Why Is It So Hard to Stop Meltdowns?

let's talk about meltdowns nuclear power has emerged as one of the most promising forms of energy as the world moves away from fossil fuels and towards cleaner Greener forms of energy the Japanese government now says two reactors are in partial meltdown and four more are are at risk there has been a nuclear accident in the Soviet Union and the Soviets have admitted that it happened the Soviet version is [Music] this but even mentioning nuclear energy immediately brings up ideas of disasters toxic radioactive wastelands and worst of all meltdowns despite reassurances from the nuclear industry we still seem to have these accidents every few decades with the most recent one occurring in Fukushima in 2011 so what's going on no matter how careful we are are meltdowns just an inevitable part of using nuclear energy and what is a meltdown exactly anyway and are there things that we can do to actually design and prevent meltdowns from occurring at all as usual it can be complicated but understanding the dangers of some of the most complex machines that we've ever built is the biggest step we can take towards making the right choice to understand and meltdowns we first need to know what causes them so let's take a look at what's happening at the heart of a nuclear power plant the Reactor Core deep inside that's where all this energy comes from fion the process of splitting atoms in a chain reaction in most reactor cores there are thousands of long metal tubes packed with fuel usually uranium when these uranium atoms are struck by a neutron they split apart and release an enormous amount of energy and additional neutrons these neutrons then go on to collide with other uranium atoms that split apart and release more neutrons and the Chain Reaction continues this cycle repeats throughout the Reactor Core over and over trillions of times per second to produce more and more heat and normally this is a kind of happy equilibrium for the plant but to maintain this balance we have to do two things control the rate of the reaction and remove the heat we control the rate of the reaction by either increasing or decreasing the number of neutrons that are available to cause atoms to split apart by inserting the control rods we absorb a lot of those extra neutrons which decreases the number of reactions that are occurring if we do the opposite and take the control rods out of the core then more neutrons are available to to go off and cause reactions with uranium atoms which causes more neutrons to be produced which produces more heat to get all of this energy out massive amounts of water are pumped through the Reactor Core taking with it the heat from the uranium fuel rods this water then exits the reactor what will go off and make Steam which will spin a turbine generator and make electricity at the same time the fuel in the reactor core is kept cool and safe individual designs will vary a little bit but most commercial plants use more or less this type of process this is the normal state of a nuclear reactor and one that hundreds of plants around the world World operate in every single day but what if we have too many neutrons or we make too much heat that we can't get out well this is when things start to go wrong what happens if we can't control the number of neutrons or water stops flowing through the Reactor Core well this is the first stage of a nuclear accident operators in the plant Safety Systems will try to stop the Chain Reaction usually by inserting the control rods this will quickly stop the chain reaction from occurring if for some reason the cooling water has been lost or isent flowing operators will turn on pumps to bring water from separate tanks through the reactor core and try try and keep the fuel cool and this would be the end of our accident most plants never actually even get to this stage but for the purposes of our demonstration let's see what happens if we continue let's say despite our best efforts we still can't get enough water to flow through the Reactor Core no problem we still inserted the control rods and stop the Chain Reaction though right yet we'd find that the reactor continues to heat up despite the fact that it's been shut down which seems really counterintuitive so what's going on here this is one of the unusual things about nuclear energy even if we had a magic wand to remove all neutrons from the Reactor Core some sort of super control rod the uranium fuel would still continue to heat up the reason for this is atomic physics it turns out for a very small percentage of uranium atoms that are struck by a neutron they don't release all of their energy right away sometimes there is a delay which could be minutes hours days or even years later this means that even if we stop the reaction with our magic control rod some of the atoms from earlier in the Chain Reaction will continue to release heat for a very long time and if we don't have water to remove that heat it will keep building up more and more this is when we get to the next stage of a nuclear accident where things will become very difficult a full-blown meltdown at this point the temperatures in our Reactor Core have become so high that the previously solid ceramic fuel will actually begin to melt as it melts it slowly flows down inside the Reactor Core liquefying any internal structural components with it forming an Unstoppable blob of red hot uranium and steel consuming everything in its path eventually it settles itself on the bottom of the reactor core and at this point Things Are really bad we've already suffered a meltdown however things can still get worse a pool of melted Fuel and metal is still in the reactor but it's also still generating heat if we don't get cooling to it soon it'll go on to the final and worst stage the liquid hot blob will eventually melt through the thick steel of the reactor vessel like an Unstoppable radioactive monster here it will spill out onto the floor of the concrete below where it will start to spread out it's at this point that we finally start to get some good news by spreading out over such a large area the radioactive blob naturally begins to cool down think of it like spreading melted chocolate over a large table it'll still be warm but not warm enough to stay liquid thankfully this is the end of our meltdown but not without considerable damage so why did this happen how did we lose control of the Chain Reaction or stop sending water to cool the Reactor Core just like any mechanical systems unexpected failures can happen in the case of the water pumps despite everyone's best effort it's possible for a pump to break or malfunction if another pump or backup water source doesn't work as expected Cooling water to the reactor can be lost the same is true with the control rods if a failure occurs either mechanical or electrical they might not be inserted when they're needed most and there's another thing most plants with safety and backup systems such as pumps and valves need electricity for those items to work this is often supplied by separate diesel generators located at the plant however if they are damaged or failed to start then other safety systems that depend on them won't work either it's also possible that the human operators could cause an accident by putting the plant into an unsafe condition although modern plants are designed to prevent this that doesn't stop a determined operator from doing something that they shouldn't this was the case at the Chernobyl plant where operators were instructed to disable safety systems specifically designed to prevent their intended actions then of course there are natural disasters like earthquakes and tsunamis although most plants are designed to handle these it is possible they could be more severe than anticipated and significant damage can still occur leading to reactors overheating and meltdowns so how scary is all of this really because the thought of a nuclear meltdown is actually really terrifying well the good news is that despite what you may have seen in movies or heard on the news the actual odds of a meltdown occurring are really really small and part of that fear comes from radiation itself it's not something that you can see feel smell or touch until it's too late adding to that fear is information or quite often lack thereof it's crucial to have accurate and timely information about what's going on however the immediate aftermath of the incident in Fukushima was a master class in confusion TECO the operator of the plant and the Japanese government were slow to release details leading to panic and speculation not knowing made everything 10 times worse however each nuclear incident while tragic has been a teacher forcing the industry to evolve the 3-m island plants suffered a partial core meltdown because operators couldn't tell an accident was even occurring disabling Safety Systems because they thought there was too much water in the core when in fact there was not enough one of the major issues at 3M Island was information overload imagine sitting in front of a wall of panels with a thousand different indicators and half of them are blinking red it's like trying to watch 10 different TV shows at the same time you're not going to understand what's going on in any of them after 3 m Island there was a revolution in how information is displayed and presented to The Operators now instead of an overwhelming fire hose of data systems are designed to show what's most crucial in the moment giving operators the right information at the right time so they can make the right decisions learning from mistakes and being able to interpret large amounts of data are important not just in nuclear energy but any technical field and if you want to see how the best do it I strongly recommend you check out this video sponsor brilliant they have fantastic interactive courses like the one explaining data variation which goes into 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people will get 20% off Brilliance annual premium subscription which is an excellent deal thanks to brilliant and all of you for supporting this channel it really goes a long way so how do we prevent meltdowns from happening the first place we look is in the design the guiding principle for designing a nuclear power plant is an idea you might be familiar with called defense in depth it's like having a castle with multiple layers of protection you'd have Moes Walls watchtowers and More nuclear reactors take a similar approach multiple layers of safety to protect against everything from human error to natural disasters along with that is redundancy and diversity this is the old saying don't put all your eggs in one basket nuclear reactors have multiple backup systems not just one take this as an example if you had a super important early meeting in the morning you probably wouldn't rely on just one alarm clock this is the same idea for controlling the reactor there are not just the control rods but chemical injection systems as well for emergency power there are diesel generators and batteries for cooling water there are separate tanks some systems are active like pumps and some are passive and use gravity the idea is that if one system fails there's another to take its place giving you multiple ways to solve the same problem and even if all those systems fail and we do eventually get to a meltdown there was one final thing that keeps everything well contained the massive reinforced concrete domes surrounding reactors are often 6 ft or about 2 m thick and airtight to prevent leaks if all else fails everything will be kept inside even so what happens if an accident goes beyond the plant itself and into the surrounding Community for that there is emergency response planning specialized teams trained to handle everything from a minor hiccup to fullscale disasters there are alert systems to notifi local communities and detailed evacuation plans in place and maybe most importantly communication plans and Specialists on hand to make sure people know what is happening and can receive any important instructions of course none of this would mean very much without one last important an function and that's oversight each country with a nuclear program has a regulatory Authority that plays the role of a strict policeman they review and approve everything the reactor design the operator qualifications the emergency plans and more and if a plant doesn't show that they can meet all of the requirements Regulators have the authority to shut it down until it's back on track okay so what about the future is it possible to design meltdown proof reactors well yes engineers and scientists have been hard at work to develop new reactor designs that will take nuclear energy into the future instead of using water for cooling which can boil off in a crisis many proposed designs use molten salts or liquid metals to cool the reactors these have the advantage of being able to withstand much higher temperatures all while operating at lower pressures which means the designs can be simpler and safer other designs look to change the uranium fuel for other options like thorium these designs can greatly increase the fuel supply and operate more efficiently without increasing the risks to safety now you're probably wondering should we just accept that everything in nuclear is safe now the short answer is that although there are reasons to be optimistic that doesn't mean that we should just blindly accept everything is okay what we consider safe is often changing the more we learn the higher our standards become it's essential that we keep questioning evaluating and innovating even with multiple layers of safety the inherent complexities mean that there's always some element of risk no matter how small a seemingly small oversight could Cascade into a big problem if we're not careful so yes be skeptical and demand the very best from every Link in the chain from the engineers who design the plants to The Operators who run them and to The Regulators Who oversee it all it is not just about learning from past mistakes it is anticipating the needs of the future as well nuclear meltdowns are rare and I mean very rare there have only been three major accidents 3M Island Chernobyl and Fukushima out of thousands of years of reactor operating history worldwide there's a great book by James mffi called Atomic accidents that goes through and analyzes what happened and why in those cases as well as some other smaller incidents you might not have heard about I'll put a link in the description so yes while it can happen and has happened the nuclear industry dissects every single accident in excruciating detail to make sure that it doesn't happen again while nuclear energy does have its risks they are more manageable than ever thanks to advancements in technology and learning from past experiences and speaking of advancements if you're intrigued by how these new designs are pushing the boundaries of safety and efficiency you want to check out this video on micro reactors where I go over how they're changing the way that we can recover from disasters like hurricanes thanks again to brilliant check out the link in the description to get 30 days for free and I'll see you in the next one

Channel: AtomicBlender

Views: 717,520

Keywords: nuclear energy, nuclear power, nuclear, nuclear energy explained, nuclear waste, advanced nuclear, nuclear reactor, fission, fukushima, fukushima nuclear disaster, radioactive waste, pacific ocean, iaea, japan, nuclear accident, chernobyl, three mile island, thorium

Id: Gpc_vF3e2PE

Length: 13min 37sec (817 seconds)

Published: Fri Oct 13 2023