Heat Transfer
HEAT GENERATION
Thermal Limits
Hot channel factors are calculated values used to take into account various uncertainties in
tolerances used in core manufacturing. For example, consider a coolant channel of the minimum
acceptable width and length, that happens to be adjacent to a fuel plate with the maximum
acceptable fuel loading. In this channel, we would now have less water than in the average
channel, receiving more heat than the normal coolant channel. For any given values of core
power and flow, this hypothetical channel would be closest to a thermal limit. Therefore, all
design considerations are based upon the hot channel factor for each core. The nuclear heat flux
hot channel factor (HFHCF) is the ratio of the maximum heat flux expected at any area to the
average heat flux for the core. The nuclear enthalpy rise hot channel factor is the ratio of the
total kW heat generation along the fuel rod with the highest total kW to the total kW of the
average fuel rod.
Thus the limitation of the peak flux value in a core is directly related to the hot channel factor.
However, in discussing flux profiles, "average" values of flux in the core are usually referred to
rather than peaks.
Average Linear Power Density
In nuclear reactors, the fuel is usually distributed in individual components which sometimes
resemble rods, tubes, or plates. It is possible to determine the average power produced per unit
length of fuel component by dividing the total thermal output of the core by the total length of
all the fuel components in the core. This quantity is called the average linear power density.
Common units for measuring average linear power density are kW/ft.
Example:
Calculate the average linear power density for an entire core if a 3400 MW reactor is
operating at full power.
Core data is:
each fuel rod is 12 ft long
264 rods/fuel assembly
193 fuel assemblies in the core
Solution:
Average linear power density
=
total thermal power
total fuel rod length
Average linear power density
=
3.4 x 106 kW
12 (264) (193)
=
5.56 kW/ft
Rev. 0
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HT-02
