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I dug more about this because it's an interesting topic. Basically we don't know how long a fusion generator will last before radioactivity forces its decommiss

I dug more about this because it's an interesting topic. Basically we don't know how long a fusion generator will last before radioactivity forces its decommissioning because none exist yet, but fortunately it's short-life isotopes, about 50-120 years before they become safe. Orders of magnitude better than fission waste. I don't know about fusion vs renewables, because renewables are better, but they need a lot of non-renewables to be manufactured. If a fusion reactor lasted 100 years, it would be a much better option than renewables.

ncmncm 4y ago
The reactor would need to be replaced frequently as the chamber walls and molten-lithium pipes weaken from neutron bombardment, every two years, maybe as long as five. By the time they could build one, there might be some way to make it last ten? It needs even bigger containment than a regular nuke because reactive molten lithium bursts into flame on contact with air. The oxidized product is an exploding cloud of vaporized radioactive drain cleaner. A thousand tons of lithium make a lot of drain cleaner. And again, by that time all our power will be cheaply supplied by renewables with no disastrous failure modes, and maintained just by taking bits down and putting up new bits, in shirtsleeves when weather favors it.
marcosdumay 4y ago
> Basically we don't know how long a fusion generator will last before radioactivity forces its decommissioning That was one of the main questions the ITER was supposed to answer, wasn't it? AFAIK earlier designs were quite short-lived, but some small changes fixed it. We will know how long they last as soon as we don't have an ITER anymore.
- ncmncm 4y ago
  It is scheduled to be done in 2035, which means in practice for projects like this 2040 or 2045, and at $25B meaning $30B+. It will surely be abandoned before then, and we still won't know. What were these small changes that fixed it? Did they have anything to do with the cost going up by 3x? Anyway, inducing radioactivity is not what would use it up. That just makes it super-expensive to do repairs. It would get used up through neutron bombardment weakening the crystal structure of the metals it is constructed of.
- pfdietz 4y ago
  No, it wasn't. ITER uses materials (like CuCrZr) that are unsuitable for a production reactor, ITER will not perform tritium breeding (except in a few experimental modules that won't be sufficient to prove that technology), and ITER will only operate at full power on DT for at most a few weeks total over its lifespan.

ncmncm 4y ago

The reactor would need to be replaced frequently as the chamber walls and molten-lithium pipes weaken from neutron bombardment, every two years, maybe as long as five. By the time they could build one, there might be some way to make it last ten? It needs even bigger containment than a regular nuke because reactive molten lithium bursts into flame on contact with air. The oxidized product is an exploding cloud of vaporized radioactive drain cleaner. A thousand tons of lithium make a lot of drain cleaner. And again, by that time all our power will be cheaply supplied by renewables with no disastrous failure modes, and maintained just by taking bits down and putting up new bits, in shirtsleeves when weather favors it.

marcosdumay 4y ago

> Basically we don't know how long a fusion generator will last before radioactivity forces its decommissioning That was one of the main questions the ITER was supposed to answer, wasn't it? AFAIK earlier designs were quite short-lived, but some small changes fixed it. We will know how long they last as soon as we don't have an ITER anymore.

ncmncm 4y ago
It is scheduled to be done in 2035, which means in practice for projects like this 2040 or 2045, and at $25B meaning $30B+. It will surely be abandoned before then, and we still won't know. What were these small changes that fixed it? Did they have anything to do with the cost going up by 3x? Anyway, inducing radioactivity is not what would use it up. That just makes it super-expensive to do repairs. It would get used up through neutron bombardment weakening the crystal structure of the metals it is constructed of.
pfdietz 4y ago
No, it wasn't. ITER uses materials (like CuCrZr) that are unsuitable for a production reactor, ITER will not perform tritium breeding (except in a few experimental modules that won't be sufficient to prove that technology), and ITER will only operate at full power on DT for at most a few weeks total over its lifespan.