Friday, April 23, 2010

But where are the sharks?

A recent radio news segment I heard was fearmongering on a laser technology that, if deployed, could potentially destroy us all in the coming nuclear apocalypse. I found a writeup here.

The idea is this: a few decades back, Some Australian researchers developed a technology to perform isotopic separation on uranium using lasers. Uranium has 2 main isotopes, 235U and 238U. 235U has a short (706 million years) half-life, while the half-life of 238U is about the age of the Earth. As a result, the Earth still has ½ of its original 238U supply, while about 63 64ths of the initial 235U has decayed. As a result, modern U has a very high 238U/235U ratio: 138:1.

It is the less abundant isotope- 235U- that undergoes neutron-induced fission in nuclear power plants, research reactors, and atom bombs. And the 238U gets in the way. So before uranium can be induced to fission, some of the 238U has to be removed. The remaining uranium after most of the 238U is removed is ENRICHED uranium. The level of enrichment depends on the purpose for which the uranium is to be used, and can result in a 238U/235U ratio of anything from 50 (low enrichment) to 0.1 (weapons grade).

The 2238U-rich uranium removed from the process is known as DEPLETED uranium, and generally has a 238U/235U ratio of about 400-500, depending on the particular source (I have a funny story about measuring this by accident- maybe some later post).

Separating isotopes requires a lot of energy- so much that it is a significant source of inefficiency in nuclear power, and one of the main technological hurdles involved in making a nuclear weapon. All the concern about Iran at the moment is related to their uranium enrichment process, for example, because election stealing, mistreatment of women, and generally thuggery are comparatively minor offences.

The big deal with laser-excitation isotope separation is that it is more efficient than previous methods. So if you have a clandestine nuclear weapons program, you can use much smaller factories, which are harder to detect. Or, if you are trying to stop global warming, you can make nuclear power generation more efficient. So the consequences of the technology depend greatly on the motives of the people deploying it.

Because of the potential negative consequences, the technology was transferred from the Australian university lab where it was developed to the US government back in the 90’s. And they classified it, so I can’t tell you the details of how it works. Especially not the details of attaching the lasers to the sharks.

The reason it has come up now is that a laser separation plant has been proposed for North Carolina. As far as I know, there are no plans for a tarheel bomb. While NC did fight the United States during the civil war, there is little evidence that the state wants to resume the conflict. They’re even considering ignoring that part of history. Unlike South Carolina, they know the war is over, and even voted for the black liberal guy in the last presidential election. So unless you’re a fanatical kosher evangelist who finds the world’s best BBQ pork to be an international outrage, North Carolina is not a rogue state.

In fact, the critics of this planned laser separation technique don’t even explain how they expect proliferation to happen. It is just a vague sentiment that if this particular nuclear technology works, it will somehow spread to the hands of the bad guys.

I don’t buy this, for the following reason. The technology has already been discovered- it is 12 years old. So rogue operators have had all that time to figure it out. Stopping a peaceful application will not prevent the bad guys from building their own systems using the theory. Building a peaceful system is only a risk if the technology from that system is then sold to the bad guys. And I don’t really see GE putting their surplus lasers on craiglist Tehran. GE makes entire reactors, and if they were in the proliferation business, they already have plenty of other ways of giving out nuclear technology.

In short, there is nothing specific about this laser system that makes it particularly likely to proliferate, so the arguments against it are general anti-nuclear efficiency arguments. So this is hardly the nightmare scenario that it was hyped up to be.

In a way, this is disappointing. I can think of some bona-fide nightmare isotope separation proliferation scenarios, and this is nowhere near what I would call worrying.

For example, geochemists often measure natural changes in isotopic ratios because these changes can tell us about various geologic or biologic processes. In generally heavy elements like U naturally separate less than light isotopes like H. But under ideal conditions, heavy isotopes can fractionate (“fractionate” is the word for natural separation). And one of the most powerful natural fractionation methods is biological activity. Photosynthesis causes most of the biosphere’s carbon isotopic fractionation, for example, and biologic fractionation has been documented in elements as heavy as Hg. So a real, bona-fine nightmare separation technology would involve not lasers, but microbes. A uranium-fractionating bacterium or yeast would be far, far more threatening than laser technology or any other technologically sophisticated system.

Unlike lasers, microbes breed. And they don’t use electricity, they just eat. So instead of needing a factory to separate isotopes, you could use a bottle. Every tub of yoghurt, every vat of beer would be a potential weapons lab. Tzatziki and chaca would become proliferation risks. And fermentation extracts such as vegemite would be proscribed as the planet’s most terrifying "V-bomb" precursors.

In short, learning that yeast had been weaponized, or that landfill methanogens were accumulating a critical mass under Fresh Kills or Woodlawn would be a nightmare scenario. This laser stuff? Bush league material for Bond Villain wannabes.

3 comments:

Jim Baerg said...

"So before uranium can be induced to fission, some of the 238U has to be removed."

Unless you have a better reactor design.
I've long thought that something that cuts the cost of separating hydrogen isotopes would be far more beneficial than an improvement in separating uranium isotopes

Chuck said...

Sure but first you need to navigate the red tape required for approving foreign reactor designs- and that's moving from science, past science fiction, and into fantasy...

Anonymous Coward said...

Re: "In short, there is nothing specific about this laser system that makes it particularly likely to proliferate."

Huh? You explained why it's more likely (than current methods) to proliferate: it's (potentially) less expensive (than current methods).

And the more resources one devotes to development of real-world plant the more one would expect to drive down the cost of producing future plants.

You don't need to have a specific "guy A hands off technology X to guy B" scheme; surely the general principle holds that as something some groups desire becomes cheaper, it becomes easier for those groups to get that thing.

This is not to say we shouldn't build the plant, which would require a more sophisticated cost/benefit analysis. But that there is a cost (in terms of possible proliferation) seems clear.