SMRs - Small modular reactors (SMRs) are a type of nuclear fission reactor. - Page 1
Forum section: electronics / general

author: BrianHG
author_rank: Super Contributor
timestamp: October 14, 2020, 12:43:46 am
content: Has anyone here done any research into these. Supposedly, there is at least 1 design which will be getting approval in the near future.https://en.wikipedia.org/wiki/Small_modular_reactor

author: m3vuv
author_rank: Super Contributor
timestamp: October 16, 2020, 09:35:35 am
content: i think they need to find a way to deal with the spent fuel waste before giving these the green light!

author: David Hess
author_rank: Super Contributor
timestamp: October 16, 2020, 02:08:05 pm
content: The spent fuel does not go anywhere because they are not designed for refueling.

author: Gyro
author_rank: Super Contributor
timestamp: October 16, 2020, 04:40:06 pm
content: Quote from: David Hess on October 16, 2020, 02:08:05 pmAs described in the video, the bottom section (the core) is designed to be removed (under water) and replaced. Sounds like refuelling to me.Lots of spent cores to deal with.

author: KaneTW
author_rank: Frequent Contributor
timestamp: October 16, 2020, 04:47:49 pm
content: I really don't understand why spent fuel is such a hot topic.1) Large parts of it are reprocessable2) There's reactors that consume nuclear waste3) We're already storing large amounts of highly toxic waste; I don't see how a leak of highly radioactive waste is significantly more dangerous than a leak of arsenic oxide or whatever.Pure fearmongering. Especially during a time where we need to solve climate issues NOW --- and not fear about issues millennia down the line, where the state of the art will have advanced significantly anyways.

author: BrianHG
author_rank: Super Contributor
timestamp: October 17, 2020, 10:49:29 am
content: Quote from: KaneTW on October 16, 2020, 04:47:49 pmPeople fear what they do not understand, yet such materials get both news air time and recognition of being powerful and connected to nuclear bombs.However, improper handling of such waste does cause problems & there is a valid trust issue with corps for profit being in control of handling and long term disposing of such materials.

author: f4eru
author_rank: Super Contributor
timestamp: October 17, 2020, 04:44:25 pm
content: Quote from: KaneTW on October 16, 2020, 04:47:49 pmYeah, let's poison our children, brilliant idea.Quote from: KaneTW on October 16, 2020, 04:47:49 pmWrong assumption. Civilizations don't work like this.

author: KaneTW
author_rank: Frequent Contributor
timestamp: October 17, 2020, 05:20:56 pm
content: Quote from: f4eru on October 17, 2020, 04:44:25 pmThere's plenty of worse shit to be poisoned by, that can leak from similar storage, than a couple of uSv/h in case of a radiation leak.Not like a leak is even particularly likely in the first place.QuoteOf course they do. Technology advances, and so do reprocessing capabilities. Waste that has been uneconomical or impossible to reprocess can be in the future. (or in some cases, already can)

author: Kleinstein
author_rank: Super Contributor
timestamp: October 17, 2020, 05:36:23 pm
content: The described modular reactor is essentially a small conventionally reactor. So the waste problem is essentially the same as with the classical reactors. Similar to current large reactors the fuel availability is limited to a limited scale use - not much more than current nuclear capacity and thus no significant CO2 reduction. It can still be a small contribution to base load at night. The high costs do not make it economical to run the reactor only part time, when energy is actually needed. So the demand side also limits it to a small contribution.There are a few positive aspects with the small modular design, especially building at a factory and not all on site. One also does not need the very large steel pieces only available in limited quantity.However there are also some principle downsides with the small size: There are more neutrons lost to the outside. So the reactor would need higher fuel enrichment and would likely run with shorter run-time on a fuel loading as there may be less possibility for reshuffling. With the cold water tank at the outside, there would be quite some heat loss and thus a lower efficiency in producing electricity. Smaller size would likely give higher neutron dose to the pressure vessel and thus a more limited life time (e.g. maybe 10-20 years instead of some 40 years for the current reactors). As the power density is likely lower, it would need more steel to build and thus more contaminated material in the end.I very much doubt the safety review would allow for multiple reactors in one pond. Chances are they would need more like individual containment buildings and this would raise the costs quite a bit. Having a door large enough to bring a new reactor unit inside would be quite a problem.To allow refueling of one reactor, while the others are still running would also need quite some barrier.

author: james_s
author_rank: Super Contributor
timestamp: October 17, 2020, 05:41:52 pm
content: Quote from: f4eru on October 17, 2020, 04:44:25 pmWhat do you think we're doing when we burn fossil fuels? Heck even fabricating solar panels uses lots of toxic materials that need to be stored or disposed of. So does mining raw materials. Name a source of energy that does not cause environmental damage or risk poisoning anyone. At this point in time nuclear is one of the cleanest sources of energy we have.

author: KaneTW
author_rank: Frequent Contributor
timestamp: October 17, 2020, 05:42:24 pm
content: I don't think this particular design is promising, but stuff like the Xe-100 reactor based off TRISO fuel are.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 17, 2020, 05:54:31 pm
content: These small modular reactors have been "just around the corner" fordecades. Just like reusing nuclear waste in any meaningful scale. Or "yo dawg not all nuclear is dangerous the thorium reactors are coming so nuclear good solar panels toxic and bad!"Yet the failure to ever deliver does not seem to slow down nuclear fanboys from using these "just around the corner" assumingly ground-breaking technologies as an argument to keep building conventional nuclear; year after year, decade after decade.Nothing wrong with that viewpoint in itself, but I just don't like mental dishonesty.Nuclear fanboys seem equally simple-minded to the fearmongers, simplifying an actually complex matter without caring about total lack of internal logic or honesty of their claims. "We have FOUR(!!!!111) redundant layers of safety" is a real classic example; not mentioning one of them fails all the time during normal operation, failure of which is not even considered anincident, and under LOCA, fails inseconds.What comes to the SMR, in general, it seems the opposite trend is true; making larger plants. This makes sense because the amount of effort that needs to be put in to protect against technical failures as well as terror threats has a large constant per-plant component, or is some kind of logarithm (or maybe square root) of the plant size.

author: Cerebus
author_rank: Super Contributor
timestamp: October 17, 2020, 10:40:57 pm
content: I have a radical suggestion.Instead of re-hashing all the pro- and anti- nuclear arguments for the \$e^{20,000}\$th time, and making dumb statements that fly in the face of obvious common sense such as impling technology does not improve over time, could people perhaps confine themselvesto the relative merits of the SMR designs.Just a thought. Crazy I know. I mean, who'dwantto have a rational, on-topic discussion when there are so many hobby horses to jump on?Yeah, sorry, probably futile, but who knows, perhaps this is the first time in history...

author: f4eru
author_rank: Super Contributor
timestamp: October 18, 2020, 09:17:13 am
content: which merits ?it's smaller, so more expensive per kWh.it's a one time use, so you have many more core packaging material to dispose of.

author: f4eru
author_rank: Super Contributor
timestamp: October 18, 2020, 09:28:55 am
content: Quote from: KaneTW on October 17, 2020, 05:20:56 pmNope. Civilizations work like this: they always rise and peak and then fall.What will happen when our actual peaking energy based civilization will have it's downfall is the same than for every other civilization downfall: non-survival critical knowledge and techniques will get lost because they are not immediately useful.Maintaining toxic drums of waste is not immediately survival critical, so they will not get maintained any more, leak, and all the non-used knowledge will get lost.After the roman empire downfall, concrete building chemistry was lost for 2000 years, because it was not necessary to build amphitheaters any more. Nobody had any interest to maintain their legacy before many centuries.After the greek civilization collapse most of the mathematics and astrophysical knowledge and techniques were lost.Nobody had any interest to maintain their legacy before many centuries later.After the sumerian civilization, most of their knowledge was lost, even if they writteneverythingdown.Nobody had any interest to maintain their legacy before many centuries later.After the mass falling of the bronze age Mediterranean civilizations, many crafts and techniques got lost for centuries.Nobody had any interest to maintain their legacy before many centuries later.Somehow, trying to survive today gets precedence over technology, every time.Civilizations will fall down. it's simply inevitable due to resource overuse. (hint: we are now using too many resources)Like it or not, it is how our human race civilizations work. All of them.Nuclear power is not a good thing because in order to not poison the next generations, it assumes civilizations will not fall, and will maintain our legacy.This very basic assumption is absolutely and utterly wrong.

author: nctnico
author_rank: Super Contributor
timestamp: October 18, 2020, 10:11:24 am
content: Quote from: Cerebus on October 17, 2020, 10:40:57 pmI agree. The suggested advantages in the video make sense to me (especially being able to build the modules in series which should bring the costs down) but in the end it comes down to the economics. There are many angles to look at it and there is no clear cut answer a modular solution is better or worst in every case.@f4eru: the error in your reasoning that civilisations fall is that currently the civilisation is global and thus spread of information spans the entire globe and not a couple of thousand square kilometers. Your simple example about how to make concrete doesn't fly nowadays. This is known world wide. The invention of book printing has helped to spread and preserve information on such a massive scale that it is unlikely information gets lost ever again.

author: f4eru
author_rank: Super Contributor
timestamp: October 18, 2020, 02:54:09 pm
content: Sure. The Sumerians also said exactly the same.Their never seen before extent of knowledge , it's dissemination, use, storage was unprecedented, at an enormous scale for the time.Still, most of it was lost for 4000 years, because it was irrelevant to people.You simply can't bet against human nature on the long run. You can't control what future generations will do with your legacy. It simply doesn't work.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 18, 2020, 02:59:25 pm
content: Quote from: Cerebus on October 17, 2020, 10:40:57 pmA good idea. Why not lead the way and give your analysis? I already gave mine although just one short paragraph, Kleinstein had more, it's a start. What doyouthink, other than "you discuss this the wrong way" meta? I'm thinking that the fundamental law of volume-to-surface area ratio plays in favor of larger plants given that even very small plants require significant protection. Distributed small modular systems tend to work well when the units can be kept very simple minimizing the ancillary costs, but this doesn't seem to be easy to achieve with nuclear fission, hence units getting bigger and bigger.

author: Cerebus
author_rank: Super Contributor
timestamp: October 18, 2020, 02:59:53 pm
content: Quote from: f4eru on October 18, 2020, 09:17:13 amYou're just making an assumption there. Probably "economies of scale" while ignoring the fact there are also "costs of size" too - ask any elephant.QuoteClearly you haven't watched the video, which discusses the refuelling cycle.

author: nctnico
author_rank: Super Contributor
timestamp: October 18, 2020, 03:03:28 pm
content: Quote from: Siwastaja on October 18, 2020, 02:59:25 pmIf I understand the video correctly then the goal is to place a number of SMR units (the video says 12) in 1 'room'. It is not like every SMR unit is installed in its own bunker. That wouldn't make sense.

author: Cerebus
author_rank: Super Contributor
timestamp: October 18, 2020, 03:12:02 pm
content: Quote from: Siwastaja on October 18, 2020, 02:59:25 pmI don't have an analysis, but I'd like to be able to hear other peoples without a torrent of irrelevancies.One thing that strikes me about what you say: a high volume-to-surface area ratio has an advantage during stable operation (low unwanted thermal losses), but is not a high volume-to-surface area ratio a disadvantage if you're trying to make an intrinsically 'safe' reactor, one that can scram to a safe low output state without external infrastructure. This design seems to take advantage of that with the only requirement a large pool of water to sit the thing in - no external pumping, control or anything else required - for safe shutdown. Fukushima failed because systems outside the core failed.

author: Cerebus
author_rank: Super Contributor
timestamp: October 18, 2020, 03:15:17 pm
content: Quote from: nctnico on October 18, 2020, 03:03:28 pmNote though that the thrust of some small reactor designs has been partly in that direction, powering remote communities or distributing generation. Thus anyone who hasn't actually watched the video may assume that aspect is part of the thrust here, which it is not.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 18, 2020, 09:51:02 pm
content: The volume to surface ratio makes a difference in many aspects. A large surface to volume ratio help with passive cooling but at the same time increases unwanted heat loss. It really helps if one can switch the heat loss off and not have constant leakage. After some 1 day the decay heat is at about 5% of nominal power. So if passive cooling is constant and designed for 1 day operation it would lose around 5%. As the temperature in operation is usually higher than with storage the loss would be even higher.A second and probably more important point are the neutrons lost: with a small core one would need a relatively thick reflector for the neutrons. So with a 4 m diameter pressure vessel one would loose something like 1-1.5 m all around to the reflector. So the actual core would be only some 1-2 m diameter and thus using some 8-25% of the cross section only. The wall material needed for a pressure vessel is proportional to the volume inside, so the added volume also adds costs.Inside the core the neutron density decays with a length typical in the 1 m range, so the outer part usually gets lower power density and uneven fuel usage. In a large reactor much of the fuel is in a more homogeneous center zone and can thus get a longer usage without much usage of control rods or fuel reshuffling. A larger core could even get away with less reflector as neutron loss is less critical.The gas cooled reactors have a pretty hard time getting away with passive cooling. There were a few pebble reactors tested and they all failed, notably the THTR 300. Much of this got unnoticed as the final accident happened in parallel to the Chernobyl accident. In a pure gas and at high temperatures graphite gets sticky and no more good sliding of the pebbles. Only a few broken ones can cause even more jams and locally block the gas flow and thus a cooling problem. So a broken pebble is truly troublesome incident. Because of the poor sliding and limited stability the pebble bed reactor is limited to small size, especially low hight. Already the relatively large (too large for the pebbles) THT300 needed highly enriched fuel and had a poor neutron efficiency and was thus too small to work an practical fuel.Those proposed small reactors would need higher enrichment, so more like 5-20% enrichment instead of the typical 3-4 % in GW size reactors. With the high enrichment this would be more expensive and without reprocessing would send quite a fraction of the fuel unused to the waste. Currently the reprocessing is expensive (considerably more expensive than new fuel), dirty and politically not wanted because of proliferation. AFAIK there was not much progress in reprocessing in the last 20 years - at least not public as much of it is classified. So it would be not just get the small reactors ready, but also get reprocessing economic and accepted.I see that the proponents of the small modular reactors plan with multiple reactors in one containment / bunker, but I very much doubt the regulation would alow this. In addition the radiation would make maintenance impossible if only 1 reactor would be running. So separate containment may also be more practical. Like with a pressure vessel the volume counts - so several small buildings would not even be necessary more expensive then one large one. Once large enough to also protect from external effects there should be no big advantage from scale. The relatively large pond for passive cooling adds to the costs - here it's more like independent of reactor size. The passive cooling adds to the size and costs over current designs.Not surprisingly some small reactor proponents also suggest thorium use. However the thorium cycle is notoriously low in neutrons. So if at all it has a chance to work with a rather large reactor and essentially not a chance to work in small scale unless using fast neutrons. They seem to add it more to add more unknowns and more difference to existing technology, so they can stay more vague. Especially in the US there seem to be strange logic that the less they know the more they could claim as possible advantages without turning red. However with more new technologies involved the probability for success also goes down exponentially.

author: nctnico
author_rank: Super Contributor
timestamp: October 18, 2020, 10:16:14 pm
content: My opinion based on what I've read about Thorium reactors is that these are highly unlikely to be ever commercially viable.

author: BrianHG
author_rank: Super Contributor
timestamp: December 09, 2020, 12:02:43 am
content: Another look at SMRs.