What is the difference between the Chernobyl reactor and the newer light water reactors?

Last April 26 marked the 36th anniversary of the explosion of the Chernobyl nuclear reactor, which is considered the largest global catastrophe on the shoulders of mankind.

This incident raised the fears of citizens around the world due to the association of human minds between everything that is "nuclear" and the annihilation of humanity.

The old reactor, which has been inactive since 2000, made news with the beginning of the Russian war on Ukraine;

Fearing that the soldiers would be exposed to radioactive hazards, or damage the reactor infrastructure, which could cause a new disaster.

Chernobyl.. the oldest generation of reactors

The Chernobyl nuclear power plant is located 130 kilometers from the Ukrainian capital, Kyiv. The plant includes 4 nuclear reactors, which were developed by the Soviet Union during the 1970s and 1980s.

According to a report on the "Live Science" website, the Soviets used the RBMK 1000 reactor at the station, which consists of 3 main parts: the reactor nucleus responsible for conducting the "chain reaction", and "Graphite rods" are responsible for controlling the continuity of chemical reactions, and the third and final part is a huge water tank used to cool the reactor, and draws its water from the Pripyat River.

According to Physics central, that reactor had a serious defect called the "positive void coefficient", which means an increase in nuclear fission rates inside the reactor as a result of increased evaporation or lack of cooling.

How does a nuclear reactor generate electricity?

The production of electricity in nuclear plants depends on fission chain reactions, and the chain reaction is a series of successive reactions whose results contribute to the occurrence of more reactions without the presence of external influences.

Obtaining such reactions in nuclear plants requires the use of radioactive materials, such as the uranium-235 used in the Chernobyl plant.

In the fission chain reaction, neutrons are released towards the atoms of the radioactive material, which leads to its splitting into two (that is, nuclear fission occurs), producing more neutrons.

The additional neutrons collide with more atoms of the radioactive material, causing the previous process to be repeated a large number of times, and the duration of the reactions depends on the amount of radioactive fuel used.

In RPMK 1000 reactors, scientists have used graphite rods as a material that absorbs excess stimulated neutrons to control the chain reaction when these rods are inserted into or removed from the nucleus;

If we want to maintain the continuity of the reaction, we remove these rods, and if we want to stop them, we lower them into the entire nucleus, and between this and that the rods control the reactions and maintain the stability of the reactor.

The generation of electricity in nuclear reactors depends on the consumption of the energy of water vapor resulting from the heat released by chemical chain reactions in order to run turbines that produce electricity, and some compare nuclear plants to large-sized boilers.

The fourth reactor at the Chernobyl plant exploded due to human errors and multiple industrial defects (Shutterstock)

Technical flaws and human errors that led to the Chernobyl disaster

Back in the dawn of April 26, 1986, the operators of reactor No. 4 at the Chernobyl nuclear plant wanted to test some of the safety systems inside the reactor, and during the test technicians shut down the reactor's safety and self-regulation systems in violation of safety rules, and pulled graphite rods from the reactor core while leaving it It works at about 7% of its power, and they shut down the water cooling system, according to the "Encyclopedia Britannica"

That night, the nucleus of that reactor exploded, and some believe that the cause of the explosion is the accumulation of vapors in the cooling pipes due to the lack of enough water to cool the reactor, and more steam means an increase in nuclear fission rates, which leads to high pressure and heat in the reactor core, and then its explosion.

Another reason suggested by some researchers is to reduce the reactor's power, which led to its instability and explosion.

When the temperature inside the RPMK 1000 reactor rises, uranium absorbs neutrons, which leads to a reduction in its activity, thus inhibiting the chain reaction, which is the opposite of what happens when the reactor operates at low energy, so chain reactions do not stabilize inside it.

The explosion led to the complete destruction of the fourth reactor, and the fires spread to 4 nearby buildings, and the sky was filled with toxic clouds, and the remains of the reactor's radioactive components rained down.

The firefighters were able to put out the first fire within a few hours, but the fires caused by the graphite columns took more than 10 days to put out.

In modern nuclear reactors, water is used to cool the reactor core and control nuclear fission (Shutterstock)

Correcting the mistakes of the past

According to a report on the "Live Science" website, newer nuclear plants can avoid previous mistakes in nuclear reactor designs by relying on water because it is a "cooler" and a "moderator" at the same time, and scientists called these reactors Light water reactors.

This type of reactor includes a large vessel containing the reactor core, the power source, surrounded by running water to cool it.

As was the case in RPMK 1000 reactors, the heat of the chain reactions vaporizes the water, and the steam powers the turbines that generate electricity.

Instead of relying on graphite to regulate the chain reaction, scientists used water to play this role.

Water slows down the speed of free neutrons resulting from nuclear fission, so the reactions stabilize, and when the reactor temperature rises, the evaporation of water increases, and the amount of water decreases, so it does not play a role in regulating the neutrons, and thus the chain reaction slows down, which prevents the reactor from exploding resulting from the increase in heat.

This type of process is known as a negative feedback loop.

Besides newer reactors, some nuclear plants still rely on RPMK-1000 reactors.

Those stations were subjected to many modifications after the Chernobyl accident, the most important of which is the addition of inhibitors for chain reactions to protect the reactor from excessive heat when operating at low power, increasing the number of graphite rods controlling the reactions with their modernization and modification so as not to exacerbate the reactions when moving, and increasing the fuel enrichment units nuclear.

Nuclear plants help us produce huge amounts of electricity, but the fear of their potential dangers, the scarcity of used nuclear fuel, and the desire to reduce global temperature;

Things that prompted various countries to go to produce clean energy derived from the sun and wind, a step to completely dispense with nuclear plants in the future.