Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
Vessel melt through
If the core cannot be reflooded, its collapse, together with that of the molten structures,
will cause the residual water at the bottom of the vessel to vaporize and, more or less
rapidly (mainly depending on the value of the reactor coolant pressure), the vessel to
rupture. (See Fig. 16.4.5.) Several rupture mechanisms are possible: creep rupture,
penetration tube ejection.
Energy (J)
10 12
10 11
10 10
10 9
10 8
10 7
10 6
10 5
10 4
0 100 200 300 400
Time (10 5 Sec.)
❙ 924 ❙
Inter. Energy
HT to pool
Fig. 16.4.5. Heat transfer from the lower head to water pool following a SBLOCA without low
pressure cold leg recirculation for a Korean PWR
16.4.3.2. Ex‐Vessel Accident Progression [3]
If the reactor coolant system at the timing of the vessel breach is at high pressure, the
corium may be violently ejected, which could lead to some scattering of the corium in the
containment (❖ risk of Direct Containment Heating: DCH). If there is water at the
bottom of the reactor pit, an interaction between the corium and the water could occur,
that is MFCI (Molten Fuel Coolant Interaction), which can be more or less violent (❖
risk of steam explosion). Following this interaction, the corium cools and the water