Fresh fuel

This eliminates the need for steam to be supplied from another source. The anode-anode recycle also heats the fresh fuel feed to the designated anode inlet temperature. 

A strong reverse flow is required to bring hot combustion products into contact with fresh fuel-air mixture and provide maximum residence time. 

Periodically, a portion of the fuel in a nuclear reactor is removed and replaced with fresh fuel. In the past, the average lifetime of fuel in the reactor was 3 years with one-third of the fuel being removed each year. More recently, attempts are being made to extend fuel lifetimes. 

The IP-SOFC bundle is then the basic unit of the IP-SOFC stack (Figure 6.2), where several bundles are coupled to a reformer in which the fresh fuel (CH4) reacts with a part of the water-rich SOFC anode off-gas, in order to produce an H2 and CO-rich gas mixture. The fuel produced by the reformer is fed in parallel to the various electrochemical bundles. The oxidant stream crosses all the bundles of the stack in series. The hot oxidant stream exiting the last electrochemical bundle flows through the reformer as well, in order to provide the heat necessary for the endothermic reforming reaction. 

Minimal by-products (tar, oil, etc.) because of rapid heating up of the fresh fuel... 

Some countries, including the Russian Federation and France, have chosen a closed fuel cycle meaning that the nuclear fuel is reprocessed in a dedicated plant, thus allowing the remaining Uraninm and Plutoninm to be incorporated into fresh fuel. 

The decisions on building the current NPPs in Finland were made in late 1960 s - early 1970 s. At that time, the prospects for nuclear energy were very promising and spent fuel was regarded as an asset due to the worth of its plutonium and uranium as nuclear fuel. Accordingly, the contract for the supply of the Loviisa NPP included clauses for the return of spent fuel to the supplier of the fresh fuel in Soviet Union. Though no such stipulations included in the supply contracts for the Olkiluoto NPP, it was taken obvious that the operator would later make contract with a French or British reprocessing company. 

The large rig has a larger heat loss during batch firing, caused by the heavier design. The ignition front, however, is well insulated by fresh fuel on one side and by partly converted fuel or char on the other, and there is only a heat loss at the walls. 

Three sizes of the same fuel have been compared. At low airflow the ignition rate is higher and front temperature lower with the larger fuel. The resistance towards heat flow into the particles increases with diameter, and more of the heat produced is transported to new layers of fresh fuels and not towards the centre of the fuel particles. The larger particles are thermally thicker, and the devolatilization rate is lower. The sub-stoichiometric regime with complete oxygen consumption starts at... 

The fuel elements in power reactor cores are distributed in zones of uranium enrichments, with the highest at the periphery to compensate for the lower neutron flux toward the periphery, and thereby achieve a flatter neutron-flux profile and higher power output. About once a year the fuel elements are discharged from the central zone of the core, and elements in the outer zones are moved inward. Fresh fuel elements are loaded... 

The fuel cycle concept is much more influenced hy the chemical behaviour of the actinides during the reprocessing of the Th-containing fuel. It could he demonstrated during the first hot operations (3.), that Np ends up quantitatively in the waste stream, hut Pu is distributed in the product streams (90 % in the Th-, 10 % in the U-stream). These facts contradict strongly the above mentioned fuel cycle strategy, since Pu is no waste component and the Pu-contaminated Th cannot he used for the fresh fuel fabrication with respect to its high specific a-activity. 

S 4.8 w/o Fresh Fuel (with BPs) 4.4 w/o Fresh Fuel (with BPs) 4.2 w/o Once Burned Fuel... 

The optimization reduced the fresh fuel enrichment required to satisfy the cycle energy requirements from 3.60 w/o to 3.40 w/o. As shown in Figure 8, the value of FAH predicted by FORMOSA-P over the fuel cycle was also reduced from 1.41 to the constraint limit (user input) value of 1.38. The optimized fuel pattern achieves substantial improvements in fuel cycle economics while at the same time improving the margin to thermal operating limits. 

The fuel slugs were pushed out of the graphite pile by fresh fuel and dropped into a pool of water that provided shielding from the intense radiation. After 60 days, the irradiated slugs were moved to chemical separation. 

When fresh fuels rods are introduced, the control rods are partially inserted to absorb some of the neutrons released. As the uranium-235 reacts and its percentage of the total mixture in the fuel rods decreases, the control rods are progressively withdrawn. In this way, a constant rate of fission can be maintained, even as the percentage of the fissionable uranium-235 diminishes (Figure 18.6). 

Figure 2.20 shows how the poisoning ratio of this chain varies if the reactor is shut down after initial operation for 7300 h for various periods of time T and then operated at a flux of 3.496 X 10 w/(cm s) for additional time T. The behavior shown in this figure is considered representative of this reactor after it has been refueled several times with one-third of the oldest fuel replaced by fresh fuel. 

A fresh fuel element containing 1 g-atom of U is exposed at time zero to a neutron flux of 10 n/(cm s). 

These changes in composition bring about changes in reactivity of the fuel, which eventually decreases to such an extent that the reactor will no longer be critical unless the spent fuel is replaced with fresh fuel. 

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