Energy From Thorium Discussion Forum

It is currently Dec 16, 2017 7:14 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 70 posts ]  Go to page 1, 2, 3, 4, 5  Next
Author Message
PostPosted: Sep 25, 2014 3:25 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
I'm doing a rough energy/materials analysis of the ESBWR system, to get a feel of the lifecycle performance of the latest reactors with modern enrichment and mining etc. Using rough figures as 5% more or less isn't meaningful in this type of analysis.

--------------------------------------------------------------------------------

To generate electricity with a nuclear plant, we first have to build the plant! Reactor building, spent fuel building, turbine building, it all adds up.

Dr. Peterson says the ESBWR uses:

50,000 metric ton steel/iron (includes rebar). Typical energy intensity of steel (varies with recycled content, lets assume low recycled content) is 25 GJ/ton. So 1,250,000 GJ input.
250,000 metric ton concrete. Not very intensive this because concrete is actually mostly sand, rock and water (rebar is counted on steel account). Only about 1 GJ. So 250,000 GJ input.

Energy used during construction. Big heavy cranes, welding, portable generators for power. I don't know the energy use exactly, so I will go with an average power use of 1 MW. If it takes 20,000 full work hours to build the plant then this amounts to 20 GWh of fuel+electric. 72,000 GJ.

So it looks like we may want to invest in the ballpark of 1,572,000 GJ to build our plant.


Top
 Profile  
 
PostPosted: Sep 25, 2014 3:32 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Part II. Now that we have the plant we need some fuel...

We dig the uranium out of the ground. Lowest grade ore today is Rossing, at around 0.025% uranium concentration. There's plenty of 0.025% uranium deposits around. Rossing reports around 600 GJ/ton U3O8 (we might do better with mining improvements in the future but lets not count on it). To fuel our reactor, we need a start core plus 10 refuel cores worth - 60 years of operation at 90% capacity factor. A core has about 165 ton UO2 (UO2 weighs about the same as U3O8). So we need about 1800 ton UO2. As this is enriched uranium (3-3.5% but less for the first core) this translates to an input of around 13,000 ton U3O8.

13,000 x 600 = 7,800,000 GJ of mining energy needed.


Last edited by Cyril R on Oct 03, 2014 8:03 am, edited 1 time in total.

Top
 Profile  
 
PostPosted: Sep 25, 2014 3:57 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Part III. Now that we have the U3O8 we have to enrich it. To do that we have to convert it to UF6 first.

First we take the U3O8 and scrape some oxygen off by reacting with hydrogen. U3O8 + 2H2 ===> 3UO2 + 2H2O. Because hydrogen is light, we only need 70 ton hydrogen to convert our 13000 ton U3O8 to 12500 tonnes or so of UO2 (again rough figures). At 200 GJ/ton hydrogen production we need 14000 GJ for this step.

Next we use hydrogen fluoride to start fluorinating the 12500 ton UO2. UO2 + 4HF ===> UF4 + 2H2O. We make abou 14500 ton UF4. We need 3750 ton HF to make it. What is the energy required to make HF? Anyone?

We now convert the UF4 to UF6: UF4 + F2 ===> UF6. We need roughly 1750 ton F2. Energy required to make F2? Anyone?


Top
 Profile  
 
PostPosted: Sep 25, 2014 4:06 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Part IV. The 16250 ton or so of UF6 that we made is now sent to the enricher. The last diffusion plant closed in 2013, so all capacity is now centrifuge (some laser may come on line but is roughly similar to centrifuge in energy needs). Average over centrifuges appears to be 60 kWh/SWU. To make our low enriched uranium we need about 6 SWU/kgU, our 1800 ton UO2 has about 1600 ton uranium in it. This brings us to 9.6 million SWU each 60 kWh, 576,000,000 kWh or 576 GWh which is 2073600 GJ.


Top
 Profile  
 
PostPosted: Sep 25, 2014 6:15 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Part V. Deconversion. This from the world-nuclear website and its sources. Now we have to get UO2 back from the UF6. To do this steam autoclaves are used. The product HF is used for conversion (recycling).

"The UF6 is first vapourised in autoclaves with steam, then the uranyl fluoride (UO2F2) is reacted with hydrogen at 700°C to yield an HF product for sale to converters and U3O8 powder which is packed into 10-tonne containers for storage."

This makes it easier to run the calculations for HF embodied energy in the conversion step, if H2 is used to make HF. The 3750 ton HF can then be made with 200 ton hydrogen, 40000 GJ worth.

Heating up 16250 ton UF6 and 2000 ton steam requires... well actually this is an exothermic process so guessing we only have to vaporize the UF6 to start the reaction and cool away excess heat (trivial pump power needed only). Summing the heat of fusion, vaporization and some latent heat to get there sums to 0.16 GJ/ton UF6, 2600 GJ.

http://web.ead.anl.gov/uranium/guide/uc ... ranium.cfm

2000 ton steam needs around 6000 GJ or so but in reality I'm guessing this would be a regenerative operation (ie autoclave cooled by heating the steam). So we don't count this one.

The second reaction recovers some hydrogen from the oxyfluoride-steam. So both hydrogen and HF are recycled so won't be counted in this stage (they will be counted in conversion).


Top
 Profile  
 
PostPosted: Sep 25, 2014 6:26 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Part VI. Fuel fabrication. Now we have the ingredients, lets fabricate the fuel.

As mentioned we have 165 ton UO2 in a core. We need 11 cores for 60 years operation assuming 1/4 the fuel is replaced every 18 months. 1800 ton UO2.

There is also 75 ton zirconium per core. 825 ton for 11 cores.

There is also stainless steel in the fuel assemblies. Guessing 35 ton based on other BWR fuel. 385 ton for 11 cores.

The UO2 needs to be pressed and heated to 1750C to make the fuel tablets. Pressing needs little energy but heating to 1750C requires about 0.3 MJ/tonUO2/K or 525 MJ. Lets call that 1 GJ/ton UO2 to account for oven heat loss and heater inefficiency. 1800 GJ.

Welding, weld anneal and forming are not large energy sinks but the embodied energy in metals is.

825 ton Zr - how much energy is needed to make Zr? Don't know so am guessing toward exaggerating this one, 10x the energy of making steel, 250 GJ/ton. 206250 GJ total.

385 ton stainless steel (actually different Ni/Cr/Fe alloys) - 60 GJ/ton, 23100 GJ total.

Total fuel fabrication: 231150 GJ.


Top
 Profile  
 
PostPosted: Sep 25, 2014 6:51 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Part VII. inputs vs outputs.

Construction of powerplant: 1,250,000 GJ + 250,000 GJ + 72,000 GJ = 1,572,000 GJ.
Mining: 7,800,000 GJ
Conversion: 14,000 GJ + 40,000 GJ (HF, hydrogen in deconversion, recycling) + 20,000 GJ (electrolysis, F2, wild guess!!) = 74,000 GJ.
Enrichment: 2,073,600 GJ, 9.6 million SWU (according to Urenco includes infrastructure embodied energy).
Deconversion: 2,600 GJ (exothermic process, product H2 and HF counted in conversion).
Fuel fabrication: 1,800 GJ + 206,250 GJ + 23,100 GJ = 231,150 GJ.

Total input: 11,753,350 GJ.

Electrical output: 1.55 GJ/s, 90% capacity factor, 60 years: 2,639,563,200 GJ.

Energy out vs energy in or EROEI: 225

Any comments or corrections?


Top
 Profile  
 
PostPosted: Sep 25, 2014 10:01 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Someone pointed out to include energy consumption in the iron mine which may not be included in the figure. Looks like typical energy consumption is 35000 kWh/kton or 0.126 GJ/ton iron oxide. In terms of per ton steel equivalent that is less than 0.2 GJ/ton which is less than 1% the energy required to produce steel from the ore.

So, small enough to be safely ignored for LCA purposes.

http://www.nrcan.gc.ca/sites/www.nrcan. ... 9B-Eng.pdf


Top
 Profile  
 
PostPosted: Sep 26, 2014 2:44 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Let's take a look at the back end of the fuel cycle.

The ESBWR figure includes a spent fuel pool and building. But we'd like to have dry casks for longer term storage. Lets assume the worst case, all steel casks (these have the highest embodied energy). It looks like typical size dry casks for BWRs need about 5 metric ton steel for every ton of spent fuel assemblies.

We have some 12500 spent fuel assemblies, this is 3000 ton of spent fuel (1800 ton UO2, 825 ton Zr, 385 ton SS). We need 150 casks of 100 tonnes empty weight storing 20 ton SNF each.

So, we need another 5x3000 = 15,000 ton steel.

We also need a robust concrete basemat to put the casks on. A 75x75 meter slab of concrete 2 meters thick would be 27,000 ton concrete. Lets add 3000 ton for rebar which would make it about 26,000 ton concrete.

Now we have 15,000 + 3000 = 18,000 ton steel = 450,000 GJ. Plus 26,000 ton concrete, 26,000 GJ.

Our spent fuel storage needs another 476,000 GJ.


Top
 Profile  
 
PostPosted: Sep 26, 2014 3:11 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Part VII v2. inputs vs outputs. Updated with mining and spent fuel energy.

Construction of powerplant: 1,250,000 GJ + 250,000 GJ + 72,000 GJ = 1,572,000 GJ.
Construction of spent fuel dry cask storage and basemat: 450,000 GJ + 26,000 GJ = 476,000 GJ
Mining uranium: 7,800,000 GJ
Mining iron ore: 13,600 GJ (68 kton steel @ 0.2 GJ/ton)
Mining concrete: 55,200 GJ (276 kton @ 0.2 GJ/ton, assume same as iron ore which is very pessimistic)
Conversion: 14,000 GJ + 40,000 GJ (HF, hydrogen in deconversion, recycling) + 20,000 GJ (electrolysis, F2, wild guess!!) = 74,000 GJ.
Enrichment: 2,073,600 GJ, 9.6 million SWU (according to Urenco includes infrastructure embodied energy).
Deconversion: 2,600 GJ (exothermic process, product H2 and HF counted in conversion).
Fuel fabrication: 1,800 GJ + 206,250 GJ + 23,100 GJ = 231,150 GJ.

Total input: 12,298,150 GJ

Electrical output: 1.55 GJ/s, 90% capacity factor, 60 years: 2,639,563,200 GJ.

Energy out vs energy in or EROEI: 215


Top
 Profile  
 
PostPosted: Sep 26, 2014 4:19 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
Next: CO2 emissions.

Lets consider a worst case where 100% of mining is diesel, 100% of steel making is coal, and 100% of concrete input is natural gas. Rest is nuclear electric.

The reasoning behind this is simple. First off we don't want to be accused of choosing low balled data. Further, mines are often remote so we can't count on a grid connection. Similarly the ESBWR location may be remote so there's possibly no electric supply in the construction phase. Coal is how we make steel. Natural gas is how we make cement. Conversion, enrichment, deconversion are not in the middle of nowhere and in fact they will likely be built in the same country that the ESBWR is built in which means the added electric demand is fully provided by the grid connected ESBWR. In other words these inputs end up being 100% nuclear electric, de facto.

So we have:

1. Coal powered: Steel. 1,700,000 GJ * 0.1 ton/GJ = 170,000 ton CO2.
2. Natural gas powered: Concrete: 762,000 GJ * 0.05 ton/GJ = 36,300 ton CO2.
3. Diesel powered: Uranium mine: 7,800,000 GJ * 0.07 ton/GJ = 546,000 ton CO2.
Iron mine: 13,600 GJ * 0.07 ton/GJ = 952 ton CO2.
Quarry, limestone, sand (concrete): 55,200 GJ * 0.07 ton/GJ = 3864 ton CO2.
Construction energy: 72,000 GJ * 0.07 = 5040 ton CO2.

https://www.theice.com/publicdocs/ccx/C ... actors.pdf

Total: 762,156 metric ton CO2.

EDIT: We also have CO2 from cement manufacture, equivalent to 0.1 ton/ton concrete, 27,600 ton CO2

Total then becomes 789756 ton CO2.

Ton CO2 per GJ: 0.0003
grams CO2 per kWh: 1.08

The lifecycle CO2 emissions from the ESBWR is one gram per kWh.


Last edited by Cyril R on Sep 29, 2014 5:42 am, edited 1 time in total.

Top
 Profile  
 
PostPosted: Sep 26, 2014 7:40 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1494
The arrival of HVDC Light will likely make grid connecting mines practical, so the mining lorries and diggers can be electric, which means that that is almost certainly a very conservative estimates.

Hell as I understand it in Quebec there are 735kV circuits that do nothing but serve mines that are a hundred miles from anything.


Top
 Profile  
 
PostPosted: Sep 26, 2014 8:38 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5056
E Ireland wrote:
The arrival of HVDC Light will likely make grid connecting mines practical, so the mining lorries and diggers can be electric, which means that that is almost certainly a very conservative estimates.

Hell as I understand it in Quebec there are 735kV circuits that do nothing but serve mines that are a hundred miles from anything.


Good because mining energy dominates everything with centrifuge enrichment now 100% of the market (previously diffusion would dominate all other inputs).

The environmental declaration of the Rossing mine talks about 80 ton CO2/ton U3O8 so around 300,000 ton. This suggests my estimate is far too high already and it is clear they are not getting 100% diesel energy. More likely more than half is actually grid electricity or some large efficient gas generator onsite to get to this good a figure.

I am being extremely pessimistic about all energy inputs to avoid discussions of cherry picking data. I find this much more convincing and productive even though it isn't actually realistic to assume 100% coal here, 100% diesel there etc.


Top
 Profile  
 
PostPosted: Sep 26, 2014 10:41 am 
Offline

Joined: Aug 29, 2008 4:55 pm
Posts: 496
Location: Idaho Falls, Idaho
They already use electric mining equipment without HVDC lines.

http://www.infomine.com/library/videos/ ... hovel.aspx

http://online.wsj.com/news/articles/SB1 ... 3395624326

http://www.youtube.com/watch?v=jt1crCelGoQ


Top
 Profile  
 
PostPosted: Sep 26, 2014 10:50 am 
Offline

Joined: Jun 19, 2013 11:49 am
Posts: 1494
Indeed, but HVDC will allow miles in Australia five hundred miles from anything to do it too.

These days they often have to use on site generators which are expensive.
If they can access electricity at grid prices it chagnes the game.


Also if we optimise for carbon emission wouldn't we expend more energy in the centrifuges to push the enrichment of the tails fraction as low as possible?
That would reduce mining and conversion/deconversion emissions.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 70 posts ]  Go to page 1, 2, 3, 4, 5  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group