[MisterTea]

No melt down? This game sucks.

On a serious note: I wonder how practical and safe it would be to build fusion pants close to city centers in order to harvest the excess heat for district heating. Would be a boon in e.g. NYC which already has a large district steam system. You can do cooling too, look up "steam absorption chiller."

[cyberax]

Fusion power plants can't "melt down". The amount of plasma inside the vacuum chamber is just around a gram.

[adrianmonk]

That's the joke, isn't it?

A fission power plant simulator lets you have fun playing through a meltdown disaster scenario. A fusion power plant simulator is "worse" because it takes away the "fun" of meltdowns. The humor is in reacting to the simulator as if it were a game (some are, but this one isn't).

[Dylan16807]

The first line reads as a joke, but then they actually ask if it's safe later in the comment.

[MisterTea]

I probably could have worded it better but while I understand the process and the inherent safety vs fission, I am no expert in the nuclear field. I suppose what I should have asked is what are the risks of e.g retrofitting a fusion reactor into an existing Con Edison facility in the middle of Manhattn, e.g. the historic IRT Powerhouse on 59th st.

[PunchyHamster]

Might not be similar to nuclear meltdown but still enough to need a lot of money to fix

[JumpCrisscross]

> Fusion power plants can't "melt down"

Eh, a core-containment failure (in any magnetically-contained system) would involve superheated hydrogen getting friendly with oxygen. That, in turn, would give neutron-impregnated barrier materials a free ride on propellant. It's not strictly a melt down. But it's in the same practical category of failure.

[gmueckl]

Ths is a massive misunderstanding of the technology. First of all, the amount of hydrogen in the reactor is tiny. The magnetic confinement severely limits the density of the plasma. The inner containment vessel is a ultra high vacuum chamber. The chemical energy that would be released by a reaction between the hydrogen in the reactor amd oxygen from the air would be less than what is released by popping a hydrogen filled balloon with a lighter.

The truly concerning failure modes would be related to release of radiation or activated materials. But that would require damaging the reactor in ways that the reactor is incapable of imparting on itself.

Overall, the technology is remarkably safe.

[JumpCrisscross]

> chemical energy that would be released by a reaction between the hydrogen in the reactor amd oxygen from the air would be less than what is released by popping a hydrogen filled balloon with a lighter

Thanks for the correction. If you're breeding lithium in the walls, might that be an incendiary concern?

[rnhmjoj]

The breeding blanket is entirely contained inside a vacuum vessel, so there isn't any oxygen to react with. Also, the are many blanket designs, but the lithium is never present in its elemental form (precisely because it would be very reactive), but in a stable chemical bond with some neutron multiplier (like lithium-lead alloys or beryllium ceramics). In some design the lithium is even immersed in the coolant itself, which is high pressure helium, so it's not going to ignite in any reasonable way.

[JumpCrisscross]

> breeding blanket is entirely contained inside a vacuum vessel, so there isn't any oxygen to react with

When the vessel works. If the vessel breaches, that lithium could ignite. Note a showstopper. But I suppose a risk to be thought about by the engineers (probably not by policymakers).

[pixl97]

There seems to be a number of different prototypes of blankets, but the average operating temperature seems to be 300-700C. Adding oxygen to some of these designs while that hot may cause metal burning. This said, many of them are ceramic designs and would likely resist combustion.

With all that said, it seems to be way less 'dangerous' material than would be in your average nuclear reactor, making it more of an industrial accident versus a planet contaminating mess.

[hunterpayne]

You are ignoring that the plasma would ignite the O2 in the air. You are also ignoring what happens when several hundred MW of energy (at about 1,000,000C) under pressure is released instantly. Anytime you have a powerplant with enough energy to be economically viable, releasing that energy at once will be a problem. Even FF PPs can explode quite violently.

[Dylan16807]

> You are ignoring that the plasma would ignite the O2 in the air.

What does this even mean?

> You are also ignoring what happens when several hundred MW of energy (at about 1,000,000C) under pressure is released instantly.

If you have a gram of hydrogen at a million degrees, it can continue putting out several hundred MW for about a fiftieth of a second.

Even if it somehow gets outside the machine with no heat loss to the structure, by the time it mixes with a few cubic meters of air it'll be down to 1000C or less.

[Symmetry]

There's only a few grams of hydrogen in the reactor's plasma, it's reaction with oxygen wouldn't be much more exciting than just losing containment. There are engineering challenges that have to be addressed but no worse than the 6 MW research reactor I used to walk by every day to my college classes in the middle of a dense city.

The proliferation risk of someone using the neutron flux to produce an atomic or dirty bomb are real but that exists no matter where it is.

[leonidasrup]

I think the proliferation risks will be in future the reason, independent of technological obstacles or costs, why US will not allow to build fusion power plants in all countries around the world.

Hybrid nuclear fusion–fission power plants have been already proposed and studied in theory.

"In general terms, the hybrid is very similar in concept to the fast breeder reactor, which uses a compact high-energy fission core in place of the hybrid's fusion core. Another similar concept is the accelerator-driven subcritical reactor, which uses a particle accelerator to provide the neutrons instead of nuclear reactions."

https://en.wikipedia.org/wiki/Nuclear_fusion–fission_hybrid

[bleepblap]

> Hybrid nuclear fusion–fission power plants have been already proposed and studied in theory.

I have a hand-wavy hard sci-fi universe I've been rolling around my head for years and I eventually came to the conclusion that fission-fusion drives would be really handy for spacecraft, since it would be much easier to start a fission reaction in a cold/dark ship than fusion because of the power requirements. Otherwise you need some other way to generate 10s or 100s of MW to start the fusion reaction.

[leonidasrup]

Using the energy of fission for spacecraft propulsion has been studied and some prototypes have been already constructed. Most of these nuclear engines should be used only outside of Earths atmosphere.

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

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

Most interesting and promising are direct nuclear propulsions, like fission-fragment rockets.

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

[DennisP]

Probably not all countries, but any NPT signatory has the right to build nuclear power plants, they just have to submit to inspections.

[leonidasrup]

This is the basic promise behind the "Treaty on the Non-Proliferation of Nuclear Weapons" (NPT).

https://en.wikipedia.org/wiki/Treaty_on_the_Non-Proliferatio...

In the text of the treaty there are promises to NPT signatories, such as:

Article IV "1. Nothing in this Treaty shall be interpreted as affecting the inalienable right of all the Parties to the Treaty to develop research, production and use of nuclear energy for peaceful purposes without discrimination and in conformity with articles I and II of this Treaty."

https://en.wikisource.org/wiki/Nuclear_Non-Proliferation_Tre...

But the hard reality of U.S. nuclear politics in regard to other countries can be read here:

"The Nuclear Fuel Cycle and The Bush Nonproliferation Initiative"

https://www.iaea.org/sites/default/files/neff.pdf

"The world’s leading nuclear exporters should ensure that states have reliable access at reasonable cost to fuel for civilian reactors, so long as those states renounce enrichment and reprocessing."

"The 40 nations of the Nuclear Suppliers Group should refuse to sell enrichment and reprocessing equipment and technologies to any state that does not already possess full-scale, functioning enrichment and reprocessing plants."

For example when United Arab Emirates wanted to build the Barakah nuclear power plant, (supplied by Korea Electric Power Corporation, not by an U.S. company), it had to sign an the Section 123 Agreement with United States of America. As part of the agreement, the UAE committed to forgo domestic uranium enrichment and reprocessing of spent fuel.

https://en.wikipedia.org/wiki/U.S.%E2%80%93UAE_123_Agreement...

To be fair, it's not only U.S. who want's the control access to nuclear technology and nuclear materials. For example India wanted to become a member of Nuclear Suppliers Group for a long time. As of 2019, China has thwarted every attempt of India's inclusion into NSG and has made it clear that status quo will remain citing "lack of consensus" among NSG members.

https://en.wikipedia.org/wiki/Nuclear_Suppliers_Group#India

Another example is South Korea. South Korea is constrained in its nuclear power policy by the 1974 Korea-US Atomic Energy Agreement. Only in November 2025 did the USA formally affirmed support for South Korea’s civil uranium enrichment and spent fuel reprocessing for peaceful uses.

https://www.armscontrol.org/act/2025-12/news/us-supports-sou...

https://world-nuclear.org/information-library/country-profil...

[cyberax]

Fission-fusion or accelerator-driven fission is pure BS. It combines the disadvantages of _both_ and none of the advantages.

Modern fission power plants are designed with a reactor vessel to last a century and to withstand high pressures and temperatures. It's built and emplaced permanently in a large concrete shielding structure.

In a hybrid design this just won't work. Fuel will need to be right next to a high-vacuum chamber that will need periodic maintenance.

[Aardwolf]

What's the effect of this in a populated area in a certain radius? Compared to nuclear power plants...

[cyberax]

Radiologically? Pretty much nothing. The regular industrial safety concerns will matter more.

The plant will have some tritium, and the material in reactor walls will get activated by the neutron flux. Some of the activated materials can disperse in case of a catastrophic explosion (e.g. a couple of large airplanes being flown the reactor building).

But the material of the walls is not volatile, so it'll stay on the site. And tritium is very volatile, so it'll quickly disperse to safe levels. You'll be able to detect them with sensitive equipment, but it won't be dangerous.

[JumpCrisscross]

> What's the effect of this in a populated area in a certain radius?

I'd imagine this is, like with fission plants, deeply dependent on the specific design.

[ExpertAdvisor01]

It already exists in many countries. They transport it through pipelines .

E.g. Temelín Nuclear Power Plant, Paks Nuclear Power Plant And many more

[MisterTea]

My question is more about the safety of locating one smack in the middle of a city. There is radiation to shield but no radioactive fuel waste. HOWEVER, worn reactor parts that need to be replaced will be piping hot when measured with a Geiger counter. So is it safe to build and operate in the middle of e.g. NYC?

And further, if they are safe, what is the public's perception of fusion? Do people hear "nuclear fusion" and immediately think nuclear disaster imagery brought about by incidents like Three Mile Island and Chernobyl?

[DennisP]

Judging by the comments I see most places, the general public's perception of fusion is "magical scifi tech that will never happen."

[Cthulhu_]

Oh I'm sure it'll happen, in like 30 years. After which they'll need to make it commercially viable, build power plants, etc.

(also it was 30 years away, 30 year ago)

[hunterpayne]

That's because it almost certainly is. Don't hate on the messengers.

[DennisP]

My point is, that's a pretty positive view of fusion. They think it's too good to be true, but if it actually happens then I doubt many people will suddenly switch into thinking it's a dirty old explodey thing like fission's public image.

[hunterpayne]

"My question is more about the safety of locating one smack in the middle of a city. "

We don't put any other type of powerplant in a city, so why would we do it for fusion? That being said, fusion won't happen in our lifetimes and even when we do get it, we probably will never really use it. Fission is just better in almost every way. It makes 5x the power per amount of fuel, it makes far less neutrons, and the temperature generated is far more usable. Oh, and fusion absolutely makes radioactive waste and a fusion failure makes a meltdown (which doesn't have to be a failure case for fission) look like a Sunday picnic.

[MisterTea]

> We don't put any other type of powerplant in a city, so why would we do it for fusion?

How did you write something so ignorant? NYC has multiple fossil fuel plants in the city centers. It would take you all of 15-30 seconds to look this up: https://en.wikipedia.org/wiki/List_of_power_stations_in_New_...

[BizarroLand]

Stop your fearmongering. Fusion's radioactive byproducts are not nearly as dangerous as fission's byproducts, and they should only be radioactive for a year to a decade at most.

From https://www.iaea.org/topics/energy/fusion/faqs

Does Fusion produce radioactive nuclear waste the same way fission does?

Nuclear fission power plants have the disadvantage of generating unstable nuclei; some of these are radioactive for millions of years. Fusion on the other hand does not create any long-lived radioactive nuclear waste. A fusion reactor produces helium, which is an inert gas. It also produces and consumes tritium within the plant in a closed circuit. Tritium is radioactive (a beta emitter) but its half life is short. It is only used in low amounts so, unlike long-lived radioactive nuclei, it cannot produce any serious danger. The activation of the reactor’s structural material by intense neutron fluxes is another issue. This strongly depends on what solution for blanket and other structures has been adopted, and its reduction is an important challenge for future fusion experiments.

Can fusion cause a nuclear accident?

No, because fusion energy production is not based on a chain reaction, as is fission. Plasma must be kept at very high temperatures with the support of external heating systems and confined by an external magnetic field. Every shift or change of the working configuration in the reactor causes the cooling of plasma or the loss of its containment; in such a case, the reactor would automatically come to a halt within a few seconds, since the process of energy production is arrested, with no effects taking place on the outside. For this reason fusion reactors are considered to be inherently safe.

[advisedwang]

> I wonder how practical and safe it would be to build fusion pants close to city centers in order to harvest the excess heat for district heating

The cost/benefit for doing this seems pretty similar between fusion as gas power. We don't usually do this with gas, so I guess it's probably not viable for fusion.

[nerdsniper]

Many cities/towns in the USA have small power plants in them (typically associated with a University, large hospital system, or central business district) which "sell" not just power, but also hot water, and steam. The steam is typically used to heat buildings. Google for "$CITY steam tunnels" or "$CITY CHP plant" to find these in your area.

San Francisco has[0][1][2][3] at least five combined heat and power plants that generate electricity and also sell steam to neighboring buildings via 72,000 feet of pipes.

I worked at a privately-owned for-profit "factory" in Santa Monica whose primary product was chilled water (their other product was warm water). They built pipelines to nearby large buildings and sold chilled water to them.

0: https://cordiaenergy.com/locations/san-francisco-3/ (2 for-profit CHP plants)

1: Skanska (for-profit)

2: San Francisco General Hospital

3: Apparently there are some "Muni" CHP plants scattered about SF as well (publicly-owned)

[markvdb]

Combined heat and electricity production is uncommon in the US, but much more so in Europe. Especially in the Baltics, Scandinavia and the Netherlands, non-CHP generation is rare. Related: higher energy cost, and elaborate local heat distribution networks.

[namibj]

Look at where the Barmen gas power plant is in Wuppertal, Germany to see....

[dheera]

> The cost/benefit for doing this seems pretty similar between fusion as gas power.

The real problem is stupid capitalism reprices everything good to the price of the non-good thing. Solar was supposed to be almost-free clean electricity, but the price of panels has been repriced to make them the same as dirty electricity.

[grishka]

Don't they already do this for existing types of power plants (gas, coal) that produce waste heat?