Who is Online

We have 125 guests and no members online

Nuclear Technology

 

 

There are presently 617 power reactors in 31 countries.   It is a mature and reliable technology and 116 older reactors have already safely completed their working life.  In general these were small machines employing old technology. The oldest Calder Hall at Seascale, Cumbria, England achieved criticality in January, 1956.  But the bulk of them, like the failed older plant at Fukushima, commenced construction in the 1960's and early 1970's.

 

Status Net generating capacity (MWe) Number of Reactors
Operating 372,791 441
Under construction 52,615 56
Shut down 38,476 116
Not operating 2,568 4
Grand Total 466,450 617

 

 

Most of us today would be dubious about boarding a Mk1 De Havilland Comet.  But that several of these crashed due to metal fatigue did not put an end to jet airliners.  We can easily distinguish various aircraft types and are generally happy with the recent technology despite the occasional crash.  We accept the very high levels of sophistication required to avoid more frequent disasters. 

But few it seems are able to distinguish one nuclear reactor technology from another. 

There are at least six broad technologies in current commercial use and each has variations depending on age and builder.

All fission reactors employ neutrons slowed-down by a moderator.  When slowed these combine with the nucleus of a heavy element such as uranium or plutonium to destabilise it.  The destabilised nucleus splits and releases further neutrons and heat.  These new neutrons are in turn slowed to result in further combinations with more heavy nuclei; and hence establish a 'chain reaction'.   

Most reactors operating in the world today employ at high pressure water as a moderator to slow the neutrons.  The high pressure water has a high boiling temperature and can be used in a heat exchanger to make steam in a secondary loop to drive turbines to make electricity.  High pressure reactors do not normally allow boiling to take place within the high pressure stage.  As a result they have a built in safety factor in that if the water in the reactor boils, due to pressure collapse or excessive heat; for example if the secondary cooling fails, moderation reduces and the reactor turns itself down.   

In addition, fission reactors are typically controlled by means of control rods containing neutron absorbing materials like: silver; indium; cadmium; boron; cobalt and hafnium; these are lowered into, or raised from, the core containing the fuel, to optimise reactor performance.

 

Cruas Nuclear Power Station
Cruas Nuclear Power Station in France 
Comprising four pressurized water reactors of 900 MW each - totalling 3600 MW 
Just three such plants would replace all the coal burning generation in NSW

 

Some older water based reactors, like Fukushima 1 to 4, were not of this pressurised design.  They are designed to produce steam directly to run the turbines; boiling the water within the reactor. 

When fully inserted the control rods stop the chain reaction.  But as we have seen at Fukushima, it can be some time before all heat generation stops and without cooling or replacement, the water in the reactor is at risk of boiling away; resulting in a potential 'meltdown'.  This did not happen to the two newer reactors (5&6) at Fukushima that were subjected to the same events.

Some other older designs like the reactor at Three Mile Island and in the old Eastern Block, like Chernobyl, use graphite as an additional moderator so that less enriched uranium could be used as fuel but these get rapidly hotter if the cooling water boils away and graphite has proven to be an additional fire/explosion risk if the reactor goes critical. 

Yet other designs use a different fluid in the primary heat loop such as molten sodium metal.  Some new designs, that are inherently meltdown immune, use pelletised fuel to heat gas that can be used to power a gas turbine.

For a more in-depth discussion of the Fukushima situation follow this link

 

No comments

Travel

Berlin

 

 

 

I'm a bit daunted writing about Berlin.  

Somehow I'm happy to put down a couple of paragraphs about many other cities and towns I've visited but there are some that seem too complicated for a quick 'off the cuff' summary.  Sydney of course, my present home town, and past home towns like New York and London.  I know just too much about them for a glib first impression.

Although I've never lived there I've visited Berlin on several occasions for periods of up to a couple of weeks.  I also have family there and have been introduced to their circle of friends.

So I decided that I can't really sum Berlin up, any more that I can sum up London or New York, so instead I should pick some aspects of uniqueness to highlight. 

Read more: Berlin

Fiction, Recollections & News

The Password

 

 

 

 

How I miss Rio.  Rio de Janeiro the most stunningly picturesque city on Earth with its dark green mountains and generous bays, embelezado with broad white, sandy beaches.  Rio forever in my heart.   Rio my a minha pátria, my homeland, where I spent the most wonderful days of my life with linda, linda mãe, my beautiful, beautiful mother. Clambering up Corcovado Mountain together, to our favela amongst the trees.

Thinking back, I realise that she was not much older than I was, maybe fifteen years.  Who knows?

Her greatest gift to me was English. 

Read more: The Password

Opinions and Philosophy

Jihad

  

 

In my novella The Cloud I have given one of the characters an opinion about 'goodness' in which he dismisses 'original sin' as a cause of evil and suffering and proposes instead 'original goodness'.

Most sane people want to 'do good', in other words to follow that ethical system they were taught at their proverbial 'mother's knee' (all those family and extended influences that form our childhood world view).

That's the reason we now have jihadists raging, seemingly out of control, across areas of Syria and Iraq and threatening the entire Middle East with their version of 'goodness'. 

Read more: Jihad

Terms of Use

Terms of Use                                                                    Copyright