IAmA chemical engineer who works with spent nuclear fuel. AMA!
Thanks to @suspended and @deimos for the suggestion!
Hey y’all, I am a basin chemistry engineer for the Department of Energy’s Savannah River Site in South Carolina. Our facility stores spent nuclear fuel from a variety of research and experimental reactors underwater. Our specialty is highly-enriched aluminum-clad fuel, but we have a diverse array of unusual fuels from around the world. A good overview of fuel types can be found here.
My primary responsibility is ensuring the basin water is kept highly pure to minimize corrosion to the fuel, as well as ensure it is free of radionuclides to the extent practicable. I’m happy to answer any questions I can about nuclear fuel, nuclear power, radioactive waste, etc.
More links:
Corrosion of Al-clad fuel
Basin overview
Thanks for offering to answer questions!
What are some of the things you've done in your career that you're most proud of?
(I realize this is more personal and less informational, so feel free to skip it if it's not the type of question you're wanting to answer.)
I’m pretty early into my career, so I haven’t had a whole lot of defining moments, not like my predecessors had (one of them was in the role for decades).
One funny moment I had recently was a saga to find yellowed bottles. The lab wanted us to stop sending samples in them, so I had to look for them. For several weeks, they kept receiving yellowed bottles, and I’d been looking all over to see where they were coming from. Finally, I found them in a closet in the basin itself (OPS had been too busy to go with me to look). We also had to transfer samples between bottles, since some hadn’t been shipped out yet but were in yellow bottles.
Do you have an opinion on floating nuclear power plants?
As a layman they've always struck me as mitigating most of the dangers/risks associated with nuclear power plants if you can solve the containment problem in the event of a leak. I'm not sure if this is still an active area of R&D?
It’s still being discussed, and has been in the past - Dr. Nick Touran did an episode on ScienceFriday and his blog. The Russian one and ThorCon have received the most attention, but an abandoned French concept from the early 2010s called FlexBlue was pretty interesting, as was the Offshore Power Systems proposal Touran discusses.
Ultimately, I believe it deserves further consideration for R&D and deployment.
You seem to have a pretty broad knowledge of projects that are out there. Would you consider putting together a post sometime that's a nexus of links with your quick takes about these projects so we can all check them out? I've followed MSRs but would love an education in some of the more interesting concepts being fielded that aren't molten-salt related. It might even make for a good wiki page here in ~enviro.
I can prep a wiki page, sure!
I think these are critical because they are mobile - this power plant can move to and hook up to any grid you like. If we had these right now, they'd be hooking up offshore of Texas and that would be the end of their power problems. Then once that's sorted it's off to the next disaster zone. This sounds like a mighty fine mission for the US Navy to take on. Right in their wheelhouse and pleasantly not a fleet for war - a fleet for green energy instead. That seems like progress.
Here's the sales pitch for nuclear fleets, if anyone else is interested in learning more.
It's the mobile bit that matters. Getting a small MSR inside a shipping container so it can be flown or driven wherever needed also fits that bill, but MSR tech is not ready for that challenge yet. That's gonna take a lot more R&D. The nuclear fleets can get started much faster than this since they don't have the space constraints on the reactor that a shipping container imposes.
I would clarify that not all designs are necessarily mobile - the Offshore Power Systems proposal utilizes large breakwaters, while even ThorCon requires a reasonable amount of shore-based support equipment.
Indeed. However, it's not hard to imagine power docks built for this purpose becoming common so the ships can move around more easily. Or multiple vendors offering different reactor options, pricing models, reactor technologies, a mobile power marketplace. Once it exists it'll get more efficient, but more important - the companies working on nuclear technologies will get their funding.
It doesn't sound like it would be any good for emergency power? Depending on where it's coming from, going by sea, it might take days or weeks to arrive, and there's going to be more to hooking it up. There are better ways to prepare for disasters. (But on the offbeat side, there is the time a Canadian town hooked up a diesel-electric locomotive to city hall.)
It seems like the main advantage of having a movable power plant would be that the utility could sell it?
The main advantage is a highly modular, standardized construction. In some cases, distance from land and an infinite heat sink are advantages as well.
This is a little bit off-topic but as someone who works within the realm of nuclear energy, I'd be interested to know what you think about the Netflix docu-tainment series Chernobyl? If you've seen it, what do you think the show got wrong, and what did it get right? Did it perpetuate any misconceptions about nuclear energy, or dispel any? Do you think it helped the public perception of nuclear power, or harmed it?
Second question: What are the costs and risks associated with re-refining spent fuel? It seems like there's a high concentration of u235 and things like plutonium in spent fuel, which could be used to power reactors. It seems like spent fuel is a much richer ore than pitchblende for example.
Haven’t seen Chernobyl. The only thing I’ll say on that subject is I’ve seen/heard some people swayed both ways on nuclear based on that alone.
The term you’re looking for is reprocessing. Conventional reprocessing is expensive, because you are performing a rather hazardous chemical process with highly radioactive material, within a thick concrete building. Additionally, enrichment is cheap, and uranium deposits are more plentiful than we thought they were in the 1950s and 60s. I’m still supportive of it, because it closes the fuel cycle and can reduce the radiotoxicity of SNF considerably (plus we maintain the operating knowledge and experience). There’s also other concepts like dry reprocessing (changing the form of spent fuel with minimal separation, e.g., AIROX) and crystallization. As far as proliferation goes, it’s not my area of expertise, but I believe that it is a small issue with sufficient international safeguards in place (and it can be solved technologically, see above).
What is the long term outlook for the fuel stores at your site? I.e. how long are you required to plan for continued storage? What’s the life span of materials under your purview? Hello to a fellow DoEer!
Some of the fuel has been storage for decades, and a study from about ten years ago shows that we could continue storage for 50+ years. I think we’ve messaged back and forth previously!
The major trend in the last 20 years has been toward passive safety - more and more reactor designs are walk away safe; they don’t need any operator intervention after the reactor scrams (shuts down). Even among designs at existing units, there’s been incorporations of lessons learned from TMI and Fukushima (Chernobyl was a very different design from Western light water reactors). One of the most notable are the FLEX buildings, which contain extra diesel generators, bulldozers, and other equipment needed to recover from a major natural disaster at the plant. If my understanding is correct (I’m not on the commercial side of things), plants now need to be able to survive two natural disasters at once (e.g., earthquake and a tsunami).
Regarding climate change, at a bare minimum existing reactors are needed to transition off coal and gas faster. I suspect existing and new reactors will be critical for anywhere for 2-20% of the world’s energy supply (I’m very interested in seeing non-electricity uses, especially marine propulsion).
To expand on the answer regarding utility of fission for climate change: As far as I understand, the time to get a reactor up and running is at least 10 years, more if you want tech that has not been practically demonstrated yet. That is generally too long for climate change.
My argument would be that renewables are well enough understood, cheap enough, and with some well understood techs we can make them baseline capable. That is good enough to beat climate change. Waiting for new reactor designs is not an option, building up capacities of existing designs has to happen right now, or won't help with climate change.
I view it like this: there will be less nuclear than most pro-nukes would like, but more than the Wind Water Solar people would like (hence the 2-20%). You’re correct that nuclear has deployment issues (although I’m hoping that will change for some of the new designs), and renewables (specifically wind and solar) are great for quick deployment, although once they get up to around 50-80%, it becomes more difficult to build out past that. Conventional hydro is often used in that role, but it is increasingly controversial, and in my mind unlikely to be built in most western countries (bar a few exceptions, like Site C in British Columbia). There are also roles for nuclear to play in process heat, district heating, marine propulsion, and remote power (Arctic towns, remote mines, etc).
I assume you mean because beyond that point, you have to worry about baseline loads, calm&dark scenarios, etc? The plan that is being floated for that by german's most relevant academic is one of batteries that can last you a few days and a reserve of a few weeks worth of synthetic methane. Those are all well understood technologies, we just have to use them.
I'm kinda against nuclear because of waste problems (we germans don't have a desert handy, kinda hard to find a suitable final storage.) and to a lesser degree safety concerns. I'm all for research into passively safe and low-waste reactors, but that should have happened 30 years ago at least. We knew climate change was going to be a problem in the 80s. But instead of doing the right thing, i.e. research renewables, fill the gap with the best nuclear we can, we did the wrong thing and filled the gap with more fossil fuels. Now that those are starting to look less and less viable, we finally look to nuclear for a solution, and it's a little late for that. The reactors europe is currently building are all projects with horrible budget and schedule overruns. Schedule overruns that we can't afford if we want to stay within the timeframe we have for decarbonization.
Do you think Thorium molten salt reactors are ever going to be commercially viable?
They’re separate questions. The thorium fuel cycle isn’t particularly game-changing outside of certain contexts (e.g., India, which has huge deposits of thorium but not uranium). We don’t have as much experience with it, and then there’s the fact that thorium isn’t even fissile, it must be irradiated to be converted to fissile U-233. There’s not a lot of advantages of it over conventional uranium, and a reasonable number of disadvantages.
On the MSR question, I’m a bit more optimistic. There’s a lot of R&D going on those designs. There’s still some hurdles to overcome (material accountability, corrosive nature of the salt, among others), and I’m still leaning toward high-temperature gas cooled reactors.
Isn't the whole point of thorium MSRs to just chuck all the radioactive stuff into the salt, such that it decomposes, giving us heat and no waste, while the thorium keeps chugging along, keeping the rest of the cycle going while decaying into mostly untroubling waste too? At least, that's what the hype tells me. Although I don't really buy into that. Maybe in several decades time.
Sorry I forgot about this. A thorium fuel cycle (usable in other reactors too, not just MSRs) still produces fission products, but it produces less actinides (plutonium, neptunium, americium, curium), which tend to drive long-term radiotoxicity concerns. Fission products (e.g., Cs-137, Sr-90, I-129, Tc-99) aren’t usable for producing energy (although they may be used as scientific and industrial isotopes). Without actinides, you can simplify repository design, as radiation levels decline to natural uranium background quicker (if you partition and transmute I-129 and Tc-99 as well, the waste packages will decline within 500 year, versus 10,000 or more for standard waste).
I agree thorium is overhyped. Virtually all of its benefits are achievable with a conventional uranium fuel cycle + reprocessing + fast reactors, and thorium has it’s own drawbacks (e.g., fuel fabrication might have to occur remotely due to daughter product gamma radiation levels). The main reason to pursue thorium, besides basic research, would be strategic. The main example being India, which has little uranium reserves, but plentiful thorium. A thorium fuel cycle for Indian power stations would enable independence from foreign nuclear fuel suppliers.
One other potential reason would be to use thorium which occurs as a byproduct of rare earth mining. The presence of thorium with domestic rare earth supplies makes mining expensive due to regulations, since the thorium is radioactive, and you must ensure worker safety during processing as well as pay for proper disposal. If you can at least sell the thorium for fuel, that could help make rare earth mining worthwhile in the U.S.
Just curious, did you ever have any work with the Navy's nuclear power program? I was a nuke so I'm always interested to see how far the Navy's reach extends.
Nope! Picked up a B.S. in chemical engineering, wasn’t actually expecting to work in the nuclear sector, but it’s the job I picked up after graduating. I do enjoy it quite a bit (great work-life balance, more traditional work culture). We do have ex-Navy Nukes on site though, we especially like them for their practical experience.