Wednesday, November 07, 2007

Burning Pu And Other Stuff

It is mentioned quite frequently that burning up excess Plutonium is the best way to restrict its availability. A few days ago I was discussing the use of a Bussard reactor as a proliferation device. I looked at why it need not be a net power producer to be a useful high flux neutron source. I looked at it from the point of turning abundant U238 into scarce (in some places) Pu239. Bomb material.

Now let us look at it from another point of view. A way to safely burn up Pu239.

Reactors with a lot of Pu in them are hard to control for technical reasons having to do with delayed neutrons. There are 1/3rd as many as with U235, which is bad for Pu.

However, with a Bussard neutron generator (as opposed to a Bussard Power Generator which would produce 1/1,000th as many neutrons for a given fusion power output) you could design a reactor that was inherently safe (can not go critical because of the geometry) that could burn up the Plutonium and provide power out. To make the reactor stop you just hit the power switch. To throttle it up or down just control the voltages on the neutron generator (the Bussard neutron generator) at the center of the reactor.

With the possibility of explosions because of fuel loading and geometry (actually steam explosions caused by power pulses) in current reactors because they have to be loaded with several years of fuel to be economical and they have to produce their own neutrons, a complete rethinking of the whole business is in order. With a proper neutron source enriched uranium might not even be needed for nuclear power.

If the Bussard Neutron Generator (burning Deuterium) produced any thing like break even (fusion energy out = electrical power in) its use at the core of a fission plant could be very workable if the fission energy gain was sufficient. With a maximum theoretical gain of 100 or so (neutron energy in + other losses vs fission energy out) this should be very workable.

I want to be very clear here to differentiate between the two types of Bussard Reactors. One would be designed to fuse Deuterium. That reaction produces a lot of neutrons. The other type of Bussard reactor burns an isotope of Boron - Boron 11 and Hydrogen (when stripped of its electron it is referred to as a proton). What I like to call the pBj reaction. proton Boron joules. Which means smash the proton into the Boron and you get energy out.

One of the things we can do to reduce out of the box proliferation is to design the p-B11 reactors to have a lower tolerance for radiation so that if they did get diverted they wouldn't last long. Then you mostly have to keep an eye on the D-D jobs with fusion outputs above 100 Kw or so. Plus the clandestine folks.

6 comments:

LarryD said...

I know that Uranium enrichment is a b****, involving large multi-stage fiddling technology (like centrifuges or laser separators). How hard is it to extract Deuterium from, say, seawater. Or freshwater.

If the Bussard Fusion Power Generator pans out (cross fingers), then any country interested in peaceful nuclear energy no longer needs to have anything to do with Uranium at all.

Anyone willing to bet that Iran would switch?

M. Simon said...

Extracting deuterium from water is easy.

Extracting Boron from sea water is also cheap.

Rob said...

You could also use it to kickstart a thorium fission reactor.

Karridine said...

Greek to me, but I love lurking here.

Write on, Friends!

ERR said...

there is a company in germany using a farnsworth hirsch type reactor to generate neutrons. If the bussard polywell can in fact generate large directed neutron beam it could fit into thorium uranium enrichment and plutonium burn design. Is the polywell still advancing or has the passing of Dr. Bussard put it back on the shelf?

M. Simon said...

The Bussard Fusion Reactor is still being researched under a Navy contract. Results are expected in 6 to 9 months.

You might find this of interest:

Bussard Reactor Funded

and this:

Dr. Bussard has died.