
 DOESTD30132000
characteristic of any significant quantity of plutonium to be packaged under this Standard.
However, even for this material, after 20 years of storage and the consequent decay of the
241
241
Pu into
Am, the subsequent increase in heat generation rate is only about 15%.
As a rule of thumb, the
20
peak heat generation rate
18
occurs about 4060 years
16
after discharge from the
14
reactor. Thus, after 20
12
Weapons
years of storage, the peak
Fuel
10
is still some 2040 years in
Power
8
the future. A reasonable
6
approach to determining
4
the peak heat generation
2
241
Pu as
rate is to treat the
0
0
10
20
30
40
50
60
70
80
241
Am. An
though it was
Years
alternative approach is to
Figure B5. Heat generation rate as a function of time for three
grades of plutonium
attempt to estimate the
timing of the peak and
then use the radioactive decay equations 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:
51
41
48
41
tpeak = 20.78 ln(0.0312 + 0.0302 f /f
+ 0.5716 f /f )
Where
tpeak is the time until the peak heat generation rate
41
241
f
is the concentration of
Pu (wt% or mass fraction)
48
238
f
is the concentration of
Pu (wt% or mass fraction)
51
241
f
is the concentration of
Am (wt% or mass fraction)
66

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