Code Manual for CONTAIN 2.0 - Federation of American Scientists

For the spherical geometry
where
~-r.
&ri = ri ~ ;
iliri+l =ri+l ‘i+l_ -r
r=
r
(10-131)
(10-132)
(10-133)
The N linear coupled equations given by Equation (10-125) are solved by using a standard
tridiagonal matrix methods.
10.5.4 Concrete Outgassing
The outgassing model for the release of HZOand COLgases from concrete heat transfer structures
is described in this section. Both evaporable and bound water are considered in the modeling of
steam release. The principal assumption made in the outgassing model is that the release is
controlled by the rate at which thermal energy is supplied for vaporization of the available water
and/or for concrete decomposition and not by gas transport effects. The concrete outgassing model
has been described in greater detail in Reference Was88. The reader should consult this reference
for additional information.
The heat conduction model discussed in Section 10.5.3 is tightly coupled to the concrete outgassing
model in two ways. First, the energy required to decompose compounds in the concrete and/or
evaporate water is accounted for in the heat conduction equation through appropriate energy sink
terms. This is done in a closely coupled manner so that gas release during a timestep is consistent
with the temperature at the end of the same timestep. Likewise, the end of timestep temperature is
used to compute the gas release from the structure. An iterative solution technique is used to
partition the heat input between that used for gas release and the heating of concrete.
Second, the thermophysical properties of the concrete are modeled as a function of temperature and
the amount of gas released from the concrete. In the model, only nodes containing CONC material
are allowed to outgas. Note that the properties of the CONC material as supplied by the properties
routines are assumed to correspond to wet concrete. However, in the outgassing routines, the loss
of evaporable water from the node is assumed to modi~ the specific heat of an outgassing node
according to the assumption that evaporable water contributes a specific heat equal to that of liquid
water. The porosity of a node, not occupied by concrete, is assumed to be equal to the mass of bound
gases released, divided by the concrete density with evaporable water removed, and the mass and
volume of concrete material in the node is correspondingly reduced. The conductivity is assumed
Rev O 10-63 6/30/97