Agreed, but grid and storage technology that will completely solve the renewable intermittence is probably as far in the future as commercial fusion reactors.

I am generally in support of solar and wind. But then, people underestimate the environmental destruction those can entail, depending on the site. Yesterday, I saw a hillside in a very rural part of Appalachia covered in solar panels. Nothing grew on the hill. Because, you know, plants would cover up the panels in no-time, so you have to vigorously keep all of it in check, with herbicides. Aside from the loss of potential carbon storage from allowing trees to grow on the hillside, which very well might offset any carbon-related gains from using solar, it's just bad for the ecology (which is exceedingly rich in the vicinity). Any farm typical for the area would be multiples of times better.

This is not intended as a rant against solar (again, I'm an enthusiastic supporter), but I'd guess a landscape of fusion generators would take fewer square meters of land than the equivalent using solar. And that is nothing to scoff at.

For terrestrial operations, sure. But we need to either overcome shielding hurdles with fission or have relatively portable fusion if we're really going to explore our solar system or the stars.

Renewables are key to having a sustainable energy economy. Fusion power is what will let us do the drastic things to recover from climate disaster that is already here.

In the grid this would take role of coal or gas plants for base load, no?

> It sounds like the T production chain might itself be quite messy.

It is: it's definitely the biggest challenge after plasma confinement.

> Molten isotopes salt and lead?

There are two main blanket technology in development: ceramic and liquid breeders. They're called breeders but are very different from the kind of breeders you have in a fission reactor. Both are based on converting lithium to tritium by capturing fusion neutrons, but in one case the lithium is in the form of solid pebbles, while in the other, in a molten mixture of lithium-lead (there are no salts AFAIK).

To produce more tritium than you start with you also need a neutron multiplier: beryllium in ceramic breeders and lead in liquid breeders. The problem is beryllium is rare (and also toxic): a 500MW reactor needs ~200 kg/year, which is not a lot, but there's very very little beryllium on earth. If you factor in the initial reactor inventory (170 t/reactor) it turns out ubiquitous fusion energy it's not sustainable if we choose beryllium. If you go with lithium-lead you need more material: 3 t/year (but remember lead is a lot heavier and more common too). If you plan to cover the world energy base load with fusion, you would need a lot of lead (~10% world annual production) but it's doable.

For me, the biggest problem right now is lithium: DT fusion needs lots of pure ⁶Li, which is extracted by enriching even more natural lithium. If we're not careful enough with recycling it from old batteries, we are likely to exhaust the world resources in a few decades.

> What do you do with when it goes bad? It may not go boom Chernobyl-style, but it's still far from the birds-in-the-sky deuterium-from-the-sea fusion dream.

The worst case scenario is still the loss of coolant accident (LoCA). The blanket is exposed to a ~2MW/m² heat load from the plasma (in addition to all kind of radiation), so failing to cool adequately a module means it will very rapidly turns into a (radioactive) molten mess that's not easy to handle. Yeah, it's bad but not nearly as bad as the same accident in a fission reactor.

The bad zone of radioactive byproducts is the half life between 10 and 1000000 years. Shorter and you can wait it out. Longer and the activity is low enough to ignore when it's spread out. When designing a fusion reactor, you can usually choose components that won't generate these undesirable nuclides. But in fission, many products are generated, so persistent contamination is practically impossible to avoid.

The whole amount of gas in the chamber is just a few grams.

Tritium is not pleasant though, but veeeeeeeeery far from anything that could do real harm: https://en.wikipedia.org/wiki/Tritium#Health_risks (you'd need to leak a lot of it continuously)

Temperature is not a very good quantity to gain intuition about plasmas (or heat transfer in general): the temperature of the electrons in a incandescent light bulb is around 10000 K, which seems very hot, but since their density is much lower than the air density, the powers involved are quite small and a light bulb is pretty safe to touch.

In the same way, a fusion plasma doesn't hold that much energy because of the extremely low density (4×10^-6 that of air). An explosion (a runaway/chain reaction) is also not possible: the reactor must continuously supplied with fuel or the fusion reactions will stop in a matter of seconds.

There are situations which could result in significant damage to the reactor components, but still not a public safety concern. Distruptions are events in which the plasma confinement is lost and a large amount of heat is released that could damage all components that face the plasma, but reactors are designed to withstand this.

Another drawback, if you like, are runaway electrons, which are populations of relativistic particles that become unbound and penetrare the vacuum vessel for several mm. Again, this is not a particular issue from a safety point of view, but they can do a lot of damage: if they hit a magnetic coil and cause a loss of the superconductivity state, the coil can heat very rapidily (due to the huge current that goes through it) and potentially melt. Replacing such a coil could cost years of maintenance, for this reason reactors are build with many fallback systems.

That would be the least of its problems.

Costing hundreds or thousands of times as much as solar + storage is a more serious problem. Since it won't be built, that is a theoretical problem. But the project can absorb an unlimited amount of money first.

The problem with fission reactors in general is that after you stop the chain reaction you've still got a tenth or so of the power output you had when it was on from decay heat for a while and you need a reliable way to get rid of that heat even in the event of a disaster. With fusion the nice thing is that the new heat stops appearing as soon as the reaction stops.

No, it doesn't in any significant quantity [1]. Besides, there are practically no high Z elements in a fusion plasma. That's because they emit bremsstrahlung radiation (power grows like Z²) and rapidly cool off the plasma. If the reaction is to be self-sustained, the plasma charge averaged over the density (Zeff) must be kept as close as possible to 1. Considering that there's only a few grams of material in a full reactor, there are virtually no heavy elements.

The radiative losses do exist, but are caused by detached atoms from the plasma facing components. Everything close to the plasma is made of light elements and specifically chosen to not produce dangerous radioisotopes when neutron activated: no high-level waste materials, meaning the half-life is lower that 10 years and they can be recycled in around 100 years.

[1]: http://www.iter.org/faq#Can_you_declare_fusion_is_really_saf...