Code Manual for CONTAIN 2.0 - Federation of American Scientists

assumed to bum instantaneously if oxygen is available in the cell. This can only occur if oxygen is
available during the same timestep when the hydrogen was produced. The rationale for this <
approach is that the hydrogen is assumed to be near the surface of the drop during the same timestep
during which it was produced. If oxygen is not available during this timestep, then it will only burn
as governed by one of the other containment combustion models (deflagration, diffusion flame
burning, or bulk spontaneous recombination). The hydrogen recombination reaction can also be
disabled by the user in one or more cells by specifying RCOMH2 = OFF in the DHEAT or DCH-
CELL input blocks.
The hydrogen burning reaction is given by
Hz+ 0.5 02+ HZO
where 2.86 x 108Joules per kilogram-mole of hydrogen are released when hydrogen recombines
with oxygen. This reaction is limited by the availability of oxygen in the cell and the amount of
hydrogen produced by DCH during the timestep. The energy released by the recombination process
is added to the atmosphere, not the drop field, as shown in Equation (6-151).
6.5 Heat Transfer
Models are included for convective and radiative heat transfer between the debris and the
atmosphere. The DCH radiation model also includes provisions for direct radiation from the debris
to containment structures, including the pool and ice condenser. The first subsection below
describes the convection model. The second subsection describes the DCH radiation model. The *
models described below apply to debris in all fields, including the airborne fields and the nonairbome
debris field.. The models do not apply to trapped debris that is transferred to the uppermost
intermediate layer in the lower cell cavity. Heat transfer for debris in the lower cell is modeled as
part of the lower cell heat transfer model as described in Chapter 5 and Section 10.6.
6.5.1 Convective Heat Transfer
Convection heat transfer from debris to gas is assumed to be by forced convection. The heat transfer
coei%cient is given by the Nusselt correlation of Ranz and Marshall [Ran52, Bir60] for forced flow
over a sphere
‘Nu,, i. = 2.0 + 0.6 N#~ NPr,g 1’3
(6-152)
where N~ujJis the Nusselt number for debris field n in cell i. The convection heat transfer rate for
each debris field is individually calculated since each field has its own temperature, T~j$,and particle
size, d..
The N~,,~and NR,~parameters in this expression are calculated using gas properties at the boundary
layer temperature, T~~,as recommended in Reference Bir60. The velocity, v,., is used as the forced
convection velocity in the Reynolds number. This velocity is calculated within the code from the ~
Rev O 662 6/30/97