MIT MechE Lectures & Colloquia
2 HN recommenders · recommended in 4 months, 2021–2026
1:16:56 · 9.7K views · May 28, 2021
An MIT colloquium by Dennis Whyte on power exhaust and first-wall cooling in fusion reactors, including recent innovations and the SPARC and ARC designs.
Recommended for realistic engineering detail on extracting heat from a tokamak.
4 comments from Hacker News
I've seen various youtube videos from their employees and CEO. From what I remember, Dennis Whyte (head of the fusion lab at MIT and CFS cofounder) says you need about Q>5 at least, to make fusion economically viable. So that must mean Qplasma > 5. SPARC is working towards that by 2025. And so far, the company, CFS, has been achieving their milestones for the performance of their magnets. The HTS magnets and coils is the main ingredient that the startup is optimizing for. Sometime in the last year, they implied that their Qplasma was much better than they minimally hoped for. I think they achieved Qplasma > 10, but Dennis was keeping the details proprietary. From all the talks I remember, they are targeting power on the grid with the ARC reactor by 2035. Edit: This is the best recent video I've seen, about SPARC and ARC. Jumped to 2:25 for Dennis Whyte. this video It's targeted to MechE students and gives a lot of details about other aspects of a potential ARC reactor design, e.g. how to get the heat out.
For those interested not only in simplified energy balance of a fusion power plant as shown in Fusion Power Plant Simulator, but in more realistic engineering of heat extraction from a tokamak I recommend the following lecture by Dr. Dennis Whyte from MIT Plasma Science & Fusion Center. Fusion Reactor First Wall Cooling this video One of the designs uses 3D printed silicon carbide vacuum vessel cooled by a layer of molten lead and a layer of FLiBe (a molten salt made from a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2)). [LINK] The lithium component of FLiBe is used for breeding of the radioactive isotope tritium, which will be extracted from the salt and used for making the deuterium-tritium fuel of the tokamak.
There many technical changes which will have to be overcome for fusion to: 1. Produce long term stable plasma. SPARC should demonstrate this. Commonwealth Fusion Systems are confident that with the magnet properties of SPARC and the conservative parameters of the SPARC plasma they can demonstrate this. 2. Produce the prototype of a fusion power plant, the ARC reactor. Commonwealth Fusion Systems has to scale up the SPARC reactor. They have to not only design, but also build and test, reactor vessel which would allow useful heat recovery and tritium breeding. Tritium is hydrogen, very small molecule that has tendency do leak through smallest cracks. It can also cause hydrogen embrittlement. 3. Produce energy from fusion on commercial scale and at competitive prices. Reactor vessel is exposed to very strong magnetic field and as result large forces. The neutrons produced from D-T plasma have energy about 13 MeV and they cause faster material degradation than in fission power plants. It's possible that frequent replacements of the reactor vessel will be needed. The reactor vessel is neutron activated low-level radioactive waste, which has to be properly disposed of. The beryllium used in some designs is quite rare (world's annual production of beryllium is 220 tons). All this issues affect the economy of fusion power plant. I confident that all this non-trivial material and engineering changes will be solved and commercial fusion power plants will exist in 50-100 years. For quic
"Fusion Reactor First Wall Cooling" this video talks about the steady-state heat transfer out of a proposed tokamak design. Around 1:09:23 they show "1.5 GW" deposited as "0.3 GW from radiative photons -> surface heating" plus "1.2 GW from 14.1 MeV neutrons -> volumetric heating". Designing the first wall and the volumetric blanket are, indeed, engineering challenges.