Refuelling

Fuel Flexible Vehicles. Using dedicated alcohol fuel vehicles pointed to the importance of a wide distribution of fueling stations. Methanol-fueled vehicles require refueling more often than gasoline vehicles. 

Natural gas, aloag with aatural gas Hquids, may also have an opportunity to provide energy as a transportation fuel. U.S. automakers are iavolved ia limited productioa of aatural gas-fueled vehicles, and approximately 500 refueling stations have been built as part of the iafrastmcture needed to support these vehicles (22). 

In the United States, CNG s initial use is in captive, centrally refueled fleets which require limited range, such as deHvery vans, taxis, or school buses. Such vehicle fleets can afford the capital cost of refueling equipment and can tolerate the slightly longer refueling times. Many utiHty companies, such as Brooklyn Union Gas (New York), have purchased CNG vehicles as a way of encouraging the development of this fuel. AH three domestic automobile manufacturers offer CNG vehicles for sale. 

A PWR can operate steadily for periods of a year or two without refueling. Uranium-235 is consumed through neutron irradiation uranium-238 is converted into plutonium-239 and higher mass isotopes. The usual measure of fuel bumup is the specific thermal energy release. A typical figure for PWR fuel is 33,000 MWd/t. Spent fuel contains a variety of radionucHdes (50) ... 

If possible comparisons are focused on energy systems, nuclear power safety is also estimated to be superior to all electricity generation methods except for natural gas (30). Figure 3 is a plot of that comparison in terms of estimated total deaths to workers and the pubHc and includes deaths associated with secondary processes in the entire fuel cycle. The poorer safety record of the alternatives to nuclear power can be attributed to fataUties in transportation, where comparatively enormous amounts of fossil fuel transport are involved. Continuous or daily refueling of fossil fuel plants is required as compared to refueling a nuclear plant from a few tmckloads only once over a period of one to two years. This disadvantage appHes to solar and wind as well because of the necessary assumption that their backup power in periods of no or Httie wind or sun is from fossil-fuel generation. Now death or serious injury has resulted from radiation exposure from commercial nuclear power plants in the United States (31). 

Approximately 25—30% of a reactor s fuel is removed and replaced during plaimed refueling outages, which normally occur every 12 to 18 months. Spent fuel is highly radioactive because it contains by-products from nuclear fission created during reactor operation. A characteristic of these radioactive materials is that they gradually decay, losing their radioactive properties at a set rate. Each radioactive component has a different rate of decay known as its half-life, which is the time it takes for a material to lose half of its radioactivity. The radioactive components in spent nuclear fuel include cobalt-60 (5-yr half-Hfe), cesium-137 (30-yr half-Hfe), and plutonium-239 (24,400-yr half-Hfe). 

Recently in some types of refuelling stations, corrosion-resistant materials have been used between the filter-water separator and the outlet pipeline and valves, usually stainless steel, rarely aluminum. If these are buried, they must have good insulating coating and be electrically separated from other tank installations by insulating couplings. 

Protection currents of a few amperes are needed for the cathodic protection of assemblies of storage tanks or refuelling stations. In this case, electrical contact with grounded installations is the main problem. For cathodic protection, these contacts must be located and electrically separated. If this is not possible, then local cathodic protection should be installed (see Chapter 12). 

The Clean Air Act of 1990 establishes tighter pollution standards for emissions from automobiles and trucks. These standards will reduce tailpipe emissions of hydrocarbons, carbon monoxide, and nitrogen oxides on a phased-in basis beginning in model year 1994. Automobile manufacturers will also be required to reduce vehicle emissions resulting from the evaporation of gasoline during refueling. 

Onboard Refueling Vapor Recovery (OR ) regulations were fust proposed m 1987 but were met with a litany of technical and safety issues that delayed the requirement. The 1990 CAA amendments required the implementation of ORVR and the EPA regulation requires passenger cars to first have the systems starting in 1998. The ORVR test will be performed in a SHED and will require that not more than 0.2 grams of hydrocarbon vapor per gallon of dispensed fuel be released from the vehicle. 

A current vehicle fuel system designed for evaporative emission control should address enhanced SHED, running loss, and ORVR emission level requirements (see Table 1). A typical vehicle fuel system is shown in Fig. 4. The primary functions of the system are to store the liquid and vapor phases of the fuel with acceptable loss levels, and to pump liquid fuel to the engine for vehicle operation. The operation of the various components in the fuel system, and how they work to minimize evaporative losses during both driving and refueling events, is described below. 

The vapor vent valves are connected to the tank vapor control valve, and ultimately to the carbon canister by tubing that is resistant to swelling in the presence of fuel vapors. The tubing material must also have a low HC permeation rate, so that the evaporative emissions are not increased due to release of HC molecules. The tank vapor control valve connects the carbon canister to two fuel tank vapor sources the vapor vent valve lines and a refueling vent tube. 

Fuel system operation during refueling events... 

Fuel system components involved in the refueling process include the fuel tank, filler pipe, filler cap, vapor control valve, liquid-vapor discriminator (LVD) valve, and the carbon canister [27,28]. During vehicle refueling, which is monitored during the integrated refueling test as outlined in Fig. 1, the following operations occur in the evaporative emission control system ... 

A vehicle fuel vapor control system must be designed to meet both driving and refueling emission level requirements. Due to the nature of hydrocarbon adsorption, this emission control is a continuous operation. 

The rate of vapor generation during refueling is a major parameter affecting the design of carbon canisters to meet ORVR requirements. 

U.S. Environmental Protection Agency, Final Rule, Control of Air Pollution From New Motor Vehicles and New Motor Vehicle Engines Refueling Emission Regulations for... 

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