The fundamental elements of Safety Analysis are the models
that simulate the response of the plant.
They are going to receive inputs from three different themes.
The first one is the event itself that are included, all of them,
in the Design Basis Events.
Here we have transients and accidents.
The second one is or are the initial conditions.
Let's say power level,
variables controlled by the different control systems,
outside temperature, wherever or whatever.
And finally, what we call "The Single Failure".
Here we have, single failures coming from operator actions
or the equipment performance.
If damage limits are not met,
it is necessary to modify some of the inputs.
And you use them as feedback.
The "impossible" event can happen.
For example, failure of the bottom of the reactor vessel.
The initial conditions can be made softer,
by reducing the linear power in the fuel pods.
Also, other things that we can do
are to improve the procedures or the training of operators
and teams who work in the plant. Or we can use new equipment
that can be incorporated to compensate that equipment
that has been assumed to fail.
It's important to draw attention to the limitations
of the use of the single error or single failure.
When being aware of those limitations, everything that is done,
is done to ensure that the operation has no errors,
and that the equipment is going to be operable.
If the damage limits are met,
then, it's essential to establish operating requirements.
And the requirements are called "Technical Specifications".
And they are going to guarantee compliance during operation.
It is important to show that, basically,
the initial analysis did not take into account
neither the organizational, nor the cultural aspects.
That leads us to say that single failure or single error hypothesis
can be inadequate.
Also, experience shows that there are many events
where there are multiple failures or errors.
What would have more positive effects in safety?
It's s question that you can ask.
We can say that the use of resources in improving analysis,
or analysis models, to deal with several errors or failures,
could be enough. Then, it could be necessary
to carry out thousands of analysis.
Or we can use the resources in improving the training
of the operating personnel and the reliability of the equipment.
That question, you can answer it in the forum,
and we will discuss it later.