I can add to this conversation.
I have a friend who shall be nameless, although anyone in the business
will know to whom I refer. He is an Australian.
He worked on nuclear power stations in the UK.
He occupied a position at or close to the top of the nuclear industry
in Australia and was I think in charge of the design of the Jervis Bay
nuclear power station that did not get built.

He told me the story of Chernobyl.
At a conference at the International Atomic Energy Authority in Vienna
in I think he said 1960, the Russians described their reactor design
which is the common design used including Chernobyl.
In the following discussion it was pointed out to the Russians that
there was a design flaw that could in certain circumstances cause a
melt down.

It was that flaw that meant the operators lost control of the reactor
when they were testing their emergency procedures.
My friend learnt of the details long before they became publically known.
The flaw had something to do with the carbon moderators storing energy.

I think it is reasonable to assume that flaw is now well known and
has been designed out in all other reactors.

> something to do with the carbon moderators storing energy.
Quite right, Bazz. As I say, even as a lifelong enthusiast of humane and responsible (as opposed to academic and commercial) science, I'm embarrassed, not only at our true lack of scientific understanding in this field:

http://www.math.columbia.edu/~woit/wordpress/?p=308

but at the crude technological implementations of it that were especially prevalent last century. A big problem is that thoughtful, well-meaning critics are put off by the complexity and the bizarre maths (which is about the best way ever invented of disguising something you don't really understand). Understanding what went wrong at Chernobyl is CONCEPTUALLY very simple, but a mathematical nightmare if you want to get technically involved. Graphite, a highly flammable substance, is the form of carbon once found in 'lead' pencils; a black, slippery, crumbly solid. In order to initiate nuclear fission, neutrons must be slowed down from their high-speed ejection from radioactive atoms to where they can 'crack' other nuclei. One way of doing this is to pass them through graphite.

So ... imagine a big room, somewhat smaller than a basketball court. Imagine this filled with blocks of graphite. Then imagine drilling holes through it and inserting rods of enriched uranium, which immediately start heating up, and continuing this until the whole thing is near red heat. "Why doesn't it burst into flame?" you will ask. Because it's sealed off from the atmosphere and filled with an inert gas. But what happens if there's a crack in the wall, and air gets in? Answer: Chernobyl.

http://en.wikipedia.org/wiki/Graphite_moderated_reactor

Things have much improved since then, but I'd be much prefer that the general public knew more about matters such as this. As I say, the CONCEPTS are usually quite simple; it's the detailed analysis that's so complex and demanding. Many opponents of nuclear power would alter their opinions radically if they'd only take time to find out more about it. Unfortunately, the High Priests of Science don't like the proles understanding these things, and maintain the aura of profound mystery and intellectual superiority on which their authority is based.