Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.
Behavior of the corium pool in the lower head is still a
critical issue in understanding of Pressurized Water Reactor
(PWR) core meltdown accidents. One of the key parameter for
assessing the vessel mechanical strength is the resulting heat
flux at the pool-vessel interface. A number of studies [1]-[3]
have already been performed to pursue the understanding of a
severe accident with core melting, its course, major critical
phases and timing and the influence of these processes on the
accident progression. Uncertainties in modeling these
phenomena and in the application to reactor scale will
undoubtedly persist. These include e.g. formation and growth
of the in-core melt pool, relocation of molten material after the
failure of the surrounding crust, characteristics of corium
arrival in residual water in the lower head, corium
stratifications in the lower head after the debris re-melting [4].
These phenomena have a strong impact on a potential
termination of a severe accident.
The main objective of the LIVE program [5] at Karlsruhe
Institute of Technology (KIT) is to study the core melt
phenomena both experimentally in large-scale 3D geometry
and in supporting separate-effects tests, and analytically using
CFD codes in order to provide a reasonable estimate of the
remaining uncertainty band under the aspect of safety
assessment. Within the LIVE experimental program several
tests have been performed with water and with non-eutectic
melts (mixture of KNO3 and NaNO3) as simulant fluids. The
results of these experiments, performed in nearly adiabatic and
in isothermal conditions, allow a direct comparison with
findings obtained earlier in other experimental programs
(SIMECO, ACOPO, BALI, etc.) and will be used for the
assessment of the correlations derived for the molten pool
behavior.
The information obtained from the LIVE experiments
includes heat flux distribution through the reactor pressure
vessel wall in transient and steady state conditions, crust
growth velocity and dependence of the crust formation on the
heat flux distribution through the vessel wall. Supporting posttest
analysis contributes to characterization of solidification
processes of binary non-eutectic melts. Complimentary to other
international programs with real corium melts, the results of the
LIVE activities provide data for a better understanding of incore
corium pool behavior. The experimental results are being
used for development of mechanistic models to describe the incore
molten pool behavior and their implementation in the
severe accident codes like ASTEC.
The paper summarizes the objectives of the LIVE program
and presents the main results obtained in the LIVE experiments
up to now.
