Fuel Channel

A fuel channel encloses the fuel bundle the combination of a fuel bundle and a fuel channel is called a fuel assembly. The channel is a square-shaped tube fabricated from Zircaloy 4 its outer dimensions are 5.455 in. (138.6 mm) x 5.455 in. (138.8 mm) x 166.9 in. (4.2 m) long. The reusable channel makes a sliding seal fit on the lower tie plate surface. The channel fastener assembly (consisting of a spring and a guard) attaches the reusable channel to the upper tie plate and a capscrew secured by a lock washer. Spacer buttons are located on two sides of the channel to properly space four assemblies within a core cell. The fuel channels direct the core coolant flow through each fuel bundle and also serve to guide the control rod assemblies. 

The use of the individual fuel channel greatly increases operating flexibility because the fuel bundle can be separately orificed and thus the reload fuel design can be changed to meet the newest requirements and technology. The channels also permit fast in-core sampling of the bundles to locate possible fuel leaks. 

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Fig. 5. The gas flow path of an AGR. Note the flow is reentrant, i.e., a fraction of the coot gas from the circulator flows up around the outside of the core entering the core from the top, then flows downward through the core, between the moderator and fuel element assembly, to the bottom where it mixes with the cool gas from the circulator and flows up the fuel channel inside the graphite fuel sleeves to the steam generators. Reprinted from [33], 1977 Wilmington Business Publishing, Dartford, U.K., with permission.

The reactor core was made up of stacks of hexagonal graphite blocks. Each fuel element block had 210 axial fuel holes and 108 axial coolant holes (Section 5, Fig. 14). The fuel particles were formed into a fuel compact (Section 5.3) and sealed into the fuel channels. 

Pressure-tubes allow the separate, low-pressure, heavy-water moderator to act as a backup hesit sink even if there is no water in the fuel channels. Should this fail, the calandria shell ilsdf can contain the debris, with the decay heat being transferred to the water-filled shield tank around the core. Should the severe core damage sequence progress further, the shield tank and the concrete reactor vault significantly delay the challenge to containment. Furthermore, should core melt lead to containment overpressure, the concrete containment wall will leak and reduce the possibility of catastrophic structural failure (Snell, 1990). 

A fuel channel in a natural uranium reactor is 5 m long and has a heat release of 0.25 MW. If the thermal conductivity of the uranium is 33 W/mK, what is the temperature difference between the surface and the centre of the uranium element, assuming that the heat release is uniform along the rod ... 

Subchannel analysis for PWR cores CHF predictions in BWR fuel channels... 

Fuel Channel. A fuel channel encloses the fuel bundle. The combination of a fuel bundle and a fuel channel is called a fuel assembly. See Fig. 6,... 

The concept of monolithic module design is associated with Argonne National Laboratories [111, 112]. Power density of about 8 kW/kg or 4kW/1 and fuel efficiency over 50% are expected to be achieved with monolithic SOFCs. The monolithic structure started with a co-flow version where the cell consists of a honeycomb-like array of adjacent fuel and oxidant channels that look like corrugated paperboard, as shown in Fig. 42. Multilayer laminates of the active cell components (anode-elec-ttolyte-cathode) are appropriately corrugated and stacked alternatively between flat multilayer laminates in the following sequence anode- interconnection material-cathode. Tape casting [111] and hot-roll calendering [113, 114] are used to fabricate the monolithic structure. A cross-flow version where oxidant and fuel channels are... 

Finally, a steady 1-D lumped stack model is introduced which uses a 0-D lumped approach for each cell in the stack. The model takes the current and power produced by each cell in the stack as input and predicts the 1 -D temperature distribution across the cells of the stack. Such models have the advantage of faster calculation time and are thus better suited for initial design calculations and control system modeling. In this model, each fuel cell is divided into three components, air channel, fuel channel and solid region (electrodes, electrolyte and the interconnect). The control volumes used for air and fuel channel components are shown by the dashed lines in Figure 5.6. The specie concentrations at the exit of air and fuel channels could be calculated using the mass and specie balances for these control volumes which are in the form... 

Here, C denotes the heat capacities, i.e. the product of mass flow rate times corresponding specific heat, T denotes temperature, and Q denotes rate of heat transfer or generation. Subscripts a, f, c, r, e denote air channel, fuel channel, cell (solid re-... 

In the above equations, hconv,a- Aa, hCOnv,f, Af, are the overall convective heat transfer coefficients and interface areas respectively between the cell and air or fuel channels. Finally, following relations are used for the average air channel and fuel channel temperatures... 

Table A.1 Convergence ofhydrogen mass fraction and temperature at the exitofthe fuel channel.

Fuel channel Navier-Stokes (2 eq.), Continuity, Energy, Conservation of species (4 eq.) 27000... 

Each cell is divided into vertical portions. Each portion is constituted of the following elements cold air, tube (t), hot air (a), cell (i, j), fuel (/), as shown in Figure 7.18. The cell elements are considered as constituted of four slices. This choice allows one to consider that each cell is in contact with four fuel channels. In a stack, fuel in these channels may be in different conditions. 

Equation (7.10) is constituted by as many terms as the number of cells facing the fuel channel. 

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