Fuel loading

Fig. 6. Initial fuel loading of PWR showiag the three enrichments where ( ) represents 3.10 wt % ( ) 2.60 ( ) 2.10 and (0) the cluster openings of...

The third control is by use of a fixed burnable poison. This consists of rods containing a mixture of aluminum oxide and boron carbide, included in the initial fuel loading using the vacant spaces in some of the fuel assembhes that do not have control clusters. The burnable poison is consumed during operation, causing a reactivity increase that helps counteract the drop owing to fuel consumption. It also reduces the need for excessive initial soluble boron. Other reactors use gadolinium as burnable poison, sometimes mixed with the fuel. 

Launched ia 1959, N. A. Savannah operated very weU. Starting ia 1962, it made a goodwill voyage around the world. It was able to travel a distance of several times the earth s circumference on one fuel loading. However, the ship was not competitive economically with oil-powered merchant ships. The shielding was quite adequate, so that the reactor was safe. Nonetheless the vessel was opposed by antinuclear groups and the N.A. Savannah was eventually retired and put on display ia Charleston, South Carolina. In 1994, the ship was transferred to Norfolk, Virginia, to be held ia reserve. 

The licensing process consists of two steps construction and operating license that must be completed before fuel loading. Licensing covers radiological safety, environmental protection, and antitru,st considerations. Activities not defined as production or utilization of special nuclear material (SNM), use simple one-step. Materials Licenses, for the possession of radioactive materials. Examples are uranium mills, solution recovery plants, UO fabrication plants, interim spent fuel storage, and isotopic separation plants. 

Fully developed fire studies have been performed over a range of fuel loadings and ventilation conditions, but primarily at scales smaller than for normal rooms. Also the fuels have been idealized as wood cribs or liquid or plastic pool fires. The results have not been fully generalized. The strength of the dimensionless theoretical implication of Equation (11.38) suggests that, for a given fuel, the fully developed, ventilation-limited fire should have dependences as... 

Most of the CIB tests involved crib arrangements having AF/A of mostly 0.75 [2] therefore, leaving this parameter out of the correlation may be justified. However, for low fuel loadings, Law recommended that the maximum temperature be reduced accordingly ... 

The CIB tests consisted of compartments with heights ranging from 0.5, 1.0 and 1.5 m with dimension ratios of D/H, W/H, H/H coded as data sets 211, 121, 221 and 441. A total of 321 experiments were conducted in still air conditions. The wood crib fuel loading ranged from 10 to 40 kg/m2 with stick spacing to stick thickness ratios of 1 and 3. The data are plotted in Figures 11.17 and 11.19. The compartment surface area, A, excludes the floor area in the plot variables. 

The amount of air that can be drawn into an enclosure to support combustion will depend on both the size and configuration of ventilation openings in the enclosure. A poorly ventilated fire will create more smoke and byproducts. Any unburnt fuel may also burn outside the enclosure, endangering adjacent areas. A fire in a structure may also cause other fuels to burn such as cables, paint, plastic equipment etc. These will add to the fuel load and to the smoke. 

Post-flashover fire models calculate the time-temperature history in a compartment by solving simplified forms of the energy, mass, and species equations. The concentration of various gaseous constituents can be monitored as well as vent flows. Some post-flashover fire models allow mechanical ventilation to be factored in the calculation. These types of models are most useful for determining the time-temperature exposure to a structure for a specific compartment and fuel load. Such time-temperature histories can be used for assessing the possibility of structural failure or fire spread to adjacent compartments. 

Heat release rate is another relevant measure of the combustibility of a material along with ease of ignition and flame spread. Smith (55) points out that the release rate data, obtained under different test exposures, will be useful in predicting the performance in actual fires under different fuel loading. Release rate data can thus be used—along with other... 

As a fuel-controlled fire grows in size and involves more fuel surface area and more fuel packages, it can reach a condition where the entire fuel load in the compartment burns at once. When this condition takes place as a transition suddenly, it is termed as flashover. The transition from fuel-controlled to ventilation-controlled conditions usually takes place at flashover event. 

Nine types of cores with different characteristics (power resource, fuel loading parameters, fuel emichment) were developed for first-generation reactor installations. Any of them could have been unloaded and stored at Gremikha. 

Two cores had 6-% fuel enrichment, the remaining cores 21 % enrichment. Mean fuel load therein was equal to 46.8 kg. According to specifications, maximal fuel bumup made up 20 % of the initial fuel load on average. 

Build fires away from nearby trees or bushes. Ash and cinders lighter than air float and may be blown into areas with heavy fuel load, starting wildfires. 

Figure 5.3 A cerrado in Brasilia during the dry season showing the fuel load in the herbaceous layer.

Kauffman et al. (1994) estimated the fuel loads along a vegetation gradient from campo limpo to cerrado sensu stricto near Brasilia. In the cerrado only 27% of the fuel load of 10 Mg ha" was comprised of graminoids the remainder was deadwood and leaf litter. They estimated the nutrient pools in combustible components in the cerrado sensu stricto to be 54.7 kg ha" N, 13.8 kg ha K, 3-5 kg ha P, and 30.5 kg ha" Ca. They concluded that the total biomass of the herbaceous layer of the cerrados was similar to that of other savanna ecosystems. The authors concluded that any loss of N due to fire was negligible compared to the N pool in the soil. Biological N fixation and precipitation inputs would compensate for such losses. Similarly, precipitation inputs would compensate for the loss of P, K and Ca (Schiavini 1983, Coutinho 1979, Pivello-... 

Data on fuel load densities in urban areas are scarce. In German compilations the following typical values for fuel loads per m of floor... 

Having now determined to total amount of nuclear electricity required, the thorium fuel input to the energy amplifiers can be calculated from the design data of Rubbia and Rubio (1996). The thermal output from the prototype design reactor is 1500 MW, with a fuel amount of 27.6 t in the reactor (Fig. 5.42). The fuel will sit in the reactor heat-generating unit for 5 years, after which the "spent" fuel will be reprocessed to allow for manufacture of a new fuel load with only 2.9 t of fresh thorium oxide supply. This means that 2.6/5 t y of thorium fuel is required for delivery of 5 x 1500 MWy of thermal power over 5 years, or 675 MWy of electric power, of which the 75 MWy is used for powering the accelerator and other in-plant loads. The bottom line is that 1 kg of thorium fuel produces very close to 1 MWy of electric power, and 1 kt thorium produces close to 1 TWh. ... 

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