Please create an account to participate in the Slashdot moderation system


Forgot your password?

Comment Re:A pellet stress simulation? (Score 1) 84

Pellets, as manufactured, are _very_ smooth. This is a decent overview I just found from Google:

They start life as powder and then are packed in a way that makes them smooth.

However, just as in any kind of manufacturing: defects happen. A working reactor will have over a million pellets in it. Somewhere in there one is going to be misshapen.

Some of what we can do is run a ton of statistically guided calculations to understand what kind of safety and design margins need to be in place to keep problems from occurring. We can also look at modifying the design of the pellets to insure safer operation. Both of these things are very difficult (and costly) to do experimentally.

My lab (INL) does a lot of experimental fuel work... but we use these detailed simulations to guide the experiments so we can use our money more wisely. It literally takes years to develop a new fuel form, manufacture it, cook it in an experimental reactor, let it cool down, slice it open and see what happened. Using these detailed simulations we can do a lot of that "virtually" to help them decide on experimental parameters so that at the end of that whole sequence they have a bunch of _very_ good experimental results instead of half of them just being failures...

Also, we do actually have a bunch of detailed experimental results to compare our simulations to. Even with this fidelity of modeling we are still not able to perfectly capture what happens in all of those experiments. Even more detailed models (like the multiscale one in the video) need to be developed to be able to truly predict all the complex phenomena that goes on in nuclear fuel.

There is still a LOT more work to do...

Comment Re:A pellet stress simulation? (Score 1) 84


Certainly the nuclear reactor industry has done "just fine" without these detailed calculations for the last 60 years. Where "just fine" is: "We've seen stuff fail over the years and learned from it and kept tweaking our design and margins to take it into account". They have use simplified models to get an idea of the behavior and it has worked for them (as far as the reactors run safely and reliably).

However, the "margins" are the name of the game here. If you can do more detailed calculations that take into account more physics and geometry you can reduce the margins and provide a platform for creating the next reactor that is both more economical and safer. If you can increase the operating efficiency of a nuclear reactor by even 1% that is millions of dollars. If you can keep something like Fukushima from happening that is even more money (some would say "priceless").

The approximate answers (using simplified models) are good - they are in the ballpark. But if you compare their output to experimental output (which we have a LOT of... and it is VERY detailed) the simplified models get the trends right... but miss a lot of the outlier data. That outlier data is important... that's where failure happens. With these detailed models we get _much_ closer to the experimental data.

To get even closer to the experimental data we have to get even more detailed. The movie showed some of our early work in multi-scale simulation: where we were doing coupled microstructure simulation along with the engineering scale simulation. That work is necessary to get the material response correct to get even closer to the experimental data.

Ultimately, if we can do numerical experiments that we have a great amount of faith in, it will allow us to better retrofit existing reactors to make them more economical and safe and design the next set of reactors.

Comment Re:And it didn't need to be (Score 2) 84

I know I shouldn't respond to AC's but I'm going to anyway:

And it didn't need to be.

As far as geometry goes, it did need to be that detailed. Firstly, the pellets are round and to get the power and heat transfer correct you have to get the geometry correct. Also, pellets have small features on them (dishes on top and chamfers around the edges) that are put there on purpose and make a big difference in the overall response of the system (the dishes, in particular, reduce the axial expansion by a lot). So the detailed geometry is a very important part of this simulation. But that's not the only reason why it's large.

Your simulating a simple heat transfer and simple expansion, NOTHING MORE, no different that any other chemical process simulation in any other factory. Just with a lot more nodes.

I already explained how that is not the case. These are fully-coupled, fully-implicit multiphysics calculations. It is _not_ just heat conduction going on. Very complicated processes like fission gas creation, migration and release and fission induced and thermal creep, and fission product swelling are all involved. Plus the heat conduction and solid mechanics and thermal contact and mechanical contact and fluid flow model (on the outside of the pin) and conjugate heat transfer. All of these processes feed and are impacted by each other. These are NOT simple calculations.

It's also an arbitrary simulation serving no purpose. You said "what is that panel is broken right there' then ran a simulation with a stupid number of nodes to soak up a computer. But the pellet was made, it exists, it didn't need your simulation to be made and the simulation make zippo difference. You can run any number of similar simulations with the damage in an infinite number of places or combination of places, and it makes zip difference to the world because you don't know where each pellet is damaged. So NONE of your simulations apply to the actual pellet.

Actually, you are very wrong. Firstly, the Missing Pellet Surface problem is a huge problem in industry. What we can do with simulation is explore boundaries of how much tolerance there can be for such missing surfaces. We can vary the missing surface size and run thousands of calculations to determine the sizes that operators need to worry about. They can then adjust their QA practices to take this information into account. We can also run simulations of full reactors and stochastically sprinkle in defect pellets and show the overall response of the system which can help in understanding how to bring a reactor back up to full power in a safe way after refueling.

As for "that pellet exists"... firstly that's not true... but even if it did, doing experiments with nuclear fuel is _very_ costly and takes years (that is something else we do at INL) in order to better target our experimental money we do simulation to guide the experiments.

Their mission statement is absolutely clear. Turn cold war spending into security theatre spending and that's your job.

I don't work in security.... there are many national labs, all with different missions, but they _all_ do non-security work. They all work with US industry to solve some of the toughest problems on the planet. They are all full of extremely smart people and they are all working to add to the competitive advantage of the US. I'm sorry that you feel that way, but if you are interested in learning more about the national labs you should get a hold of me.

Comment Re:A pellet stress simulation? (Score 5, Informative) 84

I don't get it are you looking for a Funny mod? You linked to a 2D heat transfer simulation done by Matlab. Did you even watch the video?

The second simulation (of a full nuclear fuel rod in 3D) was nearly 300 million degrees of freedom and the output alone was nearly 400GB to postprocess. It involves around 15 fully coupled, nonlinear PDEs all being solved simultaneously and fully implicitly (to model multiple years of a complex process you have to be able to take big timesteps) on ~12,000 processors.

Matlab isn't even close.

Comment Re:throw away mentality (actual arcticle link) (Score 4, Interesting) 84

It costs a _lot_ to keep these computers running (read Millions with a really big M). The power bill alone is an enormous amount of money.

It literally gets to the point where it is cheaper to tear it down and build a new one that is better in flops / Watt than to keep the current one running.

Comment Re:Top supercomputer is Google? (Score 5, Informative) 84

I've worked for the DOE for quite a few years now writing software for these supercomputers... and I can guarantee you that we use the hell out of them. There is usually quite a wait to just run a job on them.

They are used for national security, energy, environment, biology and a lot more.

If you want to see some of what we do with them see this video (it's me talking):

Comment Re:No shit (Score 1) 447

I want to watch it in hi-def. I don't own a Blu-Ray player as I've never needed one.

You want hi-def... therefore you now need a Bluray player... simple.

BTW - The Blurays of GOT are _awesome_. The video and audio quality are REALLY good and the commentary and special features are also completely worth it.

I subscribe to HBO on my Dish... but I have also purchased both of the seasons of GOT on Bluray. They are epic.

Can't wait for the new episode tonight!

Comment Re:Fixed (Score 3, Interesting) 1106

"Surely, we'll get some crackheads that at least want a $1/hour."

This doesn't work because many people will cease to shop where crackheads are running the store... thus actually reducing profits. Hiring good labor at the right price is key to bringing in money.

Comment Go Big (Score 1) 375

I use three 30" (2560x1600) Dell Monitors hooked up to my Mac Pro workstation (it has an ATi graphics card that can drive 3 natively so it's smooth as butter).

In this configuration I can stretch an Emacs window across the left two and split it into 6 vertical segments (with one horizontal split along the bottom for utility functions). On the right monitor I keep a tabbed Terminal taking up half and a tabbed browser taking up half each of those generally has 6+ tabs open at any one time (make sure your Terminal tabs get named by the directory they're in!).

I've been working with three monitors like this for about a year and half now... and I highly effective with it.

The trick to using 6 panes of source code at once? Organization. I have set guidelines about what files get opened where (I work left to right from lowest level library to highest level application)... this lets me always know where to look.

I don't know if I could go back to "just" two 30"ers....

Comment Re:It's a sad sign of the times (Score 1) 467

"close or equal to"?

really. wow, that's amazing. I would love to hear more about how the pollution involved with manufacturing solar panels, which will then generate many times their energy of manufacturing over the lifetime of the panels, is somehow "close to, if not equal to" that of, say, burning oil for home heating oil, or as gas in cars, or coal for electricity, including THEIR extraction and refining externialities.

be sure to show your work, cause that's quite a doozy of a statement. It reeks of complete bullshit, actually. How many people per year die of solar panel manufacturing related pollution and manufacturing, vs oil production AND POLLUTION AND USE? do the words "orders of magnitude apart" mean anything? check out "smog related deaths" sometime. it's illuminating. and those are generally just talking about people who actually die from the immediate consequences of smog inhalation. now consider the impact on lung disease as a whole. very small doses of critical thinking are all you need.

markets cannot adjust for externialities in any truly meaningful way without very heavy educational loads, especially for complex questions. it is why a slavish devotion to free market principles is childish and shortsighted. it's a frightfully flawed model if actual human welfare is of concern.

Comment Re:It's a sad sign of the times (Score 3, Insightful) 467

but external costs are paid via mechanisms that are NOT included in the cost of the fuel.

the medical and pollution aspects of fossil fuel use... to say nothing of the global warming costs and, up until recently, our geopolitical control costs (military)... are all costs associated with oil that we pay for via taxes, insurance premiums, and other mechanisms that don't dissuade oil usage per se.

until those externialities are captured in the cost of a barrel of oil, the playing field against clean alternatives is not level. thus the need for subsidies on clean alternatives. because the free market simply cannot handle external costs in a legitimate way.

Comment Re:Why bother without IRV (Score 1) 221

actually, in maine the democrats have realized IRV is important. strong independents just keep running and they finally got it. last time in state committee it was a party line vote to go to an IRV system.

what it will take to get the republicans on board, I'm not sure. it's cost them elections too. but here I think they assume the math favors them without IRV.

so now we're just waiting for a democratic majority again. if it's soon, we may even pass it next time.

Slashdot Top Deals

Memory fault -- brain fried