Making a summary of what we have seen,
is that what happened at Three Mile Island was
that the pressure relief valve remained open.
In total it had already happened 19 times all over the world
and one time it happened to them.
So, the turbine tripped because a demineralization
of the condenser could happen, which would caused a rise in pressure
and the opening of the Power Operated Relief Valve,
also called PORV,
which in turn causes a reactor trip.
The pressure dropped and the PORV should have closed,
but it was mechanically blocked.
The indication of close, that is a green valve in the Main Control Room,
was linked to the solenoid shot and not to the end of the race
which confused the operators.
So, they did not conceive the failure,
as they we just trained for normal operations.
They should have maintained the level in the pressurizer,
so, they started the auxiliary water supply.
What happened? More water leaked, sorry.
They did not identify it as a LOCA.
So, after that, an automatic safety injection occurred
due to the lack of reactor coolant. But they stopped it,
thinking it was spurious trip, sorry, a spurious actuation.
And the residual heat was not evacuated
because they had left the valve closed.
What can we learn from this?
Do not stop the safeguards!
The most important operational experience was
was that emergency operating procedures were created.