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
Qo
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
7000Btu
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 cp
DT
Dt
HT-02
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