Code Manual for CONTAIN 2.0 - Federation of American Scientists

user. From this information, the code tracks the birth and decay rates of each individually specified
radionuclide, and also accounts for the decay heating associated with the fission products. It should ~
be noted that only beta and gamma decay processes should in general be explicitly included, because
CONTAIN assumes that a decay results in no change in atomic weight. Alpha decay processes in
the containment environment are sufficiently slow that they (but not the parent inventories) can be
neglected during the period of a typical containment calculation. For calculations in which such
processes cannot be neglected, the user may wish to include them and adjust the reported inventories
for the included alpha masses.
For some studies of reactor accident scenarios, identifying and speci@ing the large number of decay
processes and the radionuclides involved could be tedious. To alleviate this problem, a number of
decay processes and radionuclides maybe defined by invoking an extensive fission product data
library, which provides decay information for 140 radionuclides. The decay processes considered
are given in Figure 8-2, and the radionuclides involved are given in Table 8-1. The decay
information available from the library is discussed in Section 8.2.
In order to model the decay process efficiently, CONTAIN uses a linear chain decomposition of the
decay processes involved, as discussed in detail in Section 8.3. If the user invokes the fission
product library with respect to one or more of the decay processes in Figure 8-2, the necessary
information to characterize the selected decay processes is automatically loaded. For those decay
processes not taken from the library, the user must input the linear chain parent-daughter
relationships, inventory factors, specific powers, and half-lives of the fission products involved. It
should be noted that fission product classes are treated in the input like individual radionuclides,
except that the decay chains should be of length one, the half-lives set very large, and the inventory ~
factors equal to one. The time-dependent specific decay power the user may specifj for a class is
typically obtained as the best curve fit through the total decay power of all radionuclides associated
with the class. As discussed in Section 8.3, inventory, or distribution, factors maybe required when
a given radionuclide appears more than once in the linear chain decomposition. It should be noted
that the use of inventory factors is new to the present code version. In prior versions, the user was
required to specify directly the initial masses and source rates associated with each radionuclide
occurrence within the linear chain decomposition. Each such occurrence constitutes a different
“fission chain element,” even though the same radionuclide is involved. For example, if all decay
processes stored in the library were invoked, one would be dealing with 257 fission chain elements,
taken from a set of 140 radionuclides. Consequently, the input of the chain element masses could
be considerably more cumbersome than input of the radionuclide masses.
As discussed in Section 8.4, fission products in CONTAIN are associated with various “hosts,” or
repositories. A host can be the atmosphere gas, an aerosol component, the surface of a heat
structure, or a lower cell layer or pool. Some hosts, such as the upper cell atmosphere gas or aerosols
are mobile, while others, such as the wall surfaces, are fixed. In general, the location of fission
products is specified by the user according to the host. Fission products are transported according
to the movement of the mobile hosts. Fission product masses, as treated by CONTAIN, do not
influence the dynamics of the mobile hosts, except through possible heating effects. In effect, fission
products are treated as having no dynamic mass. For some hosts, such as a minor aerosol
component, the fission product mass may constitute an important fraction of the mass associated
Rev O 8-4 6/30/97