Heat Transfer HEAT GENERATIONThe fission rate within a nuclear reactor is controlled by several factors. The density of the fuel,the neutron flux, and the type of fuel all affect the fission rate and, therefore, the heat generationrate. The following equation is presented here to show how the heat generation rate ( ) isQrelated to these factors. The terms will be discussed in more detail in the Nuclear Sciencemodules.(2-14)QG N s_{f f}V_{f}where:= heat generation rate (Btu/sec)QG = energy produced per fission (Btu/fission)N = number of fissionable fuel nuclei/unit volume (atoms/cm^{3})= microscopic fission cross-section of the fuel (cm^{2})sf= neutron flux (n/cm^{2}-sec)fV_{f} = volume of the fuel (cm^{3})The thermal power produced by a reactor is directly related to the mass flow rate of the reactorcoolant and the temperature difference across the core. The relationship between power, massflow rate, and temperature is given in Equation 2-14.(2-15)Qm c_{p D}Twhere:= heat generation rate (Btu/hr)Q= mass flow rate (lbm/hr)mc_{p}= specific heat capacity of reactor coolant system (Btu/lbm-°F)DT = temperature difference across core (°F)For most types of reactors (boiling water reactor excluded), the temperature of the coolant isdependent upon reactor power and coolant flow rate. If flow rate is constant, temperature willvary directly with power. If power is constant, temperature will vary inversely with flow rate.Rev. 0 Page 45 HT-02

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