Civil Engineering Reference
In-Depth Information
Table 6.9
Core melt frequencies per reactor year for KWU-BWR-1,300, ABWR, ABWR-II and
SWR-1000 (KERENA) [
8
,
9
,
23
,
24
]
KWU-BWR-
1,300 [
7
]
ABWR
[
25
]
ABWR-II
[
25
]
KERENA
[
26
,
27
]
10
5
*
a
10
7
10
8
10
7
Core melt frequen-
cies
[year]
Internal
events
5
1.6
4.5
<
10
6
External
events
Not given in literature
a
Can be decreased to 4.4
10
6
per year by application of accident management measures
While the frequencies of occurrence of loss-of-coolant and ATWS accident
sequences are in the range of 10
6
per reactor year, the frequencies of occur-
rence—initiated by operational transients—are in the range of 10
5
per reactor
year. The frequencies of occurrence of core melts initiated by fire or earthquake are
of a similar order of magnitude as in a German PWR, i.e. in the range of 10
6
per
reactor year. This leads to a total frequency per reactor year of 5
10
5
[
7
].
Accident management measures can reduce the frequency of occurrence per
reactor year by roughly one order of magnitude to 4.4
10
6
[
7
].
Such additional accident management measures [
21
,
22
] are e.g.
- primary pressure relief by opening of the pressure relief valves and steam
blowdown to the water pools (condensation pool) of the pressure/suppression
chamber
- additional emergency electrical power and water supply (see Sect.
6.6.2
)
6.7.1 Core Melt Frequencies for KWU-BWR-1300, ABWR,
ABWR-II and SWR-1000 (KERENA)
The core melt frequencies per reactor year for other BWRs, e.g. ABWR, ABWR-II
and KERENA are listed in Table
6.9
. Again, as in case of more recent
PWR-designs, the more recent BWR-designs, as e.g. ABWR-II and SWR-1000
(KERENA) have lower core melt frequencies per reactor year.
6.8 Release of Radioactivity as a Consequence of Core
Melt Down
The results in Tables
6.4
,
6.5
and
6.7
can be combined with results obtained from
accident consequence analyses for assumed core meltdown and subsequent con-
tainment failure. This analysis can be simplified by grouping the results into release
categories for accident sequences with the same containment failure mode. In
addition to the frequencies of occurrence, also the schedule of radioactivity release
