How Does Nuclear Waste Disposal Work?

today's video is all about nuclear waste disposal and if that sounds like it's up your alley then you've got to check out my other channel megaprojects megaprojects is a channel all about mankind's greatest achievements so you know there's plenty of profiles on nuclear ships nuclear bombs nuclear cars nuclear power and pretty much any other concept where you can squeeze in the word nuclear i'm pleased to report that megaproject has actually become so popular we had to create a sister channel called side projects where we cover similar topics but on a smaller scale so if you saw today's topic looking for more content on your nuclear-powered ice cream or whatever get yourself over to mega projects after today's video and let's just jump in [Music] 31 countries currently use some form of nuclear power with the 455 currently operational reactors generating some 393 000 megawatts of electricity it's nearly 20 percent of the world's total energy production despite high profile disasters such as chernobyl three mile island and fukushima nuclear power is actually among the safest and cleanest forms of electricity generation placing dead last in terms of deaths per kilowatt hour generated yes even behind solar and wind power unlike coal and oil nuclear power emits no greenhouse gases and unlike solar and wind and hydroelectricity it is not dependent on geographic location or local weather conditions energy experts thus predict that if the public stigma can be lifted especially with more modernly designed nuclear reactors nuclear power may be poised to make a comeback as the green energy source of the future but despite its many advantages nuclear power has one glaring achilles heel radioactive waste over the past four decades the global nuclear industry has generated some 62 500 metric tons of waste with a further 2 300 tons added every year much of which will remain dangerously radioactive for thousands of years unlike other kinds of industrial waste nuclear waste cannot feasibly be converted to a less dangerous form nor given the current political climate can much of it be reprocessed and recycled so well then how do we dispose of it while commercial nuclear power is nearly 70 years old the concept of permanent nuclear waste disposal is a surprisingly recent one in the early days of nuclear power engineers assumed the reactors would operate on a more sophisticated fuel cycle with spent fuel being reprocessed to produce new fuel elements and to remove radioactive isotopes for use in medicine scientific research and nuclear weapons much research was also performed on breeder reactors which convert non-facile isotopes into fissile ones thus generating more fuel than they consume combined these two technologies would produce relatively little high-level radioactive waste however this plan was based on the belief that earth's uranium reserves were extremely limited and when uranium was found to be far more abundant than initially assumed a once through fuel cycle without reprocessing became much more economical at the same time companies such as westinghouse and general electric found that it was much easier and cheaper to scale up existing reactors they had designed for u.s navy submarines than to develop civilian reactors from scratch as the development costs had already been subsidized by the u.s government these reactors could be sold at much more competitive prices as a result reprocessing and breeder reactors fell by the wayside and nuclear waste soon began piling up nuclear waste can be divided into three basic categories low intermediate and high level low and intermediate level waste is defined as material that will remain dangerously radioactive for less than 300 years and consists mainly of contaminated materials such as solvents tools laboratory glassware and clothing used in the processing of nuclear fuel due to the low activity and short decay timeline of this waste it is relatively straightforward to deal with typically being kept in shielded monitored storage containers on-site at nuclear power plants or processing facilities once the radioactivity decays to safe levels the material can be disposed of like any other industrial waste high-level waste consists mainly of spent fuel from nuclear reactors and is a different beast entirely for many of the radionucleotides and spent fuel can remain dangerously radioactive for tens of thousands of years as this is longer than human civilization at least in its current form is expected to survive any feasible disposal scheme must with a high degree of certainty prevent these nucleotides from leaking into the environment without any human supervision or interference over the years a number of disposal schemes have been proposed including dumping the waste in deep sea trenches placing it in tectonic subduction zones so it gets drawn into the earth's mantle or launching it into outer space however all of these proposals have been rejected for one reason or another for example the failure rate of modern rockets while low is significant enough that a launch failure causing widespread radioactive contamination is very real and an unacceptable possibility furthermore the london convention of 1972 and the basil convention of 1992 explicitly banned the disposal of radioactive waste in the oceans consequently all current waste disposal schemes are based on deep geological burial the most advanced of these projects are currently finland's oncarlo and sweden's fossmark repositories and it is these disposal models that we're going to discuss today to understand how deep geological disposal works it is first necessary to understand the composition and behavior of the radionucleotides found in spent nuclear fuel spent fuel contains four basic types of nucleotides the first of which is the remains of the fuel itself typical reactor fuel is enriched to contain around three percent of the fissile isotope uranium-235 the rest consisting of the non-fissile isotope uranium-238 as the fuel is consumed in a reactor the u-235 content will drop to around 0.8 these are among the most long-lived nucleotides in the spent fuel u-235 having a half-life of 704 million years and u-238 4.5 billion years the next components in spent fuel are the fission products these are light elements formed when uranium atoms split apart during nuclear fission and have half-lives ranging from eight hours for xenon 135 to 15 million years for iodine 129. the shortest slip fission products are intensely radioactive and produce a large amount of decay heat so much in fact that even after a reactor is shut down if the cooling system fails this decay heat can build up and cause the core to melt down therefore upon being removed from a reactor spent fuel elements are immediately placed in actively cooled storage pools the water in the pool carries away the decay heat and shields plant operators from ionizing radiation allowing the fuel to be stored for up to six years when most of the short-lived fission products will have decayed away despite the routine nature of pool storage it is actually one of the most vulnerable and dangerous steps in the fuel disposal process as a failure of the pool's cooling system can lead to serious consequences as happened during the 2011 fukushima daiichi nuclear disaster when the earthquake and subsequent tsunami knocked out emergency power to the plant the lack of cooling caused spent fuel in the storage pools to overheat generating hydrogen gas that accumulated and ignited blowing the roof off the building yet another category of radionucleotides found in spent fuel are the actinides or transuranic elements these are heavy elements produced when u-238 absorbs neutrons from the nuclear reaction these tend to have relatively long half-lives ranging from 432 years for american 241 to 379 000 years for plutonium-242 and finally there are the activation products produced by the neutron activation of non-radioactive structural materials like zirconium cladding on the fuel bundles the most common and long-lived of these is chlorine 36 with a half-life of 300 000 years it is important to note here that half-lives alone do not give an accurate picture of just how long a given isotope will remain dangerously radioactive many nucleotides do not immediately decay into stable isotopes instead undergoing a long decay chain whereby one radioactive isotope decays into another radioactive isotope and so on with the half-lives of the intermediate daughter nucleotides ranging from 4 microseconds to 160 000 years for example neptunium-237 has a decay chain 13 steps long ending in the stable isotope thallium-205 with the half-lives of the intermediate daughter nuclides ranging from four microseconds to a hundred and sixty thousand years many of these daughter nuclides are significantly more radioactive than neptunium which combined with neptunium's long half-life of two million years means that the whole decay series will remain environmentally hazardous for more than 10 000 years currently once nuclear fuel is removed from cooling pools it is placed in shielded dry casks and kept in monitored storage on site at the nuclear power plant this is how radioactive waste is handled in almost every major nuclear nation however as reliable monitoring cannot be counted on for more than 100 years or so due to political and climatic changes nations such as sweden finland and south korea have turned to deep geological repositories to safely store their waste without requiring human intervention as previously mentioned the ultimate goal of permanent disposal is to prevent dangerous radionuclides from leaking into the environment until all the most dangerous isotopes have decayed to a harmless form in deep geological disposal this is accomplished by burying the waste deep inside monolithic geological formations through which groundwater migration is minimal for example for many years atomic energy of canada limited studied the feasibility of burying nuclear waste in the canadian shield a massive formation of dense 2.5 billion-year-old granite similarly the cancelled yucca mountain repository in nevada and the current repositories at forsmark and sweden and noncarlo in finland are all dug into deep dense igneous bedrock however deep burial on its own is not enough as any single barrier against leakage can be expected to fail at some point so all current disposal schemes include multiple redundant barriers enveloping the waste in concentric protective layers like a russian nesting doll surprisingly the first and most effective of these barriers is the fuel itself the uranium used in nuclear reactors is in the form of uranium oxide a hard black ceramic-like material that is pressed into small cylindrical pellets these pellets are stacked and sealed into tubes of zirconium cladding which are then bound together to form the fuel elements uranium oxide is extremely insoluble in water and traps most of the radionuclides tightly within its crystal lattice meaning that even if bare fuel pellets were simply dumped in an open aquifer even after 10 000 years very few of these nuclides would actually escape into the environment however certain euclides such as chlorine 36 and cesium-137 are more mobile than others and could possibly leak out of the fuel pellets if the fuel cladding is breached these are collectively known as the instant release group of which only around 10 percent the instant release fraction are likely to leak out this however is nominally prevented by the next barrier the zirconium fuel cladding which due to its natural corrosion resistance is only expected to be breached after 400 000 years further protection is provided by encasing the fuel bundles in storage casks made of stainless steel titanium or copper the latter of which is so corrosion resistant it is expected to last up to a million years in the extremely unlikely event that both the storage cask and the fuel cladding are breached the casks are packed in a dense clay-like substance known as bentonite which both seals the casks against the ingress of water and acts as an ionic buffer that traps escaping radionuclides before they can reach the groundwater however this buffering action is only effective against positively charged atoms like caesium strontium and other heavy metals negatively charged ions like iodine and chlorine can still potentially get through but in order to reach aquifers used by humans and other animals these nuclides must travel through hundreds of meters of bedrock via the groundwater which in the areas where the nuclear repositories are built moves at a positively glacial pace of around one centimeter per year combined these various barriers and safeguards ensure that by the time any radionuclides leak into the environment they will have already decayed into harmless isotopes or be so dilute as to present little to no danger to the environment indeed the sheer degree of redundancy in this system can be considered overkill and then some a fact borne out by a remarkable discovery made in 1972 in a uranium mine at oclo gabon some two billion years ago when the proportion of fissile u-235 was higher than today rainwater seeping into the ground set off a nuclear chain reaction in uranium ore deposits effectively creating a natural nuclear reactor this process carried on for thousands of years until the uranium was depleted leaving behind the same collection of fission products found in spent man-made nuclear fuel yet despite the oklo deposits being located in porous sandstone through which rain and groundwater constantly percolate in other words the worst case scenario for a nuclear waste repository over the next two billion years these fission products migrated no more than a meter or so from their original source thus it is expected that modern repositories with their multiple layers of protective metal clay and dense granite should easily be able to contain our nuclear waste for at least a hundred thousand years and for more on the orclo reactors please check out our video the two billion-year-old earth-based nuclear reactor but while scientists have confidence in the passive effectiveness of deep geological repositories there is another major factor that can't be as easily accounted for future humans as nuclear repositories are expected to last hundreds of thousands of years it is more than likely that all knowledge and records of their existence will be lost over the millennia provided human civilization lasts that long how then do we prevent our distant descendants from stumbling upon our nuclear waste and unleashing an ecological disaster this question explored in depth in the 2010 danish documentary into eternity has generated considerable controversy with some experts arguing that once sealed all traces and records of the repositories should be erased so that humanity eventually forgets their existence and locations others however argue that this would increase the risk of the repositories being found by accident and that some form of warning perhaps in the form of an engraved stone monument should be left to discourage people from disturbing the sight still others argue that such a warning would only entice future explorers after all inscription's warning of curses has done little to discourage people from entering and looting ancient egyptian tombs much closer to our own time many proposed nuclear repository projects have fallen prey to another human impulse nimbyism with many citizens vehemently opposing the storage or transport of nuclear waste near their communities in the late 1970s atomic energy of canada limited began a series of studies to evaluate the feasibility of storing nuclear waste in the ontario section of the canadian shield drilling experimental boreholes to monitor groundwater migration the locals believing that nuclear waste was already being stored in the area immediately had their groundwater tested and discovered to their horror that it was radioactive the resulting public outcry forced acl to abandon the project however had anyone bothered to test the water before the researcher's arrival they would have discovered that it had been mildly radioactive all along the granite of the canadian shield being naturally full of uranium and other radioisotopes similar political forces also led to the cancellation of the yucca mounting repository project in 2011 after more than three decades of research have been conducted on the site currently only four deep geological repositories are in use or under construction in finland sweden south korea and germany was the vast majority of the world's nuclear waste still being kept above ground in dry cask storage several other repositories are in various stages of discussion and planning but given the sharp global drop in interest in nuclear power following the fukushima disaster it remains to be seen whether any of them will be brought to completion recent years have also seen renewed interest in the concept of transmutation whereby nuclear waste is converted into a less dangerous form by bombarding it with neutrons from a nuclear reactor or particle accelerator unfortunately this process is not yet feasible with today's technology as transmuting waste on a large scale would require such vast amounts of energy as to be uneconomical however it may be possible to carry out limited transmutation whereby the longest lived nucleotides such as neptunium separated out of spent fuel and converted into lighter more short-lived isotopes greatly reducing the total time the fuel remains dangerously radioactive while promising the process of separating out these nuclides is itself prohibitively expensive and research is ongoing to develop methods for selectively transmuting long-lived nuclides within the fuel itself whatever the ultimate solution it is clear that a long-term solution for dealing with radioactive waste will be the key to achieving the long-awaited nuclear renaissance so i really hope you found that video interesting if you did please do hit that thumbs up button below also as i mentioned at the beginning nuclear power is often covered on my channel mega projects which i'm going to link to below and thank you for watching

Channel: Today I Found Out

Views: 288,983

Keywords: today i found out, tifovidz12, tifo, awesome, facts, didn't know

Id: LNfvzkeWA2Q

Length: 16min 51sec (1011 seconds)

Published: Tue Jan 26 2021