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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.

#     #     #

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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20 comments
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russhuntley
russhuntley

Problem .... can't use thorium in nuclear weapons. This is the reason why it has been has never gained Congressional acceptance.

thjr19
thjr19

 @russhuntley Another myth. True, thorium cannot be used in nuclear weapons (it's not fissile), but it can be used as the raw material for fissile uranium 233.  The real question is: Would it be sensible, economic or easy to use thorium 232 to breed uranium 233?  The evidence (and science) suggests not.  Of all the nuclear weapons in existence, _none_ use uranium 233.  However, in principle, a rogue state (not a terrorist group in an Afghan cave!)  could gather together the technological expertise, develop the industrial infrastructure, do the testing and eventually have a stockpile of 233 nuclear weapons.  Quite why they would go down this path when the alternatives are well-known and proven is not clear!  In fact, the joke is that one of the ways to make fissile U-233 from fertile Th-232 requires a stock of fissile material - like plutonium 239.  Now why would I use up my precious Pu-239 to make U-233, an unknown quantity?!

 

While I'm on one myth, here's another: "Nuclear Power Plants are dangerous because their fuel and/or waste can be used to make bombs". I leave it to the reader to use Google to find why this statement is false

totterdell91
totterdell91 like.author.displayName 1 Like

just as a matter of interest, apart from being used as a moderator for nuclear fuel, pyrolitic graphite [the only type used in a reactor] has 2 other major uses as the nose cone material for ballistic missiles and as the nozzle of a rocket motor http://en.wikipedia.org/wiki/Pyrolytic_carbon

 

The odds of getting it to burn in any circumstance, below 10,000C, would appear to be very remote, even in the oxygen rich environment of a rocket motor. Any continued belief in burning nuclear graphite would be purely wishful thinking based in urban mythology, & would not stand even the most cursory examination of the known facts.

totterdell91
totterdell91 like.author.displayName 1 Like

I suppose I should comment on Graphite.

 

In order for anything to "burn", there must be oxygen present. In Molten Salt Reactors [either fuelled or cooled], the molten salt, and therefore the graphite moderator, are capped by an atmosphere of inert gas, usually Argon, up to the sealed cap. There is no oxygen to burn anything.

 

If the salt is drained from a molten salt reactor, this means that there is no radioactive material present in the reactor core, and that even if you managed to deliberately set fire to the graphite somehow [under an Inert cap gas] it would have no consequence in a sealed environment. This entire graphite "issue" is in fact a pure fantasy.

totterdell91
totterdell91 like.author.displayName 1 Like

a molten salt reactor is a completely different piece of kit to a sodium cooled  reactor.

 

To enlighten you a little, a sodium cooled reactor has solid metallic fuel rods placed in a pool of liquid metal, which is then circulated through a primary heat exchanger(HX) to a secondary coolant. The secondary coolant which can be any one of a variety of substances, is circulated through a secondary HX to a steam generator.

 

A Molten Salt Reactor has a salt as its coolant, not a metal, and certainly not sodium. Salts are visually clear and they do not react with water. In fact they are pretty well inert. The fuel in a MSR is dissolved in this salt, rather than being solid rods as in the sodium cooled reactor. The fuel salt is circulated through the core, then to a primary HX where it transfers energy to a 2nd transfer medium, which can be another [non-radioactive] salt or a gas. This secondary coolant [salt] is circulated outside the containment where its heat is fed to a working medium through the tertiary HX. The working medium which might be a gas for a brayton cycle turbine or it might be some form of steam rankin generation. Either way it is totally irrelevant because

a) the working medium is totally isolated from the fuel/coolant and

b) salts do not react with water (mostly they simply return to a solid state when cool)

 

Just in case I have been unclear, please note " A Molten Salt Reactor does not contain elemental sodium in any part, or any associated heat exchanger, or generator equipment". That goes for all Molten Salt Reactors. The comments the author has made above trying to draw some connection between sodium cooling reactors are a total waste of perfectly good electrons.

 

No molten salt used in a reactor will have any more reactivity with water than table salt. In fact salts are chosen purely because they do not react with anything. They are used as a solvent and heat transfer medium.

 

 

thjr19
thjr19

May I suggest Steven Hansen find out the difference between a "molten salt" reactor and a "sodium-cooled" reactor?  The original Telegraph article has errors in it, but the material added here is atrocious!  For example, a major difference between an MSR and current reactor designs is the use of water (steam) for heat transfer.  The latter does. The former does not.  Yet we are told: "Large power plants use a steam cycle (water heated to a gas) – regardless of the energy source – oil, gas, coal, nuclear"  My advice to readers of the article above is to Google for the truth...

econintersect
econintersect moderator

 @thjr19 http://en.wikipedia.org/wiki/Sodium-cooled_fast_reactor

 

to make large amounts of electricity - you need to make steam.

thjr19
thjr19

 @econintersect As to the Sodium-cooled fast reactor you've managed to propogate some myths about that too.

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

Listen to the people were there about the dangers of sodium as a coolant.

http://vimeo.com/35261457

 

I could go on - like the myth about graphite burning - but instead I say again: Please Google for the truth.  Because a blogger said it, does not make it true.

thjr19
thjr19

 @econintersect The veracity of the official version of the Kennedy assassination cannot be tested scientifically.  Whether or not nuclear graphite burns can be.  I showed you how this is done.  Put fire to the graphite and observe the outcome.  Did the graphite burn in Chernobyl?  The answer, I fear, is the same as the answer to the Kennedy question.  We will probably never know.  However, that's not the correct question.  Chernobyl was not an MSR.  The question therefore is: When the design of an MSR includes graphite (not all designs do), is it possible that the graphite will burn?  The answer I find in my Google searches is: No. 

econintersect
econintersect moderator

 @thjr19 like the Kennedy assassination, there is the official version, a list of alternative versions, and the truth. the official version is that the graphite burned - is it the truth, I do not know.

econintersect
econintersect moderator

the full reference:

Accidents in graphite-moderated reactors

There have been two major accidents in graphite moderated reactors, the Windscale fire and the Chernobyl disaster.

In the Windscale fire, however, the uranium fuel rather than the graphite in the reactor caught fire. The only graphite moderator damage was found to be localized around burning fuel elements.

thjr19
thjr19

 @econintersect My goodness.  You did not read your own reference.

 

:In the Windscale fire, however, the uranium fuel rather than the graphite in the reactor caught fire. The only graphite moderator damage was found to be localized around burning fuel elements.[2][3]"

econintersect
econintersect moderator

 @thjr19 your links tell nothing about myths you claim were propagated in my post.  in fact, so readers know - the EBR-II was NOT designed to produce power, it was shut down in 1994, and the disasters with sodium which were included in this post occurred after EBR-II was shut down.

 

you are shotgunning this subject without a clear concept of what it takes to produce power.  The heat generator in the plant is only half of the process - the other half is making electricity.

 

graphite burning is not a myth:

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

thjr19
thjr19

Sir, if you are going to write about the use of thorium to generate electricity, please find out the fundamentals first.

http://thoriumremix.com/2011/

Current reactors work using steam, which must be at high pressure to be efficient.

 

The MSR (or LFTR - an MSR does not have to be fueled by thorium) does not use steam.

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

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

Instead, the Brayton cycle is a better choice

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

 

 

thjr19
thjr19

 @econintersect So your plan is to give up and not produce electricity?  There is no safe way to travel.  People are slaughtered on the roads and die in their hundreds when a plane or train crashes - but please allow me to take my chances and travel.  Similarly, PV and solar are killers. 

http://nextbigfuture.com/2011/03/deaths-per-twh-by-energy-source.html

Your plan is not to put PV on roofs or build wind farms?

 

When a rational man weighs the benefits of a technology against the risks of that technology he/she must accept the benefits as long as the risks are sufficiently low enough.  I travel - by car, train, airplane, whatever.  If asked to vote, I'd vote for nuclear power.  If offered a choice between a LFTR and a PWR, I'd vote for the LFTR.

econintersect
econintersect moderator

 @thjr19 the original post in The Telegraph  was written around molten salt reactors (there was a passing reference to a liquid fluoride thorium reactor (LFTR) - as well as using thorium in existing reactors).  your point is that  LFTR does not carry the risks mentioned in my post - and you are correct.  per wikipedia, there may be a few disadvantages here too:

 

Disadvantages

LFTR's deviate strongly from today's operating commercial power reactors. A different fuel cycle (thorium rather than uranium), low pressure operation (rather than high pressure), liquid fuel (versus solid fuel), use of molten salts (rather than water or gasses), online refueling and reprocessing using pyroprocesses (opposed to off-site processing using water solvents), LFTRs are different in almost every aspect. This gives rise to a uniquely different set of design challenges and trade-offs with varying levels of design, political and inherent difficulties:

Mothballed technology. Only a few MSRs have actually been built; those experimental reactors having been constructed more than 40 years ago. This leads some technologists to say that it is difficult to critically assess the concept.[80](p200)Startup fuel. Unlike mined uranium, mined thorium does not have a fissile isotope. Thorium reactors breed fissile uranium-233 from thorium, but require a considerable amount of U-233 for the initial start up. Currently there is very little of this material available. This raises the problem of how to start up the reactors in a reasonable time frame. There are a number of ways to start up the reactors. One option is that U-233 could be produced in today's solid fuelled reactors, then reprocessing the U-233 out of the solid fuel to start up a LFTR. A LFTR can also be started up by different fissile isotopes. The two alternative options for LFTR startup are enriched uranium and plutonium from reactors or decommissioned bombs. For enriched uranium startup, a quite high enrichment is needed. Decommissioned uranium bombs have a high enough enrichment, and would simultaneously dispose of weapons grade uranium, but not enough is available to start up a large number of LFTRs. For plutonium startup, it is more difficult to separate plutonium fluoride from lanthanide fission products. For a single fluid reactor, having thorium in the fuel salt, it is also difficult to separate plutonium from thorium. One option for a two fluid reactor is to operate with plutonium or enriched uranium in the fuel salt, breeding U-233 in the blanket, but storing it instead of sending it back to the core. Instead, add makeup plutonium or enriched uranium to continue the chain reaction, similar to today's solid fuel reactors. When enough U-233 is bred, replace the fuel salt with new fuel salt, holding the U-233 as new startup fuel. A similar option exists for a single fluid reactor operating as a converter. Such a reactor would not reprocess fuel online, instead would startup on plutonium with thorium as the fertile, and add makeup plutonium. After many years the plutonium burns out and U-233 is produced in place. At the end of the reactor fuel life, the spent fuel salt can be reprocessed to recover the bred U-233 to start up new LFTRs.Salts freezing. The fluoride salt mixtures have high melting points, depending on the mixture it ranges from 300 to over 600 degrees Celsius. The salts, especially those with beryllium fluoride, are very viscous close to their freezing point. This requires careful design and freeze protection in the containment and heat exchangers. Freezing must be prevented in normal operation, during transients, and during extended station blackouts. The primary loop salt contains the decay heat generating fission products, so these help to keep the salt hot and liquid. For the MSBR, ORNL planned on keeping the entire reactor room (the hot cell) at high temperature, like an oven. This avoided the need for individual electric  ....... (read more - http://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor

 

My point remains that there is no safe way to produce base load electricity.

thjr19
thjr19

 @econintersect You continue to confuse sodium-cooled reactors with molten salt reactors.  The modern version of the  EBR, the IFR, is (as it's name says), a fast reactor.  The LFTR is a thermal reactor.  If you want to talk about the LFTR, set sodium aside.  It is irrelevant.

econintersect
econintersect moderator

 @thjr19 although whether steam being involved is not central to the point of this post, i am not understanding from any of your links where it says you make commercial electricity without steam.  http://en.wikipedia.org/wiki/Molten_salt_reactor specifically shows the process using steam.

 

i am not an expert on the Brayton cycle, i can find no evidence that it works with a sodium cooled reactor.  it has been used most successfully with  combined cycle power plants.