Civil Engineering Reference
In-Depth Information
Fig. 10.17
Exventing filter of a German PWR for pressure relief in the outer containment [
78
]
filter is achieved. Therefore, all German LWRs were equipped after the German
Reactor Safety Study Phase B [
64
] with so-called aerosol ex-venting filters having a
filter efficiency of 99.9 % [
78
,
83
,
84
]. The pressure will be relieved by opening a
valve to this exventing filter and radioactive gases and radioactive aerosols are
emitted through this filter (Fig.
10.17
).
During pressure buildup over several days, however, most of the radioactive
aerosols will have deposited already in the outer reactor containment by sedimen-
tation and thermophoresis etc.. This decreases the amount of radioactive aerosols
released to the environment by orders of magnitude [
78
].
The Role of Exventing Filters and of Double Containment with Low
Leak Rate
The efficiency of exventing filters can be demonstrated in Fig.
10.18
. In this case
the exventing filter would be opened 84 h after the initiation of the core melt
accident sequence [
85
]. The radioactive aerosols would be retained with a certain
filter efficiency within the filter. Radioactivity passing through would be released
through a 120 m high stack into the environment. Figure
10.18
shows the 70 year
committed effective dose in mSv for individuals living in certain distances from the
nuclear plant. The results include 95 % of the possible weather conditions in the
surroundings of the reactor plant. The effective doses are calculated from all
exposure pathways (inhalation, ingestion, skyshine, groundshine) (Chap.
4
).
