the neutron reaction of a neutron and cobalt-59 to yield cobalt-60 [10198 0-0] Co, a 5.26-yr half-life gamma-ray emitter. Another is the absorption of a neutron by uranium-238 [24678-82-8] to produce plutonium-239 [15117 8-5], Pu, as occurs in the fuel of a nuclear... 

As an example, consider heavy fuel oil (CH15, specific gravity, 0.95) atomized to a surface mean particle diameter of d, burned with 20 percent excess air to produce coke-residue particles having the original drop diameter and suspended in combustion products at 1204°C (2200°F). The flame emissivity due to the particles along a path of L m will be, with d in micrometers. 

Advantages of this type include an ability to burn all fuels including those containing solid particles, good turndown ratio (4 to 10 1 typically) and an insensitivity to oil conditions such as pressure and temperature. It is widely used in shell boilers, and the only real limitation is that the cup surface has to be cleaned daily. The most common atomizer layout is shown in Figure 24.7. Variants include direct driven cup and separate mounting of the primary air fan. 

---