Overview of Requirements and Current Design - The Risks of Nuclear Energy Technology - page 238

Chapter 12
Overview of Requirements and Current
Design
Abstract The possible actions on nuclear power plants caused by different aircraft
crash scenarios are described. To reduce the remaining risks of a possible crash on
the safety-relevant buildings special requirements have to be taken into account
during the design. Three groups of German nuclear power plants can be distin-
guished with respect to their resistance against the external event of an airplane
crash according to the corresponding start of construction. The development of the
structural design is described, from the first generation up to the current design.
12.1 Possible Actions
A differentiation must be made between an accidental and a deliberate forced
impact when considering a postulated aircraft impact. The impact scenarios asso-
ciated therewith have to be viewed in a differentiated way. This is considered in
more detail in Chap. 13 .
Before the requirements for the design are specified, the possible actions against
which the facility must be protected are described.
Special emphasis lies on the mechanical actions. The impact of an aircraft or
wreckage on the outer shell of the building creates an impact force of a very short
duration. In the first load phase the hit structure is only locally loaded. Depending
on the size, mass and speed of the projectile in comparison to the mass and strength
of the hit structure, the structural element will be subjected to shear, be penetrated
or even perforated. To prevent the penetration of the projectile into the structure, the
local resistance to punching shear is decisive. In this phase concrete fragments can
spall off (scabbing) the rearward side of the wall, which can act as projectiles,
endangering the mechanical components behind it.
In a second phase, the structure is globally involved in the load transfer and
excited to vibration. The structural elements of the building deform and experience
stress. Depending on the design, this can result in permanent deformations and
cracking.