5.1 Overview

Compared with designing conventional structures, designing system components and structural systems for nuclear power plants is subject to the maximum safety require­ments, which means safety systems for managing incidents must be designed to withstand extraordinary actions at safety levels 3 and 4 (cf. Section 2, Table 2.2 and DIN 25 449 [15]). These rare and extremely rare actions are divided into internal and external actions.

A summary of internal and external actions appears in Table 5.1. Typically, internal factors are induced by:

— leaks or fractures in pressurised pipes (e. g. jet loads and differential pressures)

— problems and incidents while handling fuel elements (e. g. dropped load scenarios)

— internal plant events such as fire, explosion or flood (e. g. temperature or pressure differences).

External actions break down into:

— natural actions which occur extremely rarely, such as 1 in 100,000 year earthquakes which occur according to KTA 2201.1 [37] and 1 in 10,000 year flood effects to KTA 2207 [23]

— man-made actions due to specified airplane crash and explosion pressure wave.