Chernobyl, Ukraine

Chernobyl, Ukrainian Tschornobyl, Čornobyl ‘ [t ʃ -bel], city in the Kiev region, near the confluence of the Dnieper tributary Pripjat in the Kiev reservoir and the name of the Chernobyl nuclear power plant (formerly 4,000 MW installed capacity) in the neighboring city 17 km away Pripyat (Ukrainian Pripyat, Pripjet). Before the reactor accident in 1986, Chernobyl had around 12,500 residents.

Today the city has no permanent population; Around 500 people live here in shifts and are involved in monitoring and managing the 30 km isolation zone around the nuclear power plant. The power plant personnel who used to live in Pripyat now live with their families in Slavutytsch, which was built in 1986-88, 65 km to the east. Even before 1986 there was hardly any industry in Chernobyl (small ironworks).

According to agooddir, Chernobyl was first mentioned in 1193; city ​​since 1941. The name Chernobyl became world famous due to the reactor disaster in Pripyat.

Reactor accident – procedure and causes

On April 26, 1986, a graphite-moderated pressure tube reactor of the type RBMK-1 000 (nuclear reactor), the most momentous reactor accident to date. The triggering event was a test on the turbo generators in Unit 4, which was to be carried out at low power. To do this, the thermal reactor power had to be reduced, but fell into a power range in which the reactor was unstable and should have been shut down for safety reasons. The test-related reduction in the coolant throughput in the reactor core then resulted in a sudden, uncontrolled increase in power after the start of the test, which resulted in overheating of the fuel and the fuel rods. The sudden evaporation of the cooling water due to the rise in temperature, possibly exacerbated by so-called steam explosions, first destroyed the reactor core, followed by a hydrogen explosion, the reactor chamber and the reactor building. Radionuclides released; the moderator graphite caught fire. Organizational deficiencies, operating errors and violations of the operating regulations as well as the design of the RBMK reactor with unfavorable physical and safety properties (e.g. positive reactivity coefficients) and inadequate safety equipment were essential for the course of the accident. As a result of the system, the sudden increase in power increased itself, which could not be compensated for by the control and the relatively sluggish emergency shutdown system. In addition, there was no outer safety container for the reactor as an additional safety barrier.

Radioactive emissions and radiation exposure

After ten days, after about 5,000 t of heat-insulating and radiation-absorbing material (sand, clay, dolomite, boron, lead) were dropped on the reactor and nitrogen was introduced, the graphite fire was extinguished and the massive release of radionuclides into the environment and the atmosphere was largely over. According to earlier official Soviet information, a total of 3–4% of the radioactive inventory was released (more than 2 · 10 18  Bq); However, more recent estimates by the International Atomic Energy Agency (IAEA) come to around 30% of the radioactive inventory (around 1.2 · 10 19 Bq) including the noble gases (100% release). About 240 people directly involved (reactor personnel, fire fighters, helicopter pilots) received an effective dose equivalent of several sieverts (Sv) with fatal (in 28 cases) or seriously harmful consequences. Around 116,000 people were evacuated from the most affected areas within a 30 km zone around the reactor after the accident. It must be assumed that larger parts of the population have received equivalent doses of up to 1 Sv. The 210,000 “liquidators” (about half of them soldiers) were also exposed to considerable radiation;

The “sarcophagus” is exposed to temperature and radiation from the inside as well as to attacks from erosion, corrosion and leaching and is also not earthquake-proof. As part of a renovation program (SIP, English for “shelter implementation plan”), it was therefore planned since 1997 to convert the “sarcophagus” into an ecologically safe enclosure with the help of international technical and financial support. In 2010, construction began on the new protective cover, which is 257 m wide, 108 m high and 162 m long and is expected to last for up to 100 years. In November 2016, the new protective cover was pushed over the old sarcophagus on slide rails. In July 2019, the protective cover was officially put into operation by Ukrainian President Volodymyr Selenskyj.

The assessment of radiation exposure with regard to the health consequences for the population (around 15 million people in the affected regions) is difficult because meaningful and reliable health statistics are lacking and the individual or collective equivalent doses are not precisely known. A long-term increase in the incidence of cancer (especially leukemia and thyroid cancer) in the affected areas is feared. So expected z. For example, the IAEA’s “Chernobyl Forum”, according to recent studies, reported about 4,000 additional fatal cancer cases among the former or returned residents (around 400,000) of the highly contaminated zones and the helpers who were involved in the extinguishing and rescue work. Other scientific studies of the effects of radiation include a link between the Soviet data from 1986 and those of international bodies. Depending on the risk factor used by the International Commission for Radiation Protection (ICRP), 120,300 (additional) up to 264,600 deaths within 50 years are assumed in the Chernobyl region. Reliable statements about the type and extent of late damage can only be expected in the future in the context of long-term studies. Initial results of these studies show a significant increase in thyroid cancer in some areas of Belarus, Russia and Ukraine in people who were children or adolescents at the time of the accident, which is attributed to high levels of radioactive iodine contamination. Further information on the increase in cancer incidence and radiation-related mortality is controversial and has not been conclusively checked or confirmed.

Decommissioning and dismantling of the nuclear power plant

Despite this disaster, the government of Ukraine decided at the end of 1993, with reference to energy supply bottlenecks, to keep units 1 and 3 in operation. Block 2 was taken out of service after a fire in 1991. For the final shutdown of the nuclear power plant, Ukraine demanded loans and grants totaling 2 billion euros from the G-7 countries in 1995. The Ukrainian Development Agency (NAURR) and the European Bank for Reconstruction and Development (EBRD) signed an agreement in 1997 on a Chernobyl Special Fund (CSF, “Chernobyl Shelter Fund”), from which the SIP program is to be financed with around 750 million euros. The EBRD estimates the total cost of the SIP at 2.1 billion euros, which will be raised by 40 countries and organizations. In addition to the creation of replacement capacities, the Chernobyl special fund was a prerequisite for the closure of units 1 and 3. In June 2000, the Ukrainian government set a detailed schedule for the final shutdown of the nuclear power plant for the first time: on December 15, 2000, the last working unit of the nuclear power plant became, Block 3, taken offline. In addition to the new protective cover, a dry store was also built in which over 21,000 fuel elements are dried and then concreted in. The aim is, to be able to safely store the nuclear waste in the interim storage facility for up to 100 years. After initial tests, the interim storage facility is scheduled to go into operation in July 2021.

Radiation exposure through soil contamination

In the Chernobyl region and other parts of Ukraine, Belarus and Russia, areas with a total area of ​​145,000 km 2 and a population of approx. 7 million people are contaminated by radioactive fall-out as a result of the disaster (soil contamination greater than 37 kBq / m 2), v. a. by the long-lived radionuclide cesium  137 (half-life 30 years). They can only be used to a limited extent at the moment. Sections with around 26,000 km 2 and a population of around 1 million people (185 to 1 480 kBq / m 2) as well as the 30 km zone around Pripjat (soil contamination over 1.5 MBq / m 2) are highly contaminated). It was locked and the population completely evacuated. A total of around 320,000 people were evacuated or relocated from the highly contaminated areas. Determining and assessing radiation exposure with regard to the health consequences for the population is difficult, since soil contamination in particular is extremely inhomogeneous. First detailed investigations in various areas of the highly contaminated areas show that the contamination with cesium 137 is well above the officially stated values. The additional radiation exposure of the partially illegally returned population, who mainly feeds on local cultivation, is today around 1.2 mSv / a and thus within the fluctuation range of natural exposure in Europe. The near zone of the power plant (within a radius of 5 km) is considered uninhabitable for at least another seven decades. Over ten days after the disaster, other large parts of Europe (to varying degrees) were also contaminated by the atmospheric spread of the released radioactive substances. a. Finland, Sweden, all of Central Europe, Romania and Bulgaria).

In Germany, there was greater soil contamination in the south, south-east and south-west than in the north and west (Munich approx. 35 kBq / m 2), but after a few years the pollution decreased to the levels of natural radioactivity. The resulting personal dose in the population mean is estimated to be around 1 mSv for Germany in 50 subsequent years. In comparison, the mean natural radiation exposure in Germany (natural environmental radioactivity, space radiation, etc.) is around 2–2.5 mSv per year.

Global impact

The increase in atmospheric radioactivity due to the accident can be proven globally. After the above-ground nuclear weapons tests and a serious nuclear accident in a military facility (former Soviet Union), the Chernobyl disaster caused the largest input of artificial radioactivity into the environment to date. The Chernobyl reactor accident represented a deep political and psychological turning point for the public discussion about nuclear energy generation worldwide and gave rise to an intense debate in many countries about phasing out nuclear energy (nuclear phase-out, dose, GAU, radioactivity, radiation exposure, Radiation damage, radiation protection).

Chernobyl, Ukraine