Civil Engineering Reference
In-Depth Information
Table 6.6
Core melt frequencies and large release frequencies per reactor year for KWU-PWR-
1,300, AP1000 and EPR [
8
,
9
,
23
,
24
]
KWU-
PWR-1,300
[
8
,
9
]
AP1000
[
23
]
EPR 1,600
[
24
]
10
6a
10
7
10
8
Core melt frequency per
reactor year
Internal events
8.2
4.2
8.4
10
6
10
7
10
7
External events
3
2.4
6.4
10
8
No evacuation
No re-housing
No sheltering
a
Can be decreased by about one order of magnitude by application of severe accident management
measures
About 10
7
Large radioactivity release
frequency per reactor
year
Core melt down
followed by con-
tainment failure
1.8
Table 6.7
Frequency of initiating events (BWR-1,300) [
7
]
Initiating event Frequency of initiating event per year
Loss of electrical power supply from grid 0.04
Loss of main heat sink and loss of main feed-water supply 0.3
Inadvertent opening of turbine valve or by-pass valve
0.2
Failure to close a safety and relief valve
0.1
<
10
7
ATWS with loss of main heat sink
Table 6.8
Expected frequencies for core melt down (German Reactor Risk Study [
7
]) for the
BWR-1,300 (Gundremmingen) described in Sect.
3.2.1
Frequency per
year
Initiating event
Small leak (5-150 cm
2
) in main steam line (outside
containment)
10
7
Loss of coolant
2.0
Small leak (5-150 cm
2
) in main steam line (inside
containment)
10
7
4.0
Small leak (5-150 cm
2
) in feed water line
10
7
3.0
10
6
ATWS
Loss of main heat sink, no scram
10
6
Operational
transients
Loss of electrical power from grid
3.2
10
6
Loss of main feedwater supply
5.5
10
5
Loss of main heat sink
2.0
10
5
Loss of main heat sink and loss of main feedwater
1.5
10
6
Failure to close safety and relief valve
4.1
10
5
Sum total
5
Table
6.8
lists the frequencies of core melt per year for the most important
accident sequences which can result in core meltdown, such as
- loss-of-coolant accident,
- anticipated transients without scram (ATWS),
- operational transients.
