Civil Engineering Reference
In-Depth Information
- Safe containment structures, i.e. protection from malfunction-induced releases
of radioactivity; limitation of radiation exposure to workers inside the reactor
containment and of the population outside.
5.3 Safety Concept of Nuclear Reactor Plants
The safety concept of nuclear reactor plants is based on multiple containment
structures around the radioactive materials in the reactor core (multi-barrier con-
cept) as well as on engineered safeguards components and measures ensuring such
containment.
5.3.1 Containment by Radioactivity Enclosures
The radioactive substances are enclosed in several radioactivity enclosures (see also
Chap.
3
). In a German PWR shown by way of example (Fig.
5.1
) these are
- the oxide crystal lattice of the ceramic fuel pellets (UO
2
or mixed UO
2
(PuO
2
)
oxide),
- the zircaloy cladding tubes of the fuel (welded gastight),
- the reactor pressure vessel with the closed cooling system,
- the gastight and pressure resistant steel containment (in other reactor designs a
prestressed concrete containment) enclosing the cooling systems, and the con-
crete structures shielding against radiation,
- the outer shell of steel-reinforced concrete. It has a limited sealing function. It
also protects the plant against external impacts.
5.3.2 Multiple Level Safety Principle
In addition, the safety of a nuclear power plant is ensured by multiple levels of
safety superimposed upon each other (safety concept staggered in depth) (Fig.
5.2
).
5.3.2.1 First Safety Level: Reactor Physics Design, Basic Safety,
Quality Assurance
Nuclear reactor plants must be designed to be safe in terms of reactor physics. This
includes, e.g., safety coefficients, such as the negative power coefficient, the
negative Doppler coefficient, the negative coolant temperature or void coefficient,
and the proper setting of the range of the effective multiplication constant k
eff
for
