Oddity

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Siber
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Re: Oddity

Post by 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?
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Absalom
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Re: Oddity

Post by Absalom »

Siber wrote:
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".

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Siber
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Re: Oddity

Post by Siber »

Absalom wrote: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.
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Nemo
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Re: Oddity

Post by 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.

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Re: Oddity

Post by 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.

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Siber
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Re: Oddity

Post by 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.
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discord
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Re: Oddity

Post by 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.

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Re: Oddity

Post by Nemo »

Siber wrote: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.

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Siber
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Re: Oddity

Post by Siber »

Nemo wrote:
Siber wrote: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? :D

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.
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Nemo
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Re: Oddity

Post by 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

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