Donate to Remove ads

Got a credit card? use our Credit Card & Finance Calculators

Thanks to johnstevens77,Bhoddhisatva,scotia,Anonymous,Cornytiv34, for Donating to support the site

The greenhouse effect and the heating effect of nuclear reactors

Scientific discovery and discussion
Gengulphus
Lemon Quarter
Posts: 4255
Joined: November 4th, 2016, 1:17 am
Been thanked: 2628 times

The greenhouse effect and the heating effect of nuclear reactors

#431182

Postby Gengulphus » July 29th, 2021, 11:36 am

From viewtopic.php?p=431135#p431135:

GrahamPlatt wrote:This just makes me wonder whether heating of the earth via the “greenhouse effect” isn’t simply being replaced here by direct heating via nuclear fission! What are the numbers like? Does anyone know?

Here's my stab at a very rough answer - don't expect anything at all precise, just order-of-magnitude estimates:

From https://en.wikipedia.org/wiki/Solar_irr ... 's_surface, Earth receives 1361 W/m^2 from the Sun, of which some doesn't get down to the surface due to things like reflection by clouds. The amount that gets down to the surface is around 1000 W/m^2. That's measured on a surface that is perpendicular to the Sun's rays, so the relevant area for the entire Earth is that of a near-circular disc of radius 6371 km, which comes to about 1.3 * 10^14 m^2, and so the energy arriving at the Earth's surface from the Sun is about 1.3 * 10^17 W, or 130,000,000,000 MW. And a high proportion of that energy will end up heating the Earth's surface, mainly directly but also by indirect mechanisms such as photosynthesis by plants followed by metabolism by animals, fungi, bacteria, etc, that eat the plants.

A nuclear reactor produces significantly more heat (either directly or when its electrical output is used) than its rated output in MW - I'm not certain how much more, but the reactor designers will try to make them as efficient as possible at converting the heat energy to electrical energy - so while I'd expect it to be significantly more, I wouldn't expect it to be many times more.

Together, those mean that I'm pretty certain the heating of the Earth's surface due to solar radiation is many orders of magnitude more than can be expected from even quite a lot of nuclear reactors, so I don't expect the nuclear reactors' heat output to be very significant. Also note that the "greenhouse effect" is not a producer of heating like the Sun or nuclear reactors: rather, it is an effect that makes it more difficult for already-produced heat to escape (which in the case of the whole Earth basically means radiate away into space) and so causes more of it to build up before it is escaping as quickly as it is being produced. So the "greenhouse effect" is amplifying the effect of all the heat production, and even a small amount of that amplification of the effect of solar heating on the Earth seems likely to be a good deal more significant than heat production by nuclear reactors.

So in short, yes, use of nuclear reactors will partially replace the "greenhouse effect" by direct heating via nuclear fission, but only a very small part of the "greenhouse effect" that's got rid of in that way will be replaced and the rest will be genuinely got rid of.

That doesn't mean that direct heating by nuclear fission won't be a problem, just that it won't be a global problem. Local heating of rivers, lakes, etc, by energy-intensive industrial installations certainly can be an environmental problem... And while in theory having many small nuclear reactors rather than a few big ones can help to spread the heating over larger areas and so mitigate the local environmental problems, in practice I suspect that the small reactors will be clustered in a few big sites due to economies of scale, especially with regard to logistics and security...

Gengulphus

Return to “Science”

Who is online

Users browsing this forum: No registered users and 6 guests