Comment by littlestymaar | Hacker News Reader

Comment by littlestymaar | Hacker News Reader

Parent Full thread

This is true but people tend to forget one thing: decommissioning doesn't necessarily means dismantling. Dismantling is a tough challenge (mainly because of the civil engineering part btw, which becomes difficult to manage when you add the constraints from nuclear: “What do you mean when you say we can't use dynamite? oO”) but it's only a legal obligation not an absolute one. With government support to change the law, EDF could just unload the fuel (price is well known, they do it all the time), and pickle the primary circuit in place (the price is also known, they did it a few times already) and now you have a place where all contamination (which comes from neutronic activation) is trapped inside the structure (Co60 in the rebar of the structure mostly) and the biggest risk is asbestos… (like your nearest decommissionined building in your neighborhood, even houses).

This option leaves you with a few ugly buildings in the middle of nowhere, but the cost unbeatable (even way less than decommissioning thousands of wind turbines).

> This option leaves you with a few ugly buildings in the middle of nowhere, but the cost unbeatable (even way less than decommissioning thousands of wind turbines).

Aren't you forgetting something? Buildings slowly deteriorate, even if not used. So now you have to maintain the disused reactor, for ... how long exactly?

(Amendment: wind, rain, sunlight, rodents, ... idiots with power tools ... https://en.wikipedia.org/wiki/Goi%C3%A2nia_accident )

> Buildings slowly deteriorate, even if not used. So now you have to maintain the disused reactor, for ... how long exactly?

And here comes radioactive decays to the rescue! Half-life of Co60 is a little bit more than 5 years, for instance. The important thing to consider is that dangerous radioactive materials are also the ones with the shortest half-life (because the same number of atoms emits more radiation per second), so as long as you took out the fuel[1] you don't have anything really dangerous for too long. It could still be a problem when decommissioning (because you spill everything out in a short time and you have workers just nearby) but if you let the building just decay slowly, you don't have issues.

[1]: the fuel is a bit special, because it has long half-life but it's still dangerous for two reasons. 1) it's alpha emitters, the worst kind of radioactive substance. 2) the concentration is enormous.

Co-60 isn't the only side product though. A quick Google search yields me https://mitnse.files.wordpress.com/2011/03/radiation_npp_07.... which lists:

Krypton-85 Beta/Gamma 10 years

Strontium-90 Beta 28 years

Iodine-131 Beta/Gamma 8 days

Cesium-137 Beta/Gamma 30 years

Carbon-14 Beta 5770 years

Zinc-65 Beta/Gamma 245 days

Cobalt-60 Beta/Gamma 5 years

Iron-59 Beta/Gamma 45 days

Tritium Beta 12 years

I'm also not sure where you got the idea that alpha emitters are the worst kind of radioactive substance; alpha radiation is easily shielded.

On the other hand, sure, just leaving the reactor there for 50 years may be part of a cost effective solution. https://www.dndkm.org/DOEKMDocuments/BestPractices/26-EFCOG%... (linked from https://en.wikipedia.org/wiki/Nuclear_decommissioning) claims a 71% reduction in decomissioning costs. However, this includes neither fuel waste disposal costs nor future costs for full dismantling at some point.

Alpha radiation is easily shielded from external exposure, but for that exact reason it's also the most damaging; gamma radiation, for instance, will mostly pass right through you, while alphas will deposit all of their energy right into your cells. They're shielded by your dead skin, but if you ingest or inhale them, then there's no dead skin to protect you, and all that radiation goes straight into your cells.

In fact, according to the weighting system that converts joules of energy absorbed (Grays) to severity of radiation dose (Seiverts), a joule of alpha radiation is 20 times worse than a joule of X-rays, beta radiation, or gamma rays.

And it's ingestion or inhalation that we're worried about from environmental contamination; not that the environment itself would become so radioactive, Fallout-style, that you'd take rads just from standing around - but that radioactive dust from demolition might get into the air, or that contaminants might leak into the groundwater.

Yeah, but - context. We're talking about leaving a disused reactor around in some type of safe manner. Ideally it won't be leaking... but some radioactive material is still in it. Aren't the beta & gamma radiators more dangerous, even as far as irradiating other parts of the structure itself is considered?

Neither beta nor gamma radiation will "activate" other parts of the structure to make them radioactive themselves; only neutron radiation (which can convert stable isotopes into unstable isotopes with more neutrons in them) can do that.

Nor will they weaken the structure.

So as long as people don't enter the reactor without proper precautions, there's really no reason to worry about radiation inside it. And this problem can be solved pretty well with a fence and warning signs.

> So as long as people don't enter the reactor without proper precautions, there's really no reason to worry about radiation inside it. And this problem can be solved pretty well with a fence and warning signs.

The buildings being designed as a bunker also helps. Just add a single guardian and his dog just to be sure nobody is actively trying to break through the concrete walls and you're good to go.

The parent talk about how the building material like rebars absorbs the isotopes, and then how long it can afterward be harmful.

Do those isotopes also get absorbed, and if so, at what rate? Since I don't know the physic I don't know if all isotopes can get absorbed at the same rate, but my intuition is that the answer is no. I would also guess that nuclear plants get exposed to different amount of each type of isotope, so the above table would need to include both in order to compare the radiation risk after X years.

Isn't cesium contamination the reason why the descendants of the Bikini Islanders still can't move back to their ancestral home? Same group as potassium so it gets sucked up into fruiting bodies (eg coconuts)

Cs137 is a real problem, it's radioactive enough and at the same time it has a long half-life for this kind of product. And as you say, it's metabolized so it can spread through the food chain…

Fortunately, it's a fission product so it's only released when you melt your reactor or when your reactor is in fact a bomb… (Mandatory reference to the Silly Asses short story from Isaac Asimov: https://en.wikipedia.org/wiki/Silly_Asses).

Then why is it listed in the grandparent as a product?

Because the GP took a list that mixes both fission products and activation product.

Fission products are directly created when splitting an uranium nucleus in half. They stay in the fuel rod unless it's damaged in a catastrophe. With a bomb you don't have rods, so everything is just released in the air.

You wouldn't leave the spent fuel in the reactor, that removes the first 5 elements. This leaves at most a 5 year halve life if you exclude water.

> I'm also not sure where you got the idea that alpha emitters are the worst kind of radioactive substance; alpha radiation is easily shielded.

Ahah! I considered making an appendix especially for this one because I expected some people to make this mistake, so here we are. Notice that if you're French, the mistake isn't yours but it's the official physics course for French high-schoolers which is to blame.

First of all, alpha rays are helium nucleus, they are really heavy compared to electrons (beta rays) and thus, much more energetic (energy of an order of magnitude of a few MeV vs hundreds of keV), and gamma rays in the case of radioactivity are even lower (40 keV in case of iodine for instance).

If you stand in front of a radioactive source, the radiations comes from in front of you, you can really easily shield against alpha rays (because they are big!), but you can't really shield against gamma rays (because they are just photons), then gamma rays are the most dangerous in that specific context.

But most people aren't physicists or nuclear workers, and you don't usually end up being irradiated by a radio source (the incident you talked about earlier is a good counter example though). The major risk faced by a population is not direct irradiation, it's contamination: that means, you eat food or drink water which contains some radioactive element. And now you get the radioactive source right in your body (let say the thyroid, if we're talking about radioactive iodine). Here, there is no possible shielding, so the total energy is what matters. And regarding the different kinds of rays and their ability to pass through matter, gamma rays have some chance to exit your body without ionizing a single cell, beta have less chance, and alpha have zero chance to go out.

So yes, in terms of radio protection of populations, you fear alpha rays way more than others. And if you operated a plant you are actually allowed to release a little (and subject to regulations of course) amount of beta-emitters (tritium is released in low quantities quite often for instance) but you aren't allowed to release any single atom of alpha emitters.

Also, the list you quote contains fission products (from krypton to C14) as well as activation products. Under normal conditions (I mean, no critical accident like TMI, Chernobyl or Fukushima), most fission products stays in the fuel rod, and then they won't remain in the decommissioned plant.

Zn65 and Fe59 decay quickly, Tritium will be slowly released in the water nearby (yes, that's the normal procedure and it's happening during all the plant's life) and then you have Co60.

That list is a bit misleading for anyone skimming; it has a bunch of numbers in years and in days. I was puzzling over why there is no natural Zinc-65 until I read it more carefully.

Because it's gone in 10 half lives.

The fission products are in the fuel not the primary circuit.

Half life is almost as confusing as statistics. A halflife of 5 years means 10% of the radioactivity is still there 16 years later. You'll still get 1% of the rems 33 years later, and that's if the materials don't migrate.

Alpha decays are still problematic for any material that can by aspirated or ingested. Demolition means flying dust. A leaky building means groundwater contamination. A lot of these substances are also heavy metals, so even without the alpha decay problem they are highly toxic.

Can you keep a building full of alpha sources water tight for five or six half lives?

There would be no alpha sources left in the plant, as they are confined in the fuel rods, that would be taken away from the plant. (And be managed like spent fuel, which is a totally different problem than decommissioning).

> A halflife of 5 years means 10% of the radioactivity is still there 16 years later.

But it's very likely that 10% is irrelevant.

Radioactivity is not a all or nothing thing. It exists all around you right now.

Camping out at a old abandoned nuclear power plant 20 years after it's decommissioned probably gives you less radiation exposure then you would get from a flight from California to Hong Kong.

Iz’s not about camping. It’s about water. France is timy compared to the US.

Ever heard about RO water? You can get a RO water filter for 150€ if you're concerned about contamination.

That won’t solve water table contamination. Are you going to RO plants? The soil?

It's not confusing at all, or maybe only to people with irrational fears. Just leave the building sit for 50 years and you've got 1/2^10 Co60 left.

Also dispose the vitrified spent fuel in a repository after reprocessing it.

> decommissioning doesn't necessarily means dismantling

That's kinda missing the point, the fact is that France's nuclear fleet is heavily underfunded by at least 50 billion Euro [0].

These are exactly the kind of costs regularly externalized or completely omitted when calculating the profitability of nuclear vs renewables [1].

[0] https://uk.reuters.com/article/uk-europe-nuclear/eu-short-of...

[1] https://energypost.eu/how-profitable-is-an-investment-in-nuc...

Example of one nuclear power plant being decommissioned (German TV documentary, Spring 2018):

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

Why isn't this just the default choice?

Good question. The dismantling narrative probably comes from a mix between wishful thinking from politicians and bad habits of lying all the time from the nuclear industry… I mean, the nuclear story is even brighter if we can promise we'll clean up after us right?

Reply on news.ycombinator.com