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Page Title:
Figure B-5. Heat generation rate as a function of time for three grades of plutonium |
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|  DOE-STD-3013-2004
Standard. However, even for this material, after 20 years of storage and the consequent decay
241
241
Pu into
Am, the subsequent increase in heat generation rate is only about 15%.
of the
As a rule of thumb, the peak heat generation rate occurs about 40-60 years after discharge
from the reactor. Thus,
after 20 years of storage,
20
18
the peak is still some 20-40
16
years in the future. A
14
reasonable approach to
12
Weapon
determining the peak heat
Fuel
10
generation rate is to treat
Power
8
241
Pu as though it was
the
6
241
Am. An alternative
4
approach is to attempt to
2
estimate the timing of the
0
0
10
20
30
40
50
60
70
80
peak and then use the
Years
radioactive decay equations
Figure B-5. Heat generation rate as a function of time for three
grades of plutonium
to determine the isotopic
composition and the heat
generation rate. Because the peak is so flat, a very accurate estimate of its time of occurrence is
not necessary. To estimate the timing of the peak the following equation can be used:
tpeak = -20.78 ln(0.0312 + 0.0302 f51/f41 + 0.5716 f48/f41)
Where
tpeak is the time until the peak heat generation rate
f41 is the concentration of
241
Pu (wt% or mass fraction)
f48 is the concentration of
238
Pu (wt% or mass fraction)
f51 is the concentration of
241
Am (wt% or mass fraction)
67
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