Civil Engineering Reference
In-Depth Information
Fig. 10.5
Theoretical model for steam explosion with premixing, fragmentation (trigger pulse)
and spontaneous evaporation (expansion zone) [
17
,
22
]
However, this ideal concept of the theoretical chain of events in a steam
explosion will only occur in a random process in experiments including dissipation
effects. Moreover, the core melt will never contact water as a bulk substance
because melt-through processes will always proceed in an incoherent manner in
terms of time and location [
27
].
10.3.1.3 Steam Explosion in the Reactor Pressure Vessel
Accounting for the above described discrepancies between experimental results and
the ideal theoretical models, it is now
postulated
that the molten reactor core
melting through the gridplate and falling as a molten jet into the water-filled region
below the gridplate would give rise to a steam explosion producing a maximum
amount of stress acting on the reactor head and its bolts. WASH-1400 [
8
] had
assumed that a steam explosion would cause the head of the reactor vessel to be
blown off and penetrate the outer reactor containment as a bullet (
-mode failure).
This maximum accident was the subject of many research programs between 1980
and 2010.
These are the most important findings of the associated Karlsruhe Safety
Research Program [
22
,
29
]:
α
- Studies of an assumed core meltdown accident by means of the SCADP/RELAP
[
30
,
31
] or MELCOR [
32
] computer codes led to a molten core mass of 110 ton
at a temperature of approx. 3,000 K and a pressure of 0.25 MPa above the
baseplate (the 110 ton corresponding to 85 % of the core mass of a KWU-1300
PWR). Additional studies using the MC3D [
33
,
34
] and MATTINA [
35
] com-
puter codes, which had been verified against experiments, showed that the core
