Wanna see my degree? : ) It's only a BS, but I do in fact hold a degree in aerospace engineering. I am, in fact, a rocket scientist.
Naw. I was just curious. So do you actually work in aerospace, or did you end up somewhere else? With things ramping up in the space travel market, nuclear + aerospace are about to become big ticket degrees. Let's just hope they don't hire the same idiots I saw in the DotCom boom.:-)
If you think superheated hydrogen with enough force to drive a rocket along isn't "pressurized", what would you define as pressurized?
That would be the *work* you're doing with the reactor. Pressurized reactors (like the PWR and LWR designs) are closed loop systems that attempt to both cool the reactor and power a turbine with the same working fluid. (Or possibly two fluid loops with a heat exchanger in between.) The problem with these designs is that if the reactor goes super-critical, the pressure will build up and a boiler explosion will result. That's why we don't build those designs anymore. They're death traps.
In this design, there is no working fluid passing through the reactor. The reactor itself is sealed, and will scram itself if the reaction gets out of control.
Listen, Rei, I have generally found you to be a very intelligent person, and often find myself agreeing with what you have to say. But in this case, comparing the safety of PWRs to modern reactor designs is exactly like comparing the safety of a modern diesel engine to that of a 19th century locomotive engine. The locomotive engines exploded quite a bit (killing a LOT of people), yet no one even suggests the issue of a diesel engine blowing up and killing people.
If you want to know the true travesty of shunning nuclear power, look at the statistics for the number of people killing in non-nuclear boiler explosions. Then look at the number of people killed by coal emissions. Then look at the number of people killed in the ENTIRE history of nuclear power. If you use official figures (rather than the "Chernobyl blew up, therefore it killed MILLIONS" nonsense), less than 100 people have died from nuclear power. Are those people's deaths a tragedy? Yes. But the 4,000 - 12,000 people killed in London in 1952 was a greater tragedy. As were the thousands of men killed maintaining boilers for propulsion and electricity.
Eh? There's a pressurized reactor somewhere? Where? I don't see one. (looks under a rock) Nope. None there. (Pops into the Triton engine) None here. We do have a solid reactor core with hydrogen cooling, however. It's pretty cool, because the titanium shell will melt and scram the reactor in case something goes wrong. (Hops out of engine) Now where am I going to find a portable pressurized reactor? *scratches head*
They never do understand the problem. I remember being an ignoramus, with ideas that somebody "smart" would figure out the magical technology that would make space travel happen. What I didn't realize was that:
1. It's not as easy as a Star Trek "impulse drive". 2. We already have the technology for lotsa cool space travel. 3. The technology necessary is nuclear. 4. Nuclear tech isn't as fearsome as we've made it out to be. 5. Anything that produces enough power for space travel is going to be one scary SOB of a technology. 6. Radiation is a fact of life. Get over it.
Since I've had these revelations, I've been trying to edumacate others. All too few actually listen, though.:-(
(To others who may be reading) FWIW, SS1 probably gets an Isp of about 150. The Shuttle SRBs get about 250, and the Shuttle Main Engines (the most powerful type of chemical engine in existence) get about 450. An Isp of 900 or greater means that these nuclear rockets are TWICE as efficient as our absolute best engines in existence today. That sort of efficiency gain is a rocket scientist's wet dream. Further gains can be realized by looking into technologies such as Orion and Nuclear Salt Water Rockets.
BTW, Moofie. Are you actually a rocket scientist, or are you just claiming to be one?
Nope. The gamma radiation was nowhere near as big of a problem as the reactor fuel ablation. Remember, the air passed rhrough the reactor itself! As the materials disintegrated (as they are prone to do), they would be carried out the back of the ramjet.
Gamma rays from a supersonic craft flying overhead would be a very temporary and transient problem. People on the ground would probably end up with no more than an extra REM or two.
I haven't had a chance to do a full log analysis, but I've noticed that Safari has also been on the pickup. Between the two, Microsoft may have a serious problem on their hands.:-)
The idea wasn't so bad. It was the execution. I mean, only the military would WANT to design an engine that blasts nasty radioisotopes all over creation.
The Kiwi B series fully developed the fuel system, which consisted of the uranium fuel in the form of tiny UO2 spheres embedded in a low-boron graphite matrix, and then coated with niobium carbide. Nineteen holes ran the length of the bundles, and through these holes the liquid hydrogen flowed for cooling.
Basically, they embedded tiny reactors pellets inside the graphite, then passed hydrogen around the graphite for cooling. The hydrogen would heat up, and shoot out the back of the rocket at high speeds. A rather ingenious design, but sadly impractical.
of course, shielding would make it acceptably safe, but since it was designed as a nuclear weapons delivery system, the reactor was left naked mostly to save a rather large amount of weight and allow a larger payload.
Not exactly. It wasn't just a matter of shielding. The airflow was designed to pass through the reactor. The reactor would slowly disintegrate, and the airflow would carry off highly radioactive materials. In contrast, the NERVA project passed the heat through a graphite barrier to heat the exhaust.
Beside, Project Pluto was only designed to produce 156 kN (35,000 lbs) of thrust. In contrast, the Triton engine produces a maximum of 334 kN (75,000 lbs) of thrust.
Actually, I did read that part of the article. I don't pretend to fully understand the details, but it seems like that addresses reactor malfunctions, not the risk of nuclear material being scattered.
I see your confusion. You see, the materials CAN'T be scattered under normal conditions. They are literally welded inside a titanium shell, and are quite hard themselves. Keep in mind that the type of temperatures experienced during reentry are normal operating temperatures for this type of engine.
Basically, if the engine comes down, the whole thing comes down. Then someone picks it up, dusts it off, and probably reuses it.
Indeed, which is why I propose we build one of these plants in your back yard. You can put your money where your mouth is.
Hot Damn! Can I have some of the left over Pu-238? I've been wanting to build a few nuclear batteries for a while. Just think, I'll never have to recharge my laptop again!:-D
The magnitude of damage when something goes wrong (ignoring the statistical chances, if Murphy's law doesn't alert this to you, Chernobyl and 3 Mile Island should)
Millions of people have died from Coal power. Less than 100 have died from Nuclear power. Here's an event that makes Chernobyl look like a walk in the park:
Now sit and think for a moment which technology is more dangerous. The one we've embraced (coal) that we know is killing millions, or the one we've shunned (nuclear) which has killed very few, even in the worst disaster in history?
The unwanted side effect of wide spread use of nuclear power: nuclear proliferation.
Not such a big deal when the reactor is on its way to Mars. And since the materials are U235 before the engines are activated, it will be pretty hard for "terrorists" to obtain any plutonium from them.
You might want to RTFA then, because it's actually quite fascinating. The engine is designed for reuse, and can even produce ship power while "idling". Oxygen afterburners allow for the engines to produce amazing amounts of power for very short periods of time. Basically, you could build a Mars taxi with these engines. Don't waste your ship, just dock it in LEO when you come back, then send the next crew to Mars.:-)
The Tory reactor was DESIGNED to spread as much radiation as possible over populated areas. This was considered a "bonus" by the military, as they could keep wreaking destruction even after the bombs were dropped. In short, the design was a little sadistic.
DAMMIT! Please mod this person DOWN! I posted the Coral Cache link SPECIFICALLY SO NUCLEARSPACE.COM WOULDN'T USE UP THEIR BANDWIDTH. Bruce wants this article distributed, but he doesn't have that much bandwidth! It's just a teeny little non-profit site on a single box, and now you're destroy it!
You're confusing NERVA with Orion. The NTB is about nuclear explosives, which neither the NERVA or Triton engines use. In fact, the Triton engine is really nothing more than your average, power generating reactor. It's primary difference from NERVA is that they're not trying to build the most powerful reactor in the universe.
NERVA blew CURIES of radioactive partially reacted fuel element chunks across the desert.
That might have something to do with the fact that they blew up a few engines during testing. They wanted to see what would happen in the worst case destruction of the engine, so they made sure it had a catastrophic failure. Beyond that, the graphite ablation was the largest cause of materials being spread across the area.
It's also quite possible that the Orion project ran a few tests over there as well. Since most of it is still classified, though, it's hard to say.
Did you bother checking the track record of nuclear material that has already rained down? Seems the US has done a fairly good job containing such materials. (That is, right after they figured out that it might be a good idea to do so.:-))
I call troll. The picture you linked to was the INTENTIONAL destruction of a NERVA engine. Why would they do that? To test if safety procedure were working, and gauge issues with fallout. You'll note from TFA, that this engine has even more safety features, such as a titanium shell that would prevent catastrophic spread of materials. Also, it wouldn't even be activated in the atmosphere.
And before you whine about "we don't know", go do some reading about launch accidents involving nuclear materials.
Very simply put, the NERVA engines ran so hot that the Graphite used to transfer the heat from the reactor into the exhaust would flake off and end up in the exhaust. The problem is that while the hydrogen exhaust cannot be made radioactive, the graphite can. So you'd get little specs of radioactive graphite raining down behind you. It wasn't so much graphite as to be a major concern, but many of us would rather not exhaust anything radioactive if we can help it.
Not to sound paranoid, but when the reactor overheats and falls off where does it go?
Launch profiles are designed so that everything falls into the ocean. NASA has aborted quite a few launches, and has never dropped anything on people's heads. China on the other hand...
What happens if the reactor falls off over a populated area?
Well, since it's not supposed to be activated until the craft is already outside of the atmosphere, I suppose someone gets a bump on the head. Even if we assume that the reactor overheated, the titanium shell will melt down and scram the reactor before the reactor itself melts down. It should be nice and cool (and still wrapped in titanium shielding) by the time it hits the water.
Say the reactor falls off on the way to mars. Unless there is a shift in the momentum of the ship or the reactor it'll just melt down beside the ship. Then imagine the case where the ship can separate itself from the reactor. Now how do they get back?
The mission profile suggests three engines. Unless there's a critical failure in all three, a modified flight path could be developed.
While this is probably an improvement, I'd hardly consider it safe.
Consider a chemical rocket on the way to Mars. What happens if the tanks explode? That's right, you've got no way back. Even the failure of one engine could spell doom for the mission. This engine is more powerful, and FAR safer than any chemical engine. Even if the tanks leaked on the way, fuel could still be scooped from Mar's atmosphere. No chemical rocket can make that claim.
BB: Is there a 'fail safe' operation in the event the reactor core must be shut down exiting a planetary 'gravity well' or on approach to a 'gravity well' ?
RJ: There are several features that we have adapted and evolved into the current 'TRITON' design to handle risk mitigation for the Uranium Dioxide (UO_2 ) fuel element core in a Nuclear Thermal Rocket (NTR).
We have approached this by providing an integrated, robust design the uses dual turbopumps (turbopumps provide coolant flow to the reactor in propulsion mode).
In thrust mode where you have high power operation, is where this concern has been typically addressed. The safety features that have been taken into account for risk reduction entail constant supply of reactor coolant by using dual turbopumps. This means turbopumps with their moving parts like bearings, shafts, turbines etc. may cavitate and over speed, if for some reason one of the turbopumps showed signs of malfunction or not operating within appropriate parameters, you could effectively shutdown or bypass the offending turbopump and still have coolant flow going to the reactor. This is one of the key features for propulsion mode operation to make sure coolant is available to ?flush; the reactor if it needs to be shut down when it has gotten to the full thermal power level. In power mode it's [core] sitting at an idling power-level so the amount of time for the reactor to over-heat if starved of coolant (i.e. He/Xe gas) is extremely negligible because you are running the reactor core at nearly half the maximum temperatures the core is design for. So, if in the event of something like let's say, a minor leak in the radiator during power-mode operation, you can do a shut-down of the reactor from a very moderate control state without over-heating the reactor core. Other failure mode mitigation would be to have a segmented radiator design, or have a coolant purge circuit in the design, or actually split the coolant circuit to provide redundancy. We also have several valve arrangements so that in the event of leakage in idle power mode you could shut a section of the radiator down; the temperature of the reactor is so low it would cool down on its own. This works to our favor in the ?TRITON? design because the CERMET core materials have high maximum operating temperatures since it's designed for exit temperatures near 2,700-K in the propulsion mode.
Another feature is the nature of going to a fast spectrum reactor. It allows issues such as criticality and impact immersion (e.g. wet sand or salt water) to immediately be mitigated because of the reactor neutron flux levels and the use of only a reflector and no moderator to thermalize a bulk of the neutrons. Essentially it helps to 'poison' the internal nature of the reactor so in the worst case event at launch, if the reactor were to end up in sand or saltwater it will keep it from resorting to a super-critical state. If it shuts down after a brief period of operation, like for some reason and I had to shut it down during an early phase of a human Mars mission, the 'burn-up' (fission product build-up) is so low. Even if I run it for only 5 minutes or, 10 minutes I'd have built up only a minuscule amount that could barely be measured with regards to build-up of fission products in the core. So if it did for some reason re-enter the earth?s atmosphere, the radiation levels are only slightly higher than typical naturally occurring levels.
Now, you would have to methodically go through a full risk analysis, or a whole mission point-to-point to define the 'What if scenarios' along the mission's plan to properly build in aborts for all the most probable failure modes. For example, one 'What if scenarios' would look at the failure modes for an orbit capture high-thrust burn at a planet Mars or for Lunar transport. In essence, an inve
Erm, that's the Prometheus project (part of the JIMO mission). This is a Nuclear Thermal Rocket. It works on a very different principle. (i.e. You use a nuclear reactor to heat the exhaust to high temperatures, instead of using a powerful chemical reaction.)
This design is significantly different from the NRX. For one, they didn't attempt to build the most powerful reactor in the universe. For another, they took advantage of LHOx afterburners. With both of those design choices in mind, they were then able to use a titanium shell to act as the heat sink for the reactor. Not only does it not ablate, but the titanium will melt and scram the reactor long before the reactor itself experiences meltdown.
In other words, this is an extremely safe reactor design.:-)
Slashdot Mirror
Doh! Why am I saying Titanium? They're using Tungsten (even better).
Wanna see my degree? : ) It's only a BS, but I do in fact hold a degree in aerospace engineering. I am, in fact, a rocket scientist.
:-)
Naw. I was just curious. So do you actually work in aerospace, or did you end up somewhere else? With things ramping up in the space travel market, nuclear + aerospace are about to become big ticket degrees. Let's just hope they don't hire the same idiots I saw in the DotCom boom.
If you think superheated hydrogen with enough force to drive a rocket along isn't "pressurized", what would you define as pressurized?
That would be the *work* you're doing with the reactor. Pressurized reactors (like the PWR and LWR designs) are closed loop systems that attempt to both cool the reactor and power a turbine with the same working fluid. (Or possibly two fluid loops with a heat exchanger in between.) The problem with these designs is that if the reactor goes super-critical, the pressure will build up and a boiler explosion will result. That's why we don't build those designs anymore. They're death traps.
In this design, there is no working fluid passing through the reactor. The reactor itself is sealed, and will scram itself if the reaction gets out of control.
Listen, Rei, I have generally found you to be a very intelligent person, and often find myself agreeing with what you have to say. But in this case, comparing the safety of PWRs to modern reactor designs is exactly like comparing the safety of a modern diesel engine to that of a 19th century locomotive engine. The locomotive engines exploded quite a bit (killing a LOT of people), yet no one even suggests the issue of a diesel engine blowing up and killing people.
If you want to know the true travesty of shunning nuclear power, look at the statistics for the number of people killing in non-nuclear boiler explosions. Then look at the number of people killed by coal emissions. Then look at the number of people killed in the ENTIRE history of nuclear power. If you use official figures (rather than the "Chernobyl blew up, therefore it killed MILLIONS" nonsense), less than 100 people have died from nuclear power. Are those people's deaths a tragedy? Yes. But the 4,000 - 12,000 people killed in London in 1952 was a greater tragedy. As were the thousands of men killed maintaining boilers for propulsion and electricity.
Eh? There's a pressurized reactor somewhere? Where? I don't see one. (looks under a rock) Nope. None there. (Pops into the Triton engine) None here. We do have a solid reactor core with hydrogen cooling, however. It's pretty cool, because the titanium shell will melt and scram the reactor in case something goes wrong. (Hops out of engine) Now where am I going to find a portable pressurized reactor? *scratches head*
They never do understand the problem. I remember being an ignoramus, with ideas that somebody "smart" would figure out the magical technology that would make space travel happen. What I didn't realize was that:
:-(
1. It's not as easy as a Star Trek "impulse drive".
2. We already have the technology for lotsa cool space travel.
3. The technology necessary is nuclear.
4. Nuclear tech isn't as fearsome as we've made it out to be.
5. Anything that produces enough power for space travel is going to be one scary SOB of a technology.
6. Radiation is a fact of life. Get over it.
Since I've had these revelations, I've been trying to edumacate others. All too few actually listen, though.
(To others who may be reading) FWIW, SS1 probably gets an Isp of about 150. The Shuttle SRBs get about 250, and the Shuttle Main Engines (the most powerful type of chemical engine in existence) get about 450. An Isp of 900 or greater means that these nuclear rockets are TWICE as efficient as our absolute best engines in existence today. That sort of efficiency gain is a rocket scientist's wet dream. Further gains can be realized by looking into technologies such as Orion and Nuclear Salt Water Rockets.
BTW, Moofie. Are you actually a rocket scientist, or are you just claiming to be one?
Nope. The gamma radiation was nowhere near as big of a problem as the reactor fuel ablation. Remember, the air passed rhrough the reactor itself! As the materials disintegrated (as they are prone to do), they would be carried out the back of the ramjet.
Gamma rays from a supersonic craft flying overhead would be a very temporary and transient problem. People on the ground would probably end up with no more than an extra REM or two.
I haven't had a chance to do a full log analysis, but I've noticed that Safari has also been on the pickup. Between the two, Microsoft may have a serious problem on their hands. :-)
The idea wasn't so bad. It was the execution. I mean, only the military would WANT to design an engine that blasts nasty radioisotopes all over creation.
It did both. From Wikipedia:
The Kiwi B series fully developed the fuel system, which consisted of the uranium fuel in the form of tiny UO2 spheres embedded in a low-boron graphite matrix, and then coated with niobium carbide. Nineteen holes ran the length of the bundles, and through these holes the liquid hydrogen flowed for cooling.
Basically, they embedded tiny reactors pellets inside the graphite, then passed hydrogen around the graphite for cooling. The hydrogen would heat up, and shoot out the back of the rocket at high speeds. A rather ingenious design, but sadly impractical.
of course, shielding would make it acceptably safe, but since it was designed as a nuclear weapons delivery system, the reactor was left naked mostly to save a rather large amount of weight and allow a larger payload.
Not exactly. It wasn't just a matter of shielding. The airflow was designed to pass through the reactor. The reactor would slowly disintegrate, and the airflow would carry off highly radioactive materials. In contrast, the NERVA project passed the heat through a graphite barrier to heat the exhaust.
Beside, Project Pluto was only designed to produce 156 kN (35,000 lbs) of thrust. In contrast, the Triton engine produces a maximum of 334 kN (75,000 lbs) of thrust.
Actually, I did read that part of the article. I don't pretend to fully understand the details, but it seems like that addresses reactor malfunctions, not the risk of nuclear material being scattered.
I see your confusion. You see, the materials CAN'T be scattered under normal conditions. They are literally welded inside a titanium shell, and are quite hard themselves. Keep in mind that the type of temperatures experienced during reentry are normal operating temperatures for this type of engine.
Basically, if the engine comes down, the whole thing comes down. Then someone picks it up, dusts it off, and probably reuses it.
While it's not quite the same thing, you might find this link interesting.
Indeed, which is why I propose we build one of these plants in your back yard. You can put your money where your mouth is.
:-D
Hot Damn! Can I have some of the left over Pu-238? I've been wanting to build a few nuclear batteries for a while. Just think, I'll never have to recharge my laptop again!
The magnitude of damage when something goes wrong (ignoring the statistical chances, if Murphy's law doesn't alert this to you, Chernobyl and 3 Mile Island should)
Millions of people have died from Coal power. Less than 100 have died from Nuclear power. Here's an event that makes Chernobyl look like a walk in the park:
The Great Smog
Now sit and think for a moment which technology is more dangerous. The one we've embraced (coal) that we know is killing millions, or the one we've shunned (nuclear) which has killed very few, even in the worst disaster in history?
The unwanted side effect of wide spread use of nuclear power: nuclear proliferation.
Not such a big deal when the reactor is on its way to Mars. And since the materials are U235 before the engines are activated, it will be pretty hard for "terrorists" to obtain any plutonium from them.
You might want to RTFA then, because it's actually quite fascinating. The engine is designed for reuse, and can even produce ship power while "idling". Oxygen afterburners allow for the engines to produce amazing amounts of power for very short periods of time. Basically, you could build a Mars taxi with these engines. Don't waste your ship, just dock it in LEO when you come back, then send the next crew to Mars. :-)
The Tory reactor was DESIGNED to spread as much radiation as possible over populated areas. This was considered a "bonus" by the military, as they could keep wreaking destruction even after the bombs were dropped. In short, the design was a little sadistic.
DAMMIT! Please mod this person DOWN! I posted the Coral Cache link SPECIFICALLY SO NUCLEARSPACE.COM WOULDN'T USE UP THEIR BANDWIDTH. Bruce wants this article distributed, but he doesn't have that much bandwidth! It's just a teeny little non-profit site on a single box, and now you're destroy it!
Was not NERVA somehow proscribed by the NTB?
You're confusing NERVA with Orion. The NTB is about nuclear explosives, which neither the NERVA or Triton engines use. In fact, the Triton engine is really nothing more than your average, power generating reactor. It's primary difference from NERVA is that they're not trying to build the most powerful reactor in the universe.
NERVA blew CURIES of radioactive partially reacted fuel element chunks across the desert.
That might have something to do with the fact that they blew up a few engines during testing. They wanted to see what would happen in the worst case destruction of the engine, so they made sure it had a catastrophic failure. Beyond that, the graphite ablation was the largest cause of materials being spread across the area.
It's also quite possible that the Orion project ran a few tests over there as well. Since most of it is still classified, though, it's hard to say.
Did you bother checking the track record of nuclear material that has already rained down? Seems the US has done a fairly good job containing such materials. (That is, right after they figured out that it might be a good idea to do so. :-))
I call troll. The picture you linked to was the INTENTIONAL destruction of a NERVA engine. Why would they do that? To test if safety procedure were working, and gauge issues with fallout. You'll note from TFA, that this engine has even more safety features, such as a titanium shell that would prevent catastrophic spread of materials. Also, it wouldn't even be activated in the atmosphere.
And before you whine about "we don't know", go do some reading about launch accidents involving nuclear materials.
Very simply put, the NERVA engines ran so hot that the Graphite used to transfer the heat from the reactor into the exhaust would flake off and end up in the exhaust. The problem is that while the hydrogen exhaust cannot be made radioactive, the graphite can. So you'd get little specs of radioactive graphite raining down behind you. It wasn't so much graphite as to be a major concern, but many of us would rather not exhaust anything radioactive if we can help it.
Not to sound paranoid, but when the reactor overheats and falls off where does it go?
Launch profiles are designed so that everything falls into the ocean. NASA has aborted quite a few launches, and has never dropped anything on people's heads. China on the other hand...
What happens if the reactor falls off over a populated area?
Well, since it's not supposed to be activated until the craft is already outside of the atmosphere, I suppose someone gets a bump on the head. Even if we assume that the reactor overheated, the titanium shell will melt down and scram the reactor before the reactor itself melts down. It should be nice and cool (and still wrapped in titanium shielding) by the time it hits the water.
Say the reactor falls off on the way to mars. Unless there is a shift in the momentum of the ship or the reactor it'll just melt down beside the ship. Then imagine the case where the ship can separate itself from the reactor. Now how do they get back?
The mission profile suggests three engines. Unless there's a critical failure in all three, a modified flight path could be developed.
While this is probably an improvement, I'd hardly consider it safe.
Consider a chemical rocket on the way to Mars. What happens if the tanks explode? That's right, you've got no way back. Even the failure of one engine could spell doom for the mission. This engine is more powerful, and FAR safer than any chemical engine. Even if the tanks leaked on the way, fuel could still be scooped from Mar's atmosphere. No chemical rocket can make that claim.
Well, you could always RTFA. Here:
BB: Is there a 'fail safe' operation in the event the reactor core must
be shut down exiting a planetary 'gravity well' or on approach to a
'gravity well' ?
RJ: There are several features that we have adapted and evolved into the
current 'TRITON' design to handle risk mitigation for the Uranium
Dioxide (UO_2 ) fuel element core in a Nuclear Thermal Rocket (NTR).
We have approached this by providing an integrated, robust design the
uses dual turbopumps (turbopumps provide coolant flow to the reactor in
propulsion mode).
In thrust mode where you have high power operation, is where this
concern has been typically addressed.
The safety features that have been taken into account for risk reduction
entail constant supply of reactor coolant by using dual turbopumps. This
means turbopumps with their moving parts like bearings, shafts, turbines
etc. may cavitate and over speed, if for some reason one of the
turbopumps showed signs of malfunction or not operating within
appropriate parameters, you could effectively shutdown or bypass the
offending turbopump and still have coolant flow going to the reactor.
This is one of the key features for propulsion mode operation to make
sure coolant is available to ?flush; the reactor if it needs to be shut
down when it has gotten to the full thermal power level. In power mode
it's [core] sitting at an idling power-level so the amount of time for
the reactor to over-heat if starved of coolant (i.e. He/Xe gas) is
extremely negligible because you are running the reactor core at nearly
half the maximum temperatures the core is design for. So, if in the
event of something like let's say, a minor leak in the radiator during
power-mode operation, you can do a shut-down of the reactor from a very
moderate control state without over-heating the reactor core. Other
failure mode mitigation would be to have a segmented radiator design, or
have a coolant purge circuit in the design, or actually split the
coolant circuit to provide redundancy. We also have several valve
arrangements so that in the event of leakage in idle power mode you
could shut a section of the radiator down; the temperature of the
reactor is so low it would cool down on its own. This works to our favor
in the ?TRITON? design because the CERMET core materials have high
maximum operating temperatures since it's designed for exit temperatures
near 2,700-K in the propulsion mode.
Another feature is the nature of going to a fast spectrum reactor. It
allows issues such as criticality and impact immersion (e.g. wet sand or
salt water) to immediately be mitigated because of the reactor neutron
flux levels and the use of only a reflector and no moderator to
thermalize a bulk of the neutrons. Essentially it helps to 'poison' the
internal nature of the reactor so in the worst case event at launch, if
the reactor were to end up in sand or saltwater it will keep it from
resorting to a super-critical state. If it shuts down after a brief
period of operation, like for some reason and I had to shut it down
during an early phase of a human Mars mission, the 'burn-up' (fission
product build-up) is so low. Even if I run it for only 5 minutes or, 10
minutes I'd have built up only a minuscule amount that could barely be
measured with regards to build-up of fission products in the core. So if
it did for some reason re-enter the earth?s atmosphere, the radiation
levels are only slightly higher than typical naturally occurring levels.
Now, you would have to methodically go through a full risk analysis, or
a whole mission point-to-point to define the 'What if scenarios' along
the mission's plan to properly build in aborts for all the most probable
failure modes.
For example, one 'What if scenarios' would look at the failure modes for
an orbit capture high-thrust burn at a planet Mars or for Lunar
transport. In essence, an inve
Erm, that's the Prometheus project (part of the JIMO mission). This is a Nuclear Thermal Rocket. It works on a very different principle. (i.e. You use a nuclear reactor to heat the exhaust to high temperatures, instead of using a powerful chemical reaction.)
This design is significantly different from the NRX. For one, they didn't attempt to build the most powerful reactor in the universe. For another, they took advantage of LHOx afterburners. With both of those design choices in mind, they were then able to use a titanium shell to act as the heat sink for the reactor. Not only does it not ablate, but the titanium will melt and scram the reactor long before the reactor itself experiences meltdown.
:-)
In other words, this is an extremely safe reactor design.