Civil Engineering Reference
In-Depth Information
3.2.4 Containment Building
The containment building has the function to contain releases of airborne radioac-
tivity in case of accidental conditions and shield the reactor core and cooling
systems against external impacts. The containment design chosen by the manufac-
turers is either an inner steel containment with an outer prestressed concrete shell
(KWU-PWR, AP1000) or a single (US-APWR) or a double prestressed concrete
structure (EPR) with internal liner.
In case of the Kraftwerk Union PWR (Table
3.1
), the reactor pressure vessel, the
coolant pumps, steam generators, emergency and afterheat cooling systems as well
as the vault for fresh and spent fuel elements are arranged within the reactor
building, which is enclosed in a spherical double containment (Figs.
3.8
and
3.9
).
The double containment is made up of the inner steel containment and an outer
concrete shield which is 1.8 m thick (Fig.
3.8
).
The inner steel containment is held at a lower pressure than the atmospheric
pressure. In this way only leakage from the outside to the interior of the contain-
ment is possible during normal operation. The spherical inner steel containment has
a diameter of approx. 56 m and is designed to an internal pressure of about 0.5 MPa.
If the internal design pressure of 0.5 MPa is exceeded after a core melt accident the
containment atmosphere could be slowly exhausted through a valve and special
aerosol filters which retain 99.9 % of the radioactive aerosols. Penetrations of the
piping through the containment are equipped with vented double (Fig.
3.9
) bellows
and can be checked for leaks. The outer steel reinforced concrete shield protects the
reactor against external impacts and shields the environment against radiation
exposure in case of accidents. External impacts which are considered as a design
basis for the containment are earthquakes, floods, tornados, airplane crashes, and
pressure waves generated by chemical explosions.
The EPR containment (Table
3.1
) is a cylindrical double containment of
prestressed concrete. The inner containment has a 6 mm thick steel liner. The
double concrete shield is 1.3 m (inner containment) and 1.3 m (outer containment)
or in total 2.6 m thick and has a diameter of about 75 m and a height of about 60 m
(Figs.
3.10
and
3.11
). It protects the inner part of the containment against external
events as in case of the spherical containment of the KWU-PWR. The upper part of
the inner containment houses sprinkler systems supplied with water by the contain-
ment heat removal system (CHRS) for ultimate heat removal in case of a severe
accident. Below the reactor pressure vessel, a so-called molten core spreading area
with special cooling systems is located which can cool the hot core masses in case
of a core melt accident (Figs.
3.10
and
3.11
). Leak tightness of the inner contain-
ment and filter systems guarantee extremely low releases of radioactivity to the
environment, even in case of severe accidents. Relocation or evacuation of the
The inner containment of modern European PWRs is required to withstand the
pressure resulting from large scale hydrogen combustion processes which might
