Fuel Types

Section 2 presents the assumptions and requirements upon which the INEL concept was developed. Section 3 contains an overview of the reactor concept. Section 4 lists the conclusions and recommendations. Most of the technical details and discussions are contained in the appendices. The first task was to examine plutonium destruction rates and isotopics for different neutron spectra, as discussed in Appendix A. This study lead to the adoption of a thermal reactor concept instead of reactors with fast or epithermal neutron spectra. The second task was to study the addition of seed materials for selfprotection from materials diversion. Appendix B illustrates that fission products provide the best. self-protection, and seed materials are not needed for the INEL concept. Various fuel types were investigated and are described in Appendix C. The core neutronics studies presented in Appendix D and thermal-hydraulics studies pre.sented in Appendix E were performed concurrently. An evaluation of potential offsite radiation doses 

For destruction, the total plutonium content after irradiation must be less than some fraction (such as 10%) of the original plutonium loading. 

For self-protection, the spent fuel must be activated such that 10 years after removal from the core the radioactivity is still above 100 rem/hr at 3 ft from a fuel assembly. 

Well-tested fuel types and geometries are desirable. 

Fuel reprocessing should not be required between cycles (a once-through system is desired). 

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Over the years, a variety of fuel types were employed. Originally, natural uranium slugs canned in aluminum were the source of plutonium, while lithium—aluminum alloy target rods provided control and a source of tritium. Later, to permit increased production of tritium, reactivity was recovered by the use of enriched uranium fuel, ranging from 5—93%. 

Operational Characteristics. Oxygen generation from chlorate candles is exothermic and management of the heat released is a function of design of the total unit iato which the candle is iacorporated. Because of the low heat content of the evolved gas, the gas exit temperature usually is less than ca 93°C. Some of the heat is taken up within the candle mass by specific heat or heat of fusion of the sodium chloride. The reacted candle mass continues to evolve heat after reaction ends. The heat release duting reaction is primarily a function of the fuel type and content, but averages 3.7 MJ/m (100 Btu/fT) of evolved oxygen at STP for 4—8 wt % iron compositions. 

A notable difference between the newer large machines and the somewhat smaller units is the use of multiple, reverse-flow can combustors configured annulady. Because the individual cans are relatively small, they reportedly lend themselves well to laboratory experimentation with various fuel types, including reduced-heat value synfuels (see Fuels, synthetic). A dry, low NO version of the can combustors has been developed for both gas and hquid fuel firing. NO emissions can reportedly be held below 25 ppm when firing gas fuel. By employing water injection, NO emissions can be held below 60 ppm for oil-fired units. 

The emissions from combustion processes may be predicted to some extent if the variables of the processes are completely defined. Figure 6-7 indicates how the emissions from a combustion source would be expected to vary with the temperature of the reaction. No absolute values are shown, as these will vary greatly with fuel type, independent variables of the combustion process, etc. 

General Fuel Type True Distillate Naphthas Blended Heavy Distillates Low-Ash Crudes Residuals High-Ash Crude... 

With heavy fuels, the ambient temperature and the fuel type must be considered. Even at warm environmental temperatures, the high viscosity of the residual could require fuel preheating or blending. If the unit is planned for operation in extremely cold regions, the heavier distillates could become too viscous. Fuel system requirements limit viscosity to 20 centi-stokes at the fuel nozzles. 

Gas turbines, like other mechanical devices, require inspection, maintenance, and service. Maintenance costs include the combustion system, hot-gas path, and major inspections. (See Chapter 21.) The effect of fuel type on maintenance costs is shown in Table 12-8. A cost factor is shown using natural gas as unity. The cost of maintenance is subject to great variations. Recognizing the great difficulty in establishing expected maintenance costs... 

Figure 1. Graph accounts for fuel type, sulfur, and excess air.

The fuel vacuum pipe still is also used to recover cracked gas oil from the tar formed in residuum cracking (visbreaking) processes. In this service, it it frequently referred to as a vacuum, flash unit. Pipe stills designed for the production of asphalt are usually the fuel type of unit. 

Oil burners Type Size range Dual-fuel capability Fuel type Atomizing Atomizing pressure viscosity (bar) (cS) Turndown ratio Flame characteristics Main applications... 

Gas burners Type Size Dual-fuel Fuel type Gas pressure Turndown ratio Flame Characteris tics Main applications... 

The percentage of excess air required for complete combustion varies according to fuel types and burner design. 

All fuel types contain some level of impurity or noncombustible component. For all practical purposes, the very low level of impurities found in natural gas fuels can be ignored (although during combustion, gas produces a higher percentage of moisture as compared to, say, fuel oils, and this can cause some problems downstream). For most coals, oils, and combustible process by-product fuels, however, the impact on fuel efficiency and maintenance costs can be significant and warrants the use of additives. 

Embedded in such models, in which variations were developed [12] are further detailed. The laminar burning velocity is expressed as a function of fuel type, fuel/ air ratio, level of exhaust gas recirculation, pressure, temperature, etc. Furthermore, submodels have been developed to describe the impact of engine speed, port-flow control systems, in-cylinder gross-flow motion (i.e., swirl, tumble, squish), and turbulent fluctuations u. Thus, with a wider knowledge base of the parametric impact of external variables, successful modeling of... 

There are many types of steam boilers, depending on the steam pressure, steam output and fuel type. Blowdown is required to remove the dissolved solids not removed in the boiler feedwater treatment. The efficiency of the boiler depends on its load. 

The shape and size of the flammability zone on a flammability diagram change with a number of parameters, including fuel type, temperature, pressure, and inert species. Thus the flammability limits and the LOC also change with these parameters. 

An alternative plotting format was used by Bullen and Thomas [6] for the mass loss rate, which shows the effect of fuel type in Figure 11.18. These data include an extensive compilation by Harmathy [27] for wood crib fuels (including the CIB data). Here the fuel area is included, but the compartment area is omitted. This shows the lack of... 

Table 5.11 Average energy yields of different fuel types produced from energy crops... 

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