[perihelions]

It is not true that coal is more radioactive than spent nuclear fuel. It's very much the opposite: SNF is 10^11 times more radioactive than coal per kilogram, or 10^6 times more radioactive per energy unit.

Per the EPA, US coal has, at the high end, 10^3 Becquerel/kg of natural radioactivity [0].

Spent nuclear fuel has 3 million Curies/tonne (33 MWd/kg burnup fuel, at the age of 1 year) [1], which is equal to 10^14 Bq/kg. Since 33 MWd/kg is an energy density a factor of 10^5 greater than that of coal, the normalized ratio of [radioactivity]/[energy] is 10^6.

The graph in [1] depicts the decay of SNF activity on a log-log scale. It reaches the same radioactivity level as coal (again, normalized by energy output) at about 1 million years.

I'm fairly confident I know the origin of this social media-popular pseudofact. It's this poorly-titled Scientific American [2] article from 2007, which is about the (negligible) amount of radioactivity that nuclear plants release into the environment in the course of routine operation. It is *not* about spent fuel. It's a fair—but nuanced and easy to grossly misunderstand—point that coal power plants throw up all their pollution into the environment in routine operation, while nuclear plants, by default, contain theirs.

[0] https://www.epa.gov/radiation/tenorm-coal-combustion-residua... ("TENORM: Coal Combustion Residuals")

[1] https://www.researchgate.net/figure/n-situ-radioactivity-for... ("Impact of High Burnup on PWR Spent Fuel Characteristics" (2005))

[2] https://www.scientificamerican.com/article/coal-ash-is-more-... ("Coal Ash Is More Radioactive Than Nuclear Waste [sic]" (2007)

[aftbit]

Sure, the spent fuel is considerably more radioactive per kilogram, but how many kilograms of coal does a typical plant burn in a decade, versus how many kilograms of nuclear fuel are spent?

[perihelions]

I answered that exact question! :)

[aftbit]

My mistake - I reread your post, and I understand you to be saying that a nuclear plant generates a 10^6 (USA million) times as much long-lived radioactive waste as a coal plant for each unit of energy.

As everyone acknowledges, coal plants don't contain their waste, and fly ash has bad chemical, medical, and ecological properties aside from its radioactivity. Everyone fears nuclear waste and requires it to be contained in nearly impervious vessels with century long management plans. Those same people happily let the coal plants just pump their wastes into the air and discharge captured fly ash into ponds and piles on the ground.

Coal also produces many times more fly ash by volume and mass than nuclear plants produce high-level long-lived wastes.

Luckily even fossil-fuel power generation is moving away from coal in favor of natural gas plants right now, which are cheaper and cleaner (still CO₂ though).

More about fly ash as an underappreciated pollutant:

https://www.sciencedirect.com/science/article/abs/pii/S00128...

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

[albumen]

If you did, it's not very clear.

The OP to which you replied didn't say that coal is more radioactive than spent nuclear fuel; but that radioactive waste's volume is much smaller than the fly ash produced by a single coal plant in a decade.

Is fly ash per kg more radioactive than nuclear waste? No. But you did acknowledge that the coal plant emits its waste into the atmosphere, unlike a fission plant, which I think is the more relevant point.