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 Post subject: Borehole Waste Disposal
PostPosted: Apr 13, 2010 9:50 pm 
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The April 3rd issue of New Scientist has an interesting story on borehole waste disposal (page 9). I had often heard this concept but did not realize how fool proof it really seems and that one reason we don`t hear it more was that when all the various concepts were investigated in the 70s and 80s such an ability for deep boreholes was beyond abilities then.

The basic idea is to drill 50 cm wide boreholes way down into basement rock where things seal themselves and any "ground" water is so saline that it never rises and mixes with real ground water. So go down 3 to 5 km and backfill the last km or two with high level waste and seal it up (geology itself does most of the sealing).

From molten salt reactors if we want to get rid of tiny volumes of long lived fission products or small amounts of higher actinides this seems a very interesting route. I`ve always been in favor of transmuting as much transuranics as possible instead of disposal but this really seems a great method. Salt cavity entombment is also a favorite but since it is not very deep you run the risk of the future plutonium mine scenario.

Any oilmen(women) out there with deep drilling experience care to offer conjuncture on this (in terms of fool proof sealing and how hard to drill that deep). It will surely be expensive for each borehole but if the current waste would only take a few hundred I`m sure we drop that to a tiny fraction if molten salt reactors were the main source.

David LeBlanc


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PostPosted: Apr 13, 2010 10:49 pm 
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I would guess a generous volume would be 1 m^3 / GWe-yr or about 5 meters of your borehole. One borehole should be enough to cover the output of 200-400 GWe-yr output. This could not be a significant cost.


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PostPosted: Apr 14, 2010 12:35 am 
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There are two different aspects of deep bore-hole waste disposal. Non reusable fission products can be definitely buried with reduced NIMBY problems. However, there is cladding from LWR/PHWR waste which is much more than the fission products. Currently favored thermalised LFTR designs will have graphite waste. There will also be reactor vessels and other components which are described as high level wastes.
All of these will have to be converted into stable pebbles before disposal by deep burial.
I wonder if some of more heat producing pebbles (fission products in cladding, for example) can be used as heat source for recovery of liquid/gaseous hydrocarbons? Once lowered, they will work for years or decades!


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PostPosted: Apr 14, 2010 4:55 am 
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Lets not throw anything that is potentially valuable, or will be potentially valuable away. It is better to find uses for long half life FPs, than to find acceptable ways to dispose of them. Radiation from FPs can be used in medicine, sanitation, materials testing, food processing, and may have other potential uses.


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PostPosted: Apr 14, 2010 10:45 am 
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Charles Barton wrote:
Lets not throw anything that is potentially valuable, or will be potentially valuable away. It is better to find uses for long half life FPs, than to find acceptable ways to dispose of them. Radiation from FPs can be used in medicine, sanitation, materials testing, food processing, and may have other potential uses.


The problem though Charles is we can certainly not convince the public that we can assure a use Tc99 or I129 for the next few hundred thousand years. It is a valid concern of the public that we are not imposing on future generations to clean up our own mess (yes even though we are doing that far worse with fossil fuel use). It is nice to have concrete answers for all the points opponents might raise.

Like I mentioned, I`ve always favored transmutation of as much of the transuranics as possible. However, Pu is hard to remove from the salt and Am and Cm much harder still. It will always be an individual nation`s choice on what expense to pay for such operations so it is nice to see there is a pretty fool proof and relatively inexpensive alternative for some of these long lived elements. It is pretty cheap to process salts if all we do if vacuum distill off the carrier salt and have a nice condensed package of fission products along with Pu, Am and Cm (U and Np already removed).

David L.


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PostPosted: Apr 14, 2010 11:47 am 
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David wrote:
Charles Barton wrote:
Lets not throw anything that is potentially valuable, or will be potentially valuable away. It is better to find uses for long half life FPs, than to find acceptable ways to dispose of them. Radiation from FPs can be used in medicine, sanitation, materials testing, food processing, and may have other potential uses.


The problem though Charles is we can certainly not convince the public that we can assure a use Tc99 or I129 for the next few hundred thousand years. It is a valid concern of the public that we are not imposing on future generations to clean up our own mess (yes even though we are doing that far worse with fossil fuel use). It is nice to have concrete answers for all the points opponents might raise.

Like I mentioned, I`ve always favored transmutation of as much of the transuranics as possible. However, Pu is hard to remove from the salt and Am and Cm much harder still. It will always be an individual nation`s choice on what expense to pay for such operations so it is nice to see there is a pretty fool proof and relatively inexpensive alternative for some of these long lived elements. It is pretty cheap to process salts if all we do if vacuum distill off the carrier salt and have a nice condensed package of fission products along with Pu, Am and Cm (U and Np already removed).

David L.


Shouldn't transuranics stay in? Can't they be fissioned over time? I would also favor keeping I129 in the salt until it becomes something reasonable. Keep that stuff outta thyroids.

Once it's in the borehole all other options are lost.

My hope is eventually we will have 3 to 5 neutrons / fission instead of 2 to 3; with the extra few in a wider spectrum and electrically generated.
That would make fissioning super-duper clean.

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PostPosted: Apr 14, 2010 2:22 pm 
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In practice economics will play a role. Off gases are pretty easy to isolate and I would imagine we would likely sell them but they aren't of much value so primarily it would be for the sake of not storing them.

Noble metals are a bit more difficult to predict where they come out but there is some pretty valuable stuff in there. IF (and I think only if) the valuable stuff can be isolated sufficiently then we might be able to sell this. While it makes good talking points the level of permissible residual radioactivity may well make this unattractive.


Finally, we have the salt seekers. It would be nice to isolate the Strotium for the sake of RTG's (and to reduce the heat load in the waste stream) but beyond that I'm not sure I see much value in doing anything other than to reduce the stuff to a glass form to make it hard to leach into the environment and then bury it.


BUT there is no hurry so we can simply store the stuff where it is accessible for 60 years or more and IF we come up with something more attractive to do with if wonderful. If not, we have an acceptable solution.


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PostPosted: Apr 14, 2010 9:33 pm 
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David wrote:
It is pretty cheap to process salts if all we do if vacuum distill off the carrier salt and have a nice condensed package of fission products along with Pu, Am and Cm (U and Np already removed).


Unless one minds the weight of shielding, this may be a great RTG source. The price to separate Pu (mostly Pu238 in a pure cycle) to get a clean alpha source may be justified if one needs say a RTG to power space probes.


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PostPosted: Apr 14, 2010 11:23 pm 
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Just to remind readers. A pure Th-U233 Two Fluid cycle is favored by many here. Vacuum distillation should be the simplest way to remove soluble fission products but it is quite tricky to remove the small amounts of Pu and higher from the still bottoms (might add up to about 20 kg per GWe year if we leave them with the removed fission products). This would be mostly Pu238 which is a desired isotope but we`d produce way more than would likely ever be needed. Thus borehole disposal is an interesting option.

The other favored route is a Single Fluid converter (DMSR type). In this case the question is when you finally finish with the salt (10 to 50 years later) what do you do with the tonne or so of higher actinides (U and Np are easy to remove, Pu and above are not). As Lars often mentions we have decades to decide (even decades after usage) but this borehole method seems a nice solution that doesn`t call for the expense of trying to pull out Pu, Am and Cm. We`d probably again distill off the carrier salt if for no other reason than to get a compact package.

Anyhow, nice to know our options. We can pay a bit to remove Pu, Am and Cm to transmute (economically and politically since any sort of fuel processing raises eyebrows) OR we have a safe method of disposal that is easy to explain to the lay person.

David LeBlanc


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PostPosted: Apr 15, 2010 12:07 am 
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One possibility for Pu extraction is to add titanium-fluoride to the salt before distilling (perhaps after removing the UF4). The guess is that the titanium will give up his fluorines and plate out while the UF3 and PuF3 pick up a fluorine and become sufficiently volatile for vacuum distilling. IF it works this seems pretty simple.

By the way, the TRU output from a vacuum distilling system (without added fluorine as above) is likely Np237 rather than Pu238. The fluorination system will likely pull out the Np and leave behind 238Pu.


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PostPosted: Apr 15, 2010 2:34 pm 
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There will always be a need for disposal of some parts. A borehole might be more acceptable than Yucca!


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PostPosted: Apr 17, 2010 5:19 pm 
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Quote:
BUT there is no hurry so we can simply store the stuff where it is accessible for 60 years or more and IF we come up with something more attractive to do with if wonderful. If not, we have an acceptable solution.


In the discussion of nuclear waste, one attractive idea that has been floated recently is to impose a cost on short and/or long term storage of wastes that results from reactor operation so that the market place can determine the most waste efficient nuclear technology to deploy. This is similar in concept to a carbon tax.

If such a financial waste disincentives did exist especially if these waste costs were substantial, an evaluation of design tradeoffs vis’-à-vis' nuclear waste production shall be a top priority with nothing left to chance or future resolution. In my estimate, future resolution of waste issues would not be permitted by law or regulation.

In this situation, it would be important to design up front all possible aspects of the waste stream in substantive detail just to cost the operation of the reactor compared to other energy alternatives; a prime interest of the nuclear customer.

In the current political environment, such waste costs would be very high indeed. The public is fed up with both incomplete reactor designs and with government procrastination on the nuclear waste issue and will not stand for any more of it. The design of the waste stream flow of a new reactor must be air tight.

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PostPosted: Apr 17, 2010 8:42 pm 
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Does this mean that at the end of LFTR life we can simply bring in an oil drilling rig, bore a 5 km hole, and dispose of the radioactive waste without having to transport somewhere?

Here's another reference...http://www.neimagazine.com/story.asp?storyCode=2055856


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PostPosted: Apr 20, 2010 7:11 pm 
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David wrote:
Charles Barton wrote:
Lets not throw anything that is potentially valuable, or will be potentially valuable away. It is better to find uses for long half life FPs, than to find acceptable ways to dispose of them. Radiation from FPs can be used in medicine, sanitation, materials testing, food processing, and may have other potential uses.


The problem though Charles is we can certainly not convince the public that we can assure a use Tc99 or I129 for the next few hundred thousand years. It is a valid concern of the public that we are not imposing on future generations to clean up our own mess (yes even though we are doing that far worse with fossil fuel use). It is nice to have concrete answers for all the points opponents might raise.


Oh I suppose. But I still cant understand why anyone would go to the trouble of spending money on a disposal solution more expensive than a storage solution. Just store it, and discounting is far more rewarding. We aren't here to solve problems thousands of years from now and its ludicrous for us to even try. This drilling deep boreholes because some mildly radiotoxic ash inspires fear in the uneducated just makes me cringe.


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 Post subject: Borehole disposal study
PostPosted: Aug 24, 2013 6:11 am 
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I did a small study on a borehole spent fuel sequestration system. I looked at the heat flow, required spacings and bore lengths, and costs for a system to sequester the waste from 10 gigawatt reactors over their 60 year lifetime.

I'd be interested in any comments.

Nuclear Waste Borehole Sequestration

-Iain


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