Calculation of Decay Heat

DECAY HEAT Heat Transfer Example: A 250 MW reactor has an unexpected shutdown. From data supplied by the vendor, we know that decay heat at time of shutdown will be 7% of the effective power at time of shutdown and will decrease with a 1 hr half life. Effective power at time of shutdown was 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. Q Q_o � � � � � � 1 2 time half life 8.4 MW^� � � � � � 1 2 12 hr 1 hr 2.05 x 10³ MW^� � � � � � 3.413 x 10⁶ Btu/hr 1 MW 7000^Btu hr The second method is much simpler to use, but is not useful for forecasting heat loads in the future. To calculate the decay heat load at a given point after shutdown, secure any heat removal components from the primary system or spent fuel pool and plot the heatup rate. If the mass of the coolant and the specific heat of the coolant are known, the heat generation rate can be accurately calculated. (2-17) Q m c_p DT Dt HT-02 Page 54 Rev. 0