Figure B-5. Heat generation rate as a function of time for three grades of plutonium

DOE-STD-3013-2000

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

Pu into

Am, the subsequent increase in heat generation rate is only about 15%.

As a rule of thumb, the

peak heat generation rate

occurs about 40-60 years

after discharge from the

reactor. Thus, after 20

Weapons

years of storage, the peak

Fuel

is still some 20-40 years in

Power

the future. A reasonable

approach to determining

the peak heat generation

241

Pu as

rate is to treat the

241

Am. An

though it was

Years

alternative approach is to

Figure B-5. 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:

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

241

is the concentration of

Pu (wt% or mass fraction)

238

is the concentration of

Pu (wt% or mass fraction)

241

is the concentration of

Am (wt% or mass fraction)