alt Hacker NewsI think beryllium is a better candidate. It can be grown as a single crystal and there’s lots of research into using it for shielding in nuclear lightbulb reactors.
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Beryllium is a good plasma facing material (low Z, low retention, low activation) and acts as a neutron multiplier, but it's highly toxic: only a few months ago ITER announced they scrapped the design of the first wall because working with beryllium was causing too many complications and slowing the project even more.
It's also so rare to be completely unsuitable for a power plant: a single DEMO-like reactor with a ceramic blanket (HCCB design) would require 70% of the world beryllium output to build and then burn through 200kg/year. Essentially you could only build a couple of these.
You're overlooking the other requirement of the blanket—that it captures fusion neutrons to breed tritium, and provides a self-sustaining, closed fuel cycle. Lithium is mandatory for a D+T reactor blanket, because of these reactions:
https://en.wikipedia.org/wiki/Tritium#Lithium
(Do you have a link about that beryllium nuclear lightbulb rocket? It sounds interesting).