Code Manual for CONTAIN 2.0 - Federation of American Scientists

- group number fortheradionuclide
- half-life
atomic weight
- total specific decay power (W/kg)
- gamma specific decay power (W/kg)
- most probable gamma energy (MeV)
inventory factors for initizilizing mass distributions of a given radionuclide in the set of
linear chains
The half-life, atomic weight, total specific decay power, gamma-specific decay power, and most
probable gamma energy are self-explanatory. It should be noted that the latter two quantities are
stored in the code but presently not used in models. The definitions of inventory factors and linear
chains are discussed in Section 8.3.
Because the CONTAIN fission product decay model assumes that the atomic weight of a
radionuclide remains unchanged, only radionuclides with beta and gamma decay are modeled. The
available decay processes, which are shown in Figure 8-2, are selected by the user by number from
the library for inclusion in a calculation. When a particular decay process is requested, CONTAIN
will include all of the radionuclides in that process. The end products of the decay process are also
included, and modeled with infinite half-life and zero decay power. Note that some of the end
products may in reality decay over time by alpha decay, but the alpha decay is not explicitly
modeled.
8.3 Linear Decav Chains
Fission product transmutation is modeled using the technique of linear chain resolution. [Eng68]
This technique applies to the decay of explicitly specified fission products. In the technique of linear
chain resolution, the differential equations for decay are decoupled by breaking a coupled decay
process into a system of decoupled linear chains. The resulting chains can be treated independently
so only the masses in a chain are needed to solve for the effects of decay for that chain.
To characterize decay processes not defined in the fission product library, the user must be familiar
with the concepts of a fission chain element, branching ratio, and inventory factor. Linear chain
decomposition replaces a coupled decay process with a set of linear chains, each representing a
possible decay path, beginning with the ieading radionuclide(s) of the coupled process. For example,
decay process number 17 from Figure 8-2 can be broken down into two linear chains: (1) 1°3Ru->
103mRh-> 1°3Rh,and (2) 103Ru-> 1°3Rh.A given radionuclide, such as 103Rh,may appear more than
once as an element in the set of linear chains. Each occurrence of a radionuclide constitutes a
“fission chain element.” In the above two chains, there area total of 5 fission chain elements and
3 radionuclides.
The branching ratio is the probability that a radionuclide will take a particular branch (i.e., decay to
a particular daughter) in the decay process. Therefore, the sum of all branching ratios for a
radionuclide must add to unity. The branching ratios given in Figure 8-2 indicate that 1°3Ruwill take
the 103mRhbranch as in the first linear chain above with a probability of 99.75%, and will take the
Rev. O 8-13 6/30/97