Civil Engineering Reference
In-Depth Information
and in the German Risk Study Phase A
[
10
]
can be considered impossible on
grounds of physics.
A demonstration originally proposed in USA [
45
,
46
] of the non-existence of the
α
-mode failure of the reactor containment was brought to a scientifically successful
conclusion by these detailed Karlsruhe experiments and theoretical analyses.
10.3.2 Hydrogen Detonation
WASH-1400 [
9
] and the German Risk Study Phase A [
10
] postulated conserva-
tively, with little detailed scientific and technical analysis, that a large-volume
hydrogen detonation in the outer reactor containment would cause the containment
to rupture and radioactivity to be released to the environment. This was doubted
after some first theoretical estimates by KHE [
5
-
7
]. Appropriate containment
design concepts were proposed which would be able to withstand a very conserva-
tively assumed large-volume hydrogen detonation [
7
,
47
]. This demonstrated that
containment design concepts can be conceived which can resist to such large-
volume hydrogen detonations.
These considerations were followed by many years of theoretical code develop-
ment, such as GASFLOW [
48
], DET-3D [
49
], and COM3D [
50
] and experimental
investigations, such as the RUT experiments in Russia [
51
-
55
]. The conclusion can
be drawn from these theoretical and experimental efforts that a large-volume
hydrogen detonation following a core meltdown accident can be managed by the
reactor containment of existing modern PWRs, like the Konvoi-PWRs of Kraftwerk
Union [
56
].
As a first severe accident management measure, PWRs were equipped with
so-called passive autocatalytic recombiners [
57
] able to reduce slow release-rates
of hydrogen release of approx. 0.5 kg H
2
/s during core meltdown accidents.
However, also core meltdown accidents must be accounted for with higher rates
of hydrogen release of up to 7 kg H
2
/s. The related H
2
-steam-air mixtures produced
are capable of detonating [
55
,
56
].
10.3.2.1 Load Carrying Capacity of a KWU-1,300 PWR Containment
in a Hydrogen Detonation
Analysis of the release of hydrogen in a core meltdown accident initiated by a small
leak in the primary system will be described here as an example of the kind of
analysis performed [
56
]. A small leak in the primary system with a delayed pressure
drop in the secondary steam system results in water/steam and hydrogen release
into the containment with a maximum release rate of 7 kg H
2
/s over a certain period
of time during the accident sequence [
56
]. The hydrogen is produced during the
accident sequence by overheating of the Zircaloy claddings above 1,300
C and
their chemical reaction with steam according to
