Our focus can be explained in three different points.
First, we can say that people tend to
perform the duties successfully, when the reasons to do the tasks
are clear and shared by everybody involved in the job.
To do this, safety has developed what we call safety analysis.
In the nuclear sector, it is essential
to meet each and every one of the safety requirements.
The safety analysis is performed
in a set of simplifications and limitations that everyone must know.
Those requirements are based on those simplifications and limitations
and they are quite rigorous and clear.
And finally, we must be reminded
that there are a redundancy and variety
of barriers and levels of safety.
So a breach of a specific requirement
will not generate a problem immediately.
This can generate the feeling
that those barriers are really "unnecessary".
When this is not true.
The multiplicity of safety features like barriers, procedures,
behaviors and so on, is an essential part of the safety culture.
So now we are going to expand our knowledge
in the defense-in-depth concept.
That we have already mentioned during the introduction to this NOOC.
So a question arises: What is the defense-in-depth?
In general, defense-in-depth is a concept used in many fields
from computing, to nuclear, even oil and gas industry use it.
It is also called the castle approach.
Because it is based on multiple layers of safety and security controls,
also known as barriers or defenses
that are placed all around the system we want to protect.
So we can have from moats, to towers, to walls and of course the workers
who are the bearers of the safety culture.
And we have a complete castle.
But based on these ideas,
there have been multiple industries
that have adapted it to their needs.
In the early 60s of the last century,
it started to be used also in the nuclear industry.
So it was used in the context of ensuring the nuclear reactor safety,
and it was based on the concept
that there was a lack of knowledge of the nuclear reactor operations
and the consequences of potential accidents.
So basically,
while both experience with the operation of nuclear reactor
and the knowledge base of potential
and actual consequences have increased since then,
the concept continues to be highly relevant today.
As we mentioned before, the idea is to create multiple barriers,
independent and redundant.
Creating different layers of protection and response
to challenges from minor to major.
An example of this multiplicity and redundancy
are the protection systems.
The new PWR (Pressure Water Reactor) designs come with many protection systems
and backup systems.
They acted with different set-points, variables,
and even their hardware is diverse to prevent failure
of the safety actuations.
Now we are going to see again the Swiss cheese model
and expand our knowledge.