A Brief History of: The Leningrad 1975 & Chernobyl 1982 Meltdowns (Short Documentary)

this video is sponsored by nor pass more about that later on in 1975 and 1982 a soviet-designed rbmk reactor would experience a fuel melting event and would signal the dangers of a flawed design but these signals would fall on deaf ears [Music] this one is a double bill and an intro to the rbmk reactor it will form part one of a new series of videos on chernobyl think of this as how the hobbit is to the lord of the rings which will be the chernobyl disaster of 1986. now both of these events in this video have very little in forms of official reports and this was due to the period of the time in which they existed where a soviet government would cover up any hint that eastern bloc technologies were lacking in comparison to their western counterparts today's subject i will place here on the plainly difficult disaster scale leningrad npp is a nuclear power station in suznavi bore leningrad a blast 43 miles west of modern day st petersburg however when the plant was first constructed the city was actually called leningrad construction began on the site in 1967 and was the first to use the ill-fated rbmk reactor design unit 1 first began operation in 1973 with units 2 to 4 opening in 1975 1979 and 1981 respectively each installed reactor had the same net power output of 925 megawatts of electricity how they produced much more in thermal energy now let's look at the rbmk reactor and its design the reactor's history can be traced back to the mid-1950s with the light water called graphite moderated 30 megawatts of thermal energy am1 reactor in obnisk the design was further expanded upon in the 1960s with the amb 100 and the amb 200 designs between 1964 and 1966 soviet designers needed to field a new reactor that was cheap easy to build and maintain and be capable of electricity generation and also be able to produce plutonium for nuclear weapons to facilitate this the designers opted to use light water for coolant and graphite for moderation a style which is unique to the rbmk now moderator is used to reduce the speed of fast neutrons released from fission so they can better facilitate a chain reaction ideally moderators work without capturing any neutrons leaving them as thermal neutrons so because of this most reactors need a moderator to work efficiently and different designs use different methods for moderation for example graphite light and heavy water a combination of graphite moderator and light water coolant offers up a strange result as when compared to the pwr reactor which is one of the world's most popular designs the coolant and moderator in the form of light water are the same the pwr is a very safe design as once the coolant heats up and turns into steam it loses its effectiveness as a moderator slowing down the chain reaction improving stability and eventually cooling down however the rbmk didn't have this due to having graphite as its moderator and as it does not evaporate easily still does its job even if the coolant falls away when the coolant heats up turning into steam it loses its neutron absorption capabilities creating free neutrons leading to an increase in reactivity this is known as a positive void coefficient which is not instantly a dangerous design if the working parameters of the reactor do not rely on the neutral absorption of the water to stay safe how the rbmk reactor design did rely heavily on the steam content of its core for its reactivity this has to be counted by the control rods which regulate the overall power of the reactor leading to a very fine balancing act if not properly managed an incident of a runaway can happen as the coolant heats up increasing the reactivity heating up the core more creating more steam leading to greater reactivity this is called a feedback loop creates a similar result to a diesel engine runaway as shown in this very well shot video the use of a graphite core allowed low enrichment uranium 235 fuel to be employed for power generation at only a quarter of the expense of heavy water reactors which had higher startup costs and much more complex maintenance also lower enrichment unsurprisingly cost less to make which was good for the soviet accountants the fuel was enriched to two percent and formed into pellets which were packed into a three point six five meter long zerk alloy tube forming a fuel rod 18 fuel rods were arranged cylindrically into a carriage to form a fuel assembly which was then placed inside one of the reactor cores 1693 fuel channels within the reactor each fuel assembly is positioned in its own vertical presser tube seven meters long each channel is individually cooled by pressurized water which is allowed to boil exiting at the top at about 290 degrees centigrade the steam is passed through a separator where it is sent to a high then low pressure turbine which turns to generators producing electricity after which the coolant is run through a condenser cooled by a separate coolant circuit from a nearby water source from there it is sent back to the core to complete the cycle the reactor had two separate coolant loops which mirrored each other passing through its own half of the core each loop had four pumps three for normal operation and one for backup the graphite moderator consisted of multiple blocks placed next to each other with a gap filled with a mixture of helium and nitrogen gas that formed the core region of the reactor and was around the size of a small house the graphite didn't receive any type of cooling meaning its operational temperature was around 700 degrees centigrade however the gas in between the blocks helped with heat conduction the reactor was equipped with boron carbide control rods with graphite tips and these were used to shut down and regulate the power of the reactor most of them were inserted from the top however a number of shorter rods were inserted from the bottom for axial power control the reactor had a safety shutdown in the form of the az-5 button which once activated would initiate a reactor scram the main top inserted was provided automatic manual or emergency control the automatic rods were regulated by feedback from in core detectors in addition to this some shorter rods were inserted into the bottom of the core to help combat hot spots of uneven criticality in total the rbmk at leningrad had 170 control rods the final part of the rbmk was its containment or lack thereof you see the doctrine at the time of the rbmk was that it was always going to be operated within design specs hence no risk of disaster this didn't take into account human nature for buggering things up what little protection to the outside world was provided was in the form of a reinforced concrete lined cavity that acts as a radiation shield the reactor itself sat on a steel plate and was topped by a thousand tonne steel cover the steam separators were also housed in their own separate concrete containment a contributory factor to the lower containment than other reactors was that it can be refueled whilst in power operation to achieve this a large crane is situated above the reactor this meant that building a massive concrete dome containment structure will be time consuming and more important costly now that is a basic overview of the rbmk the version installed at leningrad was a first generation design however there was a second generation design which was the type installed in chernobyl unit 4. the second gen was virtually the same however one of the main differences was increased control rods to 211 and a reduction of fuel channels to 1661 in the graphite core and now here's some words about this video sponsor nordpass nor pass is a one-stop shop for password management where security meets simplicity if you're like me then you find it hard to keep track of all your passwords for different websites i'm a very messy person and if it wasn't for mrs plainly difficult i'd be living in a bomb site and my digital life is no different so having 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you can even upgrade to a premium package which allows up to six active devices and a data breach scanner as well as many other bits and pieces this leads us back to leningrad and relatively new rbmk unit 1 on the 30th of november 1975. it's very difficult to reconstruct the accident as at the time the reactor was surrounded by secrecy however some parts of a first person account does exist from a trainee who later worked at chernobyl on the 29th of november reactor was being started up after some regular maintenance whilst powering up and reaching around 800 megawatts one of the reactors turbo generators had control issues leading to the need to lower the power to 500 megawatts to take it offline this was near 12 o'clock midnight and as with most disasters was the time for a shift changeover the nightshift was tasked with the continuation of raising the power of the reactor by accident one of the operators shut down the remaining turbo generator leading to a reactor trip causing a scram of the control rods this in combination with the reduction of the power due to the tg being taken offline increased the level of zen and poisoning within the reactor not wanting to cause too much of a delay the chief operator issued the order to put the functional tg back online and to restart the reactor the unit was restarted to the minimum controllable level however the poisoning of the reactor was at an unacceptable value reducing the operational margin to just eight control rods this meant that nearly all of the control rods had to be fully removed from the reactor in order to achieve an output level for the tg to resume power generation again a scram was triggered shutting down the reactor due to uneven neutron power this is due to the size of the rbmk core meaning that different areas could gain criticality whilst other areas remain poisoned which would lead to hot spots another restart was attempted and was more successful in reaching the minimum controllable level at 6 15 am the reactor capacity was raised to 1 000 megawatts of thermal energy by 6 33 am the power was raised to 1720 megawatts the operators had conducted too much of a fast rise of the reactor power deadly for the highly poisoned and small margin state of the reactor power levels to load the tg were achieved when operators receive warnings of low water flow levels the core had developed hot spots and the operators attempted to fight these by lowering some of the manual control odds whilst leaving the automatic ones to manage the overall power output scarily a new alarm sounded in the control room indicating moisture in the graphite near channel 13 33. the presence of moisture in the graphite moderator hinted at a rupture in the high pressure coolant tube around the fuel meaning a potential meltdown at this point the ac5 button was pushed activating a scram shutting down the reactor it was found that severe damage to the reactor core one technological channel had collapsed and 32 fuel assemblies have burned due to operating reactor in an unsafe manner the damaged channel proved difficult to remove using the refueling machine causing issues for workers due to improper confinement around 1.5 mci was released into the atmosphere and 5 kilometers from the affected power unit radiation levels were recorded at 600 milligrams an hour immediately after the fuel damage the accident was caused by the operators trying to make good the error of accidentally shutting down the operating tg by doing so they worked outside the regulations for low power operation but the management culture at the time didn't consider this a major issue well how wrong they were the soviet ministry responsible for nuclear industry was in charge at leningrad making any information about instant state secrets this meant that no operators at other rbmks would have even known about the fuel damage let alone learn from the mistakes right let's go on to the other lesser-known chernobyl incident and that is the fuel damage at unit 1 in 1982. chernobyl npp is a now shut down plant in ukraine unit 1 was the same type that was used at leningrad and was installed in 1972 achieving operation in 1977. there isn't a great deal to write about again as it was covered up at the time with the help of victor brookenov who will most likely show up again on this channel in the future however what is known from a kgb internal memorandum was like at leningrad the rbmk reactor had been shut down for maintenance and have received fuel damage the maintenance was scheduled to be complete on the 13th of september 1982 and before this the reactor had to be tested upon restarting and reaching 700 megawatts during the test run a fuel channel number 6244 was starved of water overheated and melted severely damaging the core and again leading to moisture in the graphite moderator the issue wasn't noticed for between 20 and 30 minutes before an az5 button activation allowing significant contamination of the coolant now is unknown for certain what caused the coolant starvation as initially the operators were blamed however later on a failed valve was also seen as a potential cause but it is difficult to know for certain due to the cover-up the channel was severely damaged and repair turned into a dirty radiological cleanup it took almost a year to fix the damage from the accident and the core area adjacent to the destroyed channel was out of use indefinitely the biggest issues from both these incidents was operators not working within the parameters set out from either from negligence or pressure from management the worryingly dangerous culture set out by management and their wider political sphere of nuclear power in the ussr would culminate in a much bigger disaster involving an rbmk in 1986. thank you to norpas for sponsoring this video sponsorships like this really help keep the lights on at playing difficult hq check out www.norpass.com forward slash plainly difficult to try it out for free this is a plainly difficult production all videos on the channel are creative commons attribution share alike licensed playing difficult videos are produced by me john in a sunny south eastern corner of london uk help the channel grow by liking commenting and subscribing and check out my twitter for all sorts of photos and odds and sods as well as hints on future videos i've got patreon and youtube membership as well so if you want to support the channel financially you can do through there and all that's left to say is thank you for watching

Channel: Plainly Difficult

Views: 630,472

Keywords: Atomic, Nuclear History, Education, Plainly Difficult, dark docs, History, Chernobyl, Lenningrad, Nuclear accident, RBMK, Leningrad meltdown, Chernobyl nuclear accident, Christmas, A Brief History of Chernobyl, Qxir, Tales from the bottle, Curious Droid, RBMK Nuclear reactor, Zepherus

Id: 9u_voe26ZLw

Length: 15min 54sec (954 seconds)

Published: Sat Dec 19 2020