Comments on: Why You Cannot Build a Nuclear (Fission) Reactor At home http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/ Bad Science And Scary Science Fri, 10 Apr 2015 21:52:01 +0000 hourly 1 http://wordpress.org/?v=3.7.5 By: John Huston http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-2/#comment-45170 Tue, 11 Nov 2014 04:29:17 +0000 http://depletedcranium.com/?p=13453#comment-45170 What could be built to use as a neutron gun (if your goal is to simply irradiate things) would be a linear accelerator. Unless you can get your hands on a very large quantity of radium and beryllium, this would be the way to go.

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By: Chelsey Jung http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-2/#comment-45122 Mon, 27 Oct 2014 19:15:25 +0000 http://depletedcranium.com/?p=13453#comment-45122 Many thanks for the excellent post, I was hunting for information such as this, visiting have a look at the other posts.

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By: ostlandr http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-2/#comment-44678 Tue, 20 May 2014 03:58:34 +0000 http://depletedcranium.com/?p=13453#comment-44678 LOL yeah I did it again. Learned to think in foot-pounds and pounds per square inch. Need to reprogram this obsolete brain to think in newtons and pascals. At least the watt and ampere don’t change.

Anyway, yeah, the weight of the lead coolant/shielding is a problem- we’re talking roughly 3,000 pounds- err, 1,360 kg for a 51 cm diameter x 61 cm long cylinder. That’s roughly equivalent to the dry weight of a heavy truck engine. Add a 225 kg neutron generator, and you’re at 1,600 kg or so. But then for the truck you have to add the weight of the transmission and fuel tank(s). For a Volvo FH with the 16 liter engine, autoshift transmission and max fuel capacity that would total 2,125 kg.

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By: Anon http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-2/#comment-44676 Mon, 19 May 2014 02:26:32 +0000 http://depletedcranium.com/?p=13453#comment-44676

        BMS said:

You obviously don’t work for the commercial nuclear industry in the US.

True, I also don’t design Mars probes for Lockheed Martin.

:–)

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By: BMS http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-1/#comment-44674 Mon, 19 May 2014 01:37:18 +0000 http://depletedcranium.com/?p=13453#comment-44674

        Anon said:

BTW: Who still uses pounds?

You obviously don’t work for the commercial nuclear industry in the US.

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By: Anon http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-1/#comment-44673 Mon, 19 May 2014 01:29:16 +0000 http://depletedcranium.com/?p=13453#comment-44673

        ostlandr said:

Thanks for posting that link- some good info there. My idea is based primarily on minimum size and mass, and on inherent safety. Obviously a huge accelerator is too expensive and too large for this application. Luckily, fusion power research has led to an efficient neutron generator using D-D fusion and inertial confinement: http://www.nsd-fusion.com/core-tech.php
As to efficiency, the plan is to get as much power out of every pound of reactor instead of every pound of fuel.

A high flux neutron generator isn’t going to be lightweight (and wouldn’t radiation shielding by the biggest source of mass for such a small reactor?).

BTW: Who still uses pounds?

        ostlandr said:

The original idea was to use pure Thorium metal as a fuel, in the interest of low cost and ease of handling. But it should run on any mix of fissionable and/or fertile material. Heck, the US government considers U-233 “nuclear waste” instead of potential reactor fuel.

Yeah they also consider fuel that’s been in an LWR once waste so I wouldn’t care too much what they think.

Though fissile availability if you were looking at doing it legally wouldn’t be an issue though this thread isn’t really about that.

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By: ostlandr http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-1/#comment-44672 Mon, 19 May 2014 00:26:04 +0000 http://depletedcranium.com/?p=13453#comment-44672 Thanks for posting that link- some good info there. My idea is based primarily on minimum size and mass, and on inherent safety. Obviously a huge accelerator is too expensive and too large for this application. Luckily, fusion power research has led to an efficient neutron generator using D-D fusion and inertial confinement: http://www.nsd-fusion.com/core-tech.php
As to efficiency, the plan is to get as much power out of every pound of reactor instead of every pound of fuel. The original idea was to use pure Thorium metal as a fuel, in the interest of low cost and ease of handling. But it should run on any mix of fissionable and/or fertile material. Heck, the US government considers U-233 “nuclear waste” instead of potential reactor fuel.
The operating plan is to run the reactor on the original fuel load until it won’t produce enough heat to maintain operating temperature. Then you either refuel, or swap in a new unit and refuel/refurbish the old one in an appropriate facility. The plan for waste disposal is that there won’t be enough fertile or fissile material left in the core to be worth reprocessing, so you drill appropriate sized holes in the wall of an abandoned hard-rock mine, insert spent cores, and forget.
And the one safety issue I haven’t addressed in the design is the possible failure of the steam generator coil during operation. One idea is to have the reactor vessel vented so as to allow the molten lead coolant to escape without a steam explosion throwing bits of the vessel and molten lead all over. One basis of the design is that it could be operated without coolant- major temporary radiation hazard, but no explosion or meltdown. But since the neutron source will be powered off the auxiliary generator except during startup, it will shut down in event of a steam system failure.

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By: Anon http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-1/#comment-44663 Fri, 16 May 2014 21:50:29 +0000 http://depletedcranium.com/?p=13453#comment-44663 Molten Salt Reactors have very high power density along with good neutron economy (for low critical mass) so would be ideal for small scale applications where mass is at a minimum (the military uses molten salt batteries so small scale use of molten salts is already proven, though IIRC they use chemical means to heat them when they want to use them, electric heaters would probably do for locomotives and construction equipment which would probably just leave the reactor idling when not in use anyway).

Of course an on-board reprocessing system is probably going to be too heavy for portable use.

It’s been shown to my satisfaction that sub-critical reactors don’t actually solve any of the (relatively minor compared to other energy sources) problems current reactors have while the problems their proponents claim they solve are a figment of the imagination of anti-nuclear activists so I’m not at all inclined to think staying far from critical is a good thing (unless it’s a really strange reactor that would be unsafe at critical but I can’t think of any, maybe a fission fragment rocket, certainly not something anyone would want to use on earth).

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By: ostlandr http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-1/#comment-44662 Fri, 16 May 2014 20:53:47 +0000 http://depletedcranium.com/?p=13453#comment-44662 That’s the problem- the rate of breeding U-233 from Thorium is inversely proportional to the neutron flux of the source. :( The best D-D commercial sources I’ve seen have a thermal neutron flux of “only” 10^8 neutrons/cm2. And those are sealed-tube units with a tube lifetime in the thousands of hours. Lawrence-Berkeley Labs has some designs that could theoretically produce fluxes of 10^10 or 10^12 neutrons/cm2.

The idea of this design is to burn up any fissionables in the Thorium “fuel” rod as fast as they’re produced, so there’s never anything close to a critical mass of fissile material in the core at any one time. Plus we’re talking a reactor in the 0.5 – 5 MW (thermal) range- something to power construction equipment or locomotives. We’re talking ultra-compact and portable, so liquid salts are out.

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By: drbuzz0 http://depletedcranium.com/why-you-cannot-build-a-nuclear-fission-reactor-at-home/comment-page-1/#comment-44659 Thu, 15 May 2014 16:34:53 +0000 http://depletedcranium.com/?p=13453#comment-44659 The problem with that is that the kind of neutron flux you can get from a particle accelerator is very small and won’t produce much material at all. And by “Not much” I mean, you’d be lucky to make micrograms of U-233 with a small neutron generator, like the ones that could be constructed and operated in a garage or home.

Yes, you can build a particle accelerator. There are various types, but a Farnsworth Fusor makes a reasonably good neutron generator or a spallation or fusion neutron generator could be made out of a voltage multiplier or a Van Der Graaf generator.

Using a particle accelerator was investigated as a way of producing nuclear material, but it was dismissed as being more difficult than a reactor and requiring more expense and equipment.

The kind of accelerator that would give a high enough neutron flux to actually breed fuel is not the small laboratory sized variety. It is more like the Spallation Neutron Source at Oak Ridge or something like that – really big facilities, lots of employees, major undertakings to construct.

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