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Comment by 00N8 | Hacker News Reader

I'm not convinced about their hand-waved explanation of radiation safety here:

> The long-term effects of global radiation will impact humans and will cause loss of life, but this increased global radiation is “just a drop in the bucket”. Every year, we emit more radiation from coal power plants and we have already detonated over 2000 nuclear devices. Adding one more bomb should have minimal impact on the world.

I don't think "eh, what's one more detonation?" is persuasive when you're talking about a device more than 10x the size of all previous ones put together, being set off in direct contact with the seabed. Most of the fallout from nuclear testing came from the handful of ground burst tests that weren't fully confined, so I'm skeptical that "try to make it a clean fusion design" would actually be enough here. It would be cool if that were solvable though.

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> "try to make it a clean fusion design" would actually be enough here

Most of fallout in a "regular" nuclear weapon comes from uranium fission by products and from neutrons activating the surrounding materials. In addition, most thermonuclear (fusion) bombs use natural uranium tamper to contain the fusing hydrogen. This tamper soaks up fusion neutrons and fissions, and that actually produces a significant part of the overall yield.

But that's not the only option. It's possible to use a lead tamper instead, so it won't produce any fission byproducts. The Soviet Tsar Bomba did that, and it resulted in the cleanest nuclear explosion on a per-kiloton-basis.

It's also possible to add a boron neutron absorber around the fusion stage to further limit the amount of fusion neutrons that can create dangerous activated materials.

Of course, even a relatively clean weapon is still going to produce plenty of pollution.

Wouldn't the "surrounding materials" we're worried about here be the rock itself? The Tsar Bomba was proportionately the cleanest nuke ever, but I thought that also relied on it being an air burst. The Sedan test (creating the Sedan crater using a 70%+ clean fusion warhead) released more fallout than any other US test & I thought that was because it was done in the ground at a depth where reaction products could escape. But you're saying with a clean design & boron based neutron absorbing buffer layer, we could limit neutron activation of the surrounding rock? That does sound plausible, although I don't know what it would actually take & I'm doubtful their estimated $10B budget would hold.

> But you're saying with a clean design & boron based neutron absorbing buffer layer, we could limit neutron activation of the surrounding rock?

Yes, but if the bomb is surrounded by a blanket of boron, it will absorb most of the fusion neutrons. Not _all_, but a significant part of them.

The budget is actually not unreasonable. Fusion warhead scaling is easy, especially if you are not worried about practicalities for combat applications. You just keep on adding bigger stages.

And a boron blanket is literally a boron blanket. You can't do any real engineering for it, it's going to become a highly ionized plasma within the first moments of the explosion, held together only by inertia.

You'd get the irradiated rocks either way. The difference is that you avoid some fraction of fission products of the bomb itself if it's fusion fraction is higher.

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