if the measurement time is short enough, (<1us capturing at 60 fps), the probability of interaction is low even with large number of cameras. Even then, some temporal filtering and intelligent time offsetting to separate signals, can usually fix the problem.
It only matters if you need physically accurate data - ie if your brain can't process the multi path error and correct for it. A bat sees in multi path error and has no problem with it. I assume a machine vision system can learn to perform with multipath error and indirectly account for it. ie, it sees an apple with multipath error, and still knows it's an Apple.
There are options to fix multipath and recover the underlying ground truth
1) you can do a reverse raytrace and iteratively correct for the error - somewhat expensive, but there's tricks and shortcuts to accelerate
2) hardware fix to measure the multipath component separately and subtract / correct it - there's several ways to do this - there are some patents on it that I've worked on. The same methods also can remove background signal from ambient light.
- there is waste, it's just shorter lived than fission waste and lower in quantity. The expectation is that fusion reactors will have to be regulated in almost exactly the same way as fission reactors because they are nuclear sites, with nuclear waste, and proliferation concerns.
- there is lot's of pre processing of the fuel to breed the Tritium in a molten salt blanket that surrounds the reactor and separating from the salt and then feeding it into the chamber
- there is plenty of fission and fusion fuel. Yes, there is more hydrogen around.
- tritium is used in nuclear weapons as a booster, to dramatically lower the amount of necessary fissile material
- each fusion reactor is a fast neutron source, which means it can be used to make weapons grade materials. Conveniently, it has a breeding blanket for tritium, in which other fertile fuels can be place to make weapons material: proliferation concerns are a real problem for fusion
It is, but tritium is not put into bombs. Lithium is.
- proliferation concerns are a real problem for fusion
Unless all fissile materials are banned. It is very easy to check for the existence of fissile materials. If there were no legitimate, safe reasons to have any fissile materials in use on the planet, then a global ban on fissile materials is on the table. A treaty where every nation checks on the other is reasonable. It is hard to build a secret fusion reactor, just as its hard to build a secret uranium centrifuge.
It is, but tritium is not put into bombs. Lithium is.
Both are put into bombs.
The main concern when it comes to tritium supply, regards tritium used for boosting of fission charges. Both applications are crucially important, but fusion boosting appears to require significantly larger quantities of tritium. Tritium and deuterium for boosting are supplied to the weapon from an external reservoir (gas bottle) as part of the arming process of the weapon.
Since about 5.5% of existing tritium decays every year, the tritium assigned to each weapon must be regularly replenished. This is done by removing the weapon’s tritium reservoir and exchanging it with a newly refilled reservoir (5). Figure 1.3 shows what may be such a reservoir.
From Norwegian Defence Research Establishment report "Tritium production":
We originally didn't know Lithium-7 would be useful in thermonuclear weapons. It was assumed that it would be inert and that only the Lithium-6 would react with neutrons from the fission primary and breed tritium for the fusion secondary.
Then we tested a bomb [0] and the yield on it was accidentally 2.5x greater than anticipated. So large, in fact, that it is still the largest bomb ever detonated by the USA. It turns out that Lithium-7 will also breed tritium if the neutrons are powerful enough, and emits an additional neutron to continue the reaction. Reactions that we might never have discovered (or probably not until later) if it hadn't been for this mistake.
The end result was a lot more fuel for the bomb, and the explosion was so large that many of the measuring instruments were vaporized. The large yield also contributed to a radiological disaster [1], which was then the inspiration for the original Godzilla [2].
Anyways, that's how a math/chemistry mistake lead to the most famous kaiju movie (series) of all time.
Since the reactors would ostensibly be continuously operating, the danger is the same. 10+ year half life is about as dangerous as 10000 years because you are always generating the waste.
Er, no. If you generate the same volume of waste per year, but for a fusion reactor the waste stops being a problem within a century and for a fission reactor it takes 10,000 years, at any point in time after the first 100 years, waste from a given fusion reactor will be less prevalent than waste from a given fission reactor.
It also doesn't matter that no specific nuclear reactor will have a lifetime of 10,000 years. The problem is that per megawatt of energy generated, fission theoretically creates (much) longer-lived waste than fusion. Over a longer-than-one-hundred-year timeframe, equivalent amounts of energy generation result in vastly different waste carrying costs. Fusion's waste carrying costs are much lower.
And obviously that number is even more in favor of fusion if it only takes 10 years. (ITER claims 100 years though: https://www.iter.org/sci/Fusion)
The danger is not the same between fusion and fission.
Firstly, 10 years worth of energy is inside a fission reactor and is capable of releasing most of that energy in an instant if not properly controlled. This cannot happen in a fusion reactor. A year's worth of fuel is in a gas tank on the wall and needs absurd conditions to ignite. It cannot happen spontaneously.
Secondly, the exhaust is helium-4: a stable isotape of a valuable element.
Thirdly, the neutron bombardment in a fusion reactor activate the materials they hit. If they hit lithium then they make tritium: a much needed isotape for fuel in first generation fusion reactors. The other materials they hit are chosen to have half-lives of less than 100 years. So you have a nuclear site that no one's allowed to touch for a while then you can recycle the materials. It's nothing like the transuranium nuclear waste from fission plants.
If you had a half life of 5 minutes you'd only need to store the waste for a couple hours before burying it somewhere and there's a certain (smallish) amount of high-grade waste at any given moment, no matter how long you run the reactor.
10 years isn't 5 minutes, but it means you just need to keep it secure for a few decades before burying and forgetting it rather than many human lifetimes.
Any leaks will be (to some extent) self-cleaning, insofar as they'll decay substantially within a human lifetime, so if you stop the leak you can wait a couple decades and it will have cleaned itself up. That's much better than the long-life stuff fission produces.
The materials listed on the Wikipedia page and used by the Russians are not practical for large scale use. It's simply too dangerous to have that much weapons grade material or bone seeking material out in the wild. Some isotopes are better than others, and I expect there will be strides using specifically generated isotopes that are not weapons grade, are not bone-seekers, and have much short half lives (decade not 80+ years), and have beta decay.
What's the issue with Cs-137, then? The gamma radiation?
Otherwise, is SrTiO3 really that bad? What's the risk there, someone stealing it for a dirty bomb?
The most convenient decay source is Plutonium-238 because it does not produce any gammas during the decay which would require lots and lots of shielding to protect people. It has long half life of 87 years so a reduction in power of roughly 1% per year. However, it's weapons material - not okay for wide use. This cannot be overstated. Making nuclear weapons today is very easy when you have the requisite materials (Ted Taylor of Los Alamos used to say it would take 3 guys a few months starting from scratch). With today's off the shelf timing systems, explosives, and manufacturing, it could be even faster.
Next up is Strontium, but that is quite dangerous due to human uptake in the bones. And there's polonium - very poisonous and too short a half life to be used.
I have heard from a friend in the business of a new concept that generates desirable isotopes specifically for decay heat sources in a reactor in an encapsulated form which gets rid of any weapons material or processing of radioactive material.
Sure, but you seem to be implying that government has no place in how we self-police and restrain ourselves. Nothing could be further from the truth.
Government is not an external entity which subjugates us, it is the tool by which we settle our grievances with each other without beating each other to death with rocks. To facilitate that, we give government the exclusive right to police us. And I would argue part of that duty extends to ensuring that the populace is informed and aware of the facts of the situation.
In our rush to condemn the reprehensible aspects of government we have lost sight of the goal, which is to promote civil society and respect for our fellow man.
So actually that’s the whole design of these things. You have to work to keep them running. In case of a meltdown, the fuel is passively drained by a plug.
In case anyone else was wondering how having the molten fuel pour out of the reactor is safe - it is designed to pour into a container with criticality safe geometry to stop fission:
"in an emergency situation [the fuel] can be quickly drained out of the reactor into a passively cooled dump tank. MSRs designs have a freeze plug at the bottom of the core—a plug of salt, cooled by a fan to keep it at a temperature below the freezing point of the salt. If temperature rises beyond a critical point, the plug melts, and the liquid fuel in the core is immediately evacuated, pouring into a sub-critical geometry in a catch basin. This formidable safety tactic is only possible if the fuel is a liquid." [1]
Possible, and implemented in recent reactors - for the "corium". Though in that case it's for the extreme situations, since after that the reactor is completely done for.
I would love to see what a sub-critical geometry looks like. I also wonder what kind of math and engineering they did to come up with the shape they ended up with.
In some contexts, a subcritical geometry is simply a plastic jug that's too small to hold a critical mass. Obviously they're not using plastic jugs for this, but the principle of the thing is pretty straight forward. They could create a wide 'dish' under the reactor which, if the liquid fuel were drained into, would spread the fuel out into a shallow puddle using the self-leveling property of fluids.
> I also wonder what kind of math and engineering they did to come up with the shape they ended up with.
I assume this is why some Finite Element Analysis packages come with warnings along the lines of "You must not use this to help Kim Jong-Un do you know what"
Feynman wrote of this when he was working at Los Alamos, i.e. the labourers weren't informed as to what they were really working with, so they could come very close to criticality accidents.
Well, no. A meltdown is when the stuff escapes containment and then continues undergoing fission, heating up and melting out of containment and into groundwater/the environment.
The drain tanks are shaped specifically so if the (liquid) fuel flows in, it will stop reacting. And presumably the whole apparatus (drain tanks included) is inside of a biological shield.
So a "meltdown" here just means a big hunk of solid nuclear salt inside the bio-shield. I think the idea being that you could just bury the whole thing in case of failure.
This would not be melting down. Melting down is melting out of the containment device, which this is not doing. True it is melting INTO a secondary containment device but unless it continues to melt through that it would not be a 'melt down'
Also, there is no pressure build up, which is what caused the big explosion in Fukushima. All the coolant starts boiling, turning into gas, and well the rest was in the news
Just for clarification, the big explosion at Fukushima was a hydrogen explosion. At high temperatures, fuel cladding breaks water into hydrogen and oxygen. Hydrogen collected at the highest point in the structure and later exploded.
My understanding is that these reactors are designed to have a lot of passive safety features (e.g. if all operators walk away the reactor will cool itself and go sub-critical), so quite the opposite of what you are claiming.
Those safety systems don’t exist in a shipping container sized nuclear reactor. One method that I think you’re talking about is when the temperature of the molten salts goes beyond a certain safety threshold then a heat sensitive plug is disintegrated and the Milton salts are drained into a safe underground reservoir for them to cool. (This is my recollection from that why thorium is the future video that went viral years ago) Can’t do that in a shipping container.
I was thinking of Copenhagen Atomics' Waste Burner design where they describe their passive walk-away safety features as "Prime minister safety" [1].
> The CA Waste Burner has a set of systems governed by the laws of physics that cannot be overruled by humans, and which will cause the reactor to shut down safely if something goes wrong...This means that operators are not required to watch for alarms and act in accordance. The CA Waste Burner must be able to automatically shut down before any human can react to an alarm and choose what to do. If human action were ever required for operation, other than during startup procedures, then we would consider it a design failure...
> The CA Waste Burner has a set of systems governed by the laws of physics that cannot be overruled by humans, and which will cause the reactor to shut down safely if something goes wrong.
This is really good, but humans have an amazing knack for messing stuff up and I really hope corners aren’t cut building and maintaining it.
What comes to mind is the situation in Japan where workers inadvertently had some material go critical, and while this was being investigated it was found that they were carrying waste uranium and nitric acid around by hand in buckets.
