Coolability of Ex-Vessel Corium – Quenching Melt Layers

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European Utility Requirements” on melt stabilisation for future reactors:

“…The Designer shall prove that corium would relocate in the reactor cavity in a coolable  configuration. As an alternative the Designer may include a Corium Collecting and Cooling  Device (CCCD), usually called a core-catcher, provided with a corium cooling system.

This system shall not have any active component inside the containment.“


The Problem of Coolability

Requirements for ex-vessel melt cooling

•No penetration of basement
•Safe inclusion of corium and fission products
•Safe extraction of decay heat, short-  and long-term

To be considered:
different failure modes of RPV, various melt compositions,  and release in different pours

Exclusion of high pressure RPV failure by depressurization of primary system:  Collection of melt in the reactor cavity
or in the spreading compartment


Ex-vessel corium

•Up to:    120 t oxide (UO2, ZrO2, …)
  80 t metal (steel, Zr, …)
•Melt heights:
-up to 90 cm in reactor cavity of 6 m Æ
-some 40 cm for larger spreading areas
(mainly future power plants)
•Initial temperatures up  to 3000 K
•Decay heat in the melt:
-30 MW initially
-10 MW after days

 


Melt Cooling

 

•   Passive operation
•   Safe heat removal
•   Retention of fission products
•   Stability versus mechanical,
thermal, and chemical attack
•   No adverse effects like:
– Steam explosion
– Large H2 release
 No interference with normal
plant operation and design
basis accidents
•   Low cost
•   Transparent operation (public
acceptance)
•   Licensing


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