Civil Engineering Reference
In-Depth Information
H2
15 Vol%
Vapor
40 Vol%
Vapor
40 Vol%
Fig. 10.7
Hydrogen-Steam-air mixtures in the outer containment (two different side views) of a
German PWR after an assumed core melt accident at the time of 7,950 s after begin of the accident
sequence [
56
]
Zr
þ
2H
2
O
!
ZrO
2
þ
2H
2
:
This hydrogen release is accompanied by steam release. The aggregate volume
of hydrogen released eventually into the outer containment then corresponds
roughly 855 kg H
2
[
56
]. In the further course of the accident sequence, the hydrogen
concentration in the air and steam mixture exceeds 15 vol% in parts of the reactor
containment. The spatial hydrogen distribution and the hydrogen concentration
within the mixture of air, steam, and hydrogen within the outer containment is
shown for the time of 7,950 s after begin of the accident sequence in Fig.
10.7
.This
mixture of air and steam with 550 kg of H
2
, which is able to detonate, can be
ignited, e.g., by an overloaded hydrogen recombiner. This was demonstrated in the
RUT experiments [
55
,
56
]. The calculations with the three-dimensional-time-
dependent detonation code DET3D [
49
], which also takes into account shock
wave reflections within the reactor containment, resulted in short time pressure
peaks of 2-5 MPa and impulse-type loads of 10-30 kPa·s. When the transient phase
of the detonation is over, there remains a quasi-steady-state pressure of approx.
0.58 MPa and temperatures around 1,064 K over hours. This does not jeopardize
containment integrity of the Konvoi-PWRs of Kraftwerk Union in Germany.
10.3.2.2 Structural Dynamics Response of the Spherical Steel
Containment
The results of the detonation with respect to the impulse and pressures acting on the
containment wall were used for analyses with the ABAQUS [
58
] and PLEXUS [
59
]
codes. Figure
10.8
shows the deformations arising in the spherical outer steel
containment of the reactor in the steel shell (magnified by a factor of 5) [
56
]. The
largest plastic strains of approx. 4.6 % occur in the vicinity of the materials transfer
lock and close to the upper pole (2.4 %). None of these plastic strains will cause the
steel shell of the spherical reactor containment to fail [
60
-
62
].
