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Thread: NASA to go nuclear

  1. #61
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    Quote Originally Posted by danscope View Post
    It's only the end of the world for a few people who die slowly. No problem, hey? There is the possibility that you don't know all there is about nuclear
    power.
    Question: Have you ever seen a second stage booster fail ?
    Yes, on two satellite projects on which I've worked. One went into the Pacific and the other was scattered over the Virginia coast.

    Now, a question for you: have you ever seen a safety analysis report for a nuclear launch? We have a copy of the Cassini FSAR in our office. It fills twelve big filing boxes.

    Nuclear power, in the form of isotope decay and reactor systems, is absolutely essential for the continued exploration of space. An enormous amount of work goes into the engineering for safe launches of such systems, which includes designing power sources which are not only very tough but also designed to minimize contamination even if they are breached. I don't think you appreciate that fact.

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    Quote Originally Posted by swampyankee View Post
    Nuclear power is certainly not the only power-production technology which will cause slow death: coal-fired powerplants produce quite toxic combustion byproducts and most coals contain detectable, and non-trivial, quantities of mercury (cumulative poison) and radium (radioactive). Right now, trying to reduce mercury emissions is causing quite a bit of hysteria in the fraction of US utility industry that uses coal-fired power plants.
    Coal fired power plants release about fifty tons of U-235 alone into the environment every year (stack emissions and spoil piles). This report is a real eye-opener. The yearly byproducts of coal generation, spewed into the air and dumped on the ground, contain enough U-235 to build something like eight or nine hundred of "Little Boy"-type weapons. And that doesn't even consider the much greater quantities of U-238 and thorium-232.

  3. #63
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    Such a waste of perfectly good fissionable material.

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    Hi, STS 60 , I acknowledged the reasonable use of small rtg's like cassini. The question concerns much more massive reactors ie many magnitudes larger.

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    Quote Originally Posted by danscope View Post
    Hi, STS 60 , I acknowledged the reasonable use of small rtg's like cassini. The question concerns much more massive reactors ie many magnitudes larger.

    Actually you're arguement of "what happens if the second stage explodes on launch" is EXACTLY the same arguement the Cassini protesters used, see the bolded part of one of my earlier posts. And frankly we've seen what happens when nuclear material re-enters, its not fun but no one was killed. Fear and respect are not that same.

    @STS60: Out of my own personal curiousity, the RORSAT that crashed in Canada dispersed material over 48,000 square miles. If a larger reactor with 440 kg's of uranium loaded (which appearently is what nuclear submarines have) were to re-enter, how would the greater mass effect the dispersal? Would the area be more, less, or the same?

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    Maybe I get a bit blasť about man-made radiation: I live in a part of the country where natural radiation is a significant health risk for many people, on par with smoking one or two packs of cigarettes a day. I'm not going to worry about the possibility of a few nanograms of radioactive decay products from an RTG.

    As for the reactors planned for spaceflight: since most are going to have, at most, a few kilograms of fissile material, not a few hundred. There have been many NASA studies; a very poorly filtered list should be at the other end of this link: http://ntrs.nasa.gov/search.jsp?Ntx=...0space|fission

    I do not think any of this pose significantly more risk than RTGs, and I don't think RTGs pose a significant risk. I worry much more, every day, about the psycho drivers that proliferate on I-95.
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    Yes, the cell phone zombies are very real and very dangerous. We agree.

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    Quote Originally Posted by swampyankee View Post
    Maybe I get a bit blasť about man-made radiation: I live in a part of the country where natural radiation is a significant health risk for many people, on par with smoking one or two packs of cigarettes a day. I'm not going to worry about the possibility of a few nanograms of radioactive decay products from an RTG.

    As for the reactors planned for spaceflight: since most are going to have, at most, a few kilograms of fissile material, not a few hundred. There have been many NASA studies; a very poorly filtered list should be at the other end of this link: http://ntrs.nasa.gov/search.jsp?Ntx=...0space|fission

    I do not think any of this pose significantly more risk than RTGs, and I don't think RTGs pose a significant risk. I worry much more, every day, about the psycho drivers that proliferate on I-95.
    I don't know exactly how much will be required for a propulsion system, so I used what a modern nuclear submarine uses as a reference. For comparison the RORSATs had 50 kg of U235.

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    Hi Aquitaine,

    A nuclear submarine flashes water into steam, drives turbines AND employes the cold seawater to condense that spent steam back into water for re-injection into the steam loop. From the turbine, we have options to mechanically or electrically turn what you would call a propeller to propell the submarine. This has nothing to do with the "schemes" involved with propulsion in space. Not even close.

    Best regards,
    Dan

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    Nuclear Thermal Rocket is much simpler than submarine propulsion. You simply pump liquid hydrogen into the reactor core and superheated hydrogen going out of the core goes into the nozzle. No external components are required, except for turbopump. Which is powered by the hydrogen flow anyway. http://en.wikipedia.org/wiki/Nuclear_thermal_rocket

    The NERVA reactor was a cylinder about 1m in diameter and 1m in height, and it weighted 5476 kg. At the moment, I'm unable to locate the information how much of that was fuel, but I will look into Dewar's book on NERVA after I get home. Maybe it's in there.

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    Everything we do is about risks versus rewards. Using nuclear reactors for space applications such as propulsion, power generation, or both, has some risks. We have to ask ourselves whether that risk is worth the reward. Even driving your car every day has risk, and yet we still make the decision to take that risk, based on the reward of getting to your destination quickly and in relative comfort. Using coal and oil is harmful to the environment and yet we accept those risks due to the rewards that we get.

    Nuclear reactors provide us with the most energy in a small package. If Man is ever going to actually explore space beyond Mars, nuclear reactors will have to be used. Any kind of manned interplanetary spacecraft is going to need a reliable and powerful energy source for long term missions. The only thing we presently have that can do that, is nuclear power.

    As for the risks, in my opinion, they are worth taking. We already take many risks that have long term harmful effects on our planet. Launching nuclear reactors for space operations is not going to harm our planet any more than we already do everyday. Even if we have an accident and the reactor is destroyed during launch, we can clean up the mess and go forward. In fact, I may sound a bit crazy to some, but I believe that it is worth experimenting with nukes on asteroids. I would rather gather some real data on the effects of nuclear devices on space rocks before it becomes a life and death situation with limited time left.

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    Quote Originally Posted by Trantor View Post
    ... As for the risks, in my opinion, they are worth taking. We already take many risks that have long term harmful effects on our planet. Launching nuclear reactors for space operations is not going to harm our planet any more than we already do everyday. Even if we have an accident and the reactor is destroyed during launch, we can clean up the mess and go forward. In fact, I may sound a bit crazy to some, but I believe that it is worth experimenting with nukes on asteroids. I would rather gather some real data on the effects of nuclear devices on space rocks before it becomes a life and death situation with limited time left.
    I agree with your assessment of the risk for space-based reactors, but I acknowledge that other people will not weigh the benefits as strongly as we do.
    Forming opinions as we speak

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    Quote Originally Posted by kamaz View Post
    Nuclear Thermal Rocket is much simpler than submarine propulsion. You simply pump liquid hydrogen into the reactor core and superheated hydrogen going out of the core goes into the nozzle. No external components are required, except for turbopump. Which is powered by the hydrogen flow anyway. http://en.wikipedia.org/wiki/Nuclear_thermal_rocket

    The NERVA reactor was a cylinder about 1m in diameter and 1m in height, and it weighted 5476 kg. At the moment, I'm unable to locate the information how much of that was fuel, but I will look into Dewar's book on NERVA after I get home. Maybe it's in there.
    There's no way environmentalists would approve of nuclear-thermal rocket being used anywhere near Earth. Probably nowhere within the orbit of Saturn. The exhaust is basically Chernobyl directed through a nozzle, and unless we managed to solve the problem of core erosion*, it would cause massive fallout anywhere it was used. This makes it difficult finding a place to test.

    Using nuclear reactors to power spacecraft is a great idea. For now, however, we probably shouldn't go overboard.

    *One proposed solution is a gas-core "nuclear lightbulb", where the core is surrounded by a fused-quartz shell, but gas-core reactors seem to be pretty difficult to engineer.

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    Quote Originally Posted by Siguy View Post
    There's no way environmentalists would approve of nuclear-thermal rocket being used anywhere near Earth. Probably nowhere within the orbit of Saturn. The exhaust is basically Chernobyl directed through a nozzle, and unless we managed to solve the problem of core erosion*, it would cause massive fallout anywhere it was used. This makes it difficult finding a place to test.
    This is a massive exaggeration, with essentially no resemblance to reality. The core erosion issues were largely solved by the end of the NERVA program, even the Kiwi test that intentionally vaporized a large part of the reactor (following modifications to the control mechanisms to make this possible in the first place) was nothing like Chernobyl, and even if NTRs were continuous ongoing Chernobyls, the amount of contamination reaching Earth from normal operations in the inner system or even cislunar space would likely be immeasurably small.

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    Your reassurances fall on deaf ears in Japan these days. We can read.

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    Quote Originally Posted by cjameshuff View Post
    This is a massive exaggeration, with essentially no resemblance to reality. The core erosion issues were largely solved by the end of the NERVA program, even the Kiwi test that intentionally vaporized a large part of the reactor (following modifications to the control mechanisms to make this possible in the first place) was nothing like Chernobyl, and even if NTRs were continuous ongoing Chernobyls, the amount of contamination reaching Earth from normal operations in the inner system or even cislunar space would likely be immeasurably small.
    In that case, I might have been confusing NERVA with designs for an open-cycle gas-core NTR, which would have the core itself mixing with the propellant. I would imagine that would create quite a bit of fallout.

    As far as contamination in earth-orbit, though, wouldn't it still be hazardous due to creating temporary radiation belts, like the Starfish Prime nuclear test apparently did?

    I'm not all-out opposed to nuclear-thermal rockets, I just think there needs to be a lot more R&D done before they become practical. I'm more of a nuclear-electric kind of guy.

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    Quote Originally Posted by Siguy View Post
    As far as contamination in earth-orbit, though, wouldn't it still be hazardous due to creating temporary radiation belts, like the Starfish Prime nuclear test apparently did?
    Starfish Prime was a 1.4 MT thermonuclear weapon that completely vaporized itself and ionized a bunch of upper atmosphere after fissioning as much plutonium and uranium as practical, using fusion as a source of neutrons to drive things further than a fission chain reaction alone could go. The only remotely comparable nuclear propulsion system would be an Orion operated in low Earth orbit.

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    Quote Originally Posted by danscope View Post
    Your reassurances fall on deaf ears in Japan these days. We can read.
    Really? Again you seem to be scaremongering about the risks of nuclear power without any evidence, it's this sort of attitude that's contributed to retarding nuclear propulsion.

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    Quote Originally Posted by Garrison View Post
    Really? Again you seem to be scaremongering about the risks of nuclear power without any evidence, it's this sort of attitude that's contributed to retarding nuclear propulsion.
    You can have pro- or anti- nuke feelings about lots of different applications of the technology, but please try to avoid turning this into a political discussion. In this case the accusation of 'scaremongering' seems pretty derogatory, and doesn't address the issue at hand, which has to do with NASA planning to develop in-space fission power plants.
    Forming opinions as we speak

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    Quote Originally Posted by danscope View Post
    Hi Aquitaine,

    A nuclear submarine flashes water into steam, drives turbines AND employes the cold seawater to condense that spent steam back into water for re-injection into the steam loop. From the turbine, we have options to mechanically or electrically turn what you would call a propeller to propell the submarine. This has nothing to do with the "schemes" involved with propulsion in space. Not even close.

    Best regards,
    Dan

    This misses the point I made. The amount of uranium a reactor system is loaded with depends on power output required and the amount time desired between refueling. I'm not an expert in such things, and so I used systems currently in use as a reference.


    Your reassurances fall on deaf ears in Japan these days. We can read.

    Actually the Japanese were rather unhappy with the foreign media's obsession with Fukashima in the light of the catastrophic loss of life and property from the earthquake and tsunami.

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    Quote Originally Posted by danscope View Post
    Your reassurances fall on deaf ears in Japan these days. We can read.
    Just to add to what antoniseb said, all participants should avoid derogatory comments, particularly towards other members. I'm not sure what is meant by "We can read"; I certainly hope it doesn't imply that some participants in this thread can't.
    At night the stars put on a show for free (Carole King)

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    Yes, those invested in that reactor,perhaps. I shall maintain that there is not a monolithic opinion on the safe application of nuclear energy. Television fantasy is one thing. Visions of super warp drive are grossly exaggerated
    suggestions for interplanetary travel which have the gravest doubts of fruition and carry very certain severe risks that
    aren't especially advertised and casually glossed over.
    In my humble opinion, chemical rockets will do the heavy lifting. Electricity for communications and auxiliary power on board may find NTR's as the only viable solution to a difficult engineering problem.

    Best regards,
    Dan

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    The NERVA/Rover folks had a lot of courage They did a test (appropriately named KIWI-TNT) where a reactor was first put into a supercritical mode, raising core temperature to 4000 deg. C and blew up. The test report, in all its detailed glory, can be found here: http://www.fas.org/sgp/othergov/doe/...s1/la-3449.pdf

    From the design of the test, it looks like they were trying to simulate a loss of propellant (coolant) during vehicle ascent.

    I'll just quote the conclusions:

    Out to approximately 300 ft, which is beyond the range of probable blast injury, radiation exposures would probably be fatal, being in excess of 750 rads. Between approximately 300 and 750 ft, varying degrees of radiation injury, including some fatalities, would occur as exposures would be between 100 and 750 rads. From 750 to approximately 2,000 ft downwind, little, if any, injury or clinical effects would occur, but exposures would exceed 3 rads and would require administrative investigation and reporting. Beyond approximately 1.5 mile, doses even in the path of the cloud would be below a few hundred millirad, and should present no problems.

    The seriousness of radioactive contamination is difficult to assess, since it depends so heavily on the value and potential uses of the contaminated real estate. However, 1 day after the Kivvi-TNT event, contamination exceeding 100 mR/hr was within 1.200 ft downwind and 300 ft upwind of the etst point; the 1 R/hr line at this time was 300 ft downwind and less than 100 ft upwind. By 1 week after the event the 100 mR/hr area was 300 ft downwind and less than 100 ft upwind of the test point. Within a few hours of the test, contamination above 1 mR/hr was difficult to find beyond 2 miles, although a few “hot spots” of several mR/hr were discovered out to 10 miles on the day of the test. These rapidly decayed away to insignificance. Beyond 12 miles, no contamination above 1 mR/hr was found.
    In the briefest summary, a Kiwi-TNT type of excursion, without a fission-product inventory in the reactor, creates inconsequential hazards to personneI and property beyond about 2 miles, a distance that can be reasonably expected to lie outside test areas.
    Last edited by kamaz; 2012-Mar-01 at 11:26 PM. Reason: make my summary reflect the test report

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    Los Alamos report on nuclear engines, October 1972: http://www.fas.org/sgp/othergov/doe/...1/00397413.pdf

    The reactor fuel is contained in hexagonal elements, as shown in Fig. 2, measuring roughly 1.9 cm (0.75in.) across flats; these elements are made up of a composite mixture of graphite and a solid solution of UC+W2, and contain 19 flow passages each. Hydrogen is heated by passing through these holes, which are coated with a layer of ZrC to inhibit hydrogen corrosion. The reference design contains 564 of these elements in a core that has a diamter of 0.655 m (25.8 in.) and is 0.89m (35 in.) long. The total core uranium loading is 60 kg (92.5% enriched uranium). Heating the 8.5 kg/s (18.75lb/sec) of hydrogen flow to produce the nozzle-plenum condition at maximum specific impulse requires a total thermal power of ~367 MW and results in 72 975N (16 406 lb) of thrust.
    If the NTR stage fails to start, or aborts early in flight, then there is little danger, because fresh fuel is not really radioactive. It would be more of a non-proliferation concern, then a radioactivity concern.

    However, if the stage were to reenter after the burn, with its inventory of fissile products, then it can get nasty. How many Chernobyls is 60kg of spent nuclear fuel?

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    Quote Originally Posted by aquitaine View Post
    Actually the Japanese were rather unhappy with the foreign media's obsession with Fukushima in the light of the catastrophic loss of life and property from the earthquake and tsunami.
    I wonder if you can really say "the Japanese" in that case. I suspect that people who live in Tohoku are actually aggravated that the mainstream Japanese media (and people like me, living in Tokyo for example) tend to be obsessed with the nuclear problem rather than the damage from the tsunami. So probably "some Japanese" would be a better description there.
    As above, so below

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    Quote Originally Posted by antoniseb View Post
    I agree with your assessment of the risk for space-based reactors, but I acknowledge that other people will not weigh the benefits as strongly as we do.
    My feelings as well. I don't have a particular problem with using nuclear fuel for spacecraft, but it's partly because I'm (like most people here) on the very pro side of space exploration. If I weren't, I don't think I'd be very enthusiastic about it.
    As above, so below

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    Quote Originally Posted by kamaz View Post
    Los Alamos report on nuclear engines, October 1972: http://www.fas.org/sgp/othergov/doe/...1/00397413.pdf



    If the NTR stage fails to start, or aborts early in flight, then there is little danger, because fresh fuel is not really radioactive. It would be more of a non-proliferation concern, then a radioactivity concern.

    However, if the stage were to reenter after the burn, with its inventory of fissile products, then it can get nasty. How many Chernobyls is 60kg of spent nuclear fuel?
    // removed wrong information. (wikipedia the untrustable)

    In the scenario you describe there will be no wide dispersal. so it will be nasty to clean up, but mostly localized into a small area. these engines have to be built extreemely tough just to operate in the first place. an uncontrolled re-entry wont vaporize significant amounts of radioactive materials. If any at all.

    I'm not in the nuclear launcher crowd however. I feel that chemical is the more suited technology since what you actually want during a launch is exteeme amounts of energy in a very short timeframe. and nuclear works best with medium to high power levels for long time periods.
    Last edited by Antice; 2012-Mar-02 at 12:36 AM.

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    Quote Originally Posted by kamaz View Post
    However, if the stage were to reenter after the burn, with its inventory of fissile products, then it can get nasty. How many Chernobyls is 60kg of spent nuclear fuel?
    Chernobyl blew about 6 t of fuel into the atmosphere. The I-131 release alone was estimated at 400 kg. It was a rather large reactor, running off natural (unenriched) uranium and containing about 190 metric tons of fuel, the reactor as a whole massing 240 t. I'm not sure how long reactor #4 had been operating with that fuel load, but the plant itself had been in operation for about two years, and it had been running at full capacity not long before the explosion.

    Which doesn't mean used reactors falling from the sky aren't something you want to avoid. However, it's not something that is particularly difficult to avoid...don't use low Earth orbit as a disposal orbit.

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    Quote Originally Posted by Antice View Post
    RBMK-1000 reactors have almost 117kg of uranium in them.
    In each fuel assembly (the number I found was 114.7 kg, 117 kg might be total mass or a different version of the assembly). There were up to 1661 fuel assemblies, and it was estimated that 3% of the total fuel was released.

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    Quote Originally Posted by cjameshuff View Post
    In each fuel assembly (the number I found was 114.7 kg, 117 kg might be total mass or a different version of the assembly). There were up to 1661 fuel assemblies, and it was estimated that 3% of the total fuel was released.
    Yeah. my "source"forgot to mention that. I thought it was a bit low so i went digging elsewhere.

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