What if we had commercial fusion power?

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rbelli1

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A fusion reactor would likely have on the order of 10 kg of tritium in inventory. If I calculate correctly, this is ~ 100X the radiation released at Fukushima, so an accident that released even 1% of the tritium inventory would be an equal amount to Fukushima. Also, since tritium is easily taken up by the body, it can have significant biological effects.
Only a small portion of that will be in the reactor at any given time. I would think that there would be some mechanism put in place to limit the spillage in the event of a catastrophic failure. Also when gaseous tritium is released it has the tendency to go straight up and rapidly escapes the atmosphere. Not that releases of it are healthy. Storage as oxide would prove rather more dangerous in the event of a spill.

https://www.iter.org/sci/FusionFuels

The intent is to produce the fuel as an ongoing part of operation. Only a small quantity will be needed on site at any given time. I would hope that the operators of fusion plants (if we ever get that far) will keep the inventory of expensive and dangerous fuel to a minimum.

BoB
 

phyzguy

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The intent is to produce the fuel as an ongoing part of operation. Only a small quantity will be needed on site at any given time. I would hope that the operators of fusion plants (if we ever get that far) will keep the inventory of expensive and dangerous fuel to a minimum.
BoB
Do you have a source to back this up? The reactor requires a "blanket" capable of breeding tritium. This consists of lithium, tritium, and some sort of neutron multiplier, like lead or beryllium (see the source you cited). I suspect that the blanket will be highly radioactive, and represent a large inventory of radioactive material. The source you cited also says that a typical reactor will need ~150 grams of tritium per day. Given this, a total on-site tritium inventory of 10 kg, between fuel ready to be injected and tritium resident in the blanket, seems reasonable to me. Also, the fact that the tritium is stored somewhere else instead of at the reactor site doesn't lessen the chance of a release.
 
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I agree with PeterDonis , a fusion reactor can't have a meltdown, and as of this day it can't even have a self sustaining operation as we haven't got to breakeven point in other words power in= power out or 1:1.
Also the argument about plasma having a low , in fact very low density is very correct, speaking plainly the amount of heat energy (inertia) some material has depends on its temperature and weight, plasma may have an extreme temperature but it has almost no weight, tons of Uranium have much much less temperature in a reactor core but much more weight as was mentioned here before so takes much longer to cool. (Sure the complicated explanation involves decay products and half lives etc)


So apart from tritium fusion is very safe because all the other radioactive materials are solid and can't be simply released into environment I think , right?


But I would like to disagree with PeterDonis on Fukushima. I think Fukushima can be labeled as a core meltdown much like Three Mile Island because that is essentially what happened, the cores at Fukushima lost cooling water due to no cooling pumps working and decay heat evaporating the existing water, which then led to meltdown or partial meltdown of the core as in the physical core inside the core vessel melted. The core primary containment vessel may indeed have stayed intact (not sure and too lazy to search now) but still the core inside melted so I don't think it's wrong in Fukushima case to say that there was a meltdown.
When something physically melts and causes the reactor to be deemed lost accompanied by the release of fission products (yes in gaseous state but still) into the environment then I think it is fair to say it's a meltdown, what do you think?
 
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A fission power reactor generates about 1.8% decay heat at 30 minutes post shutdown. Then for a typical 1000 MWe plant (say 3400 MWth core) at 30 minutes we need to remove 58 MW or 55,000 Btu/sec.

For tritium, wiki says specific activity is 3.57E14 Bq/gram; via 5.7 keV betas plus antineutrinos. The antineutrinos leave carrying away their energy. So if we have 10,000 g tritium * 3.57E14 Bq/gram * 5.7 keV = 2.035E19 keV/sec = 3260 joule/sec = 0.00326 MW 0r 3.1 Btu/sec. Did I do that correctly?

Then the "decay heat" in the fusion machine is 3 Btu/sec vs. 55,000 Btu/sec in the fission machine. The safety case for these two is going to be completely different.

@artis, the 100 tons of uranium in the fission core don't really matter; what does matter is that the fission products generate heat after the reactor is shutdown (no longer critical). In other words, a fission core doesn't really have an "off switch." This is the central engineering issue with fission reactor safety. Apparently the fusion machines do not have this issue (see above).
 
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I think Fukushima can be labeled as a core meltdown much like Three Mile Island because that is essentially what happened
It is true that there was core melting and damage in both cases, yes. But in TMI, the core did not melt because of lack of decay heat removal after shutdown; it melted because of a loss of coolant accident while the reactor was operating, because of a combination of faulty instrumentation, violation of NRC rules, and poor judgment on the part of the operators.

I think it is fair to say it's a meltdown, what do you think?
I think there has been enough argument about the usage of the term "meltdown" already in this thread.

As far as the public is concerned, I think the key things to focus on in any incident are:

(1) How much radiation has been released, and in what form? What precautions can be taken to minimize exposure? There is no way to describe this using a single word, whether it's "meltdown" or anything else.

(2) Can the release of radiation be controlled? If it can, as I mentioned in a previous post, then the costs and benefits of any radiation release can be discussed in advance, the timing can be planned, and the public can be warned and given time to take precautions. If the release of radiation is uncontrolled, none of those things can be done, which makes the whole event much more dangerous. There's no way to describe all this using a single word either.

My personal opinion is that the term "meltdown", in the minds of lay people, suggests, not just an event in which a fission reactor core melts, but such an event in which (1) a lot of radiation is being released outside the plant, and (2) the release is uncontrolled. In other words, a scenario like the one described in movies like The China Syndrome (in that movie, the scenario is narrowly avoided, but it is described as the core melting and sinking down through the containment walls and into the earth until it reaches groundwater, causing widespread release of radioactive water and steam). TMI met neither criterion. Fukushima arguably met criterion #1, but not #2.
 

russ_watters

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@PeterDonis the argument was instructive though about what the nuclear industry is up against with fission. Yes, using a single word creates a false equivalence between the accidents. Eliminating the word (and the associated word "core") when moving to fusion will mean A LOT to the public when it comes to the acceptance of fusion vs fission.

Not for nothing, though, but I don't think the public cares much about your criteria #2 and the difference between "uncontrolled" and unavoidable. My recollection off the top of my head is the difference between Fukushima and Chernobyl was about a factor of 10 in radiation release, but I bet the average person on the street believes they were about equal or even that Fukushima was worse (3 "meltdowns" to 1).
 
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I don't think the public cares much about your criteria #2 and the difference between "uncontrolled" and unavoidable.
If that's true, it's yet another reason to do a better job of explaining why "uncontrolled" is a worse problem than "unavoidable". To use your comparison of Fukushima vs. Chernobyl, in the former radiation release was unavoidable (it had to be done in order to minimize the overall impact), but not uncontrolled; in the latter, radiation release was uncontrolled, and I would argue that that made the impact of the latter worse than the former, even after factoring in the difference in the amounts of radiation released.
 

russ_watters

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If that's true, it's yet another reason to do a better job of explaining why "uncontrolled" is a worse problem than "unavoidable". To use your comparison of Fukushima vs. Chernobyl, in the former radiation release was unavoidable (it had to be done in order to minimize the overall impact), but not uncontrolled; in the latter, radiation release was uncontrolled, and I would argue that that made the impact of the latter worse than the former, even after factoring in the difference in the amounts of radiation released.
Yes, that was my point....though I think the last part is a cause-effect chain at least in this case: the amount released was higher for Chernobyl because [of the manner in which] it was unavoidable.
 

phyzguy

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If only public perception were influenced by these detailed arguments (like the difference between 'uncontrolled' and 'unavoidable'). We have unfortunately gotten to the point where most people seem to think that nuclear power is horribly dangerous. I don't know how we go about changing the perceptions. It's very unfortunate, because expansion of fission power plants could today be making a very positive impact on reducing greenhouse gas emissions. However, unless we can somehow change public perception, this seems politically impossible.
 

rbelli1

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Do you have a source to back this up?
Small compared to the one or more years of fuel in a fission reactor.

It would not make sense to have a full year worth of fuel then at the end of that year have even more because you are making it as you go.

Would there be a method of regulating the tritium output so as to keep your fuel level at optimal? What do you do with the excess if not?

Also, the fact that the tritium is stored somewhere else instead of at the reactor site doesn't lessen the chance of a release.
If the core explodes then the farther away your fuel is the less chance that that area get damaged by the explosion. I do understand that exploding fusion cores will not be a Chernobyl level event. Or maybe not even possible at all.
As for a general operational issue then I agree that the distance is not really a factor.

I suspect that the blanket will be highly radioactive, and represent a large inventory of radioactive material.
Yes fusion reactors will be safer than fission rather than completely safe.

BoB
 
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If the core explodes
A fusion reactor can't explode. Neither can a fission reactor, for that matter. A nuclear explosion of either type requires a very precise set of conditions, which simply cannot be met in a power reactor.
 
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It was not a nuclear explosion but it certainly was an explosion.
Ok, when you said "core explodes" that made me think you were talking about a nuclear explosion. The Chernobyl explosion was a steam explosion due to the coolant flashing to steam because of uncontrolled reactivity. (There was also a graphite fire that released radioactive material.) Even that can't happen in a fusion reactor because there is no such thing as uncontrolled reactivity: any disturbance causes the fusion reaction to shut down, not grow.
 

phyzguy

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SYes fusion reactors will be safer than fission rather than completely safe.
BoB
The problem is that fission reactors are already safer than other power generations methods, but nobody believes this, so saying fusion power plants are safer will probably fall on deaf ears. By any rational measure, fission plants are far safer than coal burning plants, and clearly safer than hydroelectric power plants. This Wikipedia page attempts to quantify the impact. A single hydroelectric dam failure killed over 170,000 people in China. By comparison, nobody is documented to have died from the radiation release at Fukushima.
 

russ_watters

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...exploding fusion cores will not be a Chernobyl level event. Or maybe not even possible at all.
Here's the problem with using the word "core" in this context: You're using it to mean "the central or most important part", which is one of the dictionary definitions. But for fission reactors, the "core" refers to the pile of radioactive material inside the central or most important part of the reactor. A fusion reactor doesn't have a pile of radioactive material in the it. So using the same word for both implies something false about the construction of fusion reactors.
 

russ_watters

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The problem is that fission reactors are already safer than other power generations methods, but nobody believes this....
This, unfortunately, is true:
https://news.gallup.com/poll/2167/energy.aspx

Among the results:
In 2016, polling had the lowest favorability perception of nuclear power in 20+ years of polling; 44%.
Is nuclear power safe? 57% yes -- fairly steady.
Increasing nuclear power: "Necessary" or "too dangerous" (odd choices....) 46-48%

https://en.wikipedia.org/wiki/Public_opinion_on_nuclear_issues
Global support:
Solar: 97%
Hydro: 91%
Coal: 48%
Nuclear: 38%
 
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I want to share a few thoughts, please don't pick on me for those.

1) Not to sound judgemental or anything but I hardly doubt that the society or the average citizen will ever care if he is even capable of understanding the peculiar technical differences between a core meltdown that is contained within the core vessel or Chernobyl type accident or a standard nuclear bomb explosion. The videos posted on internet where Fukushima outer reactor buildings exploded from accumulated Hydrogen gas to many were "nuclear explosions".
Given how we are glued to facebook and "smart"phones and all kinds of kinky little gadgets plus the complexity of modern life, well good luck with trying to make society think about complicated nuclear science stuff.


2) If we want to be very technical and precise then no one should also ever call Chernobyl a "meltdown" because it was not. In fact it was (hope i get my facts straight) a reactor whose reactivity got out of control due to operator error and added by design specifics like positive void coefficient aka positive feedback of power which led to core thermal power increasing 100 of times above max limit causing the approximately 1600 pressure tubes where fuel rods were inserted to rupture and water upon loosing pressure flashing into steam causing a massive steam explosion after which a second explosion happened the causes of which are still debated(and probably forever will be) which then accompanied by panic and lack of correct information in the hours after the accident caused mayhem and chaos. Theoretically this is what the news should read about this accident. But the news care about views so to them Chernobyl Fukushima it's all the same.

Also the wise thing to say to public would be that due to the big differences in design Chernobyl was unique and cannot happen in any western made PWR or BWR type reactor and not even in the Soviet, later Russian made VVER type reactors which are similar to western PWR types.


Also I read that often , even the mods here write that "Chernobyl would have benefited from a containment structure like the ones (reinforced concrete domes) around western reactors" but if we wish to be technically correct then is this statement accurate? I am no expert so please correct me if necessary but western type reactor containment is mainly two fold, first the reactor vessel itself then the outer dome for extra protection, but western reactors are designed such that the worst thing that can happen is a partial or full core meltdown within the core vessel which is then contained within the vessel ideally or in worst case within the reinforced dome.
Chernobyl was not a meltdown but an explosion the power of which is estimated to be up to 10 or more tons of TNT, would a western type reinforcment structure have withstood such a shockwave and gas pressure occurring in a matter of few seconds? I sort of doubt so.

For me the logical conclusion is that the RBMK-1000 reactor in the worst case scenario has the capability to go "boom" with a force that modest chemical explosives would envy so constructing a containment for such a "device" would be impractical and extremely expensive so the logical thing here would have been to not build the RBMK-1000 in the first place. Or build it and go with the risk which is what happened.
 
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Someone here said earlier that we are better off with the devils that we know than the ones we don't. I think it explains why many people fear anything nuclear- they simply don't know much about, it's just bedtime horror stories for them and so just like death , the unknown frightens us. Only unlike death which we have no control over and can't know what's on the other side with nuclear we can actually learn and understand and we have and the safety of modern reactors is a testament to that.

Reading many papers over the years I can say for sure that back when nuclear was at it's infancy the so called "meltdowns" actually happened alot more than they have in the past say 30 years. There have been various accidents in some early test reactors like the SL1 and some others but back then the media was realistic so there was no hype , now it's the other way around the technology is much much better and we have only had one major problem with Fukushima yet the "fake news" money ad revenue driven social media is all hyped up about anything they can touch.
Also back in the day , for example when Chernobyl went into "bomb mode" the news actually hired some physicists and nuclear experts and only then dared to even speculate about what has happened , somehow I don't see such attention to detail now.


One last word I want to say, I think Fukushima could have been entirely avoidable because unlike in Chernobyl where everything went wrong and it happened in a matter of 10 seconds on a reactor that was already into supercritical mode, Fukushima simply could not get backup generators working in time or at all. Given Japan's geographical location , also the location of the power plant itself sitting right next to ocean and the climate change induced increase in weather events which was already well established science and fact in 2011 I think it is simply negligence that they did not move the diesels further uphill and all of this would have been avoided, relocating some backup diesels is nothing in terms of investment money if one considers the loss after an accident like this.
 
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climate change induced increase in weather events which was already well established science
The tsunami that flooded the backup switchgear at Fukushima was due to an earthquake well offshore. It wasn't a weather event and had nothing to do with climate change. Please keep this thread focused on things relevant to the topic.
 
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Ok, point accepted , I forgot that the tsunami was after an earthquake now I remember all the videos of shaking office stuff in Japan.
Still it could have been also a weather event and with the diesels and related stuff being at such a low grade the result would probably been the same so in terms of mismanaging risks I still stand by my point. In fact this was addressed in many papers by people with expertise in the field so I'm just agreeing to expert opinion
 

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