How counting neutrons explains nuclear waste | Hacker News Reader

How counting neutrons explains nuclear waste

rootsofprogress.org

73 pointsjasoncrawford28 comments

Where did the data for this table come from? Checking Pb-208 (a memorable double-magic nucleus), it should really not be shown as undergoing alpha decay when none of the major ENDF tables show that. There is an unsourced remark on Wikipedia that this might happen, but given the half-life, I do not think scientists have ever measured a single such decay... so probably not best to include it. And if one spot check shows a mistake, how many more are there? It's a big table and ENDF data files are not pretty things....

You can see the table here: https://people.physics.anu.edu.au/~ecs103/chart/?ShowStable=...

When I click on the lead-208 box, it credits data from:

NUBASE2020: https://doi.org/10.1088/1674-1137/abddae AME2020: https://doi.org/10.1088/1674-1137/abddb0

It also only says that alpha decay is “possible”, not that it happens with any frequency—in fact, it lists Pb-208 as stable.

The photo of the lifetime waste burden is good. But of course obfuscates the waste trail before the fuel arrived at the reactor. I don't want to come off as nit-picky: its an amazing lesson how how LOW the post-energy waste burden is, done right and I wish we could learn to agree about this as a huge upside of Nuclear, compared to the mountains of fly ash, and related waste from coal, and the CO/CO2 burden.

But, we do need to pay heed to the waste cycle going in. Its not zero by a long chalk. It includes heinously bad stuff at all stages from yellowcake up. If the cycle still has Uranium Hexaflouride in it, this is why we have PTFE.

> There are advanced reactor designs that don’t rely on the fission of U-235, but rather use the far more abundant isotope U-238. Some of these reactors can burn “spent” fuel, or “depleted” uranium left over from the enrichment process—extracting something like 60 times as much energy from uranium as traditional nuclear reactors.

Does anyone have links for such reactors?

> Does anyone have links for such reactors?

https://en.wikipedia.org/wiki/Breeder_reactor you also need https://en.wikipedia.org/wiki/Nuclear_reprocessing to remove https://en.wikipedia.org/wiki/Neutron_poison which would stop the reaction.

If we did that, there would be no nuclear waste left. (Or more specifically all the waste would decay very fast, and not be a long term problem.)

> if we did that

Some "we" and/or some "they". Russia seems to be intent and making advances toward closing the fuel cycle, in efforts IMHO severely underreported on HN. (It might be better that way. I have seen reticence to stir up jealousy or something in the Anglosphere. Let them [ignorantly] go about their business.)

I believe breeder reactors can create fuel from U-238.

https://en.wikipedia.org/wiki/Breeder_reactor

The most famous of these is the Chernobyl reactor design, the RBMK. It could be run on natural uranium rather than enriched uranium and would self enrich the uranium via neutron bombardment inside the reactor.

https://en.wikipedia.org/wiki/RBMK

Of course there are some flaws in a reactor that breeds it's own enriched uranium. There's states that the neutron flux is too low so the enriched elements aren't burnt off quickly as intended. This leads to a state where the whole reactor is a highly enriched weapons grade bomb.

A reactor that runs on natural uranium is still fissioning 235U (and some of the 239Pu that has been bred, but that's true of reactors that run on low enriched U as well.)

That‘s wrong. The RBMK is not a fast reactor, it’s a pressure-channel boiling water reactor.

Fast reactors are/were for example the:

- French Superphenix - Russian BN-600/800 - German SNR-300 - Japanese Monji - American EBR II

The BN reactors are still operational.

Breeder reactors, as others have pointed out. Oklo is a modern design based on the concept: https://www.nrc.gov/reactors/new-reactors/col/aurora-oklo.ht...

Also see “Problem free nuclear power and global change”: https://www.osti.gov/biblio/614877

And “Nuclear fission power for 21st century needs”: https://www.sciencedirect.com/science/article/abs/pii/S01491...

Heavy water reactors can run on natural uranium. https://en.m.wikipedia.org/wiki/Pressurized_heavy-water_reac...

And these are still fissioning 235U. 238U by itself does not sustain a chain reaction.

Aren't heavy water reactors the most popular way that new countries have built nuclear weapons? Basically everyone but North Korea?

You don't need a reactor to make a uranium based nuclear weapon at all (you just need to enrich natural uranium to a high enough percentage of U-235).

American and Soviet plutonium production reactors were largely (perhaps even entirely? not sure) graphite moderated.

Yeah, but that graphite has to have zero boron in it, which is not easy to accomplish. You have to go to fairly crazy extremes, like regulating what kind of laundry detergent your factory workers are allowed to use.

https://en.m.wikipedia.org/wiki/Nuclear_graphite

Heavy water is simpler to get; you basically just need a lot of electricity.

https://en.wikipedia.org/wiki/CANDU_reactor

This design has a lot of practical advantages, but seems to be suffering in the market from the same capital cost disease as other reactors.

This is a bit nit-picky, but a CANDU reactor does not fission U-238. Neutrons in a CANDU reactor are still thermal neutrons, and if you put pure U-238 in a CANDU reactor it won't run. A CANDU reactor does run on uranium with a lower amount of U-235 than a standard PWR design, and it does transmute some of that U-238 into Pu-239 which it then does fission, but it doesn't directly fission U-238 and it does require some baseline ratio of U-235 to operate.

Thought exercise:

What would the consequences be of detonating an improvised truck bomb, comparable in size to the Oklahoma City Bombing [0], in the middle of the spent fuel casks at the Connecticut Yankee plant?

[0] https://en.wikipedia.org/wiki/Oklahoma_City_bombing

It depends on what you mean by middle. If you mean just placed in the middle of the configuration, probably not much. A few feet of concrete reinforced steel can resist a lot. Certainly some leaks but probably not too bad outside of the immediate vicinity.

If you put the bomb in the middle of one of the casks, it would probably impact 100,000s of people. It'd probably be pretty hard to get it there though and if you could do that, you could probably extract the radioactive material and transport it somewhere else.

A truck bomb would do barely anything to those except perhaps crack the ones immediately next to the epicenter. Local cleanup would be required, but nuclear waste containers have been generally over-engineered with things like that in mind.

The famous video of a train versus one of the transportation casks:

https://www.youtube.com/watch?v=ZY446h4pZdc

The consequences would be a very confused bomber trying really hard to find the underground parking area beneath those casks.

> The consequences would be a very confused bomber trying really hard to find the underground parking area beneath those casks.

In the Oklahoma City bombing McVeigh simply parked the van on the sidewalk in front of the building.

> He parked the Ryder truck in a drop-off zone situated under the building's day-care center

https://en.wikipedia.org/wiki/Oklahoma_city_bombing

"Under" as in the day-care being on the second floor, the truck being parked in front of the building.

He parked the truck bomb in the street in front of the building. The daycare was on the second floor.

It's weird that was so long ago now.

> 0901: McVeigh parks the truck on the sidewalk in front of the building and walks off

From the illustration on the same page, also clearly showing the location in front of the building...

https://upload.wikimedia.org/wikipedia/commons/2/26/Timothy_...

Are you thinking of the 1993 WTC bombing instead?

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