JimB said:
The reality is that in any complex system there is always the possibility of a random failure which we cannot account for.
Winterstone commented:
....we cannot account for?
Hey Jim, do you really think so - and there is nobody who can be blamed?
Maybe a poor choice of words on my part, but the point I was trying to make:
If a piece of equipment has an MTBF of say 1000 hours, Joe Public or a Politician is likely to ask "Can you guarantee that this thing will work for 1000 hours?"
A cautious engineer would reply "No, I cannot guarantee that. There is a high probablility that it will work for 1000 hours, but I cannot guarantee it"
The MTBF may be (calculated) 1000 hours, but that is a statistical thing for many units.
Any one individual unit may last for 1 hour or 1,000,000 hours.
There is no way to predict when that random failure will take place.
Boncuk commented:
I guess Fukushima was one of the worst examples you could possibly pick.
Primary cooling systems for a nuclear power plant should never be erected below shore flood line! They were put out of order with first Tsunami wave, taking care of a chain reaction of desasters in very quick order.
Maybe I misunderstood the full operation and chain of events at Fukushima.
My understanding was that the main cooling system was powered from the electrical supply grid which was put out of commission by the tsunami.
The back-up cooling system was driven by diesel generators which were also put out of commission by the tsunami.
So although there was a back-up, there was not sufficient diversity to prevent the system being completely put out of commission by the tsunami.
The possiblity of a simultaneous failure of main and back-up from a common cause had not been given enough consideration.
JimB