Next-generation nuclear fuel withstands high-temperature accident conditions

Sep 26, 2013
Cross-section of fuel pellet containing TRISO particles at 10 mm scale.

A safer and more efficient nuclear fuel is on the horizon. A team of researchers at the U.S. Department of Energy's Idaho National Laboratory (INL) and Oak Ridge National Laboratory (ORNL) have reached a new milestone with tristructural-isotropic (TRISO) fuel, showing that this fourth-generation reactor fuel might be even more robust than previously thought.

In the past three years, David Petti, director of the Very High Temperature Reactor Technology Development Office, and his team have studied the safety of TRISO . New insights come courtesy of post-irradiation examination of the fuel, which has been a team effort between INL and ORNL.

Their findings reveal that after subjecting the fuel to —far greater temperatures than it would experience during normal operation or postulated accident conditions—TRISO fuel is even more robust than expected. Specifically, the team found that even at 1,800 degrees Celsius (more than 200 degrees Celsius greater than postulated accident conditions) most fission products remained inside the fuel particles, which each boast their own primary .

"The release of fission products is very low," says Petti.

TRISO fuel particles are the size of poppy seeds. Break one open, and it looks like the inside of a tiny jaw-breaker. An outer shell of carbon coats a layer of , which coats another layer of carbon and the uranium center—where the energy-releasing fission happens. Byproducts of the fission process have the potential to escape the fuel, especially at very .

To study the fuel under accident conditions, Petti and his team placed six capsules inside INL's Advanced Test Reactor core, where they were subjected to . Then, controlled, high-temperature testing of the irradiated fuel in furnaces at INL and ORNL demonstrated that fission product release remains relatively low at high temperatures postulated to occur in accidents and beyond.

"This first series of TRISO test fuel has performed above the team's expectations, both during its three years in the ATR, and throughout the subsequent high-temperature testing," says John Hunn, ORNL project lead for TRISO fuel development and post-irradiation examination.

"The ability of the fuel to retain fission products at such high temperatures translates directly to enhanced safety of the reactor," said Paul Demkowicz, the technical lead for post-irradiation examination of TRISO fuel for the Very High Temperature Reactor program. "This sort of test data is important input for reactor design and reactor licensing."

He and his team were able to identify the few individual particles that did secrete cesium and isolate them for further analysis. They did this by dissolving the matrix that contained the particles—thousands in each chalk-sized fuel pellet.

"We've developed a tool that uses computer-controlled automation to sort through thousands of irradiated particles and identify the rare defects," said Hunn. "Careful study of these few defective particles, along with the numerous particles that perform well, allows us to complete the TRISO fuel development circle by connecting the fabrication process and material properties to performance in the reactor."

The insights gained will also "improve our ability to fabricate even better particles in the future," said Demkowicz.

Petti wants to further explore the fuel particles' limits. "If the fuel performs well at 1,800 [degrees Celsius], what about higher temperatures?" he said.

This revelation comes 11 years into INL and ORNL's joint study of TRISO fuel, which began in 2002. TRISO fuel was developed and used in Germany in the 1980s. U.S. researchers have shown that their own version of the fuel can achieve more than twice the burn-up levels—that is, the amount of the fuel that is used to release energy—clocking in at nearly 20 percent burn-up.

Explore further: Silver lining advances understanding of next-generation nuclear fuel

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antialias_physorg
4.5 / 5 (8) Sep 26, 2013
Specifically, the team found that even at 1,800 degrees Celsius (more than 200 degrees Celsius greater than postulated accident conditions) most fission products remained inside the fuel particles...

Unfortunately the temperatures in accidents like Fukushima spiked to 2800C.
So their 'postulated accident conditions' are pretty far removed from what can actually happen.
PhyOrgSux
2.3 / 5 (12) Sep 26, 2013
...but anything to keep people to accept the nuclear reaction technology is good of course (for those who make their living out of it)...
CapitalismPrevails
1 / 5 (10) Sep 26, 2013
If a LFTR was operating at Fukushima instead, no disaster would have happened. The generators would've failed so the ice cap in the drain pipe would melt because no refrigerating power available. The nuclear fuel would've flowed down the drain to a proper cooling tank. Problem solved.
brucie bee
1.8 / 5 (10) Sep 27, 2013
For those who like to 'burn' nuke fuel in lite water type class. TRISO (B&W) fuel is the best fuel design in a Quick Dump Reactor System to prevent a LOCA event.
search example: FBNR reactor

Most silly anti-nuke 'junk science' comments have no clue of nuclear potential.
TheGhostofOtto1923
1.3 / 5 (6) Sep 27, 2013
Unfoortunately the temperatures in accidents like Fukushima spiked to 2800C.
So their 'postulated accident conditions' are pretty far removed from what can actually happen.
But this max temp at fukushima was due to melting fuel,at lower temps, which never would have happened had the fuel been of this new type.

"extreme temperatures—far greater temperatures than it would experience during normal operation or postulated accident condition"

-In other words you would have to have an event which would crush these particles and somehow concentrate the fissile material, an extremely unlikely scenario (meteor strike?)
brucie bee
1.3 / 5 (7) Sep 27, 2013
IMO there is a hidden risk, that the finely dispersed fuel could still behave like the fuel inside of nuclear reactor, which could increase its temperature well above the 1800 °C limit.


I think U R overstating this senario in a Quick Dump Reactor System. Where are your facts?
antialias_physorg
4 / 5 (4) Sep 28, 2013
If a LFTR was operating at Fukushima instead, no disaster would have happened.

If an LFTR would have operated at Fukushima we would have gotten the following scenario:

Pumps stopped or emergency heaters offline.
Liquid salt frozen (i.e. no chance to restart the reactor ever again. It would have been a total writeoff)
Possible cracks and release of VERY water soluble radioactive elements (e.g. cesium fluoride) which means widespread contamination of groundwater
Possible release of uranium hexafluoride (a pretty nasty gaseous substance)
Possible breach of liquid salt cycle (which, dependent on what type of salt you use can be rather nasty in itself, as some of the salts proposed are incredibly toxic)

LFTRs are by no means accident proof (or automatically 'safe' when something happens)

The hype around them sounds EXACTLY like the hype around the reactors we have now - which were said to have an MTBF of a few million years or so (current, REAL MTBF is about 10 years).
Eikka
3.5 / 5 (2) Sep 29, 2013
(current, REAL MTBF is about 10 years).


MTBF doesn't work that way.

To give you an analog, if you calculated the MTBF of a laptop the same way you estimate it for nuclear reactors, it would be something on the order of 90 seconds, because somewhere in the world someone's laptop will break down somewhere in the next couple minutes.

That's not what it means, and suggesting otherwise is implying that nuclear reactors are doomed to break down every ten years due to some magic regardless of how they're built and maintained or where they are.

antialias_physorg
3.7 / 5 (3) Sep 29, 2013

MTBF doesn't work that way.

The MTBF quoted by the industry is not for a single reactor system but for all reactors.

The single reactor MTBF is totally irrelevant because an accident anywhere is problemaic - not just an accident at plant X.

That's not what it means, and suggesting otherwise is implying that nuclear reactors are doomed to break down every ten years

No. _A_ nuclear reactor breaks down on average every ten years. If we were to up the number of reactors to where they make any significant impact on worldwide energy production we'd be way down in the single digits in no time. (Currently nuclear supplies 5% of demand. Increasing safety standards by an order of magnitude is illusory.)
TheGhostofOtto1923
1 / 5 (5) Sep 29, 2013
No. _A_ nuclear reactor breaks down on average every ten years. If we were to up the number of reactors to where they make any significant impact on worldwide energy production we'd be way down in the single digits in no time
This is a little disingenuous isnt it? For many countries the percentage IS significant.
http://en.wikiped..._country

-France is at 74% for instance. Breaking down certainly does not mean failure and is hardly ever dangerous.
an accident anywhere is problematic
No an accident anywhere has hardly ever been problematic.

An unfortunate result of scare-mongering:

"As of June 2011, Germany and Switzerland are phasing-out nuclear power[4][5] which will be replaced mostly by fossil fuels, and a smaller part renewable energy"

-and as we know, fossil fuels produce far more nuclear contaminents in totally unremediable form. But not to worry - for germany at least, this production will take place in mainly Lebensraum countries.
Eikka
5 / 5 (1) Sep 30, 2013
The MTBF quoted by the industry is not for a single reactor system but for all reactors.


...of a certain make and model.

Using all the different reactors to calculate the MTBF is meaningless because it pitches experimental reactors from the 30's and 40's against modern designs and argue that the modern ones will blow up because the prototypes back in the day did.

If we were to up the number of reactors to where they make any significant impact on worldwide energy production we'd be way down in the single digits in no time.


But that's a non-sequitur due to the fallacy of your MTBF calculation.

You're extrapolating a trend based not on what causes the trend, but by the simple fact that a trend exists, which is like saying tomorrow I will have two wives because today I got married.

In other words, you are simply arguing that because there are old badly designed, badly build and badly maintained reactors out there, that any new reactor will have to be the same.

antialias_physorg
3.7 / 5 (3) Sep 30, 2013
Using all the different reactors to calculate the MTBF is meaningless because it pitches experimental reactors from the 30's and 40's against modern designs

As long as all those reactors are in use it's not meaningless. You can't just exclude them because they aren't up to spec. As long as they are filled with nuclear material and can melt down (or just contain amounts of radioactive waste) they're part of the system of nuclear reactors. Ignoring them does not make the danger they pose go away.

badly build and badly maintained reactors out there, that any new reactor will have to be the same.

The old reactors weren't badly designed. But buidling/operation/maintenance goes to the lowest bidder. These are machines with millions of parts from thousands of suppliers. You're telling me there's a way to make sure all of them deliver top notch material (and natural desasters remain within spec)? Not in this universe.

Theory and reality are two different things.
Eikka
5 / 5 (1) Oct 01, 2013
The old reactors weren't badly designed.


So you mean, the RMBK of Chernobyl fame wasn't a bad design with inherent safety issues?

That the Three Mile Island reactor monitoring computer system wasn't badly designed - it just happened to jam up when it was needed and prevented the operators from doing the right thing before it was too late?

That there's other examples included in the "MTBF" figure you quote, such as fires in experimental air cooled carbon pile reactors designed to make nuclear bomb fuel?

As long as all those reactors are in use it's not meaningless.


Yes, as long as THOSE reactors are in use, although now that we know their inherent flaws we can more easily avoid them.

And it still has no effect on any new reactors of other types we build, so your argument that increasing the number of reactors would increase the accident rates in the same proportion to existing reactors is still completely unfounded.

Eikka
5 / 5 (1) Oct 01, 2013
You're telling me there's a way to make sure all of them deliver top notch material (and natural desasters remain within spec)? Not in this universe.


Nirvana fallacy.

You're demanding perfection when adequate for the job is enough. Don't you think engineers know their safety margins? You'd need a really incompetent design to trust a part to its breaking point.

Also, not all of the parts in a nuclear reactor/plant are critical parts.

You're also making a false dichotomy with nuclear safety by forcing it to be an all or nothing deal. The accident at Three Mile Island for example didn't pose any real issue to the surrounding nature or population, and if future nuclear accidents can be contained like that then it's only an issue of cost.

Eikka
not rated yet Oct 01, 2013
As an analogy, if the same rhetoric against nuclear safety was applied to cars, we should not have cars today because Henry Ford's method of tightening a leather belt around the transmission axle for stopping the vehicle wasn't very effective and caused a lot of car accidents.

Because in the hundred odd years we've had cars, or so the argument goes, we would have never learned from the mistake and fixed it.

Now that we've had the Fukushima accident, do you think any officals would allow any new reactor to be built in a coastal area with crucial diesel generators below ground in the basement?

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