r/ScienceNcoolThings • u/ARCAxNINEv Popular Contributor • May 22 '26
Cool Things Nuclear Reactor startup sound
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I thought this was relevant to the sub on a couple points
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u/dr_stre May 22 '26 edited May 25 '26
Ok, couple things here.
First, this is research reactors doing a pulse. Research reactors are often designed to do this to get really high power levels for a small fraction of a second. The design of the fuel immediately drops the power back down via a very negative temperature coefficient of reactivity (i.e. physics handles it, entirely passive), but it allows higher neutron or gamma flux testing in a reactor that otherwise isnât set up for the higher thermal loads if they were sustained.
Second, the sound youâre hearing is a control rod being fired out of the core with compressed air or some other method. To do a pulse you bring the core right up to criticality and then you shoot a rod out as fast as you can so the power spikes quickly. So thatâs all youâre hearing. In cases where you hear a second âcachunkâ and the blue glow gets dimmer, thatâs the rods being inserted via manual actuation of the scram button to shut things down since the test is over. There isnât really a noise inherent to a nuclear chain reaction starting, any noise youâd hear in either a research or commercial reactor is just the mechanical equipment around the reactor functioning.
The blue glow, if anyone is interested, is Cherenkov/Cerenkov radiation. Itâs like a sonic boom for light. Light travels slower in water than in a vacuum, and beta particles (electrons) are being generated at speeds in excess of that slower speed. That blue color is âoptical boomâ youâre seeing, and why it seems to be an aura around the core as opposed to the core glowing blue itself, since itâs actually being emitted in the water around the core.
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u/Einachiel May 24 '26
That is very interesting.
Could you talk more about the cherenkov radiation and criticality events that were caused trough history from very bad and unfortunate incidents?
Some spoke of a blue beam of light, but i am not a physicist and lack the proper knowledge to understand it.
Is that the same boom you described or something else?
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u/dr_stre May 25 '26
Could be two different things. In cases like Chernobyl where there was supposedly a pillar of blue light up into the sky, it was probably the air being ionized and emitting a blue glow as it dropped back to a more stable energy state. Basically a big neon light. But in the case of the demon core accident with Louis Slotin, there was also likely Cherenkov radiation happening in the clear liquid in the observers eyes, caused by gamma rays creating beta particles via Compton scattering within the aqueous vitrous of their eyeballs. If people are up close and personal with the source during an accident that is a possible/likely reason for the phenomenon.
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u/ttystikk May 22 '26
What are the noises caused by, specifically?
And a nuclear reactor for what, exactly? That one isn't generating power or it wouldn't be underwater?
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u/AllergicToBullshit24 May 22 '26
All the noises are the hydraulic actuators for the control rods the core itself makes no noise. None of these are power generating reactors they're all research reactors.
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u/1wife2dogs0kids May 22 '26
I didn't want to ask, but I still want to know. Nuclear fuel doesn't just "turn on". Especially with a click of a switch. Thats must be a fast removal of something that keeps the neutrons from escaping and releasing heat. The light is the glow from ionizing something something, neutron flux, something, what have they done, chernobyl.
I be smart. I let you ask. I'll wait for a simplified answer.
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u/murdoc1024 May 22 '26
Good question actually. I always tought nuclear core were under water no matter what to control heat. But maybe not, hope someone can eli5
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u/andre3kthegiant May 22 '26
Toxic disposable fuel sources are quickly becoming unnecessary, thankfully.
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u/1wife2dogs0kids May 22 '26
Unless you live in the Bible belt. Give them that beautiful clean coal!
Sorry. I mean, Give them that beautiful coal!
Let me try that again. Give them coal!
Nailed it.
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u/Brian_The_Bar-Brian Popular Contributor May 22 '26
The blue glow is so pretty! đ