Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Small nuclear reactors: tiny NuScale reactor gets safety approval

popularmechanics.com

Post reply on HN
Print view View original

431–440 of 554 posts

Re: Small nuclear reactors: tiny NuScale reactor gets safety approval

#431

Post by HPsquared »

tlear wrote: post #413
i_am_proteus wrote: post #356

Earlier quoted context omitted.

Nuclear engineer here. I've read through a good portion of the regulatory submission to the NRC and have a few takeaways that oppose some of the less-well-informed takes in this thread: - The reactor differs substantially from existing PWRs by encasing the primary in double containment, using natural circulation flow for both normal operation and emergency cooling. There are no pumps needed (or installed) to move coo…

This is very interesting, can reactor like that be used on a ship or submarine(probably stupid question but I am curious). I remember reading some Tom Clancy novel that had a reactor with cooling that used no pumps as a major technical story point.

On submarines that might be a liquid metal coolant, as used on a few soviet submarine reactors. Lead-bismuth eutectic is most likely, it would be sensible to avoid sodium/potassium coolant on a submarine.

Re: Small nuclear reactors: tiny NuScale reactor gets safety approval

#432

Post by mnw21cam »

tandr wrote: post #392
thallium205 wrote: post #361

Earlier quoted context omitted.

SpaceX rocket to the sun.

Thank you. I don't get why this is not considered as an option anywhere.

Because it's a really really bad idea, for several reasons.

1. If your rocket has a failure during launch, you're likely to spread the nuclear waste over a large land area.

2. Even though we really haven't generated that much nuclear waste, it's still many many rocket-launches-worth. That gets expensive. Much more expensive than sticking it in a hole in the side of a mountain.

3. Launching something into the sun takes a huge amount of rocket fuel. It takes a Falcon-9 with a mass of ~550Mg to get a payload of ~22.8Mg into low earth orbit with a velocity of ~8km/s. The Earth is moving around the Sun at ~30km/s, so to launch into the Sun, you need to depart from the Earth at (at distance) ~30km/s. Earth's escape velocity is ~11km/s, which means that from low earth orbit, you need to get up to ~32km/s (sqrt(30^2 + 11^2)). So your ~22.8Mg payload in low earth orbit needs to include a rocket that can add ~24km/s to its velocity. If we assume a rocket with a fairly decent engine, with an Isp of 4km/s, then we can plug that into the Tsiolkovsky rocket equation. The remaining payload that can be flung into the Sun is a grand total of 57kg. All the rest of that ~22.8Mg is rocket fuel. Per SpaceX Falcon-9 launch. This is not an effective way to get rid of nuclear waste. (Note, it may be possible to increase efficiency by making use of gravity assists from other planets, but you still need to actually get to other planets first, so a pretty hard limit on the payload-into-the-Sun is the payload-to-Mars, which is ~4Mg. Still not very much.)

Re: Small nuclear reactors: tiny NuScale reactor gets safety approval

#433

Post by rmtech »

hinkley wrote: post #178
jabl wrote: post #116

Earlier quoted context omitted.

In this particular case, a power plant with these nuscale reactors would probably have survived a Fukushima type accident. One effect of being small is that the reactors are designed to be passively cooled after shutdown, using convection instead of pumped flow. So there is no need for emergency diesel generators to keep the coolant pumps running.

What's the radius around a reactor where a critical core can trigger fission in the next reactor over?

In practice, 0.

Re: Small nuclear reactors: tiny NuScale reactor gets safety approval

#436

Post by kgabis »

michaelt wrote: post #428
kgabis wrote: post #402

Earlier quoted context omitted.

You don't? The volume of water in oceans is so big that this won't be a problem as long as you don't dump it in coastal waters. Keep in mind that there's plenty of reactors from sunken nuclear submarines in oceans right now.

The kind of nuclear submarines governments are trying to raise and properly dispose of, because they're worried bioaccumulation will taint their fish stocks? [1] [1] https://www.bbc.com/future/article/20200901-the-radioactive-...

And governments are known for not over reacting to anything related to nuclear power /s

Re: Small nuclear reactors: tiny NuScale reactor gets safety approval

#437

Post by p1mrx »

michaelt wrote: post #418
p1mrx wrote: post #398

Earlier quoted context omitted.

It's literally a big hole with water in it; what are you unsure about?

Our largest manmade lakes are created by dams, and you can find plenty of example of dams failing in ways that don't take many days. If our smallest manmade lakes (swimming pools) can leak a lot, and our largest manmade lakes (dams) can also leak a lot the idea there's an in-between size that doesn't leak might need a bit of elaboration.

There's a big difference between a dam and a pool; the pool is supported by the ground, and even if you bash holes in it, the water still has to find somewhere to go. Also, pools are not typically built from concrete and stainless steel.

The safety requirement here is not "doesn't leak", it's "holds most of the water for 30 days (after which water is not required)". You would have to get an implausibly-large leak, during a situation where nobody can add more water for a month.

Re: Small nuclear reactors: tiny NuScale reactor gets safety approval

#439

Post by DrBazza »

marshray wrote: post #42

I think it's disingenuous to argue the economics of nuclear without mentioning: "DOE reported that it faced an estimated $494 billion in future environmental cleanup costs — a liability that roughly tripled during the previous 20 years." https://www.gao.gov/assets/700/696956.pdf

That's also an 'if we clean it up'. Nuclear waste decays, and there is not a lot you can do about that.

If reactors, or the placement of them, are designed to be left in-situ after decommissioning, then the cost becomes a lot less. Moving spent fuel from one site to another makes little sense when the original site has already been designated nuclear.

As others have said, this kind of number is always pitched at nuclear, and not hydro, or coal, or any other form of power.

Re: Small nuclear reactors: tiny NuScale reactor gets safety approval

#440

Post by Retric »

sergeykish wrote: post #374
Retric wrote: post #175

Earlier quoted context omitted.

An instant in geological time not a literal instant. Death of modern civilization is always a risk, but not directly from climate change. The global food surplus is projected to continue even in the worst case. Energy and raw material production is similarly not a major concern. People continue to live in Dubai which demonstrate how extreme local conditions can get without forcing exodus. Further, few places are expe…

I like your optimism, people would just live in inhabitable places or relocate and would be welcome, such gentlemen. I expect WWIII.

What specifically is going to cause mass migrations in your mind, and on what time scale? Sea level rise on the order of 5 feet in 80 years is hardly going to make most countries uninhabitable. Over longer time scales will see much larger increases, but the yearly change is never projected to be that rapid.

Water availability is a concern for farming and industry, but not really people. Desalination is cheap enough for personal use even in India. Every 10 gallons a day is an extra ~4$ per year. Projecting US use age on global poor is unaffordable, but the global poor don’t use nearly that much water.

Post reply on HN