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China's Yanlong: a small nuclear reactor strictly for district heating

cnbc.com

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Re: China's Yanlong: a small nuclear reactor strictly for district heating

#11

Post by sandworm101 »

adrianN wrote: post #9
sandworm101 wrote: post #6

>> around the same volume as an Olympic swimming pool. >> with each 400-megawatt unit capable of warming 200,000 urban households. >> with temperatures not exceeding 100 degrees Celsius, Think about that for a minute. If the water isn't going to exceed 100c but the reactor is still going to pump out 400-megawatts, it isn't going to be a calm pool. They are going to have to pump insane amounts of water in and out of t…

It is possible to regulate the output of a nuclear reactor. In case the pool boils off in some freak accident, the chain reaction also stops, because water is acting as a neutron moderator in these designs. So you only have to ensure that the residual heat from normal decay doesn't melt the reactor. That doesn't sound too hard.

>> you only have to ensure that the residual heat from normal decay doesn't melt the reactor.

Not hard if this is a passive-cooling design. My point is that at these power levels passive cooling isn't enough. Stop the pumps and the reactor may build up enough heat to start melting things very quickly, long before the pool boils dry.

Re: China's Yanlong: a small nuclear reactor strictly for district heating

#12

Post by nabla9 »

sandworm101 wrote: post #11
adrianN wrote: post #9

Earlier quoted context omitted.

It is possible to regulate the output of a nuclear reactor. In case the pool boils off in some freak accident, the chain reaction also stops, because water is acting as a neutron moderator in these designs. So you only have to ensure that the residual heat from normal decay doesn't melt the reactor. That doesn't sound too hard.

>> you only have to ensure that the residual heat from normal decay doesn't melt the reactor. Not hard if this is a passive-cooling design. My point is that at these power levels passive cooling isn't enough. Stop the pumps and the reactor may build up enough heat to start melting things very quickly, long before the pool boils dry.

Correct me if I'm wrong but isn't the idea of safe pool reactors that hydrogen-neutron heat transfer is more efficient than normal radioisotope-water heat transfer. If you shut down the pumps and heat increases, spectral hardening cools the reactor faster and disperses the energy into larger volume than convection using pumps.

Re: China's Yanlong: a small nuclear reactor strictly for district heating

#13

Post by sdfasfdsaf »

sandworm101 wrote: post #6

>> around the same volume as an Olympic swimming pool. >> with each 400-megawatt unit capable of warming 200,000 urban households. >> with temperatures not exceeding 100 degrees Celsius, Think about that for a minute. If the water isn't going to exceed 100c but the reactor is still going to pump out 400-megawatts, it isn't going to be a calm pool. They are going to have to pump insane amounts of water in and out of t…

No reactor is a calm place. The heat capacity of water changes with pressure, but not by orders of magnitude. So any 400 MW reactor has to pump similar amount of water to keep the T constant.

So the pumps have to be similarly sized, except you no longer need a pressure vessel.

Re: China's Yanlong: a small nuclear reactor strictly for district heating

#14

Post by sdfasfdsaf »

lexxed wrote: post #3

A small nuclear reactor in a swimming pool.. what could go wrong..

A lot less than in a submarine or electrical reactor. Heck McMaster U has a swimming pool sized 5 MW.

There's no pressure vessel and a massive thermal inertia. Not child's play, but very safe.

The big issue is the waste.

Re: China's Yanlong: a small nuclear reactor strictly for district heating

#15

Post by Symmetry »

vorotato wrote: post #7
lexxed wrote: post #3

A small nuclear reactor in a swimming pool.. what could go wrong..

I think this comment shouldn't be downvoted because it's a common misunderstanding rooted in how unintuitive it is that water is so good at blocking radiation.

XKCD had a really great illustration of that.

https://what-if.xkcd.com/29/

Re: China's Yanlong: a small nuclear reactor strictly for district heating

#16

Post by Symmetry »

adrianN wrote: post #9
sandworm101 wrote: post #6

>> around the same volume as an Olympic swimming pool. >> with each 400-megawatt unit capable of warming 200,000 urban households. >> with temperatures not exceeding 100 degrees Celsius, Think about that for a minute. If the water isn't going to exceed 100c but the reactor is still going to pump out 400-megawatts, it isn't going to be a calm pool. They are going to have to pump insane amounts of water in and out of t…

It is possible to regulate the output of a nuclear reactor. In case the pool boils off in some freak accident, the chain reaction also stops, because water is acting as a neutron moderator in these designs. So you only have to ensure that the residual heat from normal decay doesn't melt the reactor. That doesn't sound too hard.

Isn't the residual heat from normal decay something like 10% of the reactor output? When you split Uranium you get a lot of byproducts with short half-lives that continue decaying away even when Uranium chain reaction stops. So you've still got 40 MW to deal with, at least until those short-half-lived byproducts finish decaying.

Re: China's Yanlong: a small nuclear reactor strictly for district heating

#17

Post by adrianN »

Symmetry wrote: post #16
adrianN wrote: post #9

Earlier quoted context omitted.

It is possible to regulate the output of a nuclear reactor. In case the pool boils off in some freak accident, the chain reaction also stops, because water is acting as a neutron moderator in these designs. So you only have to ensure that the residual heat from normal decay doesn't melt the reactor. That doesn't sound too hard.

Isn't the residual heat from normal decay something like 10% of the reactor output? When you split Uranium you get a lot of byproducts with short half-lives that continue decaying away even when Uranium chain reaction stops. So you've still got 40 MW to deal with, at least until those short-half-lived byproducts finish decaying.

5% for the first few seconds: http://www.euronuclear.org/info/encyclopedia/r/residual-heat... but your point of course still stands. It's certainly not trivial to build passive-safe reactors, but it's also not impossible.

Re: China's Yanlong: a small nuclear reactor strictly for district heating

#18

Post by xbmcuser »

Stuff like this makes me feel western countries really underestimate Chinese tech chops. They are able to force stuff on the people that most countries have to cajole and negotiate with their citizens. I get cognitive dissonance from the fact that China is doing it's best to decrease coal usage where as US is tried to increase coal usage.

Re: China's Yanlong: a small nuclear reactor strictly for district heating

#19

Post by jonwachob91 »

xbmcuser wrote: post #18

Stuff like this makes me feel western countries really underestimate Chinese tech chops. They are able to force stuff on the people that most countries have to cajole and negotiate with their citizens. I get cognitive dissonance from the fact that China is doing it's best to decrease coal usage where as US is tried to increase coal usage.

>> Stuff like this makes me feel western countries really underestimate Chinese tech chops.

The west largely underestimates Chinese tech chops b/c they steal so much of our IP...

Their ability is evident in the number of Ph.D's they turn out, so why don't they invest in developing their own technology instead of stealing everyone else's? "Catching up" is not an acceptable answer with how much intellectual firepower they have.

Re: China's Yanlong: a small nuclear reactor strictly for district heating

#20

Post by jobu »

xbmcuser wrote: post #18

Stuff like this makes me feel western countries really underestimate Chinese tech chops. They are able to force stuff on the people that most countries have to cajole and negotiate with their citizens. I get cognitive dissonance from the fact that China is doing it's best to decrease coal usage where as US is tried to increase coal usage.

China has been run by technocrats for the last couple decades. Most of the current leadership has more of a political background, but president Xi Jinping has a chemical engineering degree.

http://www.scmp.com/news/china/policies-politics/article/211...

"from 1997 to 2007, all of the top leaders sitting on the innermost Standing Committee shared an engineering background"

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