Parametric Studies on Containment Thermal Hydraulic Loads during high pressure Melt Ejection in a BWR
I. Lindholm, A. Silde
The containment thermal hydraulic loads during high pressure melt ejection in a Nordic
BWR are studied parametrically with the CONTAIN and the MELCOR codes. The work
is part of the Nordic RAK-2 project.
The containment analyses were divided into two categories according to composition of
the discharged debris: metallic and oxidic debris cases. In the base case with highly
metallic debris, all sources from the reactor coolant system to the containment were
based on the MELCORBH calculation. In the base case with the oxidic debris, the
source data was specified assuming that - 15 % of the whole core material inventory
and 34 O00 kg of saturated water was discharged from the reactor pressure vessel (RPV)
during 30 seconds. In this case, the debris consisted mostly of oxides.
The highest predicted containment pressure peaks were about 8.5 bar. In the scenarios
with highly metallic debris source, very high gas temperature of about 1900 K was
predicted in the pedestal, and about 1400 K in the upper drywell. The calculations with
metallic debris were sensitive to model parameters, like the particle size and the
parameters, which Control the chemical reaction kinetics.
In the scenarios with oxidic debris source, the predicted pressure peaks were comparable
to the cases with the metallic debris source. The maximum gas temperatures (about 450-
500 K) in the containment were, however, significantly lower than in the respective
metallic debris case. The temperatures were also insensitive to parametric variations.
In addition, one analysis was performed with the MELCOR code for benchmarking of
the MELCOR capabilities against the more detailed CONTAIN code.
The calculations showed that leaktightness of the containment penetrations could be
jeopardized due to high temperature loads, if a high pressure melt ejection occurred
during a severe accident. Another consequence would be an early containment venting.