Energy From Thorium Discussion Forum

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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 26, 2014 8:41 pm 
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Joined: Mar 22, 2014 2:34 pm
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Location: Germany
So speaking about small reactors. Is the idea of MSR electric powered cars actually crazy? I guess hundreds of cars in a city would radiate a lot.


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 26, 2014 10:36 pm 
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yes that is actually crazy


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 27, 2014 1:07 am 
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The smallest nuclear reactor has to be on a watercraft, for which the reactors were originally designed. May be a railway locomotive could carry one safely. For a road vehicle you have to depend on chemistry or electro-chemistry.


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 27, 2014 7:47 am 
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Joined: Mar 22, 2014 2:34 pm
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too bad......so shielding would actually be impossible? anyone has some infos about radiation and shielding? would interest me....
Electric amphibic submarine cars with a 5-million miles range would be pretty badass...hehe


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 27, 2014 1:10 pm 
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Joined: Nov 14, 2013 7:47 pm
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Location: Iowa, USA
Curious about what it might take to have a nuclear powered over the road vehicle I did a little research. I started by looking up how much power my vehicle's power plant produces. I have a V6 that puts out about 160kW. Assuming a heavier or better performing vehicle let's assume 250kW minimum output, then add in thermal losses at 75% we get a core that must produce 1MW.

Nuclear reactor cores that produce 1MW and could fit under the hood of a common light truck has been done but there would be no shielding or mechanism to convert that heat into motion. I made no computation of the weight, just the space it would occupy.

I'll agree with jagdish, a nuclear powered vehicle would be limited to watercraft or on rails. I suppose off road vehicles could conceivably be nuclear powered but they'd have to be very large, and the economics would have to make sense. Right now anything that big can't move very far so they will run them off electricity. I'm thinking of those big open pit mine cranes.

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Disclaimer: I am an engineer but not a nuclear engineer, mechanical engineer, chemical engineer, or industrial engineer. My education included electrical, computer, and software engineering.


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 27, 2014 1:19 pm 
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Joined: Nov 14, 2013 7:47 pm
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Location: Iowa, USA
jagdish wrote:
A reactor has to go critical to produce heat/power. It has to be controlled at a constant power. How do you control fission in a sphere?


It's controlled thermally. The more heat you pull out of it the more it shrinks, the more it shrinks the higher the rate of the fissions, the higher the rate of fission the more heat it produces.

This means a very narrow operating range. Too hot and it cracks or melts down. You'll never be able to shut it down completely, it's always going to produce some power.

If you cut the sphere in half criticality can be lost by pulling the hemispheres apart. To get it going again just put them back together.

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Disclaimer: I am an engineer but not a nuclear engineer, mechanical engineer, chemical engineer, or industrial engineer. My education included electrical, computer, and software engineering.


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 27, 2014 2:47 pm 
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Joined: Mar 22, 2014 2:34 pm
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Location: Germany
actually to move a normal car u wouldnt need 1 MW ....way too much. (but for the batman type of car...hehe)

To move a normal 1.2 ton car you only need a 40 kw(peak) electric motor. An electric car consumes 15kwh for 100km at 100km/h. So more like steady 15kw.
Assuming it would generate electricity by a supercritical CO2 turbine with an efficiency of 50% you would need 80 kw thermal power from a small MSR. I read somewhere that 1 liter of MSR core volume has somewhat 80kw thermal power. Sth in that dimension.
Supercritical CO2 turbines are very small from what i've read.
I dont know how fast a MSR could boot.... but i think i heard somewhere the number of 90s for a big reactor.
Putting a battery or supercapacitor as a buffer into the design would be apropriate.


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 28, 2014 6:13 am 
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The EVOL project has concept with significant supporting physics work by the french CNSR for a liquid fueled fast reactor, so no moderator, with LiF salt with both 233UF4 and 232ThF4 in the core and a LiF-ThF4 blanket. The core is 1.1 m diameter x 1.1 m high and produces 3000 MWth.


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 28, 2014 8:15 am 
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Location: Switzerland
The core will not be the limiting factor for the size. The shielding and the power conversion system will, so you can forget about 'small' vehicles.


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 28, 2014 10:04 am 
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Joined: Mar 22, 2014 2:34 pm
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Location: Germany
not convinced....haha....the shielding might be very thick.... but the weight dont have to exceed into the immeasurable.
http://www.kingplastic.com/wp-content/uploads/King-Plasti-Shield-Literature.pdf
Admittedly, a nuclear reactor of today needs sth like 20cm steel shielding and 2 meters of steel concrete to reduce direct radiation to 10^-12, but it also produces some hundreds of MWs.
MAybe not that crazy. We#ll speak again in a thousand years. :lol:


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 28, 2014 8:11 pm 
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@jagdish: With a nearly subcritical mass, and neutron reflectors. This is how most really tiny reactors work. (Aren't they cute?)

Others: I did figure the shielding, assuming 20MRADs from the reactor, and occupational safety limits. A halving distance of lead is 1cm. So, 40cm of lead gets a 2000 hour/year exposure down to 36 millirads, about equal to an x-ray.

I think ships, locomotives, maglevs and aerotrains can easily be nuclear. Possibly buses and tractor-trailer trucks. Automobiles are probably too small.

I'm in a small minority here because I also think nuclear aircraft would be an improvement: Bingo fuel is about ten thousand hours, eliminating the most dangerous limitation in current aviation. The turbines will need service before the plane runs out of fuel. The mass ratios work well. If the reactor is out on the tail, a shadow shield for a cargo aircraft only needs to be a wall a meter in diameter and 35cm thick. This is lighter than filled fuel tanks. 5,000 feet (3km) of air is enough to shield the ground. Airports are already dangerous, but the buildings and procedures would change.

I think that if we started with nuclear aircraft, chemically-fueled aircraft would be regarded as dangerous toys.


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 28, 2014 9:48 pm 
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Joined: Feb 05, 2013 5:24 am
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I was ignoring the whimsical nuclear powered car and airplane. *cough airscatter *cough crash on takeoff/landing in a populated area.

The jet way would have to be heavily shielded and luggage/fuel/food loading be robotic. Heavy shield walls between planes.


Last edited by Ed P on Mar 29, 2014 6:54 am, edited 2 times in total.

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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 28, 2014 9:57 pm 
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Joined: Jun 19, 2013 11:49 am
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The gamma flux thrown off a reactor in the first few minutes after it is shut down could easily be a hazard.

So a crashing plane's reactor could irradiate significant numbers of people even if it had been scrammed.


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 29, 2014 7:20 am 
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Joined: Mar 22, 2014 2:34 pm
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Location: Germany
Yeah ....but really.... radiation is not the devil on earth.....its a danger, like burning fuel.(there are already 12.000 jets flying with that human risk)
Humanity should face radiation as a danger one can handle not as sth insurmountable.
Question.... When was the last time a plane crashed into a city?


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 Post subject: Re: Smallest Thorium MSR
PostPosted: Mar 29, 2014 10:51 am 
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Joined: Jun 19, 2013 11:49 am
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It doesn't have to crash in the city to cause a radiological hazard.
It just has to do the Project Pluto esque thing and overfly the built up area at relatively low altitude.

That makes it substantially more dangerous than a crashing plane with a conventional fuel load.


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