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What Happens INSIDE a Nuclear Reactor Core? - Smarter Every Day 317 (Patreon)

Published:
2026-09-26 14:42:21
Imported:
2026-10

Content

In this video, we get to understand EXACTLY what's going on inside the reactor core. Bill Ball is a legend who was very patient with me and answered all of my questions. It was quite interesting to learn that there's a self-governor built into Boiling Water Reactors (BWR) in the form of bubbles changing the reactivity in real-time. I hope you enjoy this, the latest video in the Nuclear Power Deep dive series!

I'm very close to finishing my school work, and I'm looking forward to telling you all about that.

Thank you for supporting Smarter Every Day here on Patreon! I'll be around here for a couple of hours answering questions here on Patreon, so feel free to ask away!

Regards,

Destin

Files

What Happens in a Nuclear Reactor Core? - Smarter Every Day 317

You can try AnyDesk for free. It's good. https://anydesk.com/smarter http://www.patreon.com/smartereveryday Get Email Updates: https://www.smartereveryday.com/email Check out the 50x50 Science Across America! https://5050science.com/ 50x50: Science Across America is a national series uncovering exceptional science in all 50 states. It is a production of the Independent Media Initiative in collaboration with HHMI Tangled Bank Studios, Alfred P. Sloan Foundation, and the Winn Family Foundation. See all the states at https://5050science.com/ Sticker Team!: http://www.patreon.com/smartereveryday Click here if you're interested in subscribing: http://bit.ly/Subscribe2SED ⇊ Click below for more links! ⇊ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GET SMARTER SECTION Learn more about the the Browns Ferry Plant at the Tennessee Valley Authority: https://www.tva.com/energy/our-power-system/nuclear/browns-ferry-nuclear-plant https://en.wikipedia.org/wiki/Tennessee_Valley_Authority Here's a link to an article about my visit: https://www.tva.com/the-powerhouse/stories/inside-browns-ferry ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Tweet Ideas to me at: http://twitter.com/smartereveryday Smarter Every Day on Facebook https://www.facebook.com/SmarterEveryDay Smarter Every Day on Patreon http://www.patreon.com/smartereveryday Smarter Every Day On Instagram http://www.instagram.com/smartereveryday Smarter Every Day SubReddit http://www.reddit.com/r/smartereveryday Ambiance, audio and musicy things by: Gordon McGladdery https://www.ashellinthepit.com/ http://ashellinthepit.bandcamp.com/ If you feel like this video was worth your time and added value to your life, please SHARE THE VIDEO! If you REALLY liked it, feel free to pitch a few dollars Smarter Every Day by becoming a Patron. http://www.patreon.com/smartereveryday Warm Regards, Destin

Comments

Kyle Goddard

Kids are so excited! We’re watching this tonight! Thank you Destin!

Jordan

Hi Destin, hope you are well. Thank you for all you do for the scientific community; you have re-lit my passion for science and given me the power to start my master's (here in the UK) And I love my fast neutron (WEEEEEEEEEEEEEEE!!!!) so much it's currently on the back of my phone, and every time anybody asks me about it I say it's a fast neutron and scream weeeeeeeee I love Bill, and you can see how smart he is, and he is not obnoxious about it and is happy to pass his knolage onto everyone that will listen I'm loving this deep dive series, and when I got the notification earlier, I jumped right on it and dropped everything I was doing. Also wondering if we could get an update on your PhD As an idea for something in mechanical engineering, doing something with a telephone connection museum

Daniel Turner

All the best with wrapping up your PhD.

Zak

Are you going to make a video in the simulator or control room?

Brendan Upton

I can't wait to see it! Thanks for putting in so much work!

Paul Tomblin

If the steam goes directly from the reactor vessel to the turbine, does that mean the turbine parts become radioactive?

victoryt99

I haven't watched the video yet but based on my knowledge of nuclear reactors, water acts as a natural barrier for radiation so by the time the steam gets to the turbines the water has stopped the radiation.

smartereveryday

We talked about that a little bit during the tour. i can't remember if it's on the video. In the turbine room you'll notice the turbine itself is surrounded in lead blankets. That's shielding for this reason.

smartereveryday

i'm glad you like the fast neutron. It just helps me understand what's going on to conceptualize it that way. I'll be making a video about the PhD I think. It's taken so much time and effort I think it would be fun to summarize it all.

William Slack

If saying "Rad!" at the beginning wasn't purposeful, excellent accidental punditry in a video discussing radiation. :) It seems like this might have been filmed the day you toured the reactor - that's still one of my favorite videos you've ever made and seeing the reverence and seriousness of the team working there was inspiring. I hope we can figure out how to spend less building these reactors - they do a lot of good but its hard when there are such huge cost overruns like we have seen in Georgia.

Kevin Thomas

Thank you opening peoples eyes and minds.

Richard Rastetter

Destin, you don't post frequently, but when you do it always slaps. Truly S tier content that I regularly make my less YouTube prone family watch when we get into science arguments. I only have 2 people I support on patron and although you post 10% the other account (channel 5 live worldwide) I always love the level of education you provide.

William Slack

Not in the way you might think - the "radioactive" stuff is inside the pellets inside the cladding, so the water doesn't have any of that stuff unless there's corrosion. The main radioactivity in the water is from the fast neutrons hitting water molecules that knock out an oxygen proton, turning it radioactive nitrogen-16. That does release gamma rays when the reactor is gone, but it turns back into oxygen so fast that the turbine is safe to work in when the reactor is offline.

Kenny

Destin, I love these videos! I did my undergrad in nuclear engineering and now I'm a nuclear engineer for the Navy and getting to see you put out things on topics I've worked on is amazing. Keep up everything you are doing! Also, Bill is crazy smart and really knows what he is talking about!

smartereveryday

"Bill Ball is a Coner" is something that's written all over that plant. You'll get that joke.

funzel

It brings me great joy watching your videos Destin, and it has for years. Thank you.

smartereveryday

Thank you very much for the support! It means a ton. The dissertation is slowing me down a bit, but I think it will fun to show you what that's been all about.

smartereveryday

This wasn't on the exact same day. Yes Vogtle was quite the project!

Gareth

Love the new video Destin, it really moved me ;)

smartereveryday

I enjoy learning along with you! Thanks for supporting!

Jordan

idea do a main channel vid with an update and a 2nd channel vid with all the gritty detail

Adam Schindler

Of all of the things that make Destin great at this, the combination of intelligence, knowledge and humility is the most important. I still halfway believe that he knows full well what wet steam is, but feigned ignorance for the benefit of the viewer. But let's assume that he really didn't know: the humility to say "this is kind of in my area of expertise, but I don't know" is a skill that our societal values of "never admit ignorance, naivete, or that you care" actively discourages. "I don't know" is, in practice, indistinguishable from curiosity, and that 30 seconds may be the most broadly applicable part of a generally great video.

smartereveryday

Thanks for saying kind things. While it's true that yes, I sometimes ask a question that I might have a good suspicion that I know the answer to, I will not say "I don't know" if I actually know something. That would be a lie. When Bill described it I knew wet steam by a different name, "Two phase flow", but I had never come across wet vs dry steam like this. Interesting stuff! Again, thanks for the kind words, and thanks for your steadfast support.

Carl Wandering

Well done! I never quench my thirst for knowledge.

elle 11993

Yes another nuclear power video! Love your videos, so well explained and love learning about new things! You explain it so well! I always feel I leave a video learning new things and understand things I didnt know. Keep up the amazing videos Destin. Also all the best finishing your PhD cant wait to see what your dissertation is about.

Tw

I love nuclear plants! You take something that you can use for good and bad and both are extremes in my mind. I have a question does the temperature of stem affect pressure in a pwr. In the fire department we were taught water turns to steam and expands 1700 times ex 1 gallon equals 1700 gallons of steam.

J

Thank you for being "the asker of all questions!" It's really enjoyable to go on this journey of learning with you.

Rob Windsor

What happens inside a nuclear reactor core... Stays inside a nuclear reactor core. hopefully.

Adam Schindler

The explanation of neutron temperature was really good, but I don't think that most folks have a sense of the HUGE difference between a 1-3 MeV neutron fresh out of a fission event and a thermalized 100 keV neutron. There's a 3-4 order of magnitude delta between the fission and absorption cross sections of those two neutron temperatures, and it might be helpful to show folks a graph to draw attention to the dramatic effect of moderation.

Adam Schindler

Last comment: the criticality discussion might benefit from a small addendum on prompt vs delayed neutrons and prompt vs delayed criticality. Humans can control a delayed critical reactor; physics alone is is in control of a prompt critical reactor. I think that ultimately allows you to introduce the concept of "cents" which is a useful simplification for delayed critical reactors that would allow most viewers to think about the reactor in the same basic terminology as the operators.

Josiah Reagan

The 50x50??? sounds like a plug for a podcast 🤨

Mark

I would love to see you explain what caused Chernobyl and Fukushima, and what we are doing now to prevent accidents like those. I think it will bring more awareness to how safe reactors are as NIMBY is a big problem in building new reactors, and we now have a good understanding of how reactors function so we can actually see what went wrong and understand it

Peter Cunningham

Again - GREAT STUFF. And again ... If you ever intend visiting Australia (Sydney area) then let me know. I am on FB. Am also an engineer and could organise you to present at an Engineers Aust event should you so desire.

Erin

Destin may I humbly suggest a minor change to your neutron visualization: some kind of 3D-printed "speed lines" (like in a comic, trailing lines indicating fast motion) that you can clip on to the little blue circle while it is a Fast Neutron, then unclip them when it is slow and Thermalized

Brendan Upton

I just saw the video, and it is amazing. Thank you very much for being the "Asker of all questions" :-). In a society that places so much importance on "knowing", someone who says "Let's find out" is a true beacon. I do have one question for you though . . . by any chance, are the files for that 3d printed reactor available for sharing? I would LOVE to have the files to print a pellet, bundle, assembly, core, vessel, etc. Good luck on your PhD!

Dale E

I wish we had more enthusiasm for nuclear in the UK. Seems to be a lot of opposition to them though from locals when they try build one though. I find them fascinating. Dunno if it would be possible but it would be awesome to see something about the potential future of nuclear like SMRs at the end of the series. Although not sure if that's just hype at the moment. Also if the training centre is looking for any feedback, the model might be better in grey. It's quite difficult to see in black although maybe that's just because it was a video.

Myra Badger

Destin, please make a sticker of the Brown Nuclear Reactor core assembly mock up. That was AMAZING!

Nathan Bock

Destin, this was a fascinating video. I love the conversations about how the reactors are designed to be "intrinsically safe". I put that in quotes because that phrase can have special meanings, but it's such a feat of engineering. I am curious, from Bill's explanations, it sounded like the reactor controllers can essentially control where along the height of the fuel they can have the reaction occur. Is that something you spoke to Bill about? I was sitting in my chair wanting to raise my hand and ask that question! Thank you for your awesome content!

EB

I think there's still a question of where those fast neutrons go when the water/mediator isn't there to slow them down. Another felt demo could help with that Can't wait to see part 2

Taylor DeCastro

Destin, thank you for making these. Absolutely fascinating stuff, and I love that I’m not the only one that enjoys knowing how stuff works, but why it works the way it does. Also, my wife has the fast neutron sticker on her bike helmet. It makes her go faster.

smartereveryday

I love knowing she’s zipping around like a fast neutron.

Bill

I think one of the issues you were having with understanding water and steam bubbles in the core is that only a minor percentage of the water flow through the core is actually turned to steam (my 1979 memory cell thinks it is between 10 to 20%). The core, to several feet above the top of the bundles, is always mostly water. The fluid flow through the bundles is in the nucleate boiling regime (small bubbles in mostly water). The recirc pump with jet pump assist is circulating a massive flow of water through the core sweeping the bubbles up towards the steam separator. . Say the water/steam ratio is 90/10; 90 units of water plus 10 units of steam leave the core and enter the steam separator , 10 units of steam goes up through the dryer to the steam turbine, 90 units of water drops out of the steam separator into the annular space, 10 units of water is added by the feedwater system (condensed steam return), 33 units goes out to the recirc pump and back to the jet pump nozzle, the driven flow of 33 units drags the other 67 units through the venturi and drives flow into the bottom head under the core, the 100 units of water then flow with considerable velocity up through the core. Where 10 units of steam are produced. Then the cycle repeats. . The water density due to temperature is one factor of the negative reactivity coefficient. However, the controlling factor is the void fraction (i.e. the mass fraction in the core comprised of steam bubbles). Cold water thermalizes neutrons more, hot water thermalizes neutron less, steam thermalizes neutrons hardly at all. Thus the reactor at any particular power level; determined by control rod position and adjusted by recirc flow is self controlling by the negative reactivity coefficient. Raise the recirc flow a bit and drive the bubble boundary higher into the core and a slightly higher power level will result. . I was a GE BWR Field engineer in the late 70's and early 80's. This series is very interesting.

Bill

On a BWR, the steam turbine does become slightly radioactive over time. The source of this radioactivity is tiny metal particles from pump and valve wear that pass through the core and become activated. A steam turbine deck in a BWR plant is shielded and there is limited access while the plant is running. During maintenance standard contamination avoidance procedures are used.

Mack Cullison

Hi Destin, I’ve been watching your videos ever since you taught me how to skip rocks with a perfect 17 deg tilt. Anyhow, I am a nuclear engineer now and I help the neutronics team design BWR cores at Framatome. I could get you in touch with our marketing person at Framatome. But we actually manufacture the ATRIUM 11 assemblies here in Richland, Washington. Our whole building was pretty excited when you first did the BrownsFerry tour. There are a lot of special features inside the ATRIUM 11 fuel that help it run optimally, and I would love to teach you everything that I possibly know about nuclear science. I am very thankful you’re working on a BWR, I’ve been told by PWR our fuel is eldritch. We have axial enrichment distribution in the fuel rods, as well as many different fuel rods just in a single bundle. Anyhow, I spend 40 hours a week just licensing the fuel itself. I have a guy on the BFE team that would be very camera photogenic, and would love talking about all this with you. I only sometimes work on BFE fuel. Let me know your thoughts! Mackclark123@pm.me

John W

First off, I love the fast neutron. Weeeeeeeeeeee! That cracks me up every time. Your videos on nuclear power/energy are so fascinating. It cracks me up every time. Even though I probably only understand about a half to 2/3rds of it, I’m ok with that because you make it fun. You are a uniquely good person. Thank you.

Steve Jones

Hey Destin - Maybe I missed it if you announced your plans, but did you know Nuclear Science week is coming up soon? Our local nuclear plant (https://www.duke-energy.com/energy-education/energy-centers-and-programs/brunswick-ed-center) just re-opened its visitor center this week after a long time closed (hurricane damage!) and we went to it today and they told us about a big event they're holding here later this month: https://www.nuclearscienceweek.org/post/southeastern-north-carolina-to-host-annual-nuclear-science-celebration I am wondering if you have plans to join their forum of speakers, or if you may be going somewhere else? I'm hoping to go listen on that Friday since I live quite close.