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

this video is sponsored by nor goes on further about that later in

1975

and

1982

a soviet designed rbmk reactor would experience a fuel meltdown event and would signal the dangers of a faulty design but these signals would fall on deaf ears this is a double bill and an introduction to the rbmk reactor will be part of a new video series 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 events in this video have very little in the way of official reports and this was due to the time period in which they existed , where a Soviet government covered up any hint that Eastern Bloc technologies were lacking compared to their Western counterparts.

I will place today's topic. Here, on the clearly difficult scale of the disaster, the Leningrad NPP is a nuclear power plant in Suznavi. It hit Leningrad, an explosion 43 miles west of present-day St. Petersburg. However, when the plant was first built, 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 and units 2 to 4 opened in

1975

, 1979 and 1981 respectively. Each reactor installed had the same net power of 925 megawatts of electricity, although they produced much more in thermal energy now let's look at the rbmk reactor and its design the

history

of the reactor dates back to the mid-1950s with light water called graphite moderated 30 megawatts thermal energy am1 reactor at obnisk the design was further expanded in the 1960s with the amb 100 and amb 200 designs between 1964 and 1966 the soviet designers needed to implement a new reactor that was cheap, easy to build and maintain and that was capable of generating electricity and could also produce plutonium for nuclear weapons to facilitate this, the designers opted to use light water as a coolant and graphite for moderation, a style that is unique to the rbmk.

Now the moderator is used to slow down the fast neutrons released from fission so they can better facilitate a chain reaction. Ideally, moderators work without capturing neutrons, leaving them as thermal neutrons, because of this most reactors need a moderator to operate efficiently and different designs use different moderation methods, e.g. graphite, light water and heavy. A combination of graphite moderator and light water as a coolant gives a strange result compared to the pwr reactor. which is one of the most popular designs in the world, the coolant and moderator in the form of light water are the same.

The pwr is a very safe design since once the coolant heats up and turns into vapor, it loses its effectiveness as a moderator, which slows down the chain. The reaction improves stability and eventually cools. However, the rbmk did not have this because it has graphite as a moderator and since it does not evaporate easily it still does its job even if the coolant drops out when the coolant heats up and turns into vapor it loses its absorption capabilities. of neutrons that create free neutrons leading to increased reactivity. This is known as positive vacuum coefficient, which is not instantly a dangerous design if the reactor's operating parameters do not depend on neutral water absorption to remain safe.

The reactor design relied heavily on the vapor content of its core for its reactivity, this must be accounted for by the control rods that regulate the overall power of the reactor, leading to a very fine balancing act, if not managed properly, a leak incident may occur. As the coolant warms, the reactivity increases, heating the core more and creating more vapor, resulting in greater reactivity. This is called a feedback loop. It creates a result similar to that of a runaway diesel engine, as shown in this well-shot video. The use of a graphite core allowed low-enriched uranium-235 fuel to be used for power generation at only a quarter of the cost of heavy water reactors, which had higher start-up costs and much maintenance. more complex.

Also, as expected, minor enrichment cost less, which was good for Soviet accountants. enriched to two percent and formed into pellets that were packaged in a three point six and five meter long zerk alloy tube forming a fuel rod. 18 fuel rods were arranged cylindrically on a carriage to form a fuel assembly which was then placed inside one of the reactor cores. 1,693 fuel channels within the reactor, each fuel assembly is placed in its own seven-meter-long vertical presser tube. Each channel is individually cooled with pressurized water that is allowed to boil and exits the top at approximately 290 degrees Celsius.

The steam passes through a separator where it is sent to a high and then low pressure turbine that is connected to generators that produce electricity, after which the refrigerant passes through a condenser cooled by a refrigerant circuit separate from a nearby water source, from there it is sent back to the core to complete the cycle. The reactor had two separate coolant circuits that mirrored each other and passed through its own half of the core. Each circuit had four pumps, three for normal operation and one for backup. The graphite moderator consisted of multiple blocks placed side by side with a space filled with a mixture. of helium and nitrogen gas that formed the central region of the reactor and was approximately the size of a small house, the graphite did not receive any cooling, meaning that its operating temperature was around 700 degrees Celsius, however, the The gas between the blocks helped with heat conduction.

The reactor was equipped with graphite-tipped boron carbide control rods that were used to shut down and regulate the power of the reactor, most of them were inserted from above, however, they were They inserted several

short

er rods from below for axial power. controlling the reactor had a safety shutdown in the form of the AZ-5 button which once activated would initiate a reactor shutdown the inserted main top part automatic or emergency manual control was provided the automatic rods were regulated by feedback from the core detectors In addition to this some

short

er rods were inserted into the bottom of the core to help combat hot spots of uneven criticality.

In total, the rbmk in Leningrad had 170 control rods. The final part of the rbmk was its restraint or lack thereof. You see the doctrine at the time of the rbmk was that it was always going to operate within the design specifications, therefore there was no risk of disaster, it didn't take into account human nature to mess things up, how little protection there was provided to the outside world was in the form of a cavity lined with reinforced concrete. which acts as a radiation shield the reactor itself sat on a steel plate and was covered by a thousand ton steel casing the vapor separators were also housed in their own separate concrete containment a factor that contributed to the lower containment than other reactors was that it can be refueled while in electrical operation to achieve this, a large crane is situated on top of the reactor, which means that building a huge concrete dome-shaped containment structure will take a long time and, which is more importantly, expensive.

Now that is a basic description of the rbmk, the version installed in Leningrad was a first generation design, however there was a second generation design which was the type installed in Chernobyl unit 4. The second generation was virtually the same, however one of the main differences was the increase of the control rods to 211 and a reduction of the fuel channels to 1661 in graphite. core and now here are some words about this video sponsor nordpass nor pass is a one stop shop for password management where security meets simplicity if you are like me then you will find it difficult to keep track of all your passwords for different sites Web.

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This brings us back to Leningrad and the relatively new Unit 1 of the RBMK on November 30, 1975. It is very difficult to reconstruct the accident since at that time the reactor was shrouded in secrecy, however, some parts of an account exist in first person of a trainee who later worked at Chernobyl in On November 29, the reactor was being commissioned after regular maintenance as it powered up and reached around 800 megawatts. One of the reactor's turbogenerators had control problems that led to the need to reduce power to 500 megawatts to take it offline. This was about 12 o'clock. At midnight, and as with most disasters, it was time to change shifts, the night shift was assigned the task of continuing to increase reactor power.

By accident, one of the operators shut down the remaining turbogenerator, causing the reactor to trip, resulting in a power failure. the control rods, this in combination with the reduction in power due to the tg being disconnected increased the level of zen and poisoning within the reactor, not wanting to cause too much delay, the main operator issued the order to restart the tg functional online and to restart the reactor, the unit was restarted at the minimum controllable level; However, the poisoning of the reactor was to an unacceptable value, which reduced the operating margin to only eight control rods, which meant that almost all the control rods had to be completely removed from the reactor in order to achieve a production level for the TG to resume power generation again triggered a shutdown that shut 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 while other areas remain poisoned, resulting in hot spots. Another restart was attempted, which was more successful in reaching the minimum controllable level. At 6:15 a.m., the reactor's capacity was raised to 1,000 megawatts of thermal energy. At 6:33 a.m., the power rose to 1,720 megawatts. The operators had carried out a too rapid increase in reactor power, deadly for the highly poisoned and small-margin state of the reactor. The power levels to load the tg were achieved when the operators received warnings of low water flow levels, the core had developed hot spots and the operators attempted to combat this by reducing some of the chances of manual control while letting the automatics manage general energy production.

A new alarm sounded in the control room indicating moisture in the graphite near channel 13 33. The presence of moisture in the graphite. The moderator hinted at a break in the high-pressure coolant tube around the fuel, which meant a possible meltdown. At this point the AC5 button was pressed, activating a shutdown that shut down the reactor. It was discovered that there was severe damage to the reactor core. A technological channel had collapsed and 32 fuel assemblies burned due to the reactor being operated unsafely. The damaged channel proved difficult to remove using the refueling machine, causing problems for workers due to inadequate confinement.

About 1.5 mci was released into the atmosphere and 5 kilometers from the affected power unit radiation levels were recorded at 600 milligrams per hour immediately afterof fuel damage, the accident was caused by the operators who tried to correct the error of accidentally turning off the operating tg by doing so, they worked outside the regulations for low power operation, but the management culture at the time did not consider that this was a major problem, well, how wrong they were, the Soviet ministry responsible for the nuclear industry was in charge in Leningrad and provided any information about instant state secrets, which meant that no operator of other RBMKs would have even known about the damage to the fuel and much less. let's learn from mistakes, let's move on to the other lesser known Chernobyl incident and that is the fuel damage at unit 1 in

1982

.

The Chernobyl nuclear power plant is a now closed plant in Ukraine. Unit 1 was the same type used in Leningrad and was installed in 1972 and operated in 1977. There is not much to write about again as it was covered up at the time with the help of Victor Brookenov who will probably appear again in this channel in the future, however, what is it? As known from an internal kgb memo, it was like in

leningrad

, the rbmk reactor had been shut down for maintenance and had suffered fuel damage, the maintenance was scheduled to be completed on september 13, 1982 and before this, the reactor was to be tested by restarting and reaching 700 megawatts during the test, a fuel channel number 6244 lacked water, overheated and melted, severely damaging the core and again generating moisture in the graphite moderator.

The problem was not noticed for between 20 and 30 minutes before the az5 button was activated, allowing a significant It is now unknown for certain what caused the lack of coolant, as the operators were initially blamed; However, a faulty valve was later also considered a potential cause, but it is difficult to know for sure due to how covered up the canal was. severely damaged and the repair turned into a dirty radiological cleanup. It took almost a year to repair the damage from the accident and the central area adjacent to the destroyed canal was out of use indefinitely. The biggest problem with both incidents was that the operators were not working within the established parameters, either due to negligence or pressure of The management.

The worryingly dangerous culture established by the management and its broader political sphere of nuclear energy in the ussr would culminate in a much larger disaster involving an rbmk in 1986. Thanks to norpas for sponsoring this video. Sponsorships like this really help keep the lights on in the tough game. Visit www.norpass.com. Slash clearly difficult to try for free. This is clearly a difficult production. The videos on the channel are Creative Commons Attribution Share Licensed Play Difficult videos are produced by me, John, in a sunny corner of South East London, UK. Help the channel grow by liking, commenting and subscribing, and check out my Twitter for all kinds of photos and odds.

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