Questions on Fusion

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Drakkith

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There is also a large amount of structural material that is made radioactive by the high flux of 14 MeV neutrons, and this needs to be disposed of every couple of decades because the neutrons cause it to lose structural strength. All in all I'm not sure that a fusion reactor will generate that much less radioactive material than a fission reactor.
Remember the Japan incident. Fission reactors have to be kept cool and controlled, and can relatively easily go out of control without the proper safeguards. While you may need to replace things in a fusion reactor every few decades, the security you'd have knowing that the plant will not suddenly explode is very nice. You can prepare and plan for replacing things at intervals, you cannot always plan for a disaster.

Also, it's not about the amount of material that is radioactive, it is more about the type of material, how it's stored, how easy to contain it is, and how dangerous it is biologically. Something that is more radioactive isn't necessarily worse than something else if it is much easier to contain and doesn't get absorbed into the body easily.

In addition, tritium has a large biological impact since hydrogen is a significant component of living cells.
Read this on wikipedia: HTO has a short biological half life in the human body of seven to 14 days, which both reduces the total effects of single-incident ingestion and precludes long-term bioaccumulation of HTO from the environment.

Looks like Tritium is dangerous, but probably much less dangerous than something like Iodine is. Wouldn't want to get too much of either though.
 
I'm not sure where you are getting this information. Studies that I have seen show that a typical fusion reactor would need to inventory about 1 kg of Tritium, which is about 50 million curies - not an insignificant amount of radioactive material.
I have seen studies that quote 1 and 2 kg as the Tritium requirements of reactors also. Now, I did not say this was an insignificant amount of radioactive material, I said very little tritium is needed for fusion reactions. I was considering the discussion of fission and fusion and thinking of comparable amounts for each.

If you look at other studies such as the ITER, they claim "A future fusion plant producing large amounts of power will be required to breed all of its own Tritium." Hence my remark about generating it as needed.

In addition, tritium has a large biological impact since hydrogen is a significant component of living cells. There is also a large amount of structural material that is made radioactive by the high flux of 14 MeV neutrons, and this needs to be disposed of every couple of decades because the neutrons cause it to lose structural strength. All in all I'm not sure that a fusion reactor will generate that much less radioactive material than a fission reactor.
I concur with Drakkith comments on the biological impact. In that Tritium is far less dangerous and long lasting than many fission products. I do acknowledge that it is still not a good thing and a Tritium leak should be avoided. Note that tritium is the fuel in use here and it does not produce radioactive waste, not the case in fusion.

However as you say it does result in radioactive structural materials which are problematic.
 

Drakkith

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My opinion on this. No gurantee about the accuracy, just accumulated knowledge that I think is correct.

Just looking at the possible catastrophic disasters that could happen to a Fusion reactor compared to a Fission one immediately brings into view the difference in the two.

Fission: Incident at an active reactor or fuel storage area can result in large amounts (kilograms or more) of VERY biologically dangerous isotopes to be released, such as Iodine-131, in addition to a multitude of other radioactive gases and particles. Just look at Chernobyl and the Japan incidents.

Fusion: Breach in the reactor vessel itself only results in a very small amount (measurable in grams) of materiel to be released, the only dangerous ones are Tritium. A leakage in a tritium storage tank could release large amounts of tritium, however, tritium is FAR less dangerous than something like Iodine-121 is. (And thats assuming that it is actually stored in a tank somewhere and not bred in small amounts and fed right back into the reactor) It has a much greater half life and doesn't accumulate in any specific tissue, unlike Iodine. The irradiated structure of the reactor don't form extremely hazardous isotopes (As far as i know.) and can be stored relatively easily for a shorter amount of time than fission waste products.
 
That is fine if you are only focusing on tritium. A leak of which is still dangerous but lesser than fission materials. However if it is produced on site, there are different ways of doing this, some more dangerous than others.

Also it depends on how you quantify a material as "dangerous". Some Iodine isotopes have very short half-life, others have very long ones. Iodine is dangerous if ingested because of how it affect the body, and is especial dangerous for the very young. Other materials involved in fission have no radioactive dangers but are toxic.

The irradiated structure of the reactor results in a huge amount of material to deal with. Again, not as dangerous as fission but is is still something to be managed.

Given the history of large scale engineering management of dangerous materials, especially when economics is a factor. This cannot be taken lightly.

But on the big scale of things I think fusion is much safer in operational and accidental terms than fission. Of course so far, not in financial terms and it does not actually work on a net-energy production basis.
 

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