Code Manual for CONTAIN 2.0 - Federation of American Scientists

6.2.9 Reactor Pressure Vessel (RPV) Models
The purpose of Sections 6.2.9 and 6.2.10 is to discuss RPV- and cavity-specific models in
CONTAIN. The RPV models include vessel hole ablation, single-phase debris discharge, gas
blowthrough, and two-phase debris/gas discharge. The cavity models include a number of
correlations for the entrainment rate of debris and for the total fraction of debris dispersed from the
cavity, and a Weber breakup model for determining the size of entrained debris droplets.
The user may specify one cell in a problem to represent the RPV, and one cell to represent the cavity.
The code assumes that these two cells are connected by a single gas flow path. At the start of the
problem, the user must place some initial amount of debris into the trapped debris bin in the RPV
cell by using the TRAPBIN option for debris source tables. The initial flow area between the RPV
and cavity cells must be specified by the user, and is intended to represent the initial failure of the
pressure vessel by either instrument tube penetration failure or a larger scale rupture.
Prior to gas blowthrough, debris exits the RPV in single-phase flow and is transferred from the
trapped debris bin in the RPV cell to the trapped debris bin in the cavity cell. Ablation of the hole
in the RPV is modeled, along with the height of the debris pool in the RPV. When the debris pool
depth has decreased to a critical value, gas blowthrough occurs and two-phase ejection of debris
from the RPV begins. The exit quality of the two-phase discharge is modeled, and a gas flow area
is passed to the CONTAIN flow solver at each timestep. As in single-phase discharge, debris exiting
the RPV during two-phase discharge is removed from the trapped debris bin in the RPV cell and
placed in the cavity cell trapped debris bin.
After gas blowthrough has occurred in the RPV cell, entrainment of debris from the trapped debris
bin in the cavity cell is permitted. The rate of entrainment is calculated from a user-selected
correlation, and is based on transient conditions in the cavity cell. Entrained debris is removed from
the trapped debris bin and placed in the cell atmosphere in the appropriate multifield airborne debris
bins. The size distribution of the airborne debris maybe either user-specified or determined from
a Weber breakup model. The airborne debris in the cavity cell may exit the cell or be trapped and
returned to the trapped debris bin, where it might be re-entrained during subsequent timesteps.
The user may also speci~ that a specific fraction of the debris initially in the RPV cell be entrained
in the cavity cell, either by selecting a specific value or by invoking a specific model to predict an
entrained fraction. In this case, the code employs the user-selected entrainment rate model to
estimate the entrainment rate over the duration of the RPV blowdown. The entrainment rate is then
modified so that the code will produce the specified total fraction of debris dispersed from the cavity.
The user must specify the conditions in the cavity cell that will be used to calculate both the
entrained fraction and time-dependent entrainment rate. With this option, there is no feedback
between the entrainment rate and cavity conditions as the calculation progresses; the entrainment rate
is based solely on the cavity conditions provided by the user.
The original references for all of the RPV and cavity models discussed in this document have been
cited in the appropriate places and are provided in the References. However, for guidance on the
development and use of the various entrainment rate and entrained fraction models, it is
Rev O 618 6/30/97