U238 for Aerospace Propulsion (Traveling Wave Reactor)

[mheslep]

...
One may lose as many as half the neutrons from the fission wave volume. I imagine the scattering of fast neutrons from the ash is similar to that of the fuel region. And there is leakage out the sides, and losses into the coolant and structural material.

I think originally the idea was to use a fairly large diameter cylindrical core, and start the burn in the center. I recognize heat dissipation limits the core size, but to the degree large size is possible, the losses to the sides of the cylinder shouldn't become significant except where the wave comes close to the containing structure. In those edge regions, perhaps they don't breed or burn up much fuel. In a normal enriched U reactor that would be an expensive inefficiency, but here the fuel is nearly free so perhaps they don't care. In the interview above Gilleland says he never expects to get above 50% U238 burnup. I agree this still doesn't address the cooling or moderating structures and medium.

Besides the fission products are transuranics that themselves are somewhat parasitic. I'd like to see their models.

Isn't the fission yield of transuranics from Pu-239 fission tiny in comparison to Xe, Kr, etc?

If leakeage is already 50%, I'm skeptical about achieving a viable system.

Certainly. The question is whether the TWR does in fact lose 50% of 2.9 neutrons, or not.

At the end of life, I imagine that unburned fuel will remain.

Again, U238 or even natural U. May not matter.

 

[Astronuc]

I think originally the idea was to use a fairly large diameter cylindrical core, and start the burn in the center. I recognize heat dissipation limits the core size, but to the degree large size is possible, the losses to the sides of the cylinder shouldn't become significant except where the wave comes close to the containing structure. In those edge regions, perhaps they don't breed or burn up much fuel. In a normal enriched U reactor that would be an expensive inefficiency, but here the fuel is nearly free so perhaps they don't care. In the interview above Gilleland says he never expects to get above 50% U238 burnup. I agree this still doesn't address the cooling or moderating structures and medium.

Another factor is the increase in volume of the fission products (FP) with two atoms produced per fission. If TWR produces 50% FIMA, then it should expand 50% in volume. It is my understanding that the point is to convert U-238 to Pu-239/240/241 for fissioning.

Isn't the fission yield of transuranics from Pu-239 fission tiny in comparison to Xe, Kr, etc? Certainly. The question is whether the TWR does in fact lose 50% of 2.9 neutrons, or not.

I'm thinking more along the lines of Pu-240, Pu-242, and others that might absorb neutrons but not readily fission. And the key factor is the matter of 50% loss of 2.9 neutrons. Basically one has to have at least one neutron to convert U-238, and one to fission the Pu-239, so the system can only lose 0.9 neutrons on average to other mechanisms, i.e. absorbed by FP, structure, coolant or leak out of the core (absorbed by ex-core structure/shielding).

Again, U238 or even natural U. May not matter.

I'm thinking more about the unburned fissile and fissionable (transuranic) isotopes. Certainly, it's a benefit not to worry about U-237 or Np-237.

 

[sanman]

Belgium has approved work on the construction of an Accelerator-Driven Reactor System (ADS) which uses low-enriched Uranium:

http://www.world-nuclear-news.org/WR_Approval_for_Myhhra_0503101.html

So while it's not Traveling Wave, it's still primarily U238.

Could this idea, if proven to work, then be adapted to a space vehicle?

Alright, I suppose fission products are an unavoidable hazard unacceptable for Earthly use, but for a spacecraft flying far from Earth it seems quite justifiable.

Could something like this be used to power a VASIMR rocket? How about for some kind of lunar shuttle that operated between the lunar surface and orbit, in addition to being a long-range lunar surface transport?

It says low-enriched, but it doesn't say how low. Ideally, you'd like the system to be improved to the point where it could work entirely on depleted uranium - ie. U238 alone.
Could this be conceivable?

 

[sanman]

Furthermore, regarding fission products - given that you're replacing the huge mass/weight of chemical fuel with relatively compact nuclear fuel, you could have spaceships which are much lighter, which again saves you on nuclear fuel mass, which in turn reduces your fission products. An unmanned launch vehicle might not require much reactor shielding, so you'd avoid that mass/weight penalty too.

Instead of direct heat exchange with the flowstream, supposed you used AMTEC (Alkali Metal ThermoElectric Conversion) to convert the nuclear energy into electricity. The nuclear-electric power could be used to power an upper stage, while the lower stage would be chemical.

Furthermore, you could have the chemically-propelled lower stage be a scramjet or something, which would have safer takeoff and landing than a chemical rocket. The scramjet would lift everything to just above the atmosphere, where the nuclear-electric VASIMR propulsion system would take over and propel the upper stage to orbit or beyond (eg. Moon)

With the nuclear-electric VASIMR propulsion, you could send very heavy payloads into orbit around the Moon. The VASIMR module could then ferry this mass in smaller chunks down to the lunar surface.

What's wrong with this idea?

 

[Astronuc]

VASIMR has high specific impulse and low thrust, so it has to be used outside of a gravity field where the local acceleration due to gravity is less than the acceleration provided by VASIMR.

In comparing power conversion concepts, one need only consider the kW/kg (specific power) as a figure of merit. The higher the number the better. Conversly one could look at kg/kW, in which case the smaller the number the better.

AMTEC (Alkali Metal ThermoElectric Conversion) generally has low thermal efficiency, which is tied to the thermoelectric material(s). There are TE materials that have an optimal temperature range. One also most consider how far from the reactor one would have to place the materials so that they are not activated by the neutrons (from a fissile system).

With respect to ADS - one needs a massive accelerator, and they are generally inefficient with respect to energy input vs useful energy out.

 

[sanman]

Well, let's assume that your chemically-driven lower-stage gets you to escape velocity. Then your nuclear-powered upper stage has all the time it needs to push you higher - even out to the Moon.

Accelerator size (or mass) is an engineering problem - there is no fundamental rule saying that an accelerator has to be of high mass. I would think that the closer the reactor's sub-critical state is to criticality, then the less accelerator input is required to sustain the reaction. So perhaps this could be traded off against accelerator size and power.

As for separation distance between thermoelectric materials and neutron source, well, most rocket designs are pretty long, including even many deep space concept designs, and in space you have a lot of room for separation.

If your vehicle was a lunar shuttle/ferry only operating between the lunar surface and lunar orbit, you'd still essentially be operating in a hard vacuum so that an aerodynamic geometry would not be needed.

While neutrons are electrically neutral, they are still magnetic, and so I've always wondered if it's possible to harvest their kinetic energy via a magnetic field. This would also be beneficial from a radiation standpoint. Maybe a hybrid fission-fusion reactor could do this, exploiting a tokamak's magnetic field.

 

[Astronuc]

Well, let's assume that your chemically-driven lower-stage gets you to escape velocity. Then your nuclear-powered upper stage has all the time it needs to push you higher - even out to the Moon.

A chemical system would get one to orbit (LEO), and the nuclear system would probably be completed on orbit. Then the nuclear system would take one to one's destination.

Accelerator size (or mass) is an engineering problem - there is no fundamental rule saying that an accelerator has to be of high mass. I would think that the closer the reactor's sub-critical state is to criticality, then the less accelerator input is required to sustain the reaction. So perhaps this could be traded off against accelerator size and power.

The accelerator current would drive a subcritical system, i.e. the power produced would be proportional to beam current, and ADS systems are not design with propulsion in mind, but simply to burn transactinides and transmute waste. The system could be designed to go supercritical until it achieves criticality through Doppler effect (resonance absorption), but then that assumes an thermal or epithermal system as opposed to a strictly fast reactor system. Accelerators require bending/deflection magnets for directing and focusing the beam.

The TWR is not designed for propulsion - so it can be rather massive - depending on the energy to be produced, which is given by the integral of power over time.

Generally, to minimize mass, one minimizes the core by increasing the enrichment as close to 100% as desirable. The smaller the core (and with enrichment increasing to > 90%), control becomes a key issue. Dynamic (on-line) fueling of a core would also be problematic.

As for separation distance between thermoelectric materials and neutron source, well, most rocket designs are pretty long, including even many deep space concept designs, and in space you have a lot of room for separation.

One goal is to minimize the heat transport, particularly high temperature heat which requires strong/stable (little or no creep) material at temperature.

If your vehicle was a lunar shuttle/ferry only operating between the lunar surface and lunar orbit, you'd still essentially be operating in a hard vacuum so that an aerodynamic geometry would not be needed.

Aerodynamic profile is only important in minimizing energy loss in an atmosphere. The discussion is strictly about propulsion.

While neutrons are electrically neutral, they are still magnetic, and so I've always wondered if it's possible to harvest their kinetic energy via a magnetic field. This would also be beneficial from a radiation standpoint. Maybe a hybrid fission-fusion reactor could do this, exploiting a tokamak's magnetic field.

Neutrons have a magnetic moment, which is not the same as being magnetic (they have a very weak field), and one is unlikely to collect a large mass of neutrons, and they are neutral, so they essentially pass through a magnetic field without much loss of energy.

 

[sanman]

Astronuc, thanks for your great replies as usual, which always give me pause for thought.

Well, since the neutron's cross-sectional area is small, it's too bad we don't have some material with extra-large cross-section to intercept it. I've wondered if nuclear isomers might be capable of cross-sectional geometries that might allow greater neutron-interception capabilities relative to their nuclear mass. Is it possible that a suitable nuclear isomer exists which has higher neutron-capture capability, just as some ions have higher electron affinity?

While I understand that isomers are expensive to manufacture, just think of the problems that could be solved if such a desirable material were made.

 

[Astronuc]

Astronuc, thanks for your great replies as usual, which always give me pause for thought.

Well, since the neutron's cross-sectional area is small, it's too bad we don't have some material with extra-large cross-section to intercept it. I've wondered if nuclear isomers might be capable of cross-sectional geometries that might allow greater neutron-interception capabilities relative to their nuclear mass. Is it possible that a suitable nuclear isomer exists which has higher neutron-capture capability, just as some ions have higher electron affinity?

While I understand that isomers are expensive to manufacture, just think of the problems that could be solved if such a desirable material were made.

Ah - now one appreciates the challenges of designing a nuclear reactor, particularly a small one with high power density.

Reactor design involves a tradeoff of nuclear properties and the other physical properties. There are a limited number of fissile fuels (isotopes) from which to choose. There core must maintain a stable geometry, which becomes more challenging as the temperature is increased. Then the core must contain all the fuel to be consumed, which would limit the lifetime to seconds to years depending on size and utilitization, unless the core can be refueled. Refueling usually means shutting down a reactor and replacing some fuel elements. CANDUs are designed to be refueled on-line whereby the refueling machinces operated within the pressure boundary. One machine inserts new fuel while the other extracts/receives an equivalent number of spent fuel. But CANDU are large machine not designed for propulsion.

With respect to nuclear properties, neutrons originating from fission have energies on the order of several MeV, ~ 1-10 MeV, with an average of about 4 MeV. They are considered fast, and they can travel a distance on the order of meters before interacting with most materials. However, the lighter elements can readily interact with neutrons, with hydrogen being the best at slowing down neutrons, because the proton is about the same mass and conceiveably, if a neutron hits a proton 'smack-on-center', then the neutron essentially loses all it's energy, nearly coming to a stop. It would then likely drift into a nearby nucleus and be absorbed. Deuterium is the next best stopping or slowing down medium, then Li, Be, B, C . . . . according to mass. Another property with which one must be concerned is the absorption cross-section, since the absorption by structural materials competes for neutrons with the fission process. In other words, the desirable absorption leads to fission, while the undesirable absorption leads to parasitic losses. Of course, to control the reactor, it is desirable to have a neutron aborber that can be inserted in the reactor to shut it down (make it subcritical) quickly. A physical property that goes along with neutron cross-section is the atomic density - which for most solids is on the order of 10²² atoms/cm³. Density decreases with temperature, which is an important factor when designing the fuel.

In addition to structure, a reactor systems requires a means of heat removal, otherwise the core will eventually melt or vaporize if the temperature exceeds melting or boiling points. So a core design needs a means of passing a 'working fluid' though the core and transporting the heat to a thermal conversion system - and doing so in a controlled (stable and reliable) manner. The fluid maybe single phase (gaseous or liquid), or two phase (vapor + liquid).

For turbomachinery, vapor is the preferred phase. Liquid is preferred to minimize the work used to return the coolant to the core. If the working fluid is gaseous, a compressor would be required to force the gas back to the core.

With respect to reactor cores, one can design a fast reactor core with a reflector using something like a beryllium-based reflector. Basically compact cores (particularly those using a fast neutron spectrum) need to be reflected in order to maintain a margin of controllablility.


In terms of reactor design, the following indicates the issues that must be addressed:
http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-appa.html
Part 50 Domestic licensing of production and utilization facilities
http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/

10CFR - http://www.nrc.gov/reading-rm/doc-collections/cfr/ - addresses a whole host of issues and requirements for nuclear technology.

 

[Frame Dragger]

To respond to people thinking of nuclear aircraft... I don't see how that is worse than a nuclear reactor at sea; in fact I'd much rather see a meltdown in air than water. Politics is one thing, but if the plane crashed into a body of water, THAT is the issue...
...
...
...

And yet we have many nuclear powered submarines and other naval vesels. We ALREADY live with this risk, it just feels more remote.

Add this http://www.nuclear.com/n-plants/index-Floating_N-plants.html and I think we have something to be genuinely terrified of. I can imagine cleaning a LARGE region of contaminated land, but I can't imagine the full consequences of a meltdown at sea, of that magnitude.

Aviation is frightning, because people DO think of something falling from the sky... we tend not to instinctively fear what we do to our oceans, and what the effect of the steam would be. Oh, it would be very very bad.

So, it's all political, because we're happy to live with nucelar weapons aimed down our throats at all times, because of our confidence they will never be deployed. We seem not to care if we stick nuclear weapons and reactors under or on the water... of course, planes crash in countries OTHER than ones they originated from. The politics of that *shudder*.

 

[Astronuc]

To respond to people thinking of nuclear aircraft... I don't see how that is worse than a nuclear reactor at sea; in fact I'd much rather see a meltdown in air than water. Politics is one thing, but if the plane crashed into a body of water, THAT is the issue...
...
...
...

And yet we have many nuclear powered submarines and other naval vesels. We ALREADY live with this risk, it just feels more remote.

Add this http://www.nuclear.com/n-plants/index-Floating_N-plants.html and I think we have something to be genuinely terrified of. I can imagine cleaning a LARGE region of contaminated land, but I can't imagine the full consequences of a meltdown at sea, of that magnitude.

Aviation is frightning, because people DO think of something falling from the sky... we tend not to instinctively fear what we do to our oceans, and what the effect of the steam would be. Oh, it would be very very bad.

So, it's all political, because we're happy to live with nucelar weapons aimed down our throats at all times, because of our confidence they will never be deployed. We seem not to care if we stick nuclear weapons and reactors under or on the water... of course, planes crash in countries OTHER than ones they originated from. The politics of that *shudder*.

Aircraft, ships/submarines/barges, and terrestrial power plants are all completely different systems with different engineering/technical requirements. The engineering/technology are completely different.

 

[Frame Dragger]

Aircraft, ships/submarines/barges, and terrestrial power plants are all completely different systems with different engineering/technical requirements. The engineering/technology are completely different.

Yes, and that's why the Russian approach I cited is so troubling, because they are ignoring that. Nothing that has come out of Sevmash should inspire confidence, especially the lack of care to shielding the hull against a 'burning' nuclear core, despite the consequences of a possible failure. They're just repurposing some KTL-40 (naval), and ABV-6M reactors! They're even considering a VBER-300 for later models.

That's not just warming the oven for propulsion, and the "switchover" to providing heat, power, and desalination is also a bit unclear. I'd offer more, but there is no more that has been made public, that I'm aware of.

 

[Astronuc]

Yes, and that's why the Russian approach I cited is so troubling, because they are ignoring that. Nothing that has come out of Sevmash should inspire confidence, especially the lack of care to shielding the hull against a 'burning' nuclear core, despite the consequences of a possible failure. They're just repurposing some KTL-40 (naval), and ABV-6M reactors! They're even considering a VBER-300 for later models.

That's not just warming the oven for propulsion, and the "switchover" to providing heat, power, and desalination is also a bit unclear. I'd offer more, but there is no more that has been made public, that I'm aware of.

The Russians are not ignoring that fact. The KTL-40 is a marine reactor, not an aircraft reactor. If they were to deploy it, they would have to meet the regulatory, safety and security requirements for the nation in which it was deployed, and they'd likely have restrictions due to proliferation due to the 90% enrichment.

This technology would not work in an aircraft as it is too massive. An icebreaker weighs a heck of a lot more than a 747.

As for information - please refer to a report from Norwegian authorities - http://www.nks.org/download/pdf/NKS-Pub/NKS-138.pdf

3.3 THE KLT-40 PLANT
The latest version of Russian maritime reactor plants is the KLT-40. It has been installed in the
icebreaking freighter Sevmorput and in two icebreakers, Taimyr and Vaigatch, all with one
reactor only. Much is known about this plant, because the Russian government submitted the
safety report for NS Sevmorput, [Information], to the Norwegian safety authorities in 1991 before
a visit of Sevmorput to Tromsø in 1991. This report has been the basis for many studies of
Russian marine reactors. The KLT-40 plant contains a pressurized water reactor with power
levels of 135 MWt (Sevmorput) and 171 MWt (Taimyr and Vaigatch). The information given
below has been obtained from [Information] and, strictly speaking, applies only to the Sevmorput
plant. However, data for Taimyr and Vaigatch are presumably not very different even though the
power level of their reactors is somewhat higher. The KLT-40 is in many ways similar to the OK-
900.

3.3.1 Reactor
Figure 3.7 gives a vertical cross-section of the reactor. The coolant enters the reactor tank at the
top, flows downwards through the reflector/thermal shield, up through the reactor core and from
the top of the reactor tank to the steam generator. From here, the coolant flows through the
canned circulation pump back to the reactor. The design is very compact, completely welded with
a tube-inside-tube arrangement whereby the length of the piping and number of flanges etc. of the
primary circuit is kept to a minimum, reducing the risk of leakage. The reactor tank is on the
inside provided with a stainless steel layer. The thermal shield consists, in the radial direction, of
steel-water layers and, at the top above the tank lid, of a concrete shield.
The core height is 1 m and the diameter 1.21 m. The 241 fuel elements are arranged in a
triangular lattice with a spacing of 72 mm. The fuel elements are placed in a removable insert or
basket inside the reactor tank, and movement is prevented by fixing them both at the bottom and
at the top.

Core height 1 m
Core diameter 1.21 m
Mass of U-235 in core 150.7 kg
U-enrichment 90% (weapons grade)

3.3.5 Primary Cooling Circuit
Figure 3.8 shows the primary system. The reactor is provided with four cooling loops, each of
which contains one steam generator and one circulation pump. Pressure in the primary system is
controlled by a gas pressurizing system connected to the four pressurizers. This system is based
on injection/discharge of gas. According to [Kuznesov1], coolant inlet temperature is 278° C and
outlet temperature is 318°C. According to [OKBM] and [Information], inlet temperature is 78°C,
outlet temperature 312°C and the pressure of the primary system is 130 bar. The temperature and
pressure of the steam leaving the steam generator is 290°C and 40 bar. There is an emergency
cooling system, but in addition, the reactor can run by natural circulation at 25–30% full power.

Certainly one would have to be careful with the design.

The 747-8 Freighter will be longer than the 747-400F by 5.6 m (18.3 ft) and have a maximum structural payload capability of 140 metric tonnes (154 tons) with a range of 8,130 km (4,390 nmi). Also powered by 787-technology engines, it will achieve the same environmental benefits as the 747-8 Intercontinental. The 747-8 Freighter will have nearly equivalent trip costs and 16 percent lower ton-mile costs than the 747-400, plus 16 percent more revenue cargo volume than its predecessor. The additional 120 cu m (4,245 cu ft) of volume means the airplane can accommodate four additional main-deck pallets and three additional lower-hold pallets. Operating economics of the 747-8 Freighter will be significantly superior to the A380F. The 747-8F's empty weight is 80 tonnes (88 tons) lighter than the A380F, resulting in a 24 percent lower fuel burn per ton, 21 percent lower trip costs and 23 percent lower ton-mile costs than the A380F.

. . . .

http://www.boeing.com/commercial/747family/747-8_facts.html

And compare to the An-225
Empty weight: 285,000 kg (628,315 lb)
Max takeoff weight: 640,000 kg (1,323,000 lb)
http://en.wikipedia.org/wiki/Antonov_An-225#Specifications_.28An-225.29

Of course, with the KTA-40, one would need shielding, a turbine-generator set, and high speed motors. The shielding, T-G, and motor(s) add substantial mass, such that it would be impractical for an aircraft.

The other major factor would be designing an impact resistant containment systems. Since ships massive and don't travel at high speed or high altitude, there not much of an impact to design for as there is for an aircraft. One can build a substantial containment on a ship or barge, but not so for an aircraft. Certainly one would also have to consider designing containment for missles, both natural and man-made - and this would be a simpler proposition for a ship/barge than for an aircraft.

Various governmental research organziations, e.g., US DOE, are aware of the KTA-40 and other systems, and their potential application.

 

[Hologram0110]

Do people really think that a nuclear power plane crashing on land would be better than sea?

While I really don't like the thought of any reactors in situations where their containment could conceivably fail especially in uncontrolled areas. If a reactor were to fail outside of containment, out at sea seems like one of the better places to me. Please correct me if I'm wrong, but because the oceans are so large, if an accident occurs far from land, the contamination would have been significantly diluted by the time it reaches populated areas.

Also, speeds at sea are lower than air speeds. A sinking ship will hit the sea floor much more softly than an air craft crashing on land or sea. Conceivably, we could then work to recover, or contain the reactor lost at sea before it leaks.

Also, the risks of using nuclear reactors on submarines is somewhat more justifiable because they need high energy density to stay underwater. Nuclear reactors in space also seem justifiable to me for similar reasons. There are no real reasons planes in the atmosphere would need anything other than chemical and/or electrical energy sources. They simply are not in the air long enough to justify the need. You could just use fossil fuels, biofuels, hydrogen, batteries, super/ultra capacitors ect.

Currently, solar and radioisotope generators are able to provide enough power for propulsion. I wonder if you could create a hybrid radioisotope + fission source similar to accelerator driven systems.

 

[Frame Dragger]

The Russians are not ignoring that fact. The KTL-40 is a marine reactor, not an aircraft reactor. If they were to deploy it, they would have to meet the regulatory, safety and security requirements for the nation in which it was deployed, and they'd likely have restrictions due to proliferation due to the 90% enrichment.

This technology would not work in an aircraft as it is too massive. An icebreaker weighs a heck of a lot more than a 747.

As for information - please refer to a report from Norwegian authorities - http://www.nks.org/download/pdf/NKS-Pub/NKS-138.pdf
Certainly one would have to be careful with the design.

http://www.boeing.com/commercial/747family/747-8_facts.html

And compare to the An-225
Empty weight: 285,000 kg (628,315 lb)
Max takeoff weight: 640,000 kg (1,323,000 lb)
http://en.wikipedia.org/wiki/Antonov_An-225#Specifications_.28An-225.29

Of course, with the KTA-40, one would need shielding, a turbine-generator set, and high speed motors. The shielding, T-G, and motor(s) add substantial mass, such that it would be impractical for an aircraft.

The other major factor would be designing an impact resistant containment systems. Since ships massive and don't travel at high speed or high altitude, there not much of an impact to design for as there is for an aircraft. One can build a substantial containment on a ship or barge, but not so for an aircraft. Certainly one would also have to consider designing containment for missles, both natural and man-made - and this would be a simpler proposition for a ship/barge than for an aircraft.

Various governmental research organziations, e.g., US DOE, are aware of the KTA-40 and other systems, and their potential application.

Ah, I think you're misunderstanding me... I wasn't talking about the possiblity of this reactor being used for aircraft, or any reactor. I for one, believe batteries and capacitors will lead the way before we start lofting reactors to anything less than orbit.

As for the Russians respecting treaties and the countries they'll be using this in... my sum-total response is... I don't find that comforting. In fact, I find that about as comforting as a whale might a treaty while being hunted by the Japanese. We've developed "nuclear bunker busters" in theory at least, which is fancy for "GIANT ******* Groundburst from hell". I don't see personal or national responsiblity being a factor in this, especially over a long and uncertain future.

As I said Astronuc, I'm more concerned with how they're repurposing these reactors, the AVB-6M, but the 300MW reactor is the one that really makes me want to cry.

"Useful for oil exploration"... sounds like Siberia and the arctic to me, and the last time I checked no one saw eye to eye on who follows what rules where regarding he latter. The former, is of course, still Russian, as would be many places they send this to. Meanwhile the ocean and atmosphere seem less respectful of those lines on maps as well.

Worst case scenario: A 300MW reactor experiences catastrophic failure, and an exposed core ends in the damned ocean. It doesn't take nuclear engineer to figure out the result of that... just look at our naval testing of nuclear weapons, and why we stopped blowing them underwater. Airbursts are bad, Groundbursts are terrible, an burning core in the ocean would be beyond catastrophe.

 

[Frame Dragger]

Do people really think that a nuclear power plane crashing on land would be better than sea?

While I really don't like the thought of any reactors in situations where their containment could conceivably fail especially in uncontrolled areas. If a reactor were to fail outside of containment, out at sea seems like one of the better places to me. Please correct me if I'm wrong, but because the oceans are so large, if an accident occurs far from land, the contamination would have been significantly diluted by the time it reaches populated areas.

Also, speeds at sea are lower than air speeds. A sinking ship will hit the sea floor much more softly than an air craft crashing on land or sea. Conceivably, we could then work to recover, or contain the reactor lost at sea before it leaks.

Also, the risks of using nuclear reactors on submarines is somewhat more justifiable because they need high energy density to stay underwater. Nuclear reactors in space also seem justifiable to me for similar reasons. There are no real reasons planes in the atmosphere would need anything other than chemical and/or electrical energy sources. They simply are not in the air long enough to justify the need. You could just use fossil fuels, biofuels, hydrogen, batteries, super/ultra capacitors ect.

Currently, solar and radioisotope generators are able to provide enough power for propulsion. I wonder if you could create a hybrid radioisotope + fission source similar to accelerator driven systems.

Exposed reactor + Water = Radioactive Water + LOTS of thermal energy = Radioactive Steam boiling out of the ocean. Forget what leaking does to the immediate environment... I worry about a continuous plume of what would essentially be fallout.

 

[Astronuc]

Exposed reactor + Water = Radioactive Water + LOTS of thermal energy = Radioactive Steam boiling out of the ocean. Forget what leaking does to the immediate environment... I worry about a continuous plume of what would essentially be fallout.

Reactors, including Naval Propulsion Reactors, are designed to SCRAM, i.e., rapid shutdown (subcritical). If the reactor scrams, there is no power generation, except for decay heat. In the ocean, if the ocean water gets to the core (i.e., containment and primary cooling circuit are breached), that means a lot of cooling.

Conventional LWR reactors scram in about 3 seconds.

FD, I was responding to your comment "To respond to people thinking of nuclear aircraft... I don't see how that is worse than a nuclear reactor at sea; in fact I'd much rather see a meltdown in air than water."

A meltdown in the air would be certainly problematic to anyone close to the aircraft. A crash of an aircraft would have severe radiological consequences in the vicinity of the crash, much more so than a ship sinking at sea, ostensibly with an a scrammed/shutdown reactor.

 

[Frame Dragger]

Reactors, including Naval Propulsion Reactors, are designed to SCRAM, i.e., rapid shutdown (subcritical). If the reactor scrams, there is no power generation, except for decay heat. In the ocean, if the ocean water gets to the core (i.e., containment and primary cooling circuit are breached), that means a lot of cooling.

Conventional LWR reactors scram in about 3 seconds.

FD, I was responding to your comment "To respond to people thinking of nuclear aircraft... I don't see how that is worse than a nuclear reactor at sea; in fact I'd much rather see a meltdown in air than water."

A meltdown in the air would be certainly problematic to anyone close to the aircraft. A crash of an aircraft would have severe radiological consequences in the vicinity of the crash, much more so than a ship sinking at sea, ostensibly with an a scrammed/shutdown reactor.

If the reactor SCRAMs then yes, I have minimal concern. That said, as with an aircraft or any other situation, when I say "catastrophic failure" I'm thinking of a total failure of all possible safety measures. I realize how vanishingly unlikely that is, when you can just pump neutron poisons into the chamber, but then, presumably any airborne reactor would be shielded to withstand a crash.

My point is simply that the worst-cases don't even come close. I'm not against nuclear power, but this just seems needlessly riskly, and I don't know how quickly VBER-300 could SCRAM.

Let me ask you flat out: You have a VBER-300 in the air, or in the ocean, exposed, and critical. Which do you prefer in 'that worst of all possible worlds', that I concede is incredibly unliklely barring an added human element?

 

[Hologram0110]

Someone correct me if I'm wrong, but I would suspect that naval reactors would default to an off position in the event of any sort of failure. I know that many land reactor designs require power to keep the control rods out of the core by water pressure against a spring. If water pressure is lost because of loss of power for example, the rod returns to the off position without any intervention. I would assume that similar safety measures would be included for a naval reactor.

My concern for radioactive release would be due to physical damage to the core from outside source. IE Sub hit with torpedo, plane hit with missile, that destroys the reactor core spreading the fission products that are already in the core. In that case, I'd still rather it be in the ocean then air. The ocean can better dilute things and gives more time for radioactive decay before the release could get to populated areas.

Even if somehow the reactor were rigged to stay on, I think a reactor in water would better than air.

 

[mheslep]

If the reactor SCRAMs then yes, I have minimal concern. That said, as with an aircraft or any other situation, when I say "catastrophic failure" I'm thinking of a total failure of all possible safety measures. I realize how vanishingly unlikely that is, when you can just pump neutron poisons into the chamber, but then, presumably any airborne reactor would be shielded to withstand a crash.

My point is simply that the worst-cases don't even come close. I'm not against nuclear power, but this just seems needlessly riskly, and I don't know how quickly VBER-300 could SCRAM.

Let me ask you flat out: You have a VBER-300 in the air, or in the ocean, exposed, and critical. Which do you prefer in 'that worst of all possible worlds', that I concede is incredibly unliklely barring an added human element?

I'll comment on one aspect: the reactor actually in the ocean, submerged, is not going to stay critical very long, nor are the most radioactive fission products going to become airborne and travel hundred of miles over human populations as in the possible case of a aircraft crash on land.

 

[Frame Dragger]

Well, I'll take that as some comfort then.

 

[gronkulator]

What if your 747 crashes?

10-15 tons
I'm not sure that's fair. They were abandoned, doesn't mean they didn't work.
Yes, that's a problem. Doesn't mean the problem is intractable.

I doubt this is a show stopping problem any longer. Modern aircraft carry 70ton tanks and the Space Shuttle of all things.

he didn't say they didn't work. he said they JUST didn't work. that's a weasel word. it doesn't

have any meaning, it's an emotional cue for you to backpedal. "just" implies that his factoid is too simple or straightforward for him to bother explaining.

(like his emotional state: "TWR's are a nutty idea". this is a feeling, not a rational position.)

nuke aircraft engines worked.

ICBM's probably took the mission away from the hypothetical fission-powered strategic bombers.

backtracking on the thread, these puppies may be very good for unmanned deep space propulsion. ..

used to power a xenon or argon ion engine, and power the laser communications that will have to replace RF past about 20 or 30 AU due to bandwidth issues. (new horizons will take
9 mos for data return after a very brief flyby in 2015). and then theres' some powerful radars we'd like to fly for planetary science. like too see all those liquid water oceans, under hundreds of km of ice. that will take some juice.

hardest part is a robot that lasts 60 years.

 

[Astronuc]

"TWR's are a nutty idea" is a technically accurate statement. There was no emotion in my comment.

I heard through the grape vine that some new talent has reconfigured the original design. Apparently the new configuration looks more like a fast reactor.

Still if they want to achieve 20% or greater FIMA on a homogenous fuel material, they'll have some swelling problems.

 

[gronkulator]

"TWR's are a nutty idea" is a technically accurate statement. There was no emotion in my comment.

I heard through the grape vine that some new talent has reconfigured the original design. Apparently the new configuration looks more like a fast reactor.

Still if they want to achieve 20% or greater FIMA on a homogenous fuel material, they'll have some swelling problems.

technically accurate? only if you're trained in brain science, and have examined the person who had that idea in person. and those are both NO.

this isn't a psych forum anyway.

it's purely emotional, an ad hominem attack , and argument by intimidation.

from these technically accurate facts, i infer that you aren't up to speed on the engineering here. and definitely not the physics.

 

[mheslep]

, an ad hominem attack .

No, since if there's no 'man', there's no http://en.wikipedia.org/wiki/Ad_hominem" .

 

[gronkulator]

No, since if there's no 'man', there's no http://en.wikipedia.org/wiki/Ad_hominem" .

there is. it's the person who has the idea the poster attacks as "nutty".

unless you think ideas exist , disembodied, with no person to hold them? well, that would be silly.

if you want to have a latin lesson, start with prima facie, which addresses why the earlier statements are "technically factual". then please take the latin , existentialism, and psychiatry to the correct forum(s).

 

[mheslep]

there is. it's the person who has the idea the poster attacks as "nutty".

unless you think ideas exist , disembodied, with no person to hold them? well, that would be silly.

Nonsense. People and their ideas are not the same thing. Conflating the two leads to labelling criticism of any idea as ad hominem, and that is silly.

 

[gronkulator]

Nonsense. People and their ideas are not the same thing. Conflating the two leads to labelling criticism of any idea as ad hominem, and that is silly.

add straw man argument to the above. i conflated nothing.

my remark about the ad hominem attack was in response to one remark, not two. and if there was a "lead" around here somewhere, i didn't comment on it. must be another thread.

your argument is worse thaan extremely weak it is non-existent, and like the OP you apparently have to resort to off-topic attacks on people who disagree in order to compensate for inadequate knowledge of the topic.