Fusion Discussion Thread

[Meecrob]

One thing that I have not seen mentioned so far (I hope I am not repeating) is that the large baseline power output and  waste heat from a fusion reactor can be used to improve our industrial processes. For example, the Hydrogen Reduction process of making steel would become commercially viable allowing us to make steel without fossil fuels.

This isn't simply about dollars per kilowatt/hour, or cost of construction/maintenance/decomissioning, its about a step change to new green technologies. You cannot run a steelmill on wind/solar, and you cannot make steel without producing CO2 and remain economically competitive by burning LNG/oil/coal.

Wind and solar definitely have their places, but for us to actually make a difference in our total emissions, we have to do more than change the source of electricity production; we have to rethink our applications of it.

[mikegarrison]

27 minutes ago, Meecrob said:

One thing that I have not seen mentioned so far (I hope I am not repeating) is that the large baseline power output and  waste heat from a fusion reactor can be used to improve our industrial processes. For example, the Hydrogen Reduction process of making steel would become commercially viable allowing us to make steel without fossil fuels.

This isn't simply about dollars per kilowatt/hour, or cost of construction/maintenance/decomissioning, its about a step change to new green technologies. You cannot run a steelmill on wind/solar, and you cannot make steel without producing CO2 and remain economically competitive by burning LNG/oil/coal.

Wind and solar definitely have their places, but for us to actually make a difference in our total emissions, we have to do more than change the source of electricity production; we have to rethink our applications of it.

Yeah, nuc plants typically just dump all their waste heat into a river or the ocean. They would become much more sustainable if they made better use of this.

[Pthigrivi]

7 minutes ago, JoeSchmuckatelli said:

Need over 400 modern utility-scale turbines, or over 3 million solar panels to equal the output of one average nuclear power plant.

Again it still costs 3 times as much though in lifecycle levelized cost. That is for the same spending you can produce 3 times as much with renewables. You don't need full sun, partial sun still goes into the pie and you can overbuild by 100% and still be cheaper than nuclear. Where you have more wind go with more wind, or bring it in from offshore or mountain ridges. And yeah 9%  is still impressive given the monumental task of fully overhauling a huge industrial country's energy supply (you're going for about 50% best case). For the same cost they'd only be able to add 3% if they'd spent that on nuclear, and that cost curve is going in the wrong direction long term. By all means keep existing plants running if they aren't leaking. It's better than fossil fuels and the construction cost is sunk. But if you're going to spend 20 years building new plants they're instantly going to be economically obsolete the day they come online. Much better to spend that on cheaper sources, scaling up and improving battery storage, and an efficient grid that can quickly move intermittent supply around. 

[JoeSchmuckatelli]

 

[mikegarrison]

31 minutes ago, Pthigrivi said:

Again it still costs 3 times as much though in lifecycle levelized cost. That is for the same spending you can produce 3 times as much with renewables. You don't need full sun, partial sun still goes into the pie and you can overbuild by 100% and still be cheaper than nuclear. Where you have more wind go with more wind, or bring it in from offshore or mountain ridges. And yeah 9%  is still impressive given the monumental task of fully overhauling a huge industrial country's energy supply (you're going for about 50% best case). For the same cost they'd only be able to add 3% if they'd spent that on nuclear, and that cost curve is going in the wrong direction long term. By all means keep existing plants running if they aren't leaking. It's better than fossil fuels and the construction cost is sunk. But if you're going to spend 20 years building new plants they're instantly going to be economically obsolete the day they come online. Much better to spend that on cheaper sources, scaling up and improving battery storage, and an efficient grid that can quickly move intermittent supply around. 

But if you can't get to 100%, then it doesn't matter how cheap it is.

By all means, if solar can get you 10% cheaply, then take that 10%. But you still need the other 90%, and it doesn't matter if that 90% is more expensive than solar, because you still need it.

[Pthigrivi]

12 minutes ago, mikegarrison said:

But if you can't get to 100%, then it doesn't matter how cheap it is.

By all means, if solar can get you 10% cheaply, then take that 10%. But you still need the other 90%, and it doesn't matter if that 90% is more expensive than solar, because you still need it.

You don't need to get to 100% all from one source. You're shooting for 50% solar, 50% wind eventually (more or less depending on your climate). In Germany getting from 9 to 25 or 30 on solar would be huge because peak demand is usually during the day when the sun is out and doesn't require huge amounts of storage. When it's not it's usually because a front is blowing through, which means more wind. After that you need more storage to get you through the night. They're aiming for 80% combined renewables by 2030, which if they follow through is about right. As the cost of storage comes down they can improve even on that. To bring it back to fusion, okay, maybe there's a home for that in 15-20 years in the remaining 10-15% where you run into diminishing returns on storage, but probably only if you can also bring the cost down considerably below that of nuclear. 

I love the idea of fusion. It will be amazing if it works and its cheap. And it's not like renewables don't come with their own environmental costs in terms of land use, lithium extraction, etc. But I also see a lot of too-smart people using it as a kind of excuse why we should wait and not max out renewables in the meantime because there's a holy grail just over the horizon. 

[mikegarrison]

We're talking in circles here. I think there is no way Germany can get 50% of their power from solar and 50% from wind. That much solar and wind just is not available in Germany.

You seem to think they can and will.

I guess we'll find out.

[K^2]

3 hours ago, mikegarrison said:

We're talking in circles here. I think there is no way Germany can get 50% of their power from solar and 50% from wind. That much solar and wind just is not available in Germany.

They might even be able to manage it during peak, but they don't have nearly the storage capacity to account for the variability of it, nor any plans to build the sufficient capacity, nor, really, the budget and means to do so even if they had it in the plans. Germany's "green plan" to decommission nukes and go 100% renewable using that budget is a lie. Plain and simple. It's technologically impossible to achieve, and it's not really a surprise, these exact findings were presented when the decision was made, and the decision was made anyways. It condemns Germany to having to either keep burning fossil fuels or buying electricity from neighbors who did invest in nuclear.

The truth about cheap solar and wind is that they're only cheap until you factor in storage and on-demand spikes. Once you do, they're no longer the cheap options. We just don't have the tech to build necessary storage cheaply enough to accommodate that. I hope that changes in the future, but gambling our ecosystem on being able to maybe figure out cheap energy storage at some indeterminate point in the future is reckless. Especially, when we're already past the point of no return on doing significant harm to our environment. Decommissioning existing nuclear infrastructure with nothing to replace it but coal and gas is a crime against all of humanity.

[JoeSchmuckatelli]

9 minutes ago, K^2 said:

Decommissioning existing nuclear infrastructure with nothing to replace it but coal and gas is a crime against all of humanity.

The real crime is how science allowed the politicians to be swayed by those who want nuclear vilified.

Even the worst bogeyman - nuclear waste - is fairly simple to deal with safely.

Note: I don't blame the populace.  People can be stupid.

[K^2]

1 hour ago, JoeSchmuckatelli said:

Note: I don't blame the populace.  People can be stupid.

Yeah, people can be gullible, but for the real culprit, you have to follow the money, and it's very obvious who made a lot of it on the nuclear getting scrapped in a majority of the examples we have.

Edit: And I should point out that some very educated people fell for the "we can do this with solar and wind alone," bit, because it takes a LOT of background in energy grids to really see through it.

Edited December 15, 2022 by K^2

[Nuke]

wind and solar are big random number generators in the power grid. which is not what you want when you are trying to follow the load. storage, at least the ones on the table, can only hedge the bets. are we going to send steel worker home because its overcast and still.

the problem with fusion, at least initially, is that it stands to be bloody expensive. we are going to need to go through 2 or 3 generations of power generation reactor designs for the technology to mature, with the ultimate end goal of aneutronic fusion with direct conversion. i have a feeling if forced to choose between a cheap dirty solution and a clean expensive one, the former will be the one we go with.  that is fossil fuels or renewables backed by fossil fuels. we are going to want to run next gen fission plants along side fusion plants. we should be upgrading, not demolishing those. 

[Pthigrivi]

4 hours ago, K^2 said:

They might even be able to manage it during peak, but they don't have nearly the storage capacity to account for the variability of it, nor any plans to build the sufficient capacity, nor, really, the budget and means to do so even if they had it in the plans. Germany's "green plan" to decommission nukes and go 100% renewable using that budget is a lie. Plain and simple. It's technologically impossible to achieve, and it's not really a surprise, these exact findings were presented when the decision was made, and the decision was made anyways. It condemns Germany to having to either keep burning fossil fuels or buying electricity from neighbors who did invest in nuclear.

 

They said 80% by 2030, not 100, which is not impossible to achieve, especially considering the stupendous legacy costs of nuclear which are only dwarfed by the prospect of new nuclear, which neither you nor any of the nuclear die hards seem willing to acknowledge. I don’t think we should decommission existing nuclear plants if they don’t happen to be leaking radioactive waste and require prohibitively expensive retrofits to maintain. But there is no reason to start in on new nuclear plants that will take 20 years to come online and for that reason alone are useless in combating climate change, and unfortunately wouldn’t be competitive even if they came on now. Its flushing money down the toilet. Look at the LCOEs, even compared to battery storage. Look at the long term cost trends. Its not subtle. Right now its 150$/Mwh in the US and 115$/Mwh in China. 
 

Now look at nuclear:

Its up 60% in the last 10 years. So why are we trying to climb onto a sinking ship exactly?

Edited December 15, 2022 by Pthigrivi

[Nuke]

if were making this argument, then even if fusion works, nobody will use it. it will be too expensive. history is rife with situations where cost cutting measures ended up being a bad idea in the long run. that's what got us into fossil fuel dependence in the first place. 

[K^2]

24 minutes ago, Pthigrivi said:

They said 80% by 2030

Shown to be impossible. We're already seeing their fossil usage increasing, and is projected to continue to do so, even despite the Russia situation.

25 minutes ago, Pthigrivi said:

Look at the long term cost trends.

The battery storage on these trends looks like that because of how tiny the fraction of people using battery storage at homes. Battery prices are already starting to go up, not down, because of the increased demand, and there is not enough Lithium IN THE WORLD to cover the storage Germany ALONE would need.

26 minutes ago, Pthigrivi said:

legacy costs of nuclear which are only dwarfed by the prospect of new nuclear

Which is only dwarfed by the costs of energy storage. So our alternatives are not solar/wind or nuclear. Our alternatives are nuclear or staying with at least 30-40% coal/gas indefinitely. Which, once again, is catastrophic, regardless of costs.

Costs of living in a desolate wastelands that we are building right now are way higher than costs of nuclear. And that is the ONLY way we can go 0% fossil right now, and going 0% fossil is vital  for us to have a chance of averting a global climate catastrophe.

If your entire argument is penny-pinching for the near future, you're part of what's killing our chances for a stable future, and there are no two ways about it. We have to eat the costs of nuclear now or PERISH.

[kerbiloid]

11 hours ago, mikegarrison said:

Denmark is a very small country that is almost all coastline. Switzerland is a very small country that is almost all mountains (and has 60%+ hydro). Iceland is a very small country right on the mid-Atlantic rift and gets lots of power from geothermal sources.

Denmark = 6 mln
Iceland = 0.4 mln
Switzerland = 8.6 mln

Very specific places with 15 mln of EU total 500 mln.

+10% of Germany 83 mln = 8 mln.

So, it's about 5% of EU population. And unlike 6 mln Denmark, 83 mln Germany (like also France or Britain) doesn't have a 900 mln rich neighbour as a backup UPS.

  

11 hours ago, Meecrob said:

waste heat from a fusion reactor can be used to improve our industrial processes. For example, the Hydrogen Reduction process of making steel would become commercially viable allowing us to make steel without fossil fuels.

The waste heat is called waste exactly because it's wasted instead of heating the water steam for the turbine.

It can't be utilized, it can be only dumped into the water or air. Entropy is merciless.

To make hydrogen, you need it as electricity, not as heat. You need it a concentrated, not dissipated form.

So, the best thing you can use the waste heat for is farming chickens and fishes. They like the warmth.

So, it can reduce the carbon footprint, but for the cost of local warming.
At the equator it will cause a permanent local drought, in Artctics it will cause ice melting, methane release, and cold water fauna mass extinction.
So, it has its own constrictions, and the steel production will be anyway being reduced, the recycling and economy will rule.

10 hours ago, mikegarrison said:

Yeah, nuc plants typically just dump all their waste heat into a river or the ocean. They would become much more sustainable if they made better use of this.

Entropy. They can't. You need energy to focus energy. This means that you have to produce more waste heat to manage waste heat.

On 12/13/2022 at 11:13 PM, JoeSchmuckatelli said:

pea-sized gold cylinder containing a frozen pellet of the hydrogen isotopes deuterium and tritium

According to wiki, the golden reserve of EU is ~11 000 t and of US ~8 000 t.

I hope, it's enough to make golden pellets for frozen tritium (hysterically laughing).
A golden capsule of frozen to nearly absolute zero tritium, Karl. It's a real economical breakthrough.

Well, the next step is to replace gold with much cheaper tungsten, happily they stopped making the electric spiral lamps to have it enough.

As we can see, the pellet shell has to be made of the exactly same materials as a tamper of fusion nuke secondary.
High Z, high density. Platinoids, actinoids, tungsten, tantalum...

(I forgot, did they find a tritium mine? Or still have to produce it from, say, lithium, in reactors?)

[mikegarrison]

4 minutes ago, kerbiloid said:

Entropy. They can't. You need energy to focus energy. This means that you have to produce more waste heat to manage waste heat.

Sure you can. https://en.wikipedia.org/wiki/Cogeneration

It's the same idea as using the waste heat from my car's engine to keep me warm while I drive it in the winter.

Edited December 15, 2022 by mikegarrison

[kerbiloid]

Just now, mikegarrison said:

Sure you can. https://en.wikipedia.org/wiki/Cogeneration

It's exactly what the Soviet powerplants were doing since early times. A large powerplant is called ТЭЦ/TEC ("heat and power center"). They pump the hot water to warm a nearby city.

But you can't concentrate the scattered heat, because you will lose more energy trying to do that.
While the heat is concentrated in the turbine at ~1 000 K temperature, you can transform and redirect it.
When the temperature is just 400 K, the heat is too scattered to redirect it in any other way than pumping hot water through the pipes to heat something 300 K warm, like houses, farms, fish pools.

Because of temperature gradient.

As the powerplant efficiency is exactly the difference between the original and final temperature, the hotter is the output, the weaker is the powerplant.

[Pthigrivi]

2 hours ago, K^2 said:

The battery storage on these trends looks like that because of how tiny the fraction of people using battery storage at homes. Battery prices are already starting to go up, not down, because of the increased demand, and there is not enough Lithium IN THE WORLD to cover the storage Germany ALONE would need.

Well first off thats a wild exaggeration. Second, LiB’s are really only critical for cars where weight and volume are at a premium. For grid storage we can use Sodium Ion or other technologies. I mean we’re somehow assuming that we’ll figure out all of the myriad problems with fusion in ten years but at the same time nothing will change about battery technology or production—recycling, improved manufacturing, alternate chemistries etc. This is why actual peer reviewed projections on the subject still have costs falling over the next 25 years. 

https://www.nrel.gov/docs/fy21osti/79236.pdf#page21

2 hours ago, K^2 said:

Which is only dwarfed by the costs of energy storage. 

It isn’t though, as Ive just demonstrated. Its less than nuclear and falling long term while the cost of nuclear goes up and up. And again even if you started now new nuclear plants wont come online for 15 years. You’re looking at almost 10 years of construction alone plus planning and testing. By then we’re screwed. Its not just spend all that money on nuclear or perish. There are alternatives and more efficient ways to spend that money scaling up and solving the problem right now.

Edited December 15, 2022 by Pthigrivi

[K^2]

45 minutes ago, Pthigrivi said:

Well first off thats a wild exaggeration. Second, LiB’s are really only critical for cars where weight and volume are at a premium. For grid storage we can use Sodium Ion or other technologies.

It is not an exaggeration. We don't have a solution. At the scale where you're supporting the country's grid, not having compact storage means you end up having to build megastructures to store the energy. That's not a huge improvement in cost. You basically have gravity storage on one end of the spectrum, LiPo on the other, and everything in between is some sort of a compromise. This is a grand unsolved problem. We do not have a fix for it. If you want to run numbers, be my guest. Chose your favorite method of storage, scale it up to provide several hours of uninterrupted power of some large European country (or US, if you want really scary numbers) and estimate the costs. Then compare them to the costs of nuclear for the same load. We can chase this problem back and forward, but it's really much more constructive if you just do the math once. (I can do this, but you'll just tell me I'm using the wrong energy storage, so I'm letting you pick.)

45 minutes ago, Pthigrivi said:

It isn’t though, as Ive just demonstrated. Its less than nuclear and falling long term while the cost of nuclear goes up and up.

Your own graphs show battery higher than peak gas, which is more expensive than nuclear.

And that's before we take into account that the price shown is not scalable to a country size. You really should run these numbers yourself.

45 minutes ago, Pthigrivi said:

I mean we’re somehow assuming that we’ll figure out all of the myriad problems with fusion

No, we're very much not. That's why we need nuclear energy. We have to maintain the existing grid and build new capacity. There is no alternative that is currently viable, and there might not be an alternative in a decade.

It'd be amazing if some breakthrough in batteries or fusion comes about in the next ten, even twenty years. That would literally save us. But we can't risk it. We have to do what we can with existing technologies. Not stuff that works in the lab. Not stuff we think we might figure out in the future. Our environment cannot withstand significantly more pressure than we are applying to it now. It's already collapsing under the current strain and is on borrowed time. We have to act now, and we have to act with technology we have. With current technologies, we can do 60-70% with wind and solar. The rest has to be geo, hydro, and nuclear, and the former two are situational. Countries that cannot do these, have to go nuclear.

Leaving a gap of even 20% on fossils is not acceptable. It was twenty years ago, but we missed that train. If we reduce our energy production carbon to 20% of what we're releasing now, we're still screwed. It's like planning to close 80% of the holes on a sinking ship when it already took on too much water to stay on the surface for very much longer. Zero is the only acceptable target.

Edited December 15, 2022 by K^2

[Codraroll]

6 hours ago, Pthigrivi said:

But there is no reason to start in on new nuclear plants that will take 20 years to come online and for that reason alone are useless in combating climate change, and unfortunately wouldn’t be competitive even if they came on now. Its flushing money down the toilet. Look at the LCOEs, even compared to battery storage. Look at the long term cost trends. Its not subtle. Right now its 150$/Mwh in the US and 115$/Mwh in China. 

It may be timely to ask why it takes 20 years as costs $150/MWh to run a nuclear plant. It's not necessarily because building a reactor is really, difficult and takes a long time. Some navy shipyards build them as a matter of routine. The USS Montana, a Virginia-class nuclear submarine, was laid down on May 16, 2018, and entered service on June 25, 2022. Granted, it was ordered back in 2014, but that still means a fully operational nuclear reactor went from "we should buy this" to "running nominally, captain" in barely over eight years. I doubt it's any less expensive to build a reactor to fit inside a combat submarine than in a peaceful and spacious building on land. 

Nuclear power plants become so expensive because of the volumes of red tape that have to be involved. Each plant has to be designed from the bottom up. All the parts have to be custom made and individually certified, then inspected thrice over, and the volume of documentation required probably outweighs the building itself, were it all printed on paper. The safety regimen is extremely rigorous to minimize the risk of nuclear disaster, but it's also a huge cost driver. And I highly suspect that many of these safety regulations were imposed after lengthy lobbying campaigns by "nuclear safety interest groups" whose pockets were full of coal money. Combined, they make nuclear power way too expensive and time-consuming to be worth considering, while coal and gas stand out as the cheap and easily available options, without much consideration for the dangers of that industry. I can't recall the source off the top of my head, but a while back somebody found out that more deaths could be attributed to coal mining accidents since 1940 than the entire nuclear sector - including not only the events at Chernobyl and Fukushima, but also Hiroshima and Nagasaki. 

That's not to say that all safety regulations should be abolished so every Joe's Nucular Family Shop can weld a hat rack in an old boiler to a turbine and create a reactor in their own back yard, but it might be an idea to review the regulations and see whether the accepted level of risk can be heightened a little bit if it means a tenfold reduction in cost.

[Pthigrivi]

8 hours ago, K^2 said:

Leaving a gap of even 20% on fossils is not acceptable. It was twenty years ago, but we missed that train. If we reduce our energy production carbon to 20% of what we're releasing now, we're still screwed. It's like planning to close 80% of the holes on a sinking ship when it already took on too much water to stay on the surface for very much longer. Zero is the only acceptable target.

No I agree we’re talking about whats the best solution for that last 20%. In the US we’re already using nuclear for 18%, and we should absolutely keep as much as we can going as long as its affordable. What Im arguing is that as they age out we’d be wiser to replace them with grid scale storage than new plants. The LCOE for LiB grid scale batteries was higher than peaker gas 4 years ago, but now its in the $150/mwh range and NREL projects that to continue to fall over the foreseeable future.  Ive heard a lot of doom and gloom about Li supply, maybe thats fossil fuel companies scaremongering about the future or maybe its commodity speculators juicing the market, but NREL doesn’t seem to believe its a real problem long term. Meanwhile nuclear is up at 175$/Mwh and rising. And remember we’re not trying to cover the whole nut. We’re talking about scaling up from 2% to 20% over the next 20-30 years as it replaces aging nuclear plants and whatever’s left of NG.  But more importantly that smaller fraction taken up by storage is whats going to allow us to even out supply between wind and solar so that we can spend $30-50/Mwh the rest of the time. So in 10 years when storage is covering 10% of supply at $100/Mwh, plus the $30/Mwh from renewables it took to charge them, its still going to be cheaper than nuclear, all of which accelerates the rate at which we can hit that 60-70% mark replacing fossil fuels. 

Edited December 15, 2022 by Pthigrivi

[JoeSchmuckatelli]

Molten Salt Battery 

https://www.scientificamerican.com/article/rechargeable-molten-salt-battery-freezes-energy-in-place-for-long-term-storage/

 

[Terwin]

8 hours ago, Codraroll said:

Nuclear power plants become so expensive because of the volumes of red tape that have to be involved. Each plant has to be designed from the bottom up. All the parts have to be custom made and individually certified, then inspected thrice over, and the volume of documentation required probably outweighs the building itself, were it all printed on paper. The safety regimen is extremely rigorous to minimize the risk of nuclear disaster, but it's also a huge cost driver. And I highly suspect that many of these safety regulations were imposed after lengthy lobbying campaigns by "nuclear safety interest groups" whose pockets were full of coal money. Combined, they make nuclear power way too expensive and time-consuming to be worth considering, while coal and gas stand out as the cheap and easily available options, without much consideration for the dangers of that industry. I can't recall the source off the top of my head, but a while back somebody found out that more deaths could be attributed to coal mining accidents since 1940 than the entire nuclear sector - including not only the events at Chernobyl and Fukushima, but also Hiroshima and Nagasaki. 

In the US, the Nuclear Regulatory Commission(NRC) is incentivized to have at least one, but as few as possible nuclear reactors running in the country as it can manage.  That is the federal level organization responsible for nuclear safety regulations, and they only have 2 incentives: 1) they are not needed if there are zero nuclear plants, 2) they get blamed for every negative event associated with nuclear energy generation.  Their budget is independent of how many plants they govern, and so whenever nuclear power starts to look attractive, they pile on more regulations to keep it unattractive to minimize the potential for mishaps.(fewer plants mean fewer mishaps, and higher regulatory requirements mean fewer plants, ergo, they are incentivized to have as many expensive regulations as possible without driving all of the existing plants out of business)

And any sort of attempt to scale back the costs they impose can be met with 'but we just want to keep everyone safe', which is very hard to contest politically.

I would not be surprised by similar regulatory bodies in other countries, or even just using the US nuclear regulations as the gold standard.

While getting rid of a bureaucracy is all but impossible, if the budget of the NRC were somehow attached to the number of functioning nuclear power plants, they might become more cost-effective relatively quickly.(unless the fossil fuel companies already own the board members or something, which is entirely plausible)

[darthgently]

6 hours ago, JoeSchmuckatelli said:

Molten Salt Battery 

https://www.scientificamerican.com/article/rechargeable-molten-salt-battery-freezes-energy-in-place-for-long-term-storage/

 

That 15% loss for thawing is very significant. 

I still think the killer breakthrough for renewables would be cheap room temp superconductors and a world wide grid connected with lossless transmission lines.  It's always sunny somewhere and local peak/off-peak times would cyclically offset mostly naturally as the planet rotates 

Terrestrial fusion still has many very significant hurdles, but more energy out than in is good for sure.  Until then, there is an existing fusion plant in the sky with challenges of it's own

[darthgently]

18 hours ago, kerbiloid said:

It's exactly what the Soviet powerplants were doing since early times. A large powerplant is called ТЭЦ/TEC ("heat and power center"). They pump the hot water to warm a nearby city.

But you can't concentrate the scattered heat, because you will lose more energy trying to do that.
While the heat is concentrated in the turbine at ~1 000 K temperature, you can transform and redirect it.
When the temperature is just 400 K, the heat is too scattered to redirect it in any other way than pumping hot water through the pipes to heat something 300 K warm, like houses, farms, fish pools.

Because of temperature gradient.

As the powerplant efficiency is exactly the difference between the original and final temperature, the hotter is the output, the weaker is the powerplant.

Desalination via distillation might be a good nuke cogeneration use of 400K water, at least as a preheat step if nothing else.  Now sure why distillation gets short shift once you consider costs cradle to grave costs of reverse osmosis membranes 

Edited December 16, 2022 by darthgently