Code Manual for CONTAIN 2.0 - Federation of American Scientists

Co-Eiected Primarv Svstem Water. Water co-ejected from the RPV with the melt raises many of the
same issues as co-dispersed cavity water, but there are also important differences. Co-ejected water
accompanies and/or follows the melt, and therefore cannot be dispersed from the cavity as a slug in
advance of the melt. Instead, much of the water may follow the dispersal of the debris. RPV water
will partially flash to steam upon depressurization, and the remaining water is likely to be highly
fragmented. Hence the situation may correspond more closely to the assumptions of the CONTAIN
model than is the case for scenarios involving large amounts of co-dispersed cavity water.
For scenarios involving co-ejected water, a key uncertainty is the time interval over which debris is
dispersed from the cavity. The only available “standard prescription” is to use Equation (13-4) to
estimate the debris dispersal rate and then introduce the water source in parallel, as in the case of codispersed
cavity water. However, there are several questionable features of this approach. First, we
note that it maybe more reasonable to estimate the rate at which water can be ejected from the RPV
in a side calculation and use this rate to define the water source. In addition, Equation (13-4) is
based upon experiments in which debris dispersal was driven by steam and its applicability to
dispersal by flashing primary system water is doubtful. It maybe noted that Equation (13-4) may
be shown to be consistent with the assumption that debris dispersal rates vary as rn~n,where rn~is
the steam blowdown rate (kg/s). If we assume that heat transfer from the debris vaporizes all the
RPV water ejected during the period of active debris dispersal, the steam flow rate in the cavity will
be approximately equal to the rate of water ejection from the vessel, r&. One might, therefore,
estimate the dispersal time, ~,,, for the water-driven dispersal from
t
w,e
=
(
1/2
m;
t;,e —
rnw
(13-6)
Here, t~,~and ~’ are respectively the dispersal time ~ estimated from Equation (13-3) and the steam
blowdown rate for a steam-driven event with the same RPV pressure as the actual scenario of
interest. Many factors potentially affecting dispersal rates have been neglected here, and this
approach should be used with caution and should be supplemented with sensitivity calculations.
The debris dispersal time for events involving co-ejected water should be considered quite uncertain.
It is therefore recommended that users investigate sensitivity of the results to the assumed debris
dispersal rate in calculations involving co-ejected RPV water.
Water on the Basement Floor. In most if not all accidents, there will be water on the basement floor.
Available evidence indicates that this water does not have a large effect upon DCH. For example,
the SNL/IET (Zion) experimental series included two pairs of counteqmrt tests with and without
water on the basement floor. [Al194] Comparisons of containment pressure response with the
temperature response indicated that the basement water was not vaporized on DCH time scales to
any large extent. Measured AP values and hydrogen production with and without the water were the
same to within 10% and 20Y0,respectively, maybe within experiment replication uncertainties. In
the CONTAIN analyses of the cases with basement water, the water was not included and the
analyses revealed no discrepancies that might reasonably be attributed to the neglect of the water.
Rev. O 13-45 6/30/97