Energy From Thorium Discussion Forum

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 Post subject: Price of Nuclear Power
PostPosted: Oct 05, 2015 12:01 am 
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http://www.forbes.com/sites/kensilverst ... for-now/2/
There is some lining in the cloud for continued existence of existing nuclear power. Prospects for success of new designs remain as clouded as the last decade. Unless you can compete financially, you have to go to China to get your design built.
For an MSR/LFTR to be economical/feasible, you have to cut costs and/or burn the used LWR fuel.
The economical design would demand that
1. Do not use costly/rare materials like high purity Li-7. Preferably make do with sodium even if sacrificing CR.
2. Cut rector volume by avoiding voluminous materials like graphite moderator. Go unmoderated or use constantly cooled water in tubes.
3. If you want to use thorium as fertile fuel, go for 20% LEU for fissile feed. It may or may not turn out to be a breeder. Wait for availability of U-233 to get a thorium breeder. Waste burners can get more mileage.


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PostPosted: Oct 05, 2015 8:11 am 
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Wouldn't an unmoderated core need to be larger to maintain criticality?

Moltex I think said their minimum size was like 170MWe, whereas the MSRE was 5MWt.


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PostPosted: Oct 05, 2015 9:07 am 
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Graphite moderator forms nearly 80% of a moderated core. An unmoderated core will need more fissile but be smaller. Fast reactor cores are more compact.


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PostPosted: Oct 05, 2015 3:58 pm 
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alexterrell wrote:
Wouldn't an unmoderated core need to be larger to maintain criticality?

Moltex I think said their minimum size was like 170MWe, whereas the MSRE was 5MWt.

MSRE used 33% U235 enrichment. Unacceptable for civilian reactors. That's why it could be so low power. (quote from Transatomic paper)
I read somewhere that Military naval reactors use 80% enrichment. Very compact reactors, can power through Xenon peaks, and nuclear fuel last for decades.

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PostPosted: Oct 06, 2015 9:18 am 
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Military reactors are a class by themselves. Longer fuel lives could be better achieved by using thorium as fertile feed in power reactors but the same could be applied to naval reactors too. However I was referring to power reactors only.


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PostPosted: Oct 06, 2015 6:18 pm 
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jagdish wrote:
Military reactors are a class by themselves. Longer fuel lives could be better achieved by using thorium as fertile feed in power reactors but the same could be applied to naval reactors too. However I was referring to power reactors only.

But their average power output is likely in the order of less than 20%.
Going from all ahead 1/3 to all ahead full = 3x the speed ~ 27x the power (at least for propulsion). Hydrodynamic drag power is speed cubed like air resistance, isn't it ?
Plus most navy vessels spent 50% of their lifetime at port, with the reactor shut down (to avoid thermal signatures for spy satellites).
That seemingly long lasting reactor fuel might might barely be enough for 2 maybe 3 years continuously at 100% power.
Anything over 50% speed makes too much noise which makes them easy to detect and limit their own enemy detection capabilities. I understand normal cruise is 1/3 max

Nuclear carriers also can't go too fast for long periods, their escorts suffer a lot in their cruising range if they go fast. Those Aegis Cruisers and Destroyers are major heavy fuel guzzlers. How I wish at least the carrier escorts were all nuclear.

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PostPosted: Oct 07, 2015 2:10 pm 
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macpacheco wrote:
Nuclear carriers also can't go too fast for long periods, their escorts suffer a lot in their cruising range if they go fast. Those Aegis Cruisers and Destroyers are major heavy fuel guzzlers. How I wish at least the carrier escorts were all nuclear.

I'd be satisfied if there was a nuclear oiler that made NH3 fuel for the escorts.

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PostPosted: Oct 07, 2015 10:50 pm 
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Get a factory ship for ammonia.


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PostPosted: Oct 10, 2015 1:48 am 
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jagdish wrote:
Get a factory ship for ammonia.
That is what I just said.

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PostPosted: Oct 12, 2015 10:13 pm 
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Considering true total fuel costs in theater, and fuel supply chain logisitics and security (vulnerability of the long tail, plus replenishment issues), the nuclear oiler with self generated ammonia and/or hydrocarbon fuels may become a thing. The Pentagon doen't like spending stupid amounts of money for fuel in theater.


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PostPosted: Oct 13, 2015 8:21 am 
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A MSR can be fairly advantageous for ships compared to a PWR due to Center-Of-Gravity versus Center-Of-Buoyancy issues. A relatively heavy LWR is better suited low down in the hull (and perhaps somewhat aft of the COG) but other ship design issues can be challenged by that constraint. I have read some of a Nuclear Navy/Rickover biography and noted that the navy kept raising the minimum tonnage for a nuclear-powered surface vessel. I'd imagine the navy would stick with a thermal reactor design, which likely means the core would be largely graphite and would have thinner walls than a PWR - which all helps with designing the reactor placement in the ship.


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PostPosted: Oct 14, 2015 3:41 am 
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A graphite moderated reactor, even a MSR, could be bigger and heavier than a naval PWR. Fast/un-moderated reactors and thorium-233U cycle can give compact reactors.
Such reactor could be put on a nuclear tug and provide both traction and power from a radiation safe distance in normal working to working/factory rafts.


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PostPosted: Oct 14, 2015 11:14 am 
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I would doubt that many naval vessel builders or operators would be interested in a fast spectrum reactor due to re-criticality issues from accidents/leaks of fuel into water. Also, navies may not wish to lug around the equipment for processing the salt(s) beyond sparging gases and perhaps deliberate plating out some of the metal FPs. Commercial vessels would be more likely if regulations allowed it. I can see an MSR potentially having a larger volume than an PWR, but not heavier which is the driver for the COG vs. COB vessel issues.


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PostPosted: Oct 14, 2015 11:17 am 
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Fluid fuel reactors are also problematic if the ship is pitching rolling 20 degrees either side of centreline.
Reactor would have to have a bunch of baffle plates in it - and what happens if the ship capsizes?


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PostPosted: Oct 15, 2015 1:03 am 
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E Ireland wrote:
Fluid fuel reactors are also problematic if the ship is pitching rolling 20 degrees either side of centreline.
Reactor would have to have a bunch of baffle plates in it - and what happens if the ship capsizes?
Keep the reactor enclosed and filled. P&R only present a problem if there is a wide free surface.

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