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The Great Debate©: ‘Safe’ Nuclear Power from Thorium?

by Ambrose Evans-Pritchard, telegraph.co.uk and

Thorium is touted by many as the future energy source for the world.  Thorium would be used in place of uranium and plutonium in nuclear reactors:

  • it is abundant on Earth,
  • it has good efficiency,
  • unlike uranium and plutonium is not easily weaponized,
  • and produces much less waste.

Ambrose Evans-Pritchard in a recent post at The Telegraph penned:

Princeling Jiang Mianheng, son of former leader Jiang Zemin, is spearheading a project for China’s National Academy of Sciences with a start-up budget of $350m.

The aim is to break free of the archaic pressurized-water reactors fueled by uranium — originally designed for US submarines in the 1950s — opting instead for new generation of thorium reactors that produce far less toxic waste and cannot blow their top like Fukushima.

He has already recruited 140 PhD scientists, working full-time on thorium power at the Shanghai Institute of Nuclear and Applied Physics. He will have 750 staff by 2015.

Evans-Pritchard’s post goes on to say:

Mr Jiang visited the Oak Ridge labs and obtained the designs after reading an article in the American Scientist two years ago extolling thorium. His team concluded that a molten salt reactor — if done the right way — may answer China’s prayers.

Read the entire article at The Telegraph.

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Not Too Fast With Thorium Reactors:  Molten Salts are not Benign

I am an industrial engineer who spent the 70′s working in the nuclear industry.  I am pro-nuclear.  This industry has made a lot of teething mistakes, the least of which continues to be the confidence that failure trees can be overcome.

Man cannot completely avoid failure as all the potential failure tree paths cannot be predefined.   Design must be based on the acceptance that eventually a failure path will overcome all the built-in defenses to prevent failure.  Designing around the concept that the plant will fail adds significant cost.

Thorium’s advantages are most pronounced in alternative reactor designs which use either molten salts or gas cooled – graphite moderated methods for heat exchange rather than water-cooled reactors commonly in use today.  It is these non-water heat exchange materials which introduce new potential failure paths.

From Energy From Thorium:

Sodium reacts chemically with both air and water, and will burn strongly with either. Hence sodium leaks become a significant issue with sodium cooled reactors. The history of sodium cooled reactors give scant comfort to those who argue that they are safe.

Perhaps the best known Internet video related to reactor safety is the video of Japanese reactor workers responding to a sodium leak at the Monju Sodium cooled breeder reactor. The Monju reactor has been shutdown since the 1995 accident although reportedly the Japanese plan to reopen it this year. The Japanese were fortunate that the leak occurred in a secondary sodium coolant system, and that no radiation was leaked, however the danger of working with sodium are best illustrated by a 1996 attempt by Japanese researchers to recreate the conditions that lead to the Monju accident. Researchers concluded that the liquid sodium released during the accident, could have melted steel doors, and come into contact with a cement floor. A reaction between the liquid sodium and water in the cement would have caused a violent explosion. What would have happen next is not reported but the leaked sodium was not the only sodium that could have potentially been involved in the accident. Not only does primary coolant sodium burn easily in contact with air, it is also highly radioactive.

Large power plants use a steam cycle (water heated to a gas) – regardless of the energy source – oil, gas, coal, nuclear.  Steam is run through a turbine which turns the generator.  At some point, the heat from the energy source must come in contact with water to make steam.  Sodium is a real nasty piece of work as heat exchangers always leak and sodium is one of the most corrosive elements.  Reactor coolants must go into a heat exchanger which has water on the other side (and separated by a metal which can corrode).

source: Wikipedia

The gas cooled reactors (pebble bed) have their own issues because the moderating material (graphite) burns (remember Chernobyl?).

Thorium seems to offer a lot of possibilities which we must explore because of it’s abundance.  But any statements which convey that a technology is safe are doing a disservice.  Nothing is safe with man at the wheel.

I believe nuclear energy offers the best and safest paths as a base-load energy source based on technology within reach.  And the world needs energy – limiting energy production kills economies.

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