# Tag Info

24

I'm not sure what all you've read on them, but I'll try to clarify at least a few things. I would certainly disagree with several of your assertions. For starters, you say "...they don't produce anything you could feasibly use as a source of material for nuclear weapons." Thorium reactors use Thorium as a fertile fuel that transmutes into fissile U233. ...

22

I was going to comment on other people's answers, but this was going to become too long. Almost everyone fails to separate Thorium (which is a fuel type) and reactor type. Safety is a function of the reactor type, and molten salt in particular for this question. Does the fuel choice impact ultimate reactor safety? Yes, but to a limited extent. So how ...

20

which experiment gave scientists the reason to believe nuclear fission/fussion existed Fusion was first. Francis William Aston built a mass spectrometer in 1919 and measured the masses of various isotopes, realizing that the mass of helium-4 was less than 4 times that of hydrogen-1. From this information, Arthur Eddington proposed hydrogen fusion ...

19

It's all a question of if they need it. Most that are staying within a couple AU of the sun can get sufficient power from solar panels. It's when they start getting further away that they use an RTG. For example, New Horizons, which launched in 2006 (which is considered to be 'modern' when you only launch a few probes per year) is going to Pluto, so it ...

17

Per this article on the subject: http://theenergycollective.com/nathantemple/53384/how-shutdown-and-core-cooling-japanese-reactors-likely-functions Even with rods inserted, the reactor continues to produce heat equivalent to about 3% of its full power level. This is not the same as taking a pot off the stove and letting it cool. There are still ...

15

edit: I originally had some points about the inefficiency of RTGs, but after some more research prompted by @Jeremy I found that it's not really a valid point when they're used appropriately for the spacecraft's mission. The RTGs used by Galileo at Jupiter generated 300W of power, whereas the solar panels that will be used by Juno at Jupiter will generate ...

15

If you throw a bunch a uranium ore in one blob, nothing happens. If you chemically purify the ore so that the only element present is uranium, still nothing happens. The runaway chain reaction needed for a uranium-powered bomb involves U-235, an isotope having three fewer neutrons than the most common natural isotope U-238. According to Wikipedia, The ...

14

If you read Wikipedia page about corium, they say that critical mass can be achieved locally. But if you are concerned about a critical mass allowing a nuclear explosion, the difficulty in nuclear weapon design, as told here, is to achieve the criticality fast enough. If you do not achieve criticality fast enough, your material heats and its interaction ...

12

Why could they not have a 30 meter pit below a reactor filled with water with a trap door holding the reactor up? If you read about the Molten-Salt Reactor, you will find that it has something rather similar to this. In the image below, item number 13 is a freeze valve. If the reactor overheats, the plug melts and the molten core flows down to the ...

11

The real problem with RTGs is that the US stopped making Pu238 in the 80s and has been very slow to start up production again, purchasing all our spacecraft Pu238 from the Russians (who have now also run out). I don't know about the byproducts from the breeder reactors, but Pu238 itself is actually not that dangerous to handle, and only toxic if ingested.

10

One aspect is the concern for if the spacecraft were to fail to launch correctly and ended up crashing back to earth. In such cases, the nuclear radiation pollution could be severe if it ended up crashing in inhabited areas.

10

There are many reasons for this situation. Power produced is non-adjustable. The battery produces power at nearly constant rate (slowly decaying with time). It cannot be increased and if not consumed (or stored) the power is lost. (Mentioned by DumpsterDoofus) low power density. ${}^{63}\text{Ni}$ for instance produces ~5 W/kg (and kg here is just mass of ...

9

Starting in the fifties, there was a lot of work (see RDD-8, V.C.1.g) trying to build a pure fusion weapon for mainly two reasons: they promised to be cleaner than conventional thermonuclear devices (important for peaceful uses and some of the not-so-peaceful ones) and they wouldn't need relatively scarce fissionable materials. As you can use staging to ...

9

As far as a catastrophic plasma disruption is concerned, it might be a problem for the first wall, and hence the ability to use the reactor. But despite the high energy per nucleon, the desity of the plasma is extremely low, the total energy is dominated by the energy in the magnetic fields, and thats not tremendous. Of course you do have the radioactivity ...

9

This is a cost to benefit question and can only be answered by a guess in a physics board. There is a new generation of small compact reactors that could be used for powering apartment buildings The new reactor, which is only 20 feet by 6 feet, Seems compact enough, so it is not size but weight that is important, since this weight has to be lifted. ...

8

This was (one of the few) facts reported clearly and correct in German news. The Zirconium metal of the fuel tubes reacts with water vapor at elevated temperatures (above 1200 °C if I remember correctly) The reaction is simply: Zr + 2 H2O => ZrO2 + 2 H2 This is proof, that parts (at least) of the fuel rods were not immersed in water, but it does not ...

8

This would guarantee a meltdown. They're trying to get heat out of the core because---thought the fission chain reaction has been suppressed---various unstable fission daughters continue to decay. Adding hot lead would add heat to the system and not stop this behavior. Total disaster. -- If the core does slag out, it will probably end in a hot ...

8

This question is a near duplicate of Does the "Energy Catalyzer" generate energy by converting Nickel to Copper? , but perhaps it is ok, because some time has passed, and there is more confidence in the assessment. It is not reasonable to reject Rossi out of hand, because there are observed unexplained nuclear reactions in Palladium/Deuterium ...

8

Is that correct that there are no nuclear warheads in service made of U-235, as plutonium ones are much smaller & much more efficient Maybe. Who knows precisely what people use. But publicly available information from US warheads is that they moved away from Uranium to Plutonium fission devices soon after world war II. Is that correct, that ...

7

The German THTR-300 Thorium High-Temperature Reactor operated for about 16,000 hours and the IAEA produced a report on its shutdown. So there are no physics barriers to thorium reactors: there is an existence proof for thorium reactors. That ends the relevant answer for this site. There are economic, engineering, social, political, technical, and ...

7

Nuclear power is the only way to make submarines work underneath the water for long distances without coming up because of the oxygen that all other types require. And batteries for electric engines are too heavy. Historically a submarine had to go up to just below sea level to get air through the snorkel for the engines that charge the batteries. Then ...

7

I don't know about extracting mass-energy from inside the black hole, it seeps pretty inefficient to me. Hawking radiation isn't that powerful (as well as still being highly hypothetical), building a Dyson sphere around a star is better. Remember, black holes, are, well, black. If there was enough hawking radiation, they would cease to be black and would ...

7

A lot can be, and has been, written on the subject, but I'll give you the short and sweet version. Does nuclear chain reaction start in fuel pellets even before they being installed in reactor? -- No There are several reasons why this is so. The number of spontaneous fissions of $^{235}$U is minimal. The branching ratio for that mode of decay is \$7 ...

6

The funny thing is that in the case described in the paper, pretty safe isotope (I-129) was converted into deadly dangerous I-128, I would prefer to leave it as is :-) Transmutating random mix of isotopes would give you more random mix of isotopes (garbage in->garbage out), and it's a big question if this would lead to lower integral activity. So to ...

6

Well, if you search the internet it seems there are kids out there that make the claim of having built a fusion reactor . I watched this link. Note that in .56 minute he gives a small description, and does not claim breaking even, but that he demonstrated fusion. It is a plasma that he obviously creates and manages to fusion some deuterium that is not ...

6

We already store waste by combining it with molten glass. It doesn't take very much energy - obviously no more than making glass! The main reason for not doing it is political, it cost a lot to make that plutonium and it might come in handy to build bombs one day - so we don't want to waste it by reprocessing it. (We also have a small problem of persuading ...

5

I don't have much more than a interested amateur's understanding of the construction and operation of nuclear reactors, but... If nothing else you add the task of insuring that this large, complicated system fails safely. And does so while managing the huge weight involved, despite the fact that the core is hooked to a complicated system of pipes carrying ...

5

By the time the core melts it is probably way beyond passive cooling. If you read up on the Chernobyl event they went to great lengths to prevent the core from melting its way into a water reservoir beneath the reactor (the bubbler pool) for fear it would result in a steam explosion. Three Russians in diving suits performed a suicide mission: entered the ...

5

Three countries signed a treaty banning all nuclear tests but underground ones in 1963 (https://en.wikipedia.org/wiki/Partial_Nuclear_Test_Ban_Treaty ), partly for ecological reasons. EDIT (08/3/2013): The official reasons are given in the preamble of the treaty (http://www.state.gov/t/isn/4797.htm ): "The Governments of the United States of America, the ...

5

All three isotopes of Hydrogen can undergo fusion under the right conditions. The main reason to use D or T is that they fuse more easily than H. For example, H-H fusion is primarily what drives our sun, but in the lab D-D or D-T reactions are much easier to initiate. The D-T reaction gives off 17.6 MeV of energy, D-D actually has 3 different reactions it ...

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