Chernobyl Disaster

Chernobyl disaster Perez, Millicent Mae Rafiei, Negar Rastegari, Keivon Ricardo, Michaela Salting, Lloyd Vincent Templo, Kate-lynn

Chernobyl disaster ™The Chernobyl disaster, or simply Chernobyl, was a nuclear reactor accident in the Chernobyl Nuclear Power Plant in the Soviet Union. ™The worst nuclear power plant accident in history. ™Resulting in a severe release of radioactivity into the environment following a massive power excursion which destroyed the reactor.

Chernobyl disaster ©26 April 1986 at 01:23:44 am, reactor number four at the Chernobyl plant, near Pripyat in the Ukrainian SSR, exploded. ©Further explosions and the resulting fire sent a plume of highly radioactive fallout into the atmosphere and over an extensive geographical area.

Chernobyl disaster ®The plume drifted over extensive parts of the western Soviet Union, Eastern Europe, Western Europe, Northern Europe, and eastern North America. Large areas in Ukraine, Belarus, and Russia were badly contaminated, resulting in the evacuation and resettlement of over 336,000 people. ®About 60% off the radioactive fallout landed in Belarus.

Evacuation of Pripyat

HISTORICAL SIGNIFICANCE ÖValeri Legasov compared the Chernobyl to the eruption of Mount Vesuvius which buried Pompei in AD 79. ÖThe hot ashes from Vesuvius completely covered Pompei. ÖThe radioactive debris of the Chernobyl reactor covered an area more than 5,000 km with nearly 20 million Curies of radionuclides, making human life impossible.

Nuclear power plant Ü The Chernobyl station is located near the town of Pripyat, Ukraine, 18 km northwest of the city of Chernobyl, 16 km from the border of Ukraine and Belarus, and about 110 km north of Kiev. Ü The station consisted of four reactors of type RBMK-1000, each capable of producing 1 gigawatt (GW) of electric power, and the four together produced about 10% of Ukraine's electricity at the time of the accident

Location of the Chernobyl Nuclear Power Plant

The accident ő On April 26, 1986 at 1:23:44 a.m., reactor 4 suffered a massive, catastrophic power excursion. ő Resulting in a steam explosion, which tore the top from the reactor, exposed the core and dispersed large amounts of radioactive particulate and gaseous debris, allowing air to contact the superhot core containing 1,700 tonnes of combustible graphite moderator. ő The burning graphite moderator increased the emission of radioactive particles.

The accident ¤ Although much of the nuclear fuel in the reactor core did ultimately melt, it should be noted that the disaster was not a “nuclear meltdown“. ¤ the fuel melting was not a significant contribution to the radiological consequences of the accident. ¤ the accident was not caused by a loss of coolant.

Chernobyl after the disaster. Reactor 4 (center). Turbine building ( lower left). Reactor 3 (center right)

Test of the safety device ö daytime of April 25, 1986, reactor 4 was scheduled to be shut down for maintenance as it was near the end of its first fuel cycle. ö An experiment was proposed to test a safety emergency core cooling feature during the shut down procedure. ö the experiment, the reactor would be set at a low power setting and the steam turbine run up to full speed, at which point the steam supply would be closed off and the turbines allowed freewheeling and the results recorded.

Prior to the accident ∞Daytime of April 25, the reactor's electricity output had been gradually reduced to 50%. ∞The reduction output was postponed because a regional power station went offline. ∞11:04 p.m., April 25, the reactor shut-down resume. ∞According to the plan, the test should have been finalized during the day-

Prior to the accident ÿ Alexander Akimov was chief of the night shift. ÿ Leonid Toptunov was the operator responsible for the reactors operational regime, including the movement of the control rods. ÿ The night shift was not prepared to carry out the experiment.

Prior to the accident The test plan called for the power output of reactor 4 to be reduced from its nominal 3.2 GW thermal to 0.7–1.0 GW thermal. Toptunov committed an error and inserted the control rods too far, causing the reactor power dropped to 30 MW thermal. This low power output a phenomenon called xenon poisoning becomes

Prior to the accident At this low power output it was impossible to carry out the test. To increase power, control rods were pulled out of the reactor core, beyond the correct position for normal operations, and also beyond what is allowed under safety regulations. Slowly, the reactor's power only increased to 200 MW. Yet the

Prior to the accident  1:05 a.m. on April 26 extra water pumps were started increasing the water flow.  The flow exceeded the safe limit at 1:19 a.m.  The extra water lowered the core temperature and reduced steam voids.  since water also absorbs neutrons, this decreased reactor power further.  This prompted the operators to

Prior to the accident The increased water flow led to a fall in steam production and other changes in the operating parameters. At this point the automatic control system should have shut the reactor down. To avoid this, the operators had disabled the shut down system.

Fatal experiment 1:23:04 a.m. the experiment began. The extremely unstable condition of the reactor was not known to the reactor crew. With reactor output rapidly increasing, the operators pressed the AZ-5 panic button at 1:23:40, that ordered SCRAM. The SCRAM was ordered as a response to the unexpected rapid

Fatal experiment the SCRAM actually increased the reaction rate. At this point a massive energy spike occurred. The core overheated and some of the fuel rods fracture, blocking the control rod columns. Within three seconds the reactor output rose above 530 MW.

Fatal experiment ♣ By 1:23:47 the reactor jumped to around 30 GW thermal, ten times the normal operational output. ♣ The rapid increase in steam pressure destroyed fuel channels and ruptured the large diameter cooling water pipes. ♣ Fuel rods began to melt and reached the cooling water in the flooded basement.

Fatal experiment ♦ At 1:24, the first powerful steam explosion took place. ♦ It damaged the top of the reactor hall and ejected fragments of material. ♦ The 2,000 tonne lid was blown off the reactor. ♦ A second more powerful explosion occurred about two or three seconds after the first.

Fatal experiment ♥ According to Medvedev Z. The second explosion was caused by the hydrogen which had been produced either by the overheated steam-zirconium reaction or by the reaction of red-hot graphite with steam that produce hydrogen and oxygen.

Aerial view of the damaged core. Roof of the turbine hall is damaged (center)

Lumps of graphite moderator ejected from the core. The largest lump shows an intact control rod channel.

Radiation levels ♠ The radiation levels in the worst-hit areas of the reactor building have been estimated to be 5.6 röntgen per second (R/s), which is equivalent to 20,000 röntgen per hour (R/h). ♠ A lethal dose is around 500 röntgen over 5 hours, in some areas, unprotected workers received fatal doses within several minutes.

Fire containment Shortly after the accident, firefighters arrived to try to extinguish the fires. The first one to the scene was a Chernobyl Power Station firefighter brigade under the command of Lieutenant Vladimir Pravik, who died on May 9, 1986 of acute radiation sickness.

Fire containment The immediate priority was to extinguish fires on the roof of the station and the area around the building containing Reactor No. 4 in order to protect No. 3 and keep its core cooling systems intact. The fires were extinguished by 5 a.m., but many firefighters received high doses of radiation.

Fire containment The fire inside Reactor No. 4 continued to burn until 10 May 1986. The fire was extinguished by a combined effort of helicopters dropping over 5,000 tonnes of materials like sand, lead, clay and boron onto the burning reactor and injection of liquid nitrogen.

Evacuation of Pripyat The government committee formed to investigate the accident, led by Valeri Legasov, arrived at Chernobyl in the evening of April 26. By that time two people were dead and 52 were hospitalized. the committee, faced with ample evidence of extremely high levels of radiation and a number of cases of radiation exposure.

Possible causes of the disaster ☻two official theories about the main cause of the accident. ☻1st: ‘flawed operators theory‘ ' design theory’ ☻2nd: ‘flawed

‘flawed operators theory‘ ✮effectively placed the blame solely on the power plant operators. ✮ The operators violated plant procedures and were ignorant of the safety requirements needed by the RBMK design. ✮This was partly due to their lack of knowledge of the reactor's design as well as lack of experience and training. ✮Several procedural irregularities also

‘flawed design theory’ ✐attributing the accident to flaws in the RBMK reactor design, specifically the control rods. ✐The reactor had a dangerously large positive void coefficient. ✐ A more significant flaw was in the design of the control rods that are inserted into the reactor to slow down the reaction.

‘flawed design theory’ the control rod end tips were made of graphite and the extenders were hollow and filled with water. while the rest of the rod was made of boron carbide. when the rods are initially inserted into the reactor, the graphite ends displace some coolant. greatly increases the rate of the fission reaction.

The effects of the disaster The nuclear meltdown provoked a radioactive cloud that floated not over just the modern states of Russia, Belarus, Ukraine and Moldova, but also Turkish Thrace, Macedonia, Serbia, Croatia, Bulgaria, Greece, Romania, Lithuania, Estonia, Latvia, Finland, Denmark, Norway, Sweden, Austria, Hungary, the Czech Republic and the Slovak Republic, The Netherlands, Belgium, Slovenia, Poland, Switzerland, Germany, Italy, Ireland, Franc (including Corsica) the

The effects of the disaster ☢Contamination from the Chernobyl accident was scattered irregularly depending on weather conditions. ☢Studies in countries around the area say that over one million people could have been affected by radiation.

Radioactive release ♛The Chernobyl release was controlled by the physical and chemical properties of the radioactive elements in its core. ♛Particularly dangerous are highly radioactive compounds that accumulate in the food chain, such as some isotopes of iodine and strontium. ♛At different times after the accident, different isotopes were responsible

Health of plant workers ♚237 people suffered from acute radiation sickness, of whom 31 died within the first three months. ♚135,000 people were evacuated from the area, including 50,000 from Pripyat.

Residual radioactivity in the environment ♨Rivers, lakes and reservoirs ♨The radioactive contamination of aquatic systems therefore became a major issue in the immediate aftermath of the accident. ♨In the most affected areas of Ukraine, levels of radioactivity in drinking water caused concern during the weeks and months after the accident. ♨After this initial period however, radioactivity in rivers and reservoirs

Residual radioactivity in the environment ❀Groundwater ❀Groundwater was not badly affected by the Chernobyl accident since radionuclides with short half-lives decayed away a long time before they could affect groundwater supplies.

Residual radioactivity in the environment ϋ Flora and Fauna ϋ After the disaster, four km² of pine forest in the immediate vicinity of the reactor turned ginger brown and died, earning the name of the "Red Forest". ϋ Some animals in the worst-hit areas also died or stopped reproducing. ϋ Most domestic animals were evacuated from the exclusion zone,

Chernobyl Today ö The Chernobyl reactor is now enclosed in a large concrete shelter which was built quickly to allow continuing operation of the other reactors at the plant. ö However, the structure is not strong or durable. ö A New Safe Confinement structure will be built by the end of 2011.

The Sarcophagus, the concrete block surrounding reactor #4

Assessing the disaster's effects on human health UNSCEAR states: “Among the residents of Belarus, the Russian Federation and Ukraine there had been, up to 2002, about 4,000 cases of thyroid cancer reported in children and adolescents who were exposed at the time of the accident, and more cases are be expected during the next decades. Apart from this increase, there is no evidence of a major public health

Comparison with other disasters  The Chernobyl disaster caused a few dozen immediate deaths due to radiation poisoning  a few thousand premature deaths are predicted over the coming decades.  Since it is often not possible to prove the origin of the cancer which causes a person's death  it is difficult to estimate Chernobyl's longterm death toll, which is still a hotlydebated issue

Comparison with other disasters

The failure of the Banqiao Dam (Henan, China, 1975) - where an estimated 26,000 people died from flooding and another 145,000 died during subsequent epidemics and famine. The Bhopal disaster (India, 1984) - the BBC gives the death toll as nearly 3,000 people dead initially, and at least another 15,000 have died from subsequent illnesses. The Great Smog (London, United Kingdom, 1952) -where medical services compiled statistics and found that the fog had killed 4,000 people initially, and another 8,000 died in the weeks and months that followed. The MV Doña Paz disaster, (Philippines, 1987) - this petroleum products fire at sea killed

Chernobyl after the disaster

Chernobyl after the disaster

The end!