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

Re:China's Yanlong: a small nuclear reactor strictly for dis... by Symmetry on Wednesday December 20, 2017 @11:12AM (#15970809)

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.

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Re:China's Yanlong: a small nuclear reactor strictly for dis... by vilhelm_s on Wednesday December 20, 2017 @12:12PM (#15971486)

According to one document[1]

> The decay heat produced by a reactor shutdown from full power is initially equivalent to about 5 to 6% of the thermal rating of the reactor. This decay heat generation rate diminishes to less than 1% approximately one hour after shutdown. However, even at these low levels, the amount of heat generated requires the continued removal of heat for an appreciable time after shutdown.

At 400 MW it takes about 4 hours to boil the water in an olympic swimming pool[1], so there should be some safety margin for the power to drop. Then once it is down to 1% decay heat it could boil for a couple of weeks before running dry.

[1] https://web.archive.org/web/20110316042315/http://www.hss.do...

[2] http://www.wolframalpha.com/input/?i=(specific+heat+of+vapor...

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Re:China's Yanlong: a small nuclear reactor strictly for dis... by adrianN on Wednesday December 20, 2017 @11:17AM (#15970881)

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.

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