DECAY HEATHeat TransferExample:A 250 MW reactor has an unexpected shutdown. From data supplied by the vendor, weknow that decay heat at time of shutdown will be 7% of the effective power at time ofshutdown and will decrease with a 1 hr half life. Effective power at time of shutdownwas calculated to be 120 MW. How much heat removal capability (in units of Btu/hr)will be required 12 hours after shutdown?Solution:(a) First determine the decay heat immediately following shutdown.(120 MW)(.07) = 8.4 MW decay heat at shutdown(b) Then use Equation 2-15 to determine the decay heat 12 hours later.QQ_{o}12timehalf life8.4 MW^{}1212 hr1 hr2.05 x 10^{3} MW^{}3.413 x 10^{6} Btu/hr1 MW7000^{Btu}hrThe second method is much simpler to use, but is not useful for forecasting heat loads in thefuture. To calculate the decay heat load at a given point after shutdown, secure any heat removalcomponents from the primary system or spent fuel pool and plot the heatup rate. If the mass ofthe coolant and the specific heat of the coolant are known, the heat generation rate can beaccurately calculated.(2-17)Qm c_{p}DTDtHT-02 Page 54 Rev. 0

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