3 ms·

> We already know that energy production is viable if we can solve the containment problem. No. That's only a small part of the problems. What is probably a fa

by jnxx 8y ago

> We already know that energy production is viable if we can solve the containment problem. No. That's only a small part of the problems. What is probably a far more difficult problem is the fact that any nuclear fusion which is remotely viable in this century will use a Deuterium-Tritium reaction. And tritium is an isotope which does not occur in nature - it is unstable. Therefore tritium has to be bred, using heavy water reactors. And lots, lots, of uranium. The idea is now to breed tritium, using neutrons from nuclear fusion, and further nuclear chemistry which is supposed to happen in a breeding blanket. But this runs into an additional problem, the deuterium-tritium reaction has no neutron surplus, as uranium fission has. And in addition to the very difficult task of exfiltrating traces of Tritium, one essentially needs a breeder technology (similar to Monju in Japan), and there are huge, unsolved material sciences problems, such as constructing a large structures which withstands very strong magnetic forces, very high temperatures, and a very high neutron flux, and this of course without any elements like carbon which will become radioactively activated. Oh, and I forgot, the whole process is also unlikely to be clean, because of the breeder technology needed. And all these questions are so extremely difficult, that today's large projects, like ITER, do not even address them. More on these issues for example in the article by Michael Moyer which is contained in the page below (Michael Moyer, "Fusion's false Dawn", Scientific American 302, 50 - 57 (2010) doi:10.1038/scientificamerican0310-50 ) http://energyskeptic.com/2014/why-fusion-is-still-30-years-away/ http://energyskeptic.com/2014/why-fusion-is-still-30-years-a...

philipkglass 8y ago
Tritium can be bred in any sort of fission reactor. The US has recently used light water power reactors to breed tritium for supplying the US nuclear weapons stockpile. Lithium-7 plus a high energy neutron yields tritium, helium, and a lower energy neutron. I don't know what a practically engineered system can do, but a 14.1 MeV neutron from D-T fusion formally has enough energy to transmute 5 lithium-7 nuclei into tritium and helium (each transmutation is endothermic to the tune of 2.466 MeV). I agree about the huge unsolved material science problems. I just don't think that tritium availability lies on the critical path of unsolved problems for industrial fusion power.
- pfdietz 8y ago
  | Tritium can be bred in any sort of fission reactor. Tritium deliberately made in fission reactors would cost maybe $200M/kg. A DT fusion reactor consumes 55kg of T per GW(th)-year. That would cost $11B/GW(th)-year if the T came from deliberate production in fission reactors, which is far too expensive. Even producing the startup tritium for a fusion reactor using fission reactors is problematic. There's a serious loop in the development schedule for DT reactors. They absolutely need good tritium breeding to make enough tritium, but such blankets cannot be developed without access to the large amounts of T that they themselves are needed to produce. Running around this loop is going to be laborious and painful, even after all the plasma physics issues are solved.
- jnxx 8y ago
  > I just don't think that tritium availability lies on the critical path of unsolved problems for industrial fusion power. Well. https://scholar.google.co.uk/scholar?hl=en&as_sdt=0%2C5&q=Sawan+Abdou+Tritium+breeding&btnG= https://scholar.google.co.uk/scholar?hl=en&as_sdt=0%2C5&q=Sa... http://fti.neep.wisc.edu/pdf/fdm1273.pdf http://fti.neep.wisc.edu/pdf/fdm1273.pdf M.E. Sawan and M.A. Abdou, "Physics and Technology Conditions for Attaining Tritium Self-Sufficiency for the D-T Fuel Cycle", Presented at the Seventh International Symposium on Fusion Nuclear Technology, May 22-27, 2005, Tokyo, Japan; to be published in Fusion Engineering and Design. Abstract + conclusions: "There is no practical external source of tritium for fusion energy development beyond ITER and all subsequent fusion systems have to breed their own tritium. To ensure tritium self-sufficiency, the calculated achievable tritium breeding ratio (TBR) should be equal to or greater than the required TBR. The potential of achieving tritium self-sufficiency depends on many system physics and technology parameters. [...] It is clear from the above discussion that both the required and achievable TBR values depend on many system physics and technology parameters. Many of these parameters are not yet well defined. In addition, the rapidly decreasing tritium resources imply that the time window for the availability of tritium to supply fuel for the DT physics devices is closing rapidly. It is, therefore, necessary to establish without delay an extensive R&D program to determine the “phase-space” of plasma, nuclear, material, and technological conditions in which tritium self-sufficiency can be attained. [...] Tritium self-sufficiency in DT fusion systems cannot be assured unless specific plasma and technology conditions are met. [...]
Tossrock 8y ago
ITER is specifically designed with slots for modular tritium breeding experiments to be run: https://www.iter.org/mach/TritiumBreeding https://www.iter.org/mach/TritiumBreeding
pfdietz 8y ago
"without any elements like carbon which will become radioactively activated" Carbon has very low neutron activation. Silicon carbide has been proposed as a material for fusion reactors for this reason. But otherwise your points are well taken.

by jnxx 8y ago

philipkglass 8y ago

Tritium can be bred in any sort of fission reactor. The US has recently used light water power reactors to breed tritium for supplying the US nuclear weapons stockpile. Lithium-7 plus a high energy neutron yields tritium, helium, and a lower energy neutron. I don't know what a practically engineered system can do, but a 14.1 MeV neutron from D-T fusion formally has enough energy to transmute 5 lithium-7 nuclei into tritium and helium (each transmutation is endothermic to the tune of 2.466 MeV). I agree about the huge unsolved material science problems. I just don't think that tritium availability lies on the critical path of unsolved problems for industrial fusion power.

pfdietz 8y ago
| Tritium can be bred in any sort of fission reactor. Tritium deliberately made in fission reactors would cost maybe $200M/kg. A DT fusion reactor consumes 55kg of T per GW(th)-year. That would cost $11B/GW(th)-year if the T came from deliberate production in fission reactors, which is far too expensive. Even producing the startup tritium for a fusion reactor using fission reactors is problematic. There's a serious loop in the development schedule for DT reactors. They absolutely need good tritium breeding to make enough tritium, but such blankets cannot be developed without access to the large amounts of T that they themselves are needed to produce. Running around this loop is going to be laborious and painful, even after all the plasma physics issues are solved.
jnxx 8y ago
> I just don't think that tritium availability lies on the critical path of unsolved problems for industrial fusion power. Well. https://scholar.google.co.uk/scholar?hl=en&as_sdt=0%2C5&q=Sawan+Abdou+Tritium+breeding&btnG= https://scholar.google.co.uk/scholar?hl=en&as_sdt=0%2C5&q=Sa... http://fti.neep.wisc.edu/pdf/fdm1273.pdf http://fti.neep.wisc.edu/pdf/fdm1273.pdf M.E. Sawan and M.A. Abdou, "Physics and Technology Conditions for Attaining Tritium Self-Sufficiency for the D-T Fuel Cycle", Presented at the Seventh International Symposium on Fusion Nuclear Technology, May 22-27, 2005, Tokyo, Japan; to be published in Fusion Engineering and Design. Abstract + conclusions: "There is no practical external source of tritium for fusion energy development beyond ITER and all subsequent fusion systems have to breed their own tritium. To ensure tritium self-sufficiency, the calculated achievable tritium breeding ratio (TBR) should be equal to or greater than the required TBR. The potential of achieving tritium self-sufficiency depends on many system physics and technology parameters. [...] It is clear from the above discussion that both the required and achievable TBR values depend on many system physics and technology parameters. Many of these parameters are not yet well defined. In addition, the rapidly decreasing tritium resources imply that the time window for the availability of tritium to supply fuel for the DT physics devices is closing rapidly. It is, therefore, necessary to establish without delay an extensive R&D program to determine the “phase-space” of plasma, nuclear, material, and technological conditions in which tritium self-sufficiency can be attained. [...] Tritium self-sufficiency in DT fusion systems cannot be assured unless specific plasma and technology conditions are met. [...]

Tossrock 8y ago

ITER is specifically designed with slots for modular tritium breeding experiments to be run: https://www.iter.org/mach/TritiumBreeding https://www.iter.org/mach/TritiumBreeding

pfdietz 8y ago

"without any elements like carbon which will become radioactively activated" Carbon has very low neutron activation. Silicon carbide has been proposed as a material for fusion reactors for this reason. But otherwise your points are well taken.