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Not sure if anyone would know this, but was discussing it with friends, and it seems like quite the puzzle. In short, how is nuclear fuel in reactors handled?

Logically, the nuclear fuel must be transported to the site, then placed into the reactor, then - once fully used - removed. But given the strength of the radioactivity of the elements, how on earth is this done?

Using the Chernobyl disaster as an example, the guys who had to clear up the mess weren't able to be close to the source for more than ca. 60 seconds without it being deadly. Even with lead protection, electrical circuits broke, so robots seem not to be an option. Just seems like a really difficult task to be able to transport, install, remove and dispose of the uranium without there being major hurdles.

Anyone know who it is done?!

Also, on a related topic: if a nuclear power station is decommissioned, how is the core dismantled? How can you safely remove the irradiated graphite, for example?

My friends and I spent ages debating how it could be done and we would love to know the answer!!

Thanks in advance.

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    $\begingroup$ Welcome to engineering.SE. I would suggest to keep this question about handling fuel rods and to ask the question about dismantling a decommissioned power plant as a seperate post, as this is a quite extensive topic. $\endgroup$ – OpticalResonator Mar 10 '20 at 13:07
  • $\begingroup$ It's a longish story. Begin at the beginning. The BORAX reactor $\endgroup$ – Phil Sweet Mar 10 '20 at 23:46
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The spent fuel rods stay first for around five years under water, in a Spent fuel pool (SPF), until radiation and heat reduced enough that they can be transported. For transport, they get placed in a special capsule. In case of the CASTOR (CAsk for Storage and Transport Of Radioactive material), made by German GNS, these capsules consist of a 40 cm thick cast iron wall, which again is filled with neutron moderator rods.

The trick to reduce the impact of the radiation during loading the rods into the capsules is pretty simple: do it all under water. Water happens to provide very good radiation shielding. The capsule gets moved with a crane into the water pool, the rods are placed in it, and then the closed capsule gets pulled out again. After drying, the capsules can be loaded on trains and get moved on.

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    $\begingroup$ Oh really? Water protects you from radiation? Well that's interesting. I have also just read that the radioctivity of uranium prior to it being used in nuclear facilities is next to nothing - it is apparently the by-products of its breakdown that are so heavily radioactive. $\endgroup$ – Hashamyim Mar 10 '20 at 19:07
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I work at a small research reactor---power reactors are significantly different, and I'm not qualified to say much about them. Since we don't operate constantly, our fuel burns up very slowly (the reactor's been there for ~50 years and the only change was when we swapped our original fuel for fuel from a decommissioned research reactor, for reasons unrelated to burnup. When we handle fuel we basically just make sure that it stays under a lot of water. Think "I wouldn't touch it with a ten-foot pole", except we do.

Chernobyl is a glaring exception to normal procedures. Part of the problem at Chernobyl was that all of the design features built into the fuel to make it safer to handle were useless, as they were all melted into a lump of corium. Not the normal state of affairs.

For decommissioning, the usual procedure is to just let everything sit underwater for a while to let stuff cool off a bit. After that waste is often enclosed in some sort of solid which shields against the radiation, and then left to sit some more. Looking at graphite specifically, there's recently been some fascinating research aimed at using the waste graphite as a power source in batteries!

-sol

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Freshly-prepared fuel rods (low-enriched uranium) are not lethally radioactive and do not require extraordinary handling precautions. However, once they have been put into service, extremely radioactive fission products begin to accumulate in them which renders them deadly by the time they are "burned up" and due for removal from the reactor core.

Water is nowhere near as effective at shielding as lead for example, but it is cheap and does an excellent job of carrying away heat released during decay. So you just use lots of it.

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