Civil Engineering Reference
In-Depth Information
containment. Nevertheless hydrogen recombiners in the containment are useful
for preventing or mitigating some accident sequences.
- Core melt down after a break of a pipe of the residual heat removal system in the
annulus of the containment system or core melt down after an uncontrolled large
scale steam generator tube break can be avoided by proper design.
- Containment failure after core melt down under high primary coolant pressure,
as assumed in WASH-1400 and the German risk study, can be avoided by
manual or automatic opening of pressure relief valves (ADS systems of
Chap.
3
) or—as a limiting case—reinforced anchorage of the pressure vessel
cover.
- Core melting through the bottom part of the reactor pressure vessel can be
counteracted by flooding the reactor pressure vessel on the outside with water
(severe accident measure). Similar results can be obtained by installing a molten
core spreading and cooling device (core catcher). Appropriate core catcher
designs were developed after research.
- A rising steam pressure in the inner containment after a core melt can be avoided
by water spray systems.
- A mechanically intact double containment, where the inner containment is either
a steel containment or a concrete containment with an inner steel liner, having a
leak rate of 0.3-1 % per day after a core melt accident and where the leaking
radioactive gases and aerosols are passed from the annulus through aerosol
filters to a stack can fulfill the requirements of the KHE safety concept. In this
case the contamination by radioactive fission products is essentially limited to
the site of the reactor plant. No evacuation of the population is necessary.
In summary all most severe accident consequences found in the WASH-1400 or
the German risk study can be either controlled or eliminated or managed in future
LWRs by appropriate design measures. Examples for such designs are EPR and
KERENA (SWR-1000). Concluding remarks compare the KHE safety concept with
the safety concept of presently operating reactors and more recent designs
for LWRs.
10.1
Introduction
operating about 370 nuclear reactors in 2012) in the range of damage (deaths) of
similar magnitude as other technical or power generation systems. Yet, the severe
- large areas were contaminated with Cs-134 and Cs-137 such that food produc-
tion either had to be restricted for long periods of time (the half-life of Cs-134 is
~2 years and of Cs-137 is ~30 years) or, where contamination was lower, must
be monitored for radioactivity over long time;
- the population of large areas had to be evacuated or even to be resettled.
