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25 years ago my nuke professor used to scoff at some of the claims of the fusion researchers. The problem is the high energy neutrons flying out of the reactor
by dmfdmf 12y ago
25 years ago my nuke professor used to scoff at some of the claims of the fusion researchers. The problem is the high energy neutrons flying out of the reactor will neutron-activate every material within the vicinity. He thought the radioactivity and nuclear waste of a fusion reactor could be worse than a fission reactor. Also he thought that fusion researchers were vastly underestimating the problem of neutron embrittlement of the reactor structures and components. This is a very difficult engineering and material science problem that would have to be solved even if they did get the fusion process to work.
- DennisP 12y agoWith D-T fusion you would have more activation of the reactor materials, because D-T produces such high-energy neutrons. What you wouldn't have is transuranics, which make up the bulk of our nuclear waste (and all of the really long-lived stuff), or fission products (the most radioactive stuff, like the cesium and strontium we heard about after Fukushima). But D-T is only the easiest form of fusion. Next up is D-D, which has much lower-energy neutrons. Helion is working on D-D combined with D-He3, producing only 6% of its energy as neutrons. And several outfits are hoping to manage proton-boron fusion, producing very little neutron radiation.
- dmfdmf 12y agoCorrect me if I am wrong, but each of these "steps" is a research project in their own right. The AviationWeekly article mentioned D-T fusion for the Lockheed prototype and includes a diagram with the caption "blanket absorbs neutrons to breed fuel and transfer heat to turbines". This "blanket" will be tons of material that would be activated during operation and would have to be disposed of at EOL. Also, modern materials include many trace elements within the main molecular lattice such as cobalt, chromium, etc in steel and in some ways might be more difficult to process than used fuel rods. I worked in the nuclear power industry decades ago and I don't recall the how the energy of fusion neutrons vs fission neutrons compared but I thought that in general fusion neutrons were significantly higher. Most power fission reactors also have neutron moderators which help to reduce the activation and embrittlement problems. Nevertheless, core components in fission reactors are already experiencing neutron embrittlement and has been a concern. I'm not trying to be negative on fusion power but these overly optimistic reports have to be read with a critical eye.
- DennisP 12y agoOh absolutely. There are people trying to jump right into the more advanced reactions, but Lockheed is just aiming for D-T right now. My point is just that D-T could end up being a transitional technology. Once any form of net-positive fusion is available, I'm thinking research will ramp up a lot. I haven't seen any good quantitative comparisons of D-T waste to fission, now you've got me curious.
- Mvandenbergh 12y agoI don't know about the waste being worse, since none of it will be transuranic. All short-lived activation of a few hundred years at most, you could just switch it off and mothball it really. Totally agreed about the neutron embrittlement, I think that (IFMIF aside) this issue has just been brushed aside as a materials engineering 'detail' to be dealt with as part of commercialisation in a few decades when it might actually make the whole concept of using fusion for energy impractical.
- dmfdmf 12y agoI think my prof's main point was that the volume of waste could be problematic. If a fusion reactor had a 50-60 year life it could activate a lot of material. The volume of fission reactor waste is small enough to be stored on site (so far) for decades and reprocessing can reduce that dramatically.