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Specialty Chemistry Forums => Other Sciences Question Forum => Topic started by: Enthalpy on August 26, 2020, 09:16:00 AM

Title: ITER useless
Post by: Enthalpy on August 26, 2020, 09:16:00 AM
Hello everyone and everybody!

As ITER recently celebrated some landmark with the usual spiel of "unlimited clean energy for free", I want to share my disappointment about tokamaks and nuclear fusion.

========== Tritium from external sources ==========

The only conceivable reaction in a tokamak in foreseeable future is D-T fusion, but our environment contains no tritium in useful amount, because the production events are rare and T decays quickly.

T is presently produced in uranium reactors, where excess neutrons irradiate Li, or in Candu reactors, D. This can't be upscaled:
========== Tritium regeneration ==========

Alternately, a fusion reactor would breed its own tritium. Neutron irradiation of Li is considered. The public hears about this, but nothing more.

Alas, T breeding is difficult and has drawbacks:
========== Neutron multiplication ==========

All considered (all possible?) processes seek to multiply the neutrons to regenerate T. A 14MeV fusion neutron breaks a heavy atom like Pb to release several neutrons of lesser energy. Though:
While the public may discover these drawbacks, (a part of) the fusion community knows them well and investigated two decades ago the bombardment of heavy atoms by fusion neutrons and the resulting pollution.

I should come back with figures about the pollution.

Marc Schaefer, aka Enthalpy
Title: Re: ITER useless
Post by: Enthalpy on August 27, 2020, 05:08:06 PM
Examples here of pollutant production at a Pb-Li coolant meant to regenerate tritium. Doc in the Handbook of Chemistry and Physics and in Peter Reimer 's PhD thesis:

204Pb makes 1.4% of natural Pb. The neutron doubling process is efficient (2.1b over 5.3b at 14MeV) and leaves 203Pb, decaying in 2.2 days by electron capture of 0.97MeV with γ emission.

206Pb makes 24% of natural Pb. When hit by a 14MeV neutron, it can emit an α to leave 203Hg, decaying in 47 days by β- with a 0.28MeV γ. Section for this production is only 0.7mb over 5.3b at 14MeV but 206Pb is abundant.

Investigating more would bring more cases.

1.4% abundance or 0.7mb reaction section may look rather small, but:
Now, one may argue that isotopes 204 and 206 could be removed from Pb...
In a leak of hot coolant, I imagine the 16% lithium ignite in air (or don't they?), with the fire releasing in the atmosphere the contained pollutants.

Marc Schaefer, aka Enthalpy
Title: Re: ITER useless
Post by: Enthalpy on September 03, 2020, 12:19:26 PM
Is there any neutron multiplier better then Pb?

More efficient ones, sure there are: Pu and 235U. They even provide 200MeV in addition to the neutrons. But then you don't need D-T any more.

100Mo and elements near Pb were investigated too. I didn't check their waste nor efficiency, but all usual descriptions prefer Pb.

Poitevin, who conceived tritium breeding blankets, suggests Be. I assert there isn't enough Be on Earth to feed the D-T reaction.

We have >100 000 t of beryllium according to Usgs ( (
that's the "resources" or exploitable ore. The "reserves", profitable at present economic conditions, are smaller.

If 9g Be produce ~1.4 mole of T that provides 25MeV/atom heat converted to 35% in electricity, the output is 130 TJe/kg of Be or 13 000 EJe.

From Wiki, in 2017 Mankind consumed (
580EJ of which 92EJ were electricity.

If other uses continue to need 270 t/year of beryllium, resources cover :
Unless someone sees a better neutron multiplier, we have only Pb and its radioactive waste.

Marc Schaefer, aka Enthalpy
Title: Re: ITER useless
Post by: Enthalpy on September 08, 2020, 03:56:08 AM
Earth offers 20 000 000 t molybdenum resource according to Usgs
of which 9.6% are 100Mo, only 1.7× as many moles as beryllium.

Same conclusion: there isn't enough molybdenum on Earth, we have only Pb and its radioactive waste.

Marc Schaefer, aka Enthalpy