Hacker News Reader

Comment by agoldis | Hacker News Reader

Okay, did some search:

- When two hydrogen nuclei combine, they produce an enormous amount of energy. That process is known as nuclear fusion.

- Light nuclei have to be heated to extremely high temperature, it is challenging to create a controlled, safe fusion reactor that offers more energy than it consumes. Once we have such we’d have a near-limitless source of clean energy.

- Nuclear fusion does produce radioactive waste. However, in contrast to fission produced wastes, they are short lived and decay to background levels in a very short time.

- Tokamaks try to do just that.

View on HN

I will add:

- While the products of the fusion reaction are short-lived, operating a fusion reactor will active materials in the reactor and create some longer-lived radioisotopes.

- Unlike a fission reactor, which is loaded with months to years worth of fuel, a fusion reactor would have fuel constantly injected. So operator action to stop injecting fuel would stop the nuclear reaction.

Can either you or your parent poster say what "short lived" and "longer-lived" would be roughly?

https://www.quora.com/Does-nuclear-fusion-produce-waste says "typically less than 30 years for neutron activated fusion chamber materials"

Longer-lived would be thousands of years for the steel structure until it is manually handable. 50-100 years for remote handling.

> It was shown that wait times are required in the order 50–100 years for the remote handling recycling option and hundreds (Li4SiO4) to thousands (Eurofer) years for hands-on handling.

Source: https://doi.org/10.1016/S0022-3115(02)01273-4

I recall from a talk a couple of years back ( so not sure I got it correctly) that after 50-100 years you can basically walk into the fusion reactor without having to worry about radiation.

There is ongoing research about what to use as chamber wall material. The difficulty is that the material needs to be able to withstand high temperatures, minimize the impurities released when hit by a particles from the fusion plasma and ideally produce short lived and/or harmless isotopes when activated by the fusion radiation. Unfortunately, the metals most used and best known in engineering have the tendency to produce pretty nasty isotopes. The current best candidates are tungsten based alloys.

> Once we have such we’d have a near-limitless source of clean energy.

In some dystopian future, an AI figures out this is a most efficient use of matter and the entire Earth gets used as fuel for fusion reactions

Reply on news.ycombinator.com