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October 17, 2005



Thanks for another great post.

These reactors seem to solve the saftey concerns that plauged older nuclear designs (at least well enough to put my mind at ease in that category). So that still leaves the three areas the MIT study you mentioned plans to look at: economic competitiveness, nuclear proliferation concerns and waste disposal concerns.

At ~$1,000 kW, it seems like it should be economically competitve. As far as nuclear proliferation concerns, do you know anything about what quantities of plutonium this reactor design produces?

Waste concerns seem to be the big problem here. I have yet to hear a satisfactory plan for disposing of the waste. The previous post you wrote on recycling nuclear waste seemed to have potential though. This plant seems to more completely consume its fissionable fuel than typcial reactors. How would this affect the potential to recycle the waste from this type of reactor? Would it still be feasable/desirable to recycle the waste rather than store it in geological vaults?

I'm still not sold on nuclear. With the safety issue 'solved' that's a step in the right direction but we're gonna have to find a suitable solution for the waste problem before I'm gonna start advocating nukes over clean coal (IGCC w/ co2 sequestration)
. Why not use a domestically plentiful source of fuel that doesnt produce radioctive waste that will stick around for generations?


One glaring error in the post:
The gas is then cooled, compressed and reheated before being returned to the reactor.
That should probably say "The gas is then cooled and compressed before being reheated in the reactor."

I think the waste issue is overblown. Each pellet is a very big "fruit" around a rather small "pit", where all the fissionables are. If it were up to me, I'd let the pellets cool for ten years or so and then use abrasive-jet machining or electrical-discharge machining to remove most of the bulk of the pellet cladding, leaving a bit of graphite around the spent uranium and drastically reducing the volume. The "pits" could be buried or reprocessed.

James Fraser

Eskom describes the process as follows:

"Helium at a temperature of about 500 ¦C is introduced into the top of the reactor.
After the gas passes between the fuel balls, it leaves at the bottom at a temperature of about 900 ¦C.

This gas passes through three turbines.

The first two turbines drive compressors and the third generator, from where the power emerges.

At that stage the gas is about 600 ¦C.It then goes into a recuperator where it loses excess energy and leaves at about 140 ¦C.

A water-cooled precooler takes it down further to about 30 ¦C.

The gas is then repressurised in a turbo-compressor before moving back to the regenerator heat-exchanger, where it picks up the residual energy and goes back into the reactor."

A very similar description is on the PBMR website. You can follow the process easily on the included flow diagram - too bad the temperatures are not on the diagram. Restating the description to put the emphasis on the gas temperature entering the reactor: The gas is leaving the generator turbine at 600 C and is cooled in the recuperator to 140 C, the gas leaving the high pressure compressor is heated additionally in the recuperator to 500 C before entering the reactor. That would imply that the temperature leaving the high pressure compressor was on the order of 100 C which seems a little low, but 500 C would be too high. This situation results from the very high operating temperature in the reactor.


Point. But recuperators/heat exchangers are usually mentioned as a separate process instead of generic "reheat".

Helium is particularly good for this, because the ratio of specfic heats (gamma) is about 5/3 as opposed to diatomic gases which are about 7/5 at room temperature. This translates to a greater temperature change per unit of pressure change in compression and expansion.


The waste disposal problem is somewhat overblown. In the first place far less "ash" is produced than in conventional fuel power plants and these vent directly to the atmosphere. Coal-fired power plants, especially those using anthracite coal, also spew radiation, more annually than was released in the Three Mile Island accident.

Secondly and more importantly critics assume that the waste will eventually seep into the environment, causing death and mayhem. Not likely; by the time Yucca starts leaking under the worst-case scenario we'll have long since pulled all the nuclear material back out for reprocessing and subsequent disposal elsewhere. At some point within the next 200 years we'll start shooting the stuff into the sun where it can radiate to the environment to its heart's content and no one will care.

If we make the assumption that civilization collapses before we get to this point and people forget how to dispose of the stuff, the repositories are in remote locations and extremely difficult to get to w/o advanced technology anyway and the kind of disaster that would destroy civilization would ALREADY have caused so much damage to the ecosystem that a little radiation in the ground water around the repositories would be little more than "bouncing the rubble". The survivors of said worldwide catastrophe, if any, would barely notice.


good posting.i like it. thank u. :)-


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Web Royalty

very good posting,i liked it.
thank you for this post.


Icon Enterprises

Icon construction chemicals are a Manufacturers and Suppliers of Construction Chemicals and Water Proofing contractors in Bangalore India.

Robert Hargraves

More information and graphics are available in a blog that served as a tutorial on PBR. You can also download and adapt a presentation from it.
(Read it oldest to newest for the best learning experience.)


Icon construction chemicals are a Manufacturers and Suppliers of Construction Chemicals and Water Proofing contractors in Bangalore India.for more details visit http://www.iconconstructionchemicals.com/


Warkin Equipments Pvt. Ltd. is a Manufacturers & Exporters of Oil Chillers, Oil Coolers, Air oil coolers & Water coolers in India.

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Nice schematics - they make understanding the whole process easier.


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I agree that your environment should be conducive to restful sleep.

I think it is even more important to prepare your mind and body for sleep.
Old-fashioned though it may seem, my grandmother taught me to first, lie in bed and relax your body, starting with your toes and working up to your scalp, focusing on nothing else while you do this.

Then, begin to clear your mind of that little voice that keeps reminding you of all the things you need to do tomorrow.

Picture the dream you want to have. Decide where you want to go in your dream, picture it and focus on that picture.

You will get better and better at this with practice.

Try it. You’ll like it!!!

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