ICARE/CATHARE-V2.1 is based on a coupling between ICARE2 V3mod2.0 (best-estimate vessel degradation code developed at IRSN) and CATHARE2 V2.5mod7.1 (best-estimate thermalhydraulics code co-developed by CEA, FRAMATOME-ANP, EDF and IRSN). This second version of the computer code, under development at IRSN, offers new modelling capabilities compared with ICARE/CATHARE-V1.
Particularly, it is possible to simulate the whole vessel with ICARE, and so to have a better estimation of the lower plenum behaviour (fuel coolant interaction, lower head failure) as well as of the upper plenum behaviour. An other important feature is the possibility to compute multi dimensional two-phase flows in the vessel, which gives a better accuracy in case of blockages resulting from material melting and relocation.
The aim of this work is to demonstrate the interest to use ICARE/CATHARE-V2 in the future, instead of ICARE/CATHARE-V1.
The first part of this presentation shows that, without activating the new V2 models (in order to be able to judge two comparable runs), the ICARE/CATHARE-V2 (1D) correctly reproduces the results obtained with ICARE/CATHARE-V1, with an equivalent CPU time.
It can however be underlined that these two simulations have highlighted a non negligible sensitivity of the front end phase to the conditions chosen by the user to account for the accumulator discharge.
In addition, a comparison of ICARE/CATHARE-V2 (1D) versus a standard CATHARE2-V2.5 computation is also be presented, to be considered as a non regression test on the front end phase.
Coming back to the late degradation phase, a sensitivity study (still on 1D simulations) to a “simple” fuel coolant interaction model (just to account for the vaporisation of the remaining water located in the lower plenum at the time of corium slumping from the core) highlighted how the standard ICARE/CATHARE V1 calculations could underestimate the steam flow entering the core during these periods of melt slumping, thus leading to underestimate hydrogen production.
Then, in order to illustrate few of the new V2 modelling improvements, the last part of this presentation is focused on the results obtained with ICARE/CATHARE-V2 (2D) and a preliminary comparison is realised with ICARE/CATHARE-V2 (1D).
This 1D-2D comparison (still under progress) points out in particular the important role (corium retention before the slumping into the lower head) which could be played in the course of the accident by the core support plate.
Moreover, it has to be stressed that the 2-D simulation was successfully performed up to the vessel rupture (stop of the calculation due to the detection of the lower head failure).