bullpitt
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Joined: Sat Mar 06, 2004 7:09 am

RE: Nuclear Powered Aircraft In Future?

Mon Oct 15, 2007 6:12 pm

Hi all

Quoting Nzrich (Reply 32):
Correct ie New Zealand that is 100% totally nuclear free

You're wrong.  Silly There consider yourself corrected.

Ok seriously now. Nuclear free zones are politicians specially greenies' mumbo yumbo, trying to confuse the general public. Let me put it this way do you have dental surgeries in New Zealand? Hospitals? Heavy industry? Quality control facilities? because if you do most of them will have some type of nuclear facility. In fact in a Hospital you can find some very dangerous shit and the control is far less than any nuclear power plant.
These are my principles but if you don't like them I have others
 
2175301
Posts: 1633
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RE: Nuclear Powered Aircraft In Future?

Tue Oct 16, 2007 12:16 am

OK, this is an area where I have some expertise ( I work in a nuclear power plant):

If you visit Idaho you can see the two nuclear reactors that were built as test engines for possible US Military applications along with the first nuclear electrical generation power plant.

The project was stopped for 4 basic reasons: Shielding, weight, radiological contamination from a crash, and cost.

While reactor design has improved a lot since then you are not going to eliminate the weight and crash concerns.

However, the ideal nuclear system can indeed power a "jet" type engine (Brayton Cycle). The compressor sends compressed air to the reactor core, where the air is heated to potentially several thousand degrees, and then the hot air is exhausted through the nozzle after shedding some energy in the power turbine needed to turn the compressor.

Control and durability of such a reactor to allow it to rapidly ramp up and down are hurdles that are currently unsolved even if the weight and crash issues did not exist.

INL (the Idaho DOE nuclear development and test laboratory, where the aircraft engine test reactors are) is working on hot gas reactor designs right now for a high efficiency Brayton cycle engine which is aimed more at electrical power generation than anything (and the pebble bed reactor is a lessor efficient Brayton cycle engine design). I am unsure of the funding for construction of a test reactor - and I suspect it will be 10 to 15 years before even a test reactor is built.

http://nuclear.inl.gov/

Key in nuclear reactor design is that it is not currently possible to operate a reactor at the temperatures needed for a brayton cycle unless the reactor is very massive - just from a structural standpoint. More mass is needed for radiological shielding; and more yet if the reactor is designed to be contained in a criticality accident (to keep the zoomies contained and not spread all over the countryside).

A Steam Cycle reactor used for power plants also requires very massive structures for support and for containment (and the US did a very wise thing by requiring containment building just in case the "improbable" went wrong).

The world (and US) is just getting ready to start construction of the 3rd generation nuclear power plant designs - which will be much safer than previous generations of plants, I have read the papers and seen the preliminary 4th generation designs (expected commercialization timetable 25+ years from now), and also the summary papers on the 5th generation design hurdles that will take considerable material research in order to build (expected commercialization assuming materials are found would be 50+ years from now).

None of those designs will ever be weight efficient for use on a conventional aircraft, even if you could ensure that their would not be a criticality event or a crash.

On the fusion side of things.... I helped build portions of one of the latest fusion plasma experiments built in the US (is this machine cool or what... http://www.hsx.wisc.edu/ ), and helped build a vessel to research the flow of cooling fluids for a fusion reactor (sorry - no cool pictures).

Any commercial fusion reactor is at least 50 years out; and they are also massive machines and require some degree of radiation shielding as well (not as much as a fission reactor). Due to what is known about the potential shapes a fusion reactor will require to be cooled by liquid metals (liquid sodium is the best bet)- which require a very massive system. By the time you add it all up this system is just as massive as a fission reactor; and I do not believe that anything that is currently conceived of as a real fusion reactor will ever be light enough for use on a conventional aircraft.

Of course, someone may well come up with a different idea on how to do fusion in the future. Figure at least decades from any idea to any commercially available system (the HXS device was at least 20 years from idea to first successful operation).

As others pointed out - the nuclear reactors used in spacecraft (and certain science or spy applications) do not produce much power at all and are not suitable for use in aircraft. Their are two forms of these reactors: Thermal Decay Heat devices that produce minimal electrical current via a thermocouple device, and higher temperature nuclear reaction devices that are not started until after they reach outer space (or are placed on the the ocean floor or a mountain top). These nuclear reaction devices can produce a fair amount of power by the use of a lot more and higher temperature thermocouple devices; and despite the fact that they do not have any degree of shielding they are in fact quite heavy for the power they produce . Both kinds of units can produce suitable electrical power for 20+ years (The Voyager Satellites launched I believe in the late 70's are still transmitting usable data to earth because of their nuclear "batteries"). I do not believe that nuclear reaction devices are currently being planned to be built - I do believe that a few were built.

OK so what can we do - and what does the future really hold:

Hydrocarbon based fuels will continue to be the fuel of aircraft for probably the next 100 years unless something really unknown comes along. Hydrogen will not be directly used due to the problems storing and handling it. However, hydrogen can be easily converted to hydrocarbons as needed. Thus the concept of a hydrogen powered future - with hydrocarbon jet fuel being produced for aircraft is a very viable future as we currently have the technology needed to build it.

Hydrogen will be produced first by electrolysis of water using power generated by nuclear power plants. This has already been costed out as part of the NP 2010 study: http://www.ne.doe.gov/np2010/neNP2010a.html

INL is working to develop the material technologies needed for a high temperature gas cooled nuclear reactor that will make hydrogen from water via high temperature chemical process that will be much more efficient than electrolysis. Currently known materials cannot withstand the required temperatures; but are close enough that it is felt that we should have suitable materials to test in a decade or so.

The US currently has the technical capability to start construction on a Hydrogen based infrastructure. The petrochemical industry already has Hydrogen pipelines that supply some of the oil refineries (current hydrogen production is from natural gas). If the US were to start down a path of building 10 nuclear reactors a year for hydrogen and electrical production the US could be oil import free in about 50 years and retire most coal fired generation (assuming expanding our current energy usage at recent historical rates). This would also assume a substantial amount of wind and solar generation (but wind and solar will never be economical to provide our base-load energy needs).

Of course, someone might wake up tomorrow - or sometime in the future - with an exciting idea on how to generate usable energy by a totally unknown process today. If they do - then that may well allow the flying cars of the future...

I wish you all the best.
 
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Stitch
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RE: Nuclear Powered Aircraft In Future?

Tue Oct 16, 2007 12:46 am

Quoting 2175301 (Reply 51):
I wish you all the best.

And I thank you for your excellent summary, sir.
 
jetjeanes
Posts: 911
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RE: Nuclear Powered Aircraft In Future?

Tue Oct 16, 2007 3:50 am

When certain aircraft are crush in the boneyards there are large weight ballest that are loaded with enough radioactivity to set off and alarm on the trucks hauling them off,, how it gets there i dont dont know unless its years in service in the air
i can see for 80 miles
 
rwessel
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Joined: Tue Jan 16, 2007 3:47 pm

RE: Nuclear Powered Aircraft In Future?

Tue Oct 16, 2007 4:08 am

Quoting Phoenix9 (Reply 39):
According to this site, 1 cubic foot of uranium has the same energy as 7.2 million barrels of oil (crude I assume) and that only a fraction of this energy is harnessed in today's reactors. That means that the actual amount of uranium required to power a jet should be relatively small ( few grams??) which could also help mitigate the radiation produced.

You cannot build a fission pile with that small an amount of Uranium. A major factor is the number of neutrons that escape before triggering a secondary fission. That amount is more or less dependant on the ratio between the surface area and volume of Uranium (or whatever you're using for fuel). More specifically it's mean free path of a neutron in the substance in question vs. the number of potential neutron emitters (which more or less works out as the surface area to volume ratio). A several gram piece has way too much surface area - amply demonstrated by the ability to make a multi-kilogram sphere of 85%+ U235, which, until hit with an external neutron source and severely compressed, is a (very) mildly radioactive, but otherwise inert, lump.

OTOH, a too big lump is inherently dangerous. For example, there was an accident in Japan in 1999 where workers filled some containers of excessive size with an uranyl nitrate solution. That caused a chain reaction - a criticality accident - (since there was no longer enough surface area on the "lump" to allow enough neutrons to escape to prevent one), and several workers were killed. The correct containers (which should have been used) were specifically sized and shaped to be below the criticality limit.

And the hypothetical "1 cubic foot" lump of U-235? *Way* past the criticality limit - you'll get to see a nice blue glow just before you die, while the cube melts itself into a puddle (which will hopefully spread out enough to drop under the limit).

A nuclear reactor works by straddling that boundary. The control rods (assuming that kind of reactor design) absorb neutrons, effectively increasing the loss rate. With the control rods inserted, enough neutrons escape the pile or are absorbed by the control rods to prevent an accelerating chain reaction. With the control rods out, only the surface area loss is left, and the reaction will accelerate. (Of course it's all a bit more complex than that, there are other fixed parts of the reactor structure which absorb neutrons, plus there are substances which effectively slow down some neutrons which makes them more likely to trigger another fission, but the basic relation is the ratio between the number of neutrons triggering new fissions vs. the number lost from the reactor).

A fission warhead works by compressing the Uranium (or whatever) so that the surface area (and thus neutron loss) is greatly reduced, but the number of potential neutron sources is unchanged. That compression is what makes a very small fission warhead possible. The lack of compression is what makes a "several gram" fission pile impossible.

Also, the radiation produced is related to the amount of power produced, so the amount of fissionables onboard doesn't really impact that, except in an accident where the material may be scattered.
 
rwessel
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RE: Nuclear Powered Aircraft In Future?

Tue Oct 16, 2007 4:22 am

Quoting Tdscanuck (Reply 27):
Why would you use steam for the aircraft application? Easiest nuclear engine is to just run ram air through the nuclear pile...voila, hot high pressure gas!

A problem with fission piles is that they don't really get all that hot, at least in normal operation, there's too much structure that won't last long at really elevated temperatures. The steam turbines for nuclear plants are designed to an entirely different set of operating parameters than those on fossil fuel plants. They operate with saturate steam as opposed to the superheated steam preferred in most large generating plants, and therefore have to deal with much more severe corrosion problems in the turbines and plumbing (not to mention lower efficiency).

Pebble bed reactors are a bit of an exception temperature wise.
 
2175301
Posts: 1633
Joined: Wed May 16, 2007 11:19 am

RE: Nuclear Powered Aircraft In Future?

Tue Oct 16, 2007 3:11 pm

Quoting Rwessel (Reply 55):
A problem with fission piles is that they don't really get all that hot, at least in normal operation, there's too much structure that won't last long at really elevated temperatures. The steam turbines for nuclear plants are designed to an entirely different set of operating parameters than those on fossil fuel plants. They operate with saturate steam as opposed to the superheated steam preferred in most large generating plants, and therefore have to deal with much more severe corrosion problems in the turbines and plumbing (not to mention lower efficiency).

Pebble bed reactors are a bit of an exception temperature wise.

Actually, we could easily build reactors that operate at twice the current temperatures of most power plant reactors with existing metals - and they would be durable. The Pebble bed reactor is not really an exception based on temperature and work well within known material properties.

In addition there were a series of nuclear superheated steam power plants built - and some are still operating (I believe this was a B&W design).

The reason that all new nuclear power plants (generation 3 plants) stick with saturated steam has more to do with the ease of control and the ability to design plants that are closer to an "inherently safe" mode than "requires active intervention" to prevent a meltdown in certain design basis accident scenarios.

Aggressive material research is underway to allow the construction of a high temperature gas cooled reactor that would operate at twice the temperature of the Pebble Bed reactor and be durable. I believe that in 10 to 15 years that we will have figured out how to do that. Generation 4 power plants may well move away from steam, and I expect generation 5 plants to be all gas cooled.

Concerning the Pebble Bed reactor. Pebble Bed is not necessarily the panacea that its proponents make it out to be. Key concerns are the fact that the surface of the pebble (graphite) creates dust that circulates around on the gas cycle. This spreads radioactivity everywhere in the cycle and erodes the compressor and power turbine blading. The spent fuel pellets are not reasonably re-processable either, and require twice the disposal volume as current fuel assembly design (assuming current fuel assemblies are not reprocessed).

The major claimed cost savings on a Pebble Bed reactor is because it is "so safe" that it does not need a containment building. I believe that within the US all power reactors will always require a containment building. Chernobyl designed reactors were also "so safe" that the chance of an accident was totally minuscule, so was Three Mile Island. Both meltdowns were caused by human error (if they had just let the automatic safety systems work neither plant would have melted down: for Chernobyl they purposely disabled the safety systems to run a test at a design point that the reactor was known to be unstable, Three Mile Island operators turned key pumps off after the safety systems auto started them). The fact that the US conservatively required containment buildings - despite their huge cost - is the main difference between what happened outside of these plants. Containment buildings are a design that works - and works well - to protect the health and safety of the public.

I have heard people claim that the pebble bed reactor is so inherently safe that people can't hurt it.... My life experiences - and years of experience in nuclear power suggest that the people who claim that really misjudges the creativity of the human mind to muck something up, do something totally unexpected, or do something that we do not know the long term effects of (example: use the wrong cleaner on the reactor vessel and it can crack years later).... My vote is for Containment Buildings for Pebble Bed Reactors. Let them get a couple hundred years of service without any incidents before I would reconsider.
 
rwessel
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Joined: Tue Jan 16, 2007 3:47 pm

RE: Nuclear Powered Aircraft In Future?

Wed Oct 17, 2007 12:05 am

Quoting Rwessel (Reply 54):
The major claimed cost savings on a Pebble Bed reactor is because it is "so safe" that it does not need a containment building. I believe that within the US all power reactors will always require a containment building. (...) My vote is for Containment Buildings for Pebble Bed Reactors. Let them get a couple hundred years of service without any incidents before I would reconsider.

I agree, but one thing that would greatly help something like a pebble bed design is that you don't need anywhere near the size containment building as you do with a PWR. For a PWR your containment building needs to contain a worst case steam explosion (hence the very large sizes), which is simply not something that can happen to a PBR (since there's no water in the reactor).
 
2175301
Posts: 1633
Joined: Wed May 16, 2007 11:19 am

RE: Nuclear Powered Aircraft In Future?

Wed Oct 17, 2007 1:46 am

Quoting Rwessel (Reply 57):
I agree, but one thing that would greatly help something like a pebble bed design is that you don't need anywhere near the size containment building as you do with a PWR. For a PWR your containment building needs to contain a worst case steam explosion (hence the very large sizes), which is simply not something that can happen to a PBR (since there's no water in the reactor).

I disagree in how it actually plays out in cost. Building any containment building is a very expensive proposition. Building one with 4 times the volume is probably only twice the cost of the smaller one.

The exact design issue for containment size for a PWR is a Main Steam Line Break - or a faulted Steam Generator which would release a lot of steam into containment. There are several strategies for having a smaller containment building: Less water in the secondary side of the steam generator, higher allowed pressure in containment, use of ice blocks in Containment that would quickly condense the steam, use of Containment Fan Cooling systems that would start condensing the steam from the moment it is released. Across the current US nuclear fleet there are a variety of sizes of containment's due to these different strategies. I note that the AP1000 PWR (3rd generation PWR design that will be built soon) design has a fairly small containment compared to many existing plants.

In addition to the space for steam expansion - the fact is that there is a lot of other equipment inside the containment building that will always need to be there - so the containment building will never be just small enough to house the reactor and will always be larger.

Also, it is far cheaper to build one large containment for a 1100 + MW plant (AP 1000) than it is to build 11 small containment structures for 11 Pebble Bed reactors (at 100 MW each).

I also note that Westinghouse is working with the international community to design and approve a nominal 300 - 400 MW nuclear unit for countries that do not need 1000 + MW units. The AP 600 design is already pre-approved for use as well (about 700 MW).

I understand that the French designed 3rd generation plant is a bit larger than the AP 1000.

There are several Boiling Water Plant designs as well (BWR) and I believe that the containment buildings are a bit smaller than for PWR's (I believe that the world wide nuclear power plant fleet is about 1/3 BWR and 2/3 PWR, with a few oddballs tossed in - Great Britain has several gas cooled reactors that are approaching the end of their usefull life).

I think the proposed hot gas cooled reactor will make the Pebble Bed design obsolete fairly soon. No graphite dust, hotter temps mean higher plant efficiency, and not limited to relatively small sized plants (but could be used for small sized plants).

From a staffing standpoint - I fail to see how a small nuclear plant would ever be cost effective for most normal situations in the world - regardless of technology; and yes, I have played the game of what if we didn't need staff for this or that due to a change in design. More to the point is what staff will every nuclear power plant need regardless of size.
 
baron95
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RE: Nuclear Powered Aircraft In Future?

Wed Oct 17, 2007 3:30 am

The only way a nuclear powered civil airliner will fly is by using the nuclear power indirectly. There are basically 3 options in order of feasibility.

1 - Nuclear to generate hydrogen from water - hydrogen to generate hydrocarbon fuels - hydrocarbon fuels to power airplane. Feasible in 10 years

2 - Nuclear to generate hydrogen - hydrogen to power airplane if you solve storage issue. Feasible (maybe) in 20 years.

3 - Nuclear to generate electricity - electricity to charge batteries - batteries to power airplane. Feasible (maybe) in 30 years if you solve the electrical storage density of batteries.

# 3 would be the real breaktrhough, but battery power density would need to improve by a factor of 2000-4000 for it to become feasible. Driven by cell phones and laptops, power densities of exotic batteries are improving at less than 10%/year. I only mentioned 30 years as that is enough time for 2 or 3 step jumps in matterials/performance to happen. But I remain skeptical that we can ever get there.
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