Civil Engineering Reference
In-Depth Information
valid anymore for future LWR designs following the KHE safety concept, e.g. EPR
and SWR-1000 (KERENA).
With the above new research results the curves of Fig.
10.1
shrink to very
small damage consequences close to the ordinate
[
8
]
. Core melt down accidents
will no longer lead to large scale contamination of areas outside the reactor
plant. Figure
10.2
shrinks to areas which belong to the vicinity of the nuclear
plant containment only.
While these statements apply to the safety concept of future LWRs, e.g. EPR or
SWR-1,000 (KERENA), they also will apply to a very large extent to the new LWR
designs in the USA (AP1000) and Japan (ABWR-II) described in Chap.
3
.
The above statements, however, apply only partially to the majority of LWRs
operating around 2013 in the world. Many of these LWRs were built from 1970 on
and are constructed on safety design concepts and principles as they were analyzed
in WASH-1400 [
9
] and the German Safety Studies Phase A [
10
] and Phase B [
64
].
10.3.9.1 Applicability of the Above New Research Results to Presently
Operating LWRs and Future
The research results of Sect.
10.3.1
(steam explosion) can—after thorough exam-
ination—also be applicable to other PWR pressure vessels, if their design is similar
to the design of KWU-1,300 pressure vessels (experiments described in
Sects.
10.3.1.3
and
10.3.1.4
were only performed for the KWU-1,300 pressure
vessels). Results for hydrogen detonations (Sect.
10.3.2
) were only reported for
the KWU-1,300 PWR containment design up to now (spherical steel containment
56 m inner diameter and 5.8 cm thickness). Similar conclusions can certainly also
be drawn after appropriate analysis for the EPR containment during still ongoing
licensing processes.
However, most of the new PWR designs—described in Chap.
3
—and of pres-
ently operating PWRs appear to rely on the installation of hydrogen recombiners
only. This is not sufficient as reported in Sect.
10.3.2
for the KWU-PWR. There
exist accident sequences, where despite the installation of hydrogen recombiners,
large scale hydrogen detonations can occur, because the hydrogen production rate is
too high. Therefore, this case must be examined for each PWR design separately.
Most of the presently operating BWRs have inner containments which are
inertized by nitrogen to avoid hydrogen ignition. They are also equipped with
hydrogen recombiners to avoid pressure build up by hydrogen. In case of pressure
buildup above the limiting pressure of the inner containment exventing filters could
relieve the containment pressure.
If the reactor cavity of PWRs, e.g. AP600 or AP1000 can be flooded in case of
threatening core melting then a core catcher can be avoided. If the flooding of the
reactor pressure vessel with water on the outside is not considered sufficient and the
decision is taken to equip a new PWR with a core catcher, then research is necessary
for such a new core catcher design [
95
,
96
].
