Future plants extreme and practicable solutions

The ability to choose between extreme solutions and simpler, more easily implemented, solutions is hindered by the uncertainty still present in our knowledge of some key phenomena in the field of severe accidents listed in the preceding section. The practical feasibility of the studied solutions must always take account of inherent drawbacks compromising safety itself (in many cases a safety provision adopted with certain situations in mind is detrimental in other conditions) and cost (which, if excessive, could put a plant out of the market). 

Appendix 15 on Safety Cage shows an example of dimensioning a solution of the extreme t5Tte, with the objective of listing the orders of magnitude of the dimensions and of the provisions required. 

In order to give an idea of the solutions suggested in this study, the following summary is given which 

A first cornerstone of the defence strategy, already incorporated in the AP600 design, is the voluntary depressurization of the primary system in case of the danger of inadequate core cooling. A feature of this type was proposed and thoroughly studied for the first time at the start of the 1980s for pressurized reactors (see Appendix 10 on Primary Depressurization Systems). 

The primary depressurization eliminates at the source, all the severe accident sequences with a pressurized primary system (i.e. direct containment heating, destructive reaction forces due to perforation of the vessel, etc.). Moreover, in case of malfunction of the high pressure cooling systems, it allows the cooling of the core by intermediate pressure accumulators and low pressure systems. 

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