Oddity

[Absalom]

If you have an engine that doesn't destructively interact with it's exhaust, and has an exhaust velocity limited only by it's power supply and "active length", then it has the potential to take it's exhaust up to ~99% of c.

Not precisely, no. Seems you may be applying mechanical physics here. The limit on Vasmir is the strength of the magnetic bottle b-field which is derived from the super conductor used. Granting an infinite power source is insufficient without accommodating the physical limits of superconductors and the mass of the cooling systems needed. These are low thrust to weight drives that deliver delta V over long periods.

I don't know whose posts you've been reading, but you certainly have not been reading mine. Let me repeat myself, for at least the third time: I am talking about using a Vasimr as a plasma generator component inside of an electric rocket which then accelerates that plasma to a higher velocity, thereby increasing the thrust.

PLEASE make certain that you understand what I wrote above before you reply to this. The limits of the Vasimr are not directly the limitations of what I'm talking about, because the Vasimr is nothing but an over-glorified spark-plug. I have not been talking about the actual acceleration stage of this engine, except in the most generic of terms.

Your note about superconductors and cooling systems is presumably relevant, but not by way of the Vasimr. It's relevance would be in relation to the other plasma accelerator stages.

Saying "radiation falls" seems rather ludicrous to me. Fallout is persistent radiative pollution. Gamma radiation? Once it's gone you just pick up the pieces. Fallout? You can't live there again until it's decayed, and the knowledge that it was ever present pollutes the mind-share of that plot of land for years, or decades, thereafter.

Gamma radiation moves at the speed of light. As soon as you measure it, it is gone

So fallout is bad because its scary. Not because it presents physical bodily harm. "Fallout" is a boogeyman. To illustrate my point again, you separated Gamma radiation and held it as a distinct case from fallout. This is inaccurate. Gamma, as well as beta and alpha, are different modes of decay of the physical material which constructs 'fallout'. Alpha decay is when an unstable element spins off a helium-4 atom. Beta spins out either an electron or a positron and either increases or decreases (respectively) the atomic number without altering atomic mass. Gamma radiation consists of high energy photon emissions. The source of which, for this discussion, is the excited state of the atom resulting from the other two forms of decay. In the end, the only thing that matters is the measurable harm from exposure, which is measured in Sieverts. Uranium Bromide enriched to 20% posses no radiological risk in the worst case scenarios here.

Separating Gamma radiation from fallout is not inaccurate, because a defining feature of fallout is that it decays, thereby generating radiation. Alpha and beta might be considered fallout because they are capable of decaying into further forms of radiation (I'm long enough out of school to not remember), but gamma can't.

The very fact that gamma rays are photons mean that they cannot decay. The fact that gamma rays cannot decay means that they are not fallout. Hence, gamma rays are not fallout. Neither is infrared, or the radio spectrum, or microwaves, or ultraviolet, or any other "color" of photon.

Talk about over engineering. The radiation effects of enriched Uranium Bromide weve been so focused on for two pages can, as noted, be stopped by a simple piece of paper. In any catastrophic situation the radiation is a non issue, and especially so when compared to the difficulties dealing with the catastrophic fault of a rocket.

You and I are so very much not talking about the same thing. You are talking about the initial "containment failure", basically the "boom". I'm talking about the aftereffects, which could be compared to the smoke and debris. We're talking about different time-scales here.

In fact, I actually said that a bigger boom was better than sustained radiation. Seriously, I said this, go back and look. I'm not worried about pad workers either, I'm worried about wherever else it might crash. To the best of my knowledge most of the launch pads that might be used for this stuff (at least here in the US) are distant enough from population centers that a containment failure there would be unlikely to have major consequences. Oh, sure, you might have a few personal tragedies, but crack the containment casing of one of these in the vicinity of a city, and you might have a year or three of school-child radiation poisoning. It's just like in war, you're sad when your guys die, but the enemy want's them to survive too, so that you'll be dragged down by caring for them.

[Nemo]

PLEASE make certain that you understand what I wrote above before you reply to this. The limits of the Vasimr are not directly the limitations of what I'm talking about, because the Vasimr is nothing but an over-glorified spark-plug. I have not been talking about the actual acceleration stage of this engine, except in the most generic of terms.

Your note about superconductors and cooling systems is presumably relevant, but not by way of the Vasimr. It's relevance would be in relation to the other plasma accelerator stages.

I understand perfectly well. I'll be more clear. It doesnt matter. Any electric drive you strap to it for any kind of afterburner is going to face the same difficulty. It won't produce any benefit past the given strength of the magnetic field. The containment b-field is your weak spot, this is true for all plasma drives, and strapping on more tubing/equipment ad infinitum (the infinite power I granted earlier) does not over come that. I say you are misapplying physical understandings because this idea can work with physical medium. Like more stages in a turbine compressor, or an afterburner, but, fluid mechanics, mechanical physics, arent what need to be applied here.

Separating Gamma radiation from fallout is not inaccurate...

The very fact that gamma rays are photons mean that they cannot decay. The fact that gamma rays cannot decay means that they are not fallout. Hence, gamma rays are not fallout. Neither is infrared, or the radio spectrum, or microwaves, or ultraviolet, or any other "color" of photon.

I dont know how else to say it, your understanding of the science is off. Gamma Alpha and Beta are all by-products of nuclear decay. An unstable isotope of an element changes into a more stable state by releasing energy. The unstable element constitutes the fallout. In our case, enriched Uranium Bromide. Radiation from fallout comes in each of the three modes, alpha beta and yes gamma too. The mode of decay and the concentration of decay determine the strength of the effect. The would be measured in the aforementioned Becquerel. This imparts ionizing energy on a mass measured in Gray. The gray is then factored for effect and finally becomes the Sievert. It is the Sievert dose of ionization which may or may not be harmful. You can no sooner separate gamma radiation from fallout than alpha or beta.

You and I are so very much not talking about the same thing. You are talking about the initial "containment failure", basically the "boom". I'm talking about the aftereffects, which could be compared to the smoke and debris. We're talking about different time-scales here.

Theres a reason for that. I was granting the worst case failure of the rocket. The effect of the radiation is directly proportional to the density of the decaying element. I said it starting on the last page:

No one gets exposed to anything harmful at a launch failure and the exposure decreases with altitude and speed.

An illustration may be helpful, think of a water balloon. The harder you throw it the more dispersed the water. The faster the rocket is traveling, and the higher its altitude, the lower the concentration of any resulting, ahem, "fallout". Quite the opposite of killing the innocent little school children, but zomg think of teh childrun!, there will be no measurable impact. I can state this definitively. Since you are not content with the highest density exposure scenario I presented, create your own and run the math. I'd like to see the numbers.


Now if you want to say Uranium bromide itself is just so dangerous that itll kill people if it leaks out from the enrichment facility or transport... First, again, a leak wouldnt create enough exposure to be a radiological risk even if it were to happen. (see above about running numbers) Which...

https://www.youtube.com/watch?v=ZY446h4pZdc

The CEGB are, however, convinced they've proved their point. They say if this doesn't reassure their critics, then nothing will.

Not a problem, I should think.





edit: to help with the math - 3 tons of Uranium bromide enriched to 20% yields .6 tons of U-235 which produces, in total, 1.2 times the radioactivity of 1 gram of radium-226 and imparts .13 milligrays per hour/1.1 gray a year at 1 meter

http://www.wolframalpha.com/input/?i=Be ... ranium+235

edit's edit: I was wrong. 3 tons of uranium listed in zurbin's titan ship was the u-235 component. Also, was done in metric not short tons, I didn't specify to wolfram last night. What I get doing that at 2 am.

http://www.wolframalpha.com/input/?i=Be ... ranium+235


3 tons u-235 is equivalent to 7.2 times one gram of radium-226 producing .79 milligray an hour/6.9 gray a year at 1 meter.

[Absalom]

PLEASE make certain that you understand what I wrote above before you reply to this. The limits of the Vasimr are not directly the limitations of what I'm talking about, because the Vasimr is nothing but an over-glorified spark-plug. I have not been talking about the actual acceleration stage of this engine, except in the most generic of terms.

Your note about superconductors and cooling systems is presumably relevant, but not by way of the Vasimr. It's relevance would be in relation to the other plasma accelerator stages.

I understand perfectly well. I'll be more clear. It doesnt matter. Any electric drive you strap to it for any kind of afterburner is going to face the same difficulty. It won't produce any benefit past the given strength of the magnetic field. The containment b-field is your weak spot, this is true for all plasma drives, and strapping on more tubing/equipment ad infinitum (the infinite power I granted earlier) does not over come that. I say you are misapplying physical understandings because this idea can work with physical medium. Like more stages in a turbine compressor, or an afterburner, but, fluid mechanics, mechanical physics, arent what need to be applied here.

I still can't help but think there's probably some electric drive capable of the 1g range under sufficient power, but you properly aimed at my point this time, so I'll ignore that.

Separating Gamma radiation from fallout is not inaccurate...

The very fact that gamma rays are photons mean that they cannot decay. The fact that gamma rays cannot decay means that they are not fallout. Hence, gamma rays are not fallout. Neither is infrared, or the radio spectrum, or microwaves, or ultraviolet, or any other "color" of photon.

I dont know how else to say it, your understanding of the science is off. Gamma Alpha and Beta are all by-products of nuclear decay. An unstable isotope of an element changes into a more stable state by releasing energy. The unstable element constitutes the fallout. In our case, enriched Uranium Bromide. Radiation from fallout comes in each of the three modes, alpha beta and yes gamma too. The mode of decay and the concentration of decay determine the strength of the effect. The would be measured in the aforementioned Becquerel. This imparts ionizing energy on a mass measured in Gray. The gray is then factored for effect and finally becomes the Sievert. It is the Sievert dose of ionization which may or may not be harmful. You can no sooner separate gamma radiation from fallout than alpha or beta.

Merriam-Webster's Collegiate Dictionary, Tenth edition: fall-out 1a: the often radioactive particles stirred up by or resulting from a nuclear explosion and descending through the atmosphere; also: other polluting particles (as volcanic ash) descending likewise b: descent (as of fallout) through the atmosphere 2a: a secondary and often lingering effect, result, or set of consequences

When reading the entry, it's quite clear that it favors persistent particles with a half-life, a.k.a. not photons of any form that I have ever heard of, but I can see the room for misunderstanding, so I'll rephrase:
This is bad because of radioactive "dust". The photon burst from detonation doesn't matter, so forget about it, it'll do nothing more than distract you. What matters is that the consequence of containment failure is radioactive pollution.



At any rate, this doesn't matter to me anyways. I see no need for the things in the foreseeable future because an Earth-Mars cycler is supposed to take ~2-3 years for the trip (one way, I think), which should be a perfectly acceptable time frame (if it isn't, then I have to ask either why you built your one-time cost cycler station so small, or why someone so impatient is being considered for such a mission at all). A Vasimr (or likely a number of other technologies, in sufficient numbers of thruster units) should be perfectly acceptable as a way to insert the cycler into it's orbit, no need for a NSWR. I'm of the opinion that if you need to go somewhere under power, then it probably isn't somewhere to send a manned mission right now.

At the same time, it has little to no chance of spewing radiative pollution in the case of an accident, which makes it politically superior. People don't like having stuff thrown around their property, e.g. Australia made the US pay up for littering when SpaceLab (or was it the other one?) crashed on their territory. To help you understand what I mean, bring me your car fore a paint job. I'll be using a rough-texture brush instead of spray paint, and you'll be running the risk of me using the ugliest shade of green imaginable, but you've just got to accept that risk, and it's harmless so obviously it's the Right Thing To Do (TM), right? Oh course not, it's a stupid idea because there is no sensible reason to do it.

And there's the question of why (other than impatience, or Zubrin's pulp-scifi fantasies) we would want such a power of rocket at this early stage of space travel. I don't think you ever explained why SpaceX (or any other rocket company) would even want to launch a NSWR. The only possibility that I can think of is that Zubrin wants to, and I don't care what Zubrin wants.

[Nemo]

The photon burst from detonation doesn't matter, so forget about it, it'll do nothing more than distract you. What matters is that the consequence of containment failure is radioactive pollution.

You still misunderstand. Yes gamma is produced by fissile reactions, as are other forums of radiation, but it also is produced as a by-product of nuclear decay. Cobalt-60 undergoes beta decay. Its decay chain is: 60/27Co → 60/28Ni + e− + νe + gamma rays.

Energy transfers between the three levels generate six different gamma-ray frequencies

The gamma is spit off to equalize energy states, you can treat it almost as you would the remainder in a whole number fraction. 7 divided by 2 is 3 with a remainder of 1. 1 would be shot off as gamma energy to balance the equation, if that helps. So, in effect, what you said was true. The photon burst from detonation doesn't matter. You are still being bombarded by ionizing photons anyway.




While on the topic of nuclear detonation/fissile reaction as opposed to decay we should note in that context "fallout" is much much more than just the transuranic chain resulting from fission. This is because of a process known as neutron activation. The excess neutrons from the detonation impact with surrounding material adding neutrons and imparting energy (kinetic form) to otherwise stable isotopes. They become unstable and the material decays, generating more ongoing radiation in alpha beta and gamma forms. This is largely what is referred to as 'fallout' from the above definition. If we refer to the Castle Bravo and Crossroads test series (particularly the Baker shot) we find that ground based detonations are more lethal than air burst. Air burst detonations produces less of this kind of sympathetic radiation in part because oxygen can take up to 3 neutrons before becoming unstable. Ground burst detonations have a ready supply of more easily activated material which is cast off by the explosion and carried down wind. This is also why the US pursued the Enhanced Radiation Weapon aka: Neutron Bomb for use against tank columns in a European theater war. Air burst detonation in the vicinity of a tank column would create an extreme local radiation effect in the short to mid term while limiting down range fallout when compared to a ground based detonation of a conventional nuke that would otherwise be required to neutralize the column.



Conventional nuke?

[Absalom]

The photon burst from detonation doesn't matter, so forget about it, it'll do nothing more than distract you. What matters is that the consequence of containment failure is radioactive pollution.

You still misunderstand. Yes gamma is produced by fissile reactions, as are other forums of radiation, but it also is produced as a by-product of nuclear decay. Cobalt-60 undergoes beta decay. Its decay chain is: 60/27Co → 60/28Ni + e− + νe + gamma rays.

No, I do not misunderstand. Fallout emits radiation, such as: alpha rays, beta rays, and photons. If something does not emit radiation, then it is not fallout, because fallout emits radiation. Gamma rays (and other "colors" of photons) do not emit radiation, and therefor are not fallout.

I am NOT talking about the radiation, I am talking about it's precursors, the actual fallout. The assorted particles that produce radiation are what I am talking. How are you so consistently failing to grasp this, despite the fact that I am intentionally writing it in the plainest way that I can think of?

While on the topic of nuclear detonation/fissile reaction as opposed to decay we should note in that context "fallout" is much much more than just the transuranic chain resulting from fission. This is because of a process known as neutron activation. The excess neutrons from the detonation impact with surrounding material adding neutrons and imparting energy (kinetic form) to otherwise stable isotopes. They become unstable and the material decays, generating more ongoing radiation in alpha beta and gamma forms. This is largely what is referred to as 'fallout' from the above definition.

Dust such as that is included in fallout, correct. Particles of this sort are what I am talking about. I am talking about emitters, radio-actives, metaphorical ticking time bombs; not something that had already cleared out before you realized it was there, and itself can therefor be relegated to history books. I am not talking about the radiation, I am talking about a classification of things that are defined by the fact that they emit radiation. Those are the things that nobody wants littering their backyards.

[Nemo]

I am not talking about the radiation, I am talking about a classification of things that are defined by the fact that they emit radiation. Those are the things that nobody wants littering their backyards.

Then... you are talking about radiation. Radiation can be measured. Measured radiation may or may not be harmful. .79 milligray an hour 1 meter from 3 tons assuming no shielding. Shielding which need only be as thick as a piece of paper. Thats not harmful. Things that are not harmful can still be feared though. Like Bogeymen. Full circle. Discussion has hit recursion.

[discord]

nemo: there is a area you are skipping here, containment failure(aka *boom*) where materials disperse rapidly and probably undergo changes, it is in the nature of nuclear booms to involve change, that dispersal of material(and changes of nearby materials due to radiation) and the long lasting effects of such is known as 'fallout'.

so, we put a shitload of weapons grade uranium in a high performance engine, push it....and you are saying there is no chance whatsoever of a 'boom'? and as long as it is outside the body there is not much danger involved, it's when usually airborne particles get INSIDE things get nasty.

just like with guns shot placement is everything, lying on the ground doing nothing, not very dangerous at all, in the air being breathed in....not so good, even then the radiation of uranium is not the biggest issue, it being a rather toxic metal however is, and whatever it decayed into when it went 'boom' is another matter entirely, and probably much more volatile.

and finally, in space this would probably not be a problem whatsoever, getting it there might however.

[Nemo]

nemo: there is a area you are skipping here, containment failure(aka *boom*)

Im going to assume by *boom* you mean an explosive fissile reaction right? I do think I mentioned that as a possibility, what was it...

As critical mass is a function of density, any uncontrolled dispersal of the fuel defeats the concentration required for detonation. Water itself, which the uranium salt would be suspended in, is virtually non-compressible.

Oh two posts actually:

We looked into weaponizing uranium bromide in the 40s with the Manhattan project, they couldn't do it.

I certainly didn't elaborate though. The history here is that during the project they looked into weaponizing many different forms of uranium, including its salts like uranium bromide. The project saw more viable opportunity elsewhere and moved on. After the war, Edward Teller - father of the hydrogen bomb - went back and pursued this line of thought trying to weaponize other forms. While he didn't weaponize u-bromide he did weaponize u-hydride. Lets assume for a minute the man knew what he was doing, and that a hydride based reaction has a better yield than a bromide one. Two such devices were tested in shots Ruth and Ray.





Ruth didn't even destroy the tower it was mounted on. Ray managed 200 tons of TNT in explosive force.



Since from what I understand you're not discussing a leak resulting in fission, Im going to assume we are discussing a chemical rocket explosion as the cause. This would be most similar to an implosion device, causing a criticality event by compression. Without having a fuel tank to refer to we have no way of knowing what manner of neutron moderation would be used. However, its not impossible to establish boundary conditions. While we have been discussing 20% enriched fuel, 90% was suggested as a possibility. Lets assume then that the density of the fuel can be increased in the tank by a factor of 4.51 times before a criticality event. In practical applications its likely that the 20% tank would not carry the same mass of neutron moderation as a 90% tank, but right now its the only way I can see to establish that boundary. Since I believe it to be too high, we can set a lower end figure as well. Does a density increase by a factor of 1.1, or a 10% increase in fuel density before criticality, sound acceptable? Time for some lazy napkin math.

Ok, the fuel is suspended in water as a salt solution, can we assume its well mixed and evenly distributed? Would make a poor fuel otherwise. Sea water has a density of 1026kg a cubic meter at the surface with a pressure equivalent to 1 atmosphere at 14.69 psi . It also has a density of 1060kg a cubic meter at 8.184km depth, that of the Marianas Trench, with a pressure of 12,184 psi.

http://www.wolframalpha.com/input/?i=sea+water+pressure
http://www.wolframalpha.com/input/?i=se ... re+8.184km

Thats an increase in density of what, not even 4% for an 800 fold increase in pressure? I think the tank would rupture first, and any tank rupture would decrease density. Distributing the material over an area, as would be expected in an explosion, is counter productive to a fissile reaction. But, what the hell, lets assume one happens anyway. It lacks the neutron reflector or tamper, and the explosive force acting on the tank would not be evenly distributed as is necessary to create an explosive reaction in an implosion device. Any fissile reaction that does happen during the explosion would be self moderating. As it is suspended in water any high energy input, be it the heat from the chemical explosion or fission, will quickly convert that water to highly expansive steam. This would separate and disperse any fissile reactions acting against criticality. More akin to a fart in a tornado than a fart in the wind.



All of this ignores the possibility of simply adding some manner of neutron poison to the tank or its surrounding area in the rocket as a precaution. Boric acid comes to mind. Water soluble, simply toss a tank of that between the power and the payload. Apply explosion and the shockwave poisons the fuel. Hate to waste mass on that if it really is such an outside possibility as I think it is.

[discord]

"These would be stored in tanks that would prevent a critical mass from forming by some combination of geometry or neutron absorption (for example: long tubes made out of boron in an array with considerable spacing between tubes)." <--- from the wikipedia page on NSWR.

the basic idea of NSWR is to have a continuous pre-boom going on in the exhaust nozzle of a rocket, akin to the orion drive but much lighter since specific impulse is much lower, without having something keeping the fuel from going boom it will by simple proximity, again this is not a big issue in space, but it just might be when getting it TO space.....do note, any 'crash' scenario is likely to cause a 'boom' scenario as the fuel tanks rupture and fuel pooling heating up(as it is designed to) very rapidly, boiling away water which happens to be the moderator, soon you will get critical mass, and boom.

not saying it is a bad idea, just pointing out that playing with high performance nuclear engines on a minimum weight platform means some design compromises, and when the fuel you have is effectively weapons grade uranium get enough of it close together without moderating effects will get you a 'boom' perhaps not a multi megaton boom, but even a small nuclear boom is enough to throw the material around in a rather large area, causing even more spread fallout, and making cleanup a bloody nightmare on earth....in space of course not a single sane one would care.

[Nemo]

very rapidly, boiling away water which happens to be the moderator, soon you will get critical mass, and boom.

The water is not the moderator, its the medium. As it escapes its not leaving exposed fuel rods as it would in a light water reactor, its taking the salt with it. Thats why I said self moderating. Any reaction that does take place serves to undermine the ongoing reaction.

without having something keeping the fuel from going boom it will by simple proximity

Eh. "Boom" isnt the word I would use. Theres no boom. Theres no pre-boom. There is a fissile reaction, a criticality event. Which is drastically different from a nuclear explosion. Its the difference between lighting fire to a small pile of gunpowder or pouring the gunpowder into a pipe, sealing it up, and lighting that off. And like you said, it requires proximity. Density. That proximity wont be maintained in a crash.

[Siber]

The water is not the moderator, its the medium. As it escapes its not leaving exposed fuel rods as it would in a light water reactor, its taking the salt with it. Thats why I said self moderating. Any reaction that does take place serves to undermine the ongoing reaction.

Correct me if I'm wrong, but aren't salts generally left behind when salt water boils? Hypothetically, leaving aside the complexities of a real crash scenario, if you've got a big pool of NSWR fuel that's over the critical point, my understanding is the the pool experience ever rising concentrations of fissile material, and thus rising temperatures and faster boiling? I'm not saying it'd ever reach the point of a classic nuclear detonation, because that needs very very carefully created conditions to happen, but it could get quite hot in both senses, couldn't it?

[Absalom]

The water is not the moderator, its the medium. As it escapes its not leaving exposed fuel rods as it would in a light water reactor, its taking the salt with it. Thats why I said self moderating. Any reaction that does take place serves to undermine the ongoing reaction.

Correct me if I'm wrong, but aren't salts generally left behind when salt water boils? Hypothetically, leaving aside the complexities of a real crash scenario, if you've got a big pool of NSWR fuel that's over the critical point, my understanding is the the pool experience ever rising concentrations of fissile material, and thus rising temperatures and faster boiling? I'm not saying it'd ever reach the point of a classic nuclear detonation, because that needs very very carefully created conditions to happen, but it could get quite hot in both senses, couldn't it?

Stop it, all you'll achieve is to get him to start debating the definition of "boil".

[Siber]

Stop it, all you'll achieve is to get him to start debating the definition of "boil".

Well, I've been in agreement with him more often than not through your debates so far, so maybe I'd learn something from that too.

[Nemo]

Yes the salt is left behind when you boil in a pot. What would happen in this case is a little different. Remember the container itself is the neutron moderator not the water, without a physical tank to refer to its a bit too ambiguous but tubes constructed out of boron were proposed. In the scenario presented, a crash or explosion resulting in containment failure, the fissile reaction is brought on by removing the salt from its moderator. A hole in the tank. Nature abhors a vacuum, that is, it dislikes pressure differences. The well mixed salt will move with the water to fill that void and once outside as the water converts to steam from either the energy of the explosion, or crash, or even some amount fissile reaction, the salt will be dispersed. Will there be salt left in the container? Well, there wont be a container to speak of in a few fractions of a second, but any salt that is left in the tank as would salt in a pot of boiled water is resting on its moderator so its not an issue and I overlooked it.

Its the salt that escapes that matters and it will be acted on and scattered. The more energetic either the salt or the water the more dispersal you see. In a pot of water, the salt never gets the energy to overcome gravity. Thats not an issue in these scenarios. More later, Im going to be late for work.

[Nemo]

Hypothetically, leaving aside the complexities of a real crash scenario...

Touching base with a little time. Given the constraints you've listed, yes. The assumption Im making is that there is no neutron moderation besides the water, and the water is not in a closed loop so that it can freely escape, and there is no other energy input. Given that setup taken from a cold start and that it has reached criticality, I imagine it would reach super criticality at some point. Quick note: criticality is self sustaining fission whereas super criticality is self escalating fission. If we close the loop - requires heat exchange - and/or add some manner of neutron moderating tankage I imagine it could maintain criticality instead. Thorium flouride salt reactors operate in a similar principle but require a neutron infusion to start the reaction (nswr fuel is self starting) and these reach a criticality peak where the boil retards the fission reaction preventing super criticality.

[Siber]

Given that, I can imagine failure modes where you end up with fair amounts of NSW on the ground pooling outside of the tanks. Those failure modes may not be very likely, I'm not especially qualified to say, but they seem at the very least plausible and worth serious study if one were actually building one of the things.

[discord]

nemo: as i agreed, once in space it will probably work just fine, and safeguards will be shiny and all, the problem could arise GETTING it to space, crash scenario during ascent would be.....bad. or you could get a similar situation crashing on some other planetoid, but that would probably be uninhabited and therefor no one with a working brain would care about fallout just the crash in itself.

"In an NSWR the nuclear salt-water would be made to flow through a reaction chamber and out an exhaust nozzle in such a way and at such speeds that the peak neutron flux in the fission reaction would occur outside of the vehicle.[1]" sounds like 'boom' time to me, just a very short boom....just like the orion drive just more continuous and controlled.

scenario as follows, rocket boost to space starts, failure, transport falls down due to gravity, crash, containment breach, fuel pools(again due to gravity), fuel heats up due to nuclear reaction, medium of moderation boils away(leaving salts behind), leading to increased proximity and heat(which leads to a loop), super criticality achieved, it goes faster and faster, *boom*.

small boom, but boom none the less.

only way to avoid this possibility is not to transport enough material at the same time, which would be annoying but doable.

[Nemo]

Given that, I can imagine failure modes where you end up with fair amounts of NSW on the ground pooling outside of the tanks. Those failure modes may not be very likely, I'm not especially qualified to say, but they seem at the very least plausible and worth serious study if one were actually building one of the things.

As in, Im guessing here, a leak in a tank at the pad prior to launch? Pressure test the tank prior to fueling. Keep neutron moderating boric acid solutions on standby. Honestly Id be more worried about human error. Assuming weve all played ksp right? Someone sets the nswr main engine to stage with the primary chemical boosters. Admit it, youve done it! Or, more plausibly, the suits ignore the engineers warnings about a criticality 1 part.

scenario as follows, rocket boost to space starts, failure, transport falls down due to gravity, crash, containment breach, fuel pools(again due to gravity), fuel heats up due to nuclear reaction, medium of moderation boils away(leaving salts behind), leading to increased proximity and heat(which leads to a loop), super criticality achieved, it goes faster and faster, *boom*.

small boom, but boom none the less.

While a confined pool of unmoderated nswr fuel poses a problem I have a few issues here. First, where is the range safety officer? A failed booster leading to uncontrolled ascent or descent is grounds for a key turn. What crash would result in fuel pooling and congregating rather than spreading out and dispersing? Finally, even a super-critical fissile reaction is not a boom, not even a small one. Youtube video for reference: http://www.youtube.com/watch?v=hOHIFHZBfbA Burning gunpowder. Thats enough to powder to fire several bullets if used explosively. But an explosive reaction requires a certain set of circumstances that are not present. In a similar manner, the circumstances required for even a small *boom* are not present in the scenario presented. I mentioned before the lack of tamper and neutron reflector. These are the key elements. Together they act as the pipe in a pipe bomb, redirecting energy back into the material.

[Siber]

Given that, I can imagine failure modes where you end up with fair amounts of NSW on the ground pooling outside of the tanks. Those failure modes may not be very likely, I'm not especially qualified to say, but they seem at the very least plausible and worth serious study if one were actually building one of the things.

As in, Im guessing here, a leak in a tank at the pad prior to launch? Pressure test the tank prior to fueling. Keep neutron moderating boric acid solutions on standby. Honestly Id be more worried about human error. Assuming weve all played ksp right? Someone sets the nswr main engine to stage with the primary chemical boosters. Admit it, youve done it!

Pft. I can get anywhere in the solar system on well less than half of a single NSWR tank when I mod them into KSP, who needs chemical boosters?

Off the top of my head I'm mainly imagining an engine failure in the launch stage, and then the tanks manage to make it to the ground largely intact but crack on impact. There might be a splash, but natural flowing might also lead to reconcentration in short order.

[Nemo]

Where is your range safety officer?
Goes-G incident
https://www.youtube.com/watch?v=N1XE_awXEA4
First ever ICBM Atlas missile launch - Confidential btw! Dont tell the Russians...
https://www.youtube.com/watch?v=_WP0wbeSce8


In a failure of the rocket motors or guidance the RSO destructs the vehicle to ensure that it does not pose such a harm. Though some times it may be a bit redundant.
Titan IV A-20
http://youtu.be/nqlgUuYQU30?t=35s