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Comment by tlocke | Hacker News Reader

If cost were the only thing you cared about, then no nuclear power stations would ever be built, they're simply much more expensive than gas, wind or solar. From an environmental point of view you wouldn't have nuclear either, the reason is that you can't turn it up and down as you can with gas, and so you always need to the gas to make up the difference between supply and demand. So really, nuclear is in competition with wind and solar, and nuclear will always lose out because it's so expensive.

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Is it true you can't adjust the output of a nuclear plant? I thought I heard something about being to slide the cooling rods from "minimal output" to "Chernobyl", but I'm not a nuclear person.

Sure they can adjust output. Some are not licensed to do so, but that's more a paperwork hindrance than any actual physical reason. They can ramp about as fast as other generators using a steam cycle, like ccgt or coal. There are some situations like when you're at the end of the fuel cycle if you ramp down quickly you might have trouble starting quickly again due to Xe poisoning. But, if there was a reason to, the control system can be designed to provide sufficient excess reactivity to power through events like that (e.g. naval reactors).

That being said, since most of the cost of a nuclear power plant is the capital cost, every time you're not generating at full power is time you're generating less revenue to cover the capital costs. So even in a hypothetical lowest cost zero carbon system with very high penetration of variable renewables (solar, wind), the nuclear plants would be mostly running flat out.

Thank you for this detailed explanation!

Nuclear plants can adjust output, but not quickly. As reaction rates change the composition of the core itself changes, which further modifies reaction rates. Ramping up to full power might take a plant 12 hours. While this is fine for dealing with seasonal variation in demand, or compensating for another plant going down for maintenance, it can't deal with the short term spikes in demand that happen throughout any given day. There are some designs that can ramp up faster, but they are uncommon at least in the US. All plants can decrease output quickly (critical for safety) but without that quick ramp up its still not suitable for dealing with short term dips.

That being said, fuel represents only a tiny fraction of the cost of nuclear power, so it's fine to run a nuclear reactor at close to max power 24/7 and just use excess power for tasks like water desalination or simply vent off steam instead of passing it through the turbines when demand is lower.

> use excess power for tasks

Or sink it into stored hydrogen via electrolysis.

Exactly. Fresh water, clean fuels, carbon capture, waste decomposition, battery charging, there are plenty of productive uses for excess power.

But then there is no argument left for nuclear in the first place!

Once you have scalable storage for excess energy, renewables and their fluctuations are simply cheaper, safer and greener, right?

Having something useful you can do with excess energy is not the same as scalable storage sufficient to deal with all fluctuations in renewables.

Sure if you have a solar plant producing too much power, you can use that power to generate hydrogen, and that hydrogen can be burned later as a clean energy source. But generating and storing and using enough hydrogen to consistently get you through the night is substantially harder.

Further, renewables are not simply cheaper, safer, and greener. From a safety perspective nuclear is by orders of magnitude safer. Green-ness is a nebulous concept but in terms of damage to the environment nuclear is way better than solar or hydro and comparable to wind and geothermal. Solar and Wind are cheaper than nuclear in terms of nameplate capacity, but their load factor is dramatically lower and their lifetimes are much shorter, to replace a 1 GWe nuclear plant you basically need 3 GW of solar capacity, which are going to have to be replaced twice over the same lifetime, and 12,000 MWh of storage capacity.

> From a safety perspective nuclear is by orders of magnitude safer.

Citation please. And make sure it's the renewable we mostly talk about for this conversation, not hydro that cannot be scaled up much more.

Nuclear is orders of magnitude safer than what? Fossil fuel, yes, but not renewables? (https://ourworldindata.org/safest-sources-of-energy)

It's hard to say any one technology is "greener" than another when they have vastly different types of impacts...

* Nuclear waste remains a big issue for all except the newer reactors, which are uncommon, with little to no planned upgrades to existing generation or storage facilities

* Solar runs into land use concerns & endangered species, along with battery-related supply issues (child labor for mining minerals, political issues for where those materials are usually mined from, etc.), waste issues for end-of-life panels and batteries

* Large hydro devastates river and riparian ecology, not to mention local human communities all up and down the watershed. It has non-negligible greenhouse gas emissions too, between altering river carbon stores and using a metric asston of concrete.

Most of those concerns can be improved upon in human lifetimes. In terms of climate change though, arguably the priority should be to get "good enough" technologies deployed widely and quickly enough to change the emissions trajectory ASAP, if it's not already too late (it probably is). In that sense both nuclear and renewables are a net positive (in an off-the-cuff cost-benefit analysis weighing the urgency of climate change vs future issues).

But of all the types, nuclear alone leaves behind a non-trivial issue for thousands of years into the future. We can fix most other energy mistakes within a decade or few; not so much nuclear waste creation and storage, especially in an era of increasing geopolitical instability and waning democratic checks & balances. Stable and safe nuclear power relies not just on technological and economic factors, but also on stable and safe world regimes and balances of power that can limit both combat and proliferation, especially to non-state actors. None of those can be guaranteed in this century. Domestic regulations aside, existing nuclear powers have a strong vested interest in limiting nuclear access to nations outside of existing blocs/alliances.

I would be strongly pro-nuclear in an idealized world run by sane scientists and engineers, but that's very much NOT the world we live in.

Unless it's given massive subsidies like Hinkley point C.

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