Great simplified explanation. We have a lot of Danish politicians, that should be sat down and watch this channel to at least get the basics of nuclear power, before they exclude it.
We have excellent geography for renewable energy production in DK. MW production from our off shore wind farms is much cheaper than nuclear measured in strike prices.
@@thoso1973 We do but we also need a base power. As it is now we get that from gas and coal. 19+6% on aveage. So this a 25% base power to ensure that we are not totally dependent on the weather. That is the part I wish be get from nuclear.
@@steffenjespersen247 We have an integrated electricity grid with Norway, Sweden and Germany for that purpose: to sell our surplus electricity when we have windy weather and to buy electricity when we have low wind generation. To add, we are researching how to efficiently storage electricity generated from wind turbines, the surplus electricity that doesn't need to be transmitted into the grid as it is produced. If we wanted to build nuclear plants here, we should have done so in the 70s and 80s. It's too expensive now considering the other alternatives open to us.
@@thoso1973 The problem is When we have a surplus of Wind power and that happens more an more often all the countries around us have as well. So we end up giving the electricity to them for a tiny price and sometimes even pay for them to take it. But yes storing surplus wind energy would let us increase wind energy even more, but as it is right now we have no viable way. Personally I would think a system where owners could connect their electric cars to the grid and set them to only fully charge on surplus energy (but then pay no tax) would be a great. Most people could easily limit their electric car to half in the work week.
The trick is to add just as much knowledge continue I understand the basics. Then you add in stuff like void coefficients, delayed neutrons, moderators, wigner disease, Xenon poisoning. And that makes you watch other videos to really gain a finer understanding of something
Brilliant presenter and gifted teacher. These lucky students are in the presence of a professor they will likely never have anyone get close to in terms of his ability to explain complex theorems while remaining engaging.
The usual way to do this is to simply flip the video with editing software... So you should probably applaud the editor for the mouse click. While I'm sure a few people might be particularly good at writing backwards it's a fairly unusual skill. Also notice that the presenter is writing with his left hand which makes it even more likely that he is actually a right handed person who is flipped as 90% of people are right handed.
What a BRILLIANT presentation. I hope his F2F students know how lucky they are! One point FWIW: the UK also had a graphite moderated reactor design; several of which are still generating electricity today. Like the RBMK, the AGR (Advanced Gas-cooled Reactor) is built around a massive graphite core but, unlike the Russian design, the primary circuit coolant is HP carbon dioxide. The concept offered higher thermal efficiency than PWRs of that era and a key design requirement was that all secondary steam & turbine systems downstream of the reactor's primary circuit would be identical to those used in the UK's coal-fired power stations (a requirement American PWRs could not meet - almost certainly a case of political priorities hiding behind engineering, & economics).
It feels irresponsible to not mention decay heat after the chain reaction has been stopped. Even if there is no chain reaction, you still have to deal with nuclear decay producing heat. Nuclear decay happens spontaneously when an unstable element sheds some energy and becomes a more stable element. While the chain reaction can be stopped, nuclear decay can not. For example, at fukushima daiichi the chain reaction was stopped super early, but when the backup generators were flooded and there no longer was any cooling to the core, the decay heat melted the fuel. The cladding for the fuel pellets released hydrogen gas, and suddenly, there was a Hindenburg going on (in the containment vessel, i think)
The multiple hydrogen explosions happened in the containment buildings, not in the vessel. I think they had to vent the pressure in the reactor vessels into the containment building to keep the vessels from failing. The problem is, there is oxygen in the ambient air of the containment building and any sort of spark can set off the hydrogen / air mixture since hydrogen gas has such a wide range of ignitable fuel to air ratios. More so than any fossil fuel. These explosions caused the reactor vessels to fail anyway, but venting the gas buildup in them bought time and made a bad situation less worse. Some reports said the TEPCO employees at Fukushima were seriously considering abandoning the plant as to not risk personal radiation exposure, leaving it to smolder and release radiation for who knows how long.
@@saultcrystals Another very important fact to the Fukushima disaster was the fact their level scale for the water level in the reactor vessel boiled away, giving false readings in the control room. In BWR's (Boiling Water Reactors), measuring the true water level is an extremely difficult task and is reasonably achieved by measuring pressure differentials at various heights and compare that to a precalibrated level (which is essentially a tube with a fixed water level). If this boils away, due for example if a tidal wave knocks out emergency cooling systems, the control room will get false readings. Edit: Meaning they will make incorrect decisions. Something else worth mentioning, the release of hydrogen gas mentioned is caused by oxidization of the Zirconium alloy that makes up the cladding when it passes above ~1200 deg C and comes into contact with water (last part is very important). It's not caused by the overheating in itself. Most BWR plants in the world have dedicated systems to keep the containment building below critical pressure and vent unwanted gases, basically enormous rupture discs that lead to even bigger gas filters. When these were developed in the early 90s the Japanese chose to not construct such systems. Why? I'm guessing an equal part economical and Japanese workmanship pride culture. As someone who studies nuclear engineering I might be biased, but the Fukushima disaster had far more variables than simply a massive tidal wave.
The problem with fukushima reactor was...bad design. And not efficient. The BIGGEST problem there is you CAN'T harvest the fission products so they continue to breaking the device. The ceramic material is their coffin-it produce enormous temperature difference&stress so ceramic just breaks. Failed technology from 50's. Already OUTDATED in 80's... If TEPCO bought let's say CANDU like Koreans did...there would be not problems. "Due to the arrangement used in CANDU, only the single tube being refuelled needs to be depressurized. This allows the CANDU system to be continually refuelled without shutting down, another major design goal"
@trublu97, extreme cost. United Nuclear will sell you a kilogram of high purity heavy water for $725. A CANDU reactor holds about 250,000 liters of heavy water, which is about 11% heavier than light water of the same volume. Or about 280,000 kilograms. Presumably you get a discount for such a large order, but if not the price comes to $200-million. On the plus side heavy water is a much better moderator than light water. Light water absorbs a few neutrons, heavy water much less so. Fuel enrichment is not necessary with CANDU. 0.7% U-235 works. In fact the reactor works down to about 0.5% U-235. If a country wants to pursue a nuclear weapons program they'll need uranium enrichment facilities anyway, so CANDU is less attractive.
you can see him writing looking at us, he writes in such way we can read the text, he definetly writes in reverse. also i got 6 at the test, got scammed by the teacher so i picked 7 as a grade i wish for so the max grade was 7... i learned the subject so well i could get a 9-10 if they gave me the max grade 10 test... @@mikek.9980
I think it's due to the camera settings. Done intentionally (in reverse) so we can read it. I think he is right-handed and is writing normally - but it's flipped by the camera to the mirror image. So instead of looking backwards and showing him writing with his right hand - it looks 'normal' but it appears he's writing with his left.
@@bc-guy852 Could be, I'm having a hard time imagining how that would work. I had a client once who was in the Navy and his job was to write backwards on a clear board (in the bridge of a ship) for the officers on the other side of the board to be able to read and I think I assumed he was doing something similar. I enjoy the videos either way.
@@shawnaramaable Oh there is that as well! I remember a weather forecaster who did the weather report behind a glass and did the report writing with BOTH hands - from outside to inside - and ended the forceast with a word with 'OO' in it (like COOL) and then he would put his face behind it and appear to be behind glasses. Written in reverse and with both hands - at the same time. Impressive! But I think this - is the use of modern technology and different ways digital camera's process images.
Is this true for Pressurized Water Reactors? Because in that case you have three different water circuits, the primary circuit where the water is the moderator and transports the heat to the secondary circuit; the secondary circuit where water is transformed into steam to drive the turbine and then condensed again via the third circuit which is simply the cooling circuit, i.e. in the water towers... In that case, wouldn't the primary circuit keep the nuclear fission operation on-going since water does not evaporate due to the high pressure?
A radioactive "start up" source that generates neutrons is used to start the fission chain reaction. After the first refueling cycle, the fission products in the fuel supply all the neutrons the reactor needs. Most fuel cycles, a third of the fuel assemblies are replaced with new ones. The rest of the fuel is shuffled around the core for even burn up.
the reaction stops but the fuel is still there releasing radiation and heat.. So instead of explosions you have a meltdown. time frame changes from seconds/minutes to hours. Its an improvement but still sux
right, but I'd think because the chain reaction isn't happening anymore significantly less atoms are going to release energy because if the neutrons are too fast to cause other atoms to fission, then the only fissioning happening is the slow natural rate of the half-lives
*Could you use a magnetic field as a moderator? And if you can and when you shut off the field would the fission products dissipate safely just flying off or would a concentrated wave of fission products still fly off but be in a concentrated state OR would they say state concentrated in the core of the reactor lingering?* P.S. You never said how much water is needed to be used as the moderator.
The fuel still creates heat through radiochemical decay even when moderated, if your not removing the heat by passing water over the fuel it the temperature will continue to ruse until a meltdown occurs.
There's a great 3-part video on this channel about Three Mile Island. I think it's titled "How TMI Happened". Basically, human fraud and stupidity. It was an older generation of reactor, too, that could NOT be left uncovered.
Why the fuck did they build graphite moderated RMBK reactors then? I am sure this science was known to the Soviets in the 60's and 70's. Was it just as stated in the series Chernobyl that it was much cheaper to build graphite moderated reactors?
It doesn't matter if you're teaching nuclear physics or 18th century French romance poetry: you define your terms, explain the fundamentals, give examples. Every teacher can learn from this exceptional lecturer.
Also some old french design did the same. However as the gas does not absorb neutrons they have not a positive void coefficient like RBMK so they are not really more dangerous than other water moderated design.
Theoretically, fission can occur anywhere at any time. If there is an object that can’t absorb certain atoms in certain ways, then fusion can theoretically occur At that point this only shows weapons grade fission and I believe there is a difference.
The faster you watch the video, the less likely you are going to learn anything. Didn't you hear the professor, "the slower the neutron, the more likely it is to cause a fission." So, slow the video down to 0.25% speed, and just let the information trickle on in slowly.
Is it possible to make a more efficient fission weapon that uses less concentrated fuel, but replaces some of the fuel with a moderator? Like 70% fuel, 30% moderator. Less energy dense, but seems like anything you can do to slow down the neutrons increases the resultant fission likelihood by orders of magnitude
Slowing down the neutrons slows down the speed at which the chain reaction proceeds, giving time for the bomb material to be dispersed by the heat of the developing explosion. So, very little of the uranium gets fissioned. Because of the short time scales involved in nuclear explosions, they require fast neutrons.
Sooo aren't navy reactors at 90% enriched fuel....left out core geometry. High fuel density doesn't equal a bomb. High fuel density plus proper geometry equals a bomb. Also the Chernobyl happened due to crappy design leading to positive void coefficient in combination with the graphite tipped control rods. Graphite is used by several different reactor designs and are perfectly safe. And biggest thing left out is decay heat after a reactor is scrammed.
I am new to the nuclear industry. I am incredibly appreciative of this professor. His ability to teach complex subjects in a fun and insightful way is amazing! Thank you!
Professor i still have a hard time understanding how the reaction would stop once the moderator is evaporated, shouldnt the reaction keep going until there is s nice Elefant Foot at the bottom iof thr reactor? How does the reactiion stop and where does the energy go??
Without a moderator the neutrons being expelled are too fast, the chance of neutron absorption and fission drops and you stop producing new neutrons. The neutrons you have slowly escape the reactor.
Can anyone explain why a submarine reactor can operate with weapons-grade uranium without going critical? Those fuel rods are enriched to 90% or higher.
You need to get to a ratio of 1 fission causing 1 fission. If your reactor is small a lot of the neutrons are gonna leave the reactor. Thus you need more uranium 235 to be sure to be able to sustain the reaction. If i have a enormeus lump of uranium i can even sustain chain reaction in it without enriching it. Candu's work on this process. However if i want to make something small i need to have a very high enrichment to be able to sustain the chain reaction even when losing a lot of neutrons to the outside world. Thus i need highly enriched fuel. Control rods then help keep the reaction stable. Critical means the reaction is stable 1 fission causes 1 fission on average. sub critical means the reaction is going down 1 fission -> >1 fission's. Nuclear weapons don't go critical. They go super critical.
@@pokekick4185 Makes sense, but then how does a sub reactor sustain that near the end of its ~25-year fuel cycle, when much of its fuel has been consumed? Is it simply a matter of having more control rods in place to keep the stack from going super critical? Could a sub reactor theoretically go super critical if all control rods were withdrawn? In a commercial reactor the reaction stops without the moderator and cannot reach super critical under any circumstances. >20% U-235 is considered weapons grade.
You start with more control rods in the core and slowly retract them over the course of the reactors lifetime. Highly enriched fuel can also wait out certain neutron poisons till they decay on their own. The reactor would also not like explode but instead melt down (read the fuel/core of the reactor become a 1000 degree liquid and start flowing down.) Getting uranium to explode takes quite a lot of effort in compressing and timing it. A sub reactor is also much smaller reactor surrounded by water that can take the heat a lot better than air. Making problems like cooling a lot easier to solve.
Something smell. If uranium go fission after absorbing neutron...from WHERE the neutron at first? 8:30 - this is catastrophy scenario for all LWRs...when water disappear, core caugh meltdown. That is WHY we should abandon that idea...
Okay 1 very rare way of nuclear decay is spontaneous fission. Meaning a very heavy atom decides to break in 2 without outside influence. This happens in less than 1 out of a million normal decays for a few rare isotopes among these are U235, U238, Pu 239 and Pu240. This means the first neutrons can come from this process. Because there are no neutron poisons in the fuel yet this means the chain reaction can speed up every fission producing more neutrons than it took to get it. Slowly the fission products accumulate and the reaction becomes stable between absorbing neutrons and causing fissions until a ratio of 1 fission producing 1 fission. ( control rods smooth this process out.)
I love how I didn’t apply myself in college at all and now I watch physics videos with my free time.
Same
I’m in 8th I just love science lol
They never taught us anything this interesting in school
@@JusTryNcthat’s because they had to teach down to the slowest kids in the class…
Great simplified explanation.
We have a lot of Danish politicians, that should be sat down and watch this channel to at least get the basics of nuclear power, before they exclude it.
We have excellent geography for renewable energy production in DK. MW production from our off shore wind farms is much cheaper than nuclear measured in strike prices.
@@thoso1973 We do but we also need a base power.
As it is now we get that from gas and coal.
19+6% on aveage.
So this a 25% base power to ensure that we are not totally dependent on the weather.
That is the part I wish be get from nuclear.
@@steffenjespersen247 We have an integrated electricity grid with Norway, Sweden and Germany for that purpose: to sell our surplus electricity when we have windy weather and to buy electricity when we have low wind generation. To add, we are researching how to efficiently storage electricity generated from wind turbines, the surplus electricity that doesn't need to be transmitted into the grid as it is produced. If we wanted to build nuclear plants here, we should have done so in the 70s and 80s. It's too expensive now considering the other alternatives open to us.
@@thoso1973 The problem is When we have a surplus of Wind power and that happens more an more often all the countries around us have as well.
So we end up giving the electricity to them for a tiny price and sometimes even pay for them to take it.
But yes storing surplus wind energy would let us increase wind energy even more, but as it is right now we have no viable way.
Personally I would think a system where owners could connect their electric cars to the grid and set them to only fully charge on surplus energy (but then pay no tax) would be a great.
Most people could easily limit their electric car to half in the work week.
Beautifully said!
You know someone is incredibly knowledgeable when they can explain such abstract concepts so easily! Thank you prof!
The trick is to add just as much knowledge continue I understand the basics. Then you add in stuff like void coefficients, delayed neutrons, moderators, wigner disease, Xenon poisoning. And that makes you watch other videos to really gain a finer understanding of something
Your the best, Prof, the way you teach me nuclear physics. David makes physics so easy and simple to understand.
Brilliant presenter and gifted teacher. These lucky students are in the presence of a professor they will likely never have anyone get close to in terms of his ability to explain complex theorems while remaining engaging.
I applaud his ability to write words backwards for us to comprehend properly
The usual way to do this is to simply flip the video with editing software... So you should probably applaud the editor for the mouse click. While I'm sure a few people might be particularly good at writing backwards it's a fairly unusual skill. Also notice that the presenter is writing with his left hand which makes it even more likely that he is actually a right handed person who is flipped as 90% of people are right handed.
What a BRILLIANT presentation. I hope his F2F students know how lucky they are!
One point FWIW: the UK also had a graphite moderated reactor design; several of which are still generating electricity today. Like the RBMK, the AGR (Advanced Gas-cooled Reactor) is built around a massive graphite core but, unlike the Russian design, the primary circuit coolant is HP carbon dioxide. The concept offered higher thermal efficiency than PWRs of that era and a key design requirement was that all secondary steam & turbine systems downstream of the reactor's primary circuit would be identical to those used in the UK's coal-fired power stations (a requirement American PWRs could not meet - almost certainly a case of political priorities hiding behind engineering, & economics).
Thanks Professor, the best and easy to understand explanation about fission
I dont know how I ended up here but I am now 0.098% smarter. Thanks guy in a brown suit!
Great video. Is the professor basically writing “backwards” from his perspective, because the screen seems to be between him and the camera?
such a simple process and yet, how much expense of time and genius and thought and trial and error it took to set it all up!
This is the best video I ever saw about nuclear fusion. thanks so much!
Fission lol
It feels irresponsible to not mention decay heat after the chain reaction has been stopped.
Even if there is no chain reaction, you still have to deal with nuclear decay producing heat. Nuclear decay happens spontaneously when an unstable element sheds some energy and becomes a more stable element. While the chain reaction can be stopped, nuclear decay can not. For example, at fukushima daiichi the chain reaction was stopped super early, but when the backup generators were flooded and there no longer was any cooling to the core, the decay heat melted the fuel. The cladding for the fuel pellets released hydrogen gas, and suddenly, there was a Hindenburg going on (in the containment vessel, i think)
The multiple hydrogen explosions happened in the containment buildings, not in the vessel. I think they had to vent the pressure in the reactor vessels into the containment building to keep the vessels from failing. The problem is, there is oxygen in the ambient air of the containment building and any sort of spark can set off the hydrogen / air mixture since hydrogen gas has such a wide range of ignitable fuel to air ratios. More so than any fossil fuel. These explosions caused the reactor vessels to fail anyway, but venting the gas buildup in them bought time and made a bad situation less worse. Some reports said the TEPCO employees at Fukushima were seriously considering abandoning the plant as to not risk personal radiation exposure, leaving it to smolder and release radiation for who knows how long.
@@saultcrystals Another very important fact to the Fukushima disaster was the fact their level scale for the water level in the reactor vessel boiled away, giving false readings in the control room. In BWR's (Boiling Water Reactors), measuring the true water level is an extremely difficult task and is reasonably achieved by measuring pressure differentials at various heights and compare that to a precalibrated level (which is essentially a tube with a fixed water level). If this boils away, due for example if a tidal wave knocks out emergency cooling systems, the control room will get false readings. Edit: Meaning they will make incorrect decisions.
Something else worth mentioning, the release of hydrogen gas mentioned is caused by oxidization of the Zirconium alloy that makes up the cladding when it passes above ~1200 deg C and comes into contact with water (last part is very important). It's not caused by the overheating in itself.
Most BWR plants in the world have dedicated systems to keep the containment building below critical pressure and vent unwanted gases, basically enormous rupture discs that lead to even bigger gas filters. When these were developed in the early 90s the Japanese chose to not construct such systems. Why? I'm guessing an equal part economical and Japanese workmanship pride culture.
As someone who studies nuclear engineering I might be biased, but the Fukushima disaster had far more variables than simply a massive tidal wave.
The problem with fukushima reactor was...bad design. And not efficient.
The BIGGEST problem there is you CAN'T harvest the fission products so they continue to breaking the device. The ceramic material is their coffin-it produce enormous temperature difference&stress so ceramic just breaks.
Failed technology from 50's. Already OUTDATED in 80's...
If TEPCO bought let's say CANDU like Koreans did...there would be not problems.
"Due to the arrangement used in CANDU, only the single tube being refuelled needs to be depressurized. This allows the CANDU system to be continually refuelled without shutting down, another major design goal"
@trublu97
Let's see:
ruclips.net/video/vggzl9OngaM/видео.html
*Canadian Nuclear Safety Commission - CNSC* see no problems.
@trublu97, extreme cost. United Nuclear will sell you a kilogram of high purity heavy water for $725. A CANDU reactor holds about 250,000 liters of heavy water, which is about 11% heavier than light water of the same volume. Or about 280,000 kilograms. Presumably you get a discount for such a large order, but if not the price comes to $200-million.
On the plus side heavy water is a much better moderator than light water. Light water absorbs a few neutrons, heavy water much less so. Fuel enrichment is not necessary with CANDU. 0.7% U-235 works. In fact the reactor works down to about 0.5% U-235. If a country wants to pursue a nuclear weapons program they'll need uranium enrichment facilities anyway, so CANDU is less attractive.
Naturally born brilliant
this guy can write in reverse, GREAT!
also thanks for teaching me what to say in physics exam
No, he doesn't!
you can see him writing looking at us, he writes in such way we can read the text, he definetly writes in reverse.
also i got 6 at the test, got scammed by the teacher so i picked 7 as a grade i wish for so the max grade was 7... i learned the subject so well i could get a 9-10 if they gave me the max grade 10 test... @@mikek.9980
Your backwards handwriting is better than my handwriting will ever be.
I think it's due to the camera settings. Done intentionally (in reverse) so we can read it. I think he is right-handed and is writing normally - but it's flipped by the camera to the mirror image. So instead of looking backwards and showing him writing with his right hand - it looks 'normal' but it appears he's writing with his left.
@@bc-guy852 Could be, I'm having a hard time imagining how that would work. I had a client once who was in the Navy and his job was to write backwards on a clear board (in the bridge of a ship) for the officers on the other side of the board to be able to read and I think I assumed he was doing something similar. I enjoy the videos either way.
@@shawnaramaable Oh there is that as well! I remember a weather forecaster who did the weather report behind a glass and did the report writing with BOTH hands - from outside to inside - and ended the forceast with a word with 'OO' in it (like COOL) and then he would put his face behind it and appear to be behind glasses. Written in reverse and with both hands - at the same time. Impressive!
But I think this - is the use of modern technology and different ways digital camera's process images.
But those rods still generate decay heat that required a functional coolant system even if all fission activity has been shut down.
The newer Plants cool passively by air convection.
Astute observation. He addresses this in other videos
If all prof were like this I wouldn’t hate college
Wish i had a profesor like this in Croatia.
Prof do you have a video explaining fast neutron reactors or breeder reactors? Curious to know how one can maintain reaction with fast neutrons.
Is this true for Pressurized Water Reactors? Because in that case you have three different water circuits, the primary circuit where the water is the moderator and transports the heat to the secondary circuit; the secondary circuit where water is transformed into steam to drive the turbine and then condensed again via the third circuit which is simply the cooling circuit, i.e. in the water towers... In that case, wouldn't the primary circuit keep the nuclear fission operation on-going since water does not evaporate due to the high pressure?
Holy shit that made so much sense
What causes the nuclear reation to start in a nuclear reactor? Where does the first neutron come from?
A radioactive "start up" source that generates neutrons is used to start the fission chain reaction. After the first refueling cycle, the fission products in the fuel supply all the neutrons the reactor needs. Most fuel cycles, a third of the fuel assemblies are replaced with new ones. The rest of the fuel is shuffled around the core for even burn up.
How does he write backwards so well?
Reversed. Check, ring and clock in the right hand in the video.
Good explanation. I still do not understand the role of U238 in the nuclear reactor. Is there another video that explains it?
How come Russia used fast reactors in some of their early nuclear sub designs?
love these videos 👍👍
This stuff should be teached in school. When people understand something it isn't evil anymore.
“Teached”
Discernment
the reaction stops but the fuel is still there releasing radiation and heat.. So instead of explosions you have a meltdown. time frame changes from seconds/minutes to hours. Its an improvement but still sux
right, but I'd think because the chain reaction isn't happening anymore significantly less atoms are going to release energy because if the neutrons are too fast to cause other atoms to fission, then the only fissioning happening is the slow natural rate of the half-lives
This guy gives me the motivation to stay in college
Why no videos on carbon energy
Never knew nuclear reactors used turbans
*Could you use a magnetic field as a moderator? And if you can and when you shut off the field would the fission products dissipate safely just flying off or would a concentrated wave of fission products still fly off but be in a concentrated state OR would they say state concentrated in the core of the reactor lingering?*
P.S. You never said how much water is needed to be used as the moderator.
Can u give me your social media Instagram 🆔 or Facebook 🆔 . I want to discuss a few points on this topic . Plz
3:00
Supposing "do or die" means it has to be Fission asap isn't enough of a reason. Not a pleasant thought.
Why is Energy (eV) Referred to as "Speed"
I thort eV was energy not Speed ¿¿¿¿
Kinetic energy
If water is the moderator how did 3 mile island melt down
The fuel still creates heat through radiochemical decay even when moderated, if your not removing the heat by passing water over the fuel it the temperature will continue to ruse until a meltdown occurs.
Thank for the clarification
There's a great 3-part video on this channel about Three Mile Island. I think it's titled "How TMI Happened".
Basically, human fraud and stupidity. It was an older generation of reactor, too, that could NOT be left uncovered.
Atomic energy production.
Why the fuck did they build graphite moderated RMBK reactors then? I am sure this science was known to the Soviets in the 60's and 70's. Was it just as stated in the series Chernobyl that it was much cheaper to build graphite moderated reactors?
Chernobyl can't happen, he says. But what happened at Three Mile island??
Doesn't mention that plutonium easily fissions from fast neutrons
That's because he's talking about U235. He's not talking about plutonium.
Nuclear energy.
Now I know how Nuclear Fission works, I don't need you,
So moderator = gas, run out of gas fire stops
It doesn't matter if you're teaching nuclear physics or 18th century French romance poetry: you define your terms, explain the fundamentals, give examples. Every teacher can learn from this exceptional lecturer.
Ratio factor.
British reactors are graphite moderated and gas cooled...
Also some old french design did the same. However as the gas does not absorb neutrons they have not a positive void coefficient like RBMK so they are not really more dangerous than other water moderated design.
He is an awesome teacher. I totally understand everything he is teaching. I subscribed.
Actually R B M K - Reaktor Bolshoy Moshchnosti Kanalnyy - is the correct designation for the reactor types found at Chernobyl. Not R M B K.
Thank you, this is informative
The absolute best explanation of nuclear fission. Thank you
Sounds like a giant radioactive steam bomb, but at least it won't go nuclear.
Theoretically, fission can occur anywhere at any time. If there is an object that can’t absorb certain atoms in certain ways, then fusion can theoretically occur At that point this only shows weapons grade fission and I believe there is a difference.
B Reactor? N Reactor?
You’re a wonderful teacher! I would have loved to attend your class.
I watch these on 2x speed and with loud headphones to learn as fast as possable
The faster you watch the video, the less likely you are going to learn anything. Didn't you hear the professor, "the slower the neutron, the more likely it is to cause a fission." So, slow the video down to 0.25% speed, and just let the information trickle on in slowly.
You’re explaining very witty. Have you ever considered a position in advanced education? 😂
Where did the neutron that caused the initial fission reaction come from?
Great explanation but where was the “and that’s all you need to know about...”
Is it possible to make a more efficient fission weapon that uses less concentrated fuel, but replaces some of the fuel with a moderator? Like 70% fuel, 30% moderator. Less energy dense, but seems like anything you can do to slow down the neutrons increases the resultant fission likelihood by orders of magnitude
Slowing down the neutrons slows down the speed at which the chain reaction proceeds, giving time for the bomb material to be dispersed by the heat of the developing explosion. So, very little of the uranium gets fissioned. Because of the short time scales involved in nuclear explosions, they require fast neutrons.
@@jeromemalenfant6622 Can u give me your social media Instagram 🆔 or Facebook 🆔 . I want to discuss a few points on this topic . Plz
Mass energy conversion factor.
Watching #1 in the new play lists.
Sooo aren't navy reactors at 90% enriched fuel....left out core geometry. High fuel density doesn't equal a bomb. High fuel density plus proper geometry equals a bomb.
Also the Chernobyl happened due to crappy design leading to positive void coefficient in combination with the graphite tipped control rods. Graphite is used by several different reactor designs and are perfectly safe.
And biggest thing left out is decay heat after a reactor is scrammed.
US Navy (slide rule) Nuke then civilian plants enjoying your videos
This belongs in more classrooms around the world.
I am new to the nuclear industry. I am incredibly appreciative of this professor. His ability to teach complex subjects in a fun and insightful way is amazing! Thank you!
I'm just about to go into my nuclear engineering degree, what's the industry been like for you so far?
Professor i still have a hard time understanding how the reaction would stop once the moderator is evaporated, shouldnt the reaction keep going until there is s nice Elefant Foot at the bottom iof thr reactor?
How does the reactiion stop and where does the energy go??
Without a moderator the neutrons being expelled are too fast, the chance of neutron absorption and fission drops and you stop producing new neutrons.
The neutrons you have slowly escape the reactor.
Can anyone explain why a submarine reactor can operate with weapons-grade uranium without going critical? Those fuel rods are enriched to 90% or higher.
You need to get to a ratio of 1 fission causing 1 fission. If your reactor is small a lot of the neutrons are gonna leave the reactor. Thus you need more uranium 235 to be sure to be able to sustain the reaction. If i have a enormeus lump of uranium i can even sustain chain reaction in it without enriching it. Candu's work on this process. However if i want to make something small i need to have a very high enrichment to be able to sustain the chain reaction even when losing a lot of neutrons to the outside world. Thus i need highly enriched fuel. Control rods then help keep the reaction stable.
Critical means the reaction is stable 1 fission causes 1 fission on average. sub critical means the reaction is going down 1 fission -> >1 fission's. Nuclear weapons don't go critical. They go super critical.
@@pokekick4185 Makes sense, but then how does a sub reactor sustain that near the end of its ~25-year fuel cycle, when much of its fuel has been consumed? Is it simply a matter of having more control rods in place to keep the stack from going super critical? Could a sub reactor theoretically go super critical if all control rods were withdrawn? In a commercial reactor the reaction stops without the moderator and cannot reach super critical under any circumstances. >20% U-235 is considered weapons grade.
You start with more control rods in the core and slowly retract them over the course of the reactors lifetime. Highly enriched fuel can also wait out certain neutron poisons till they decay on their own.
The reactor would also not like explode but instead melt down (read the fuel/core of the reactor become a 1000 degree liquid and start flowing down.) Getting uranium to explode takes quite a lot of effort in compressing and timing it. A sub reactor is also much smaller reactor surrounded by water that can take the heat a lot better than air. Making problems like cooling a lot easier to solve.
Something smell.
If uranium go fission after absorbing neutron...from WHERE the neutron at first?
8:30 - this is catastrophy scenario for all LWRs...when water disappear, core caugh meltdown. That is WHY we should abandon that idea...
Okay 1 very rare way of nuclear decay is spontaneous fission. Meaning a very heavy atom decides to break in 2 without outside influence. This happens in less than 1 out of a million normal decays for a few rare isotopes among these are U235, U238, Pu 239 and Pu240. This means the first neutrons can come from this process. Because there are no neutron poisons in the fuel yet this means the chain reaction can speed up every fission producing more neutrons than it took to get it. Slowly the fission products accumulate and the reaction becomes stable between absorbing neutrons and causing fissions until a ratio of 1 fission producing 1 fission. ( control rods smooth this process out.)