Chernobyl Disaster
Gayathre
The Chernobyl disaster was one among the two nuclear energy accidents rated with maximum severity on the International Nuclear Event Scale. Chernobyl is a city, 130 km from Kyiv in the Ukraine republic of Soviet Union. 36 years ago, in 1986, an accident occurred in the reactor no:4 of the Chernobyl power plant due to the flawed reactor design that was operated by inadequately trained personnel.
Nuclear Reactor
Nuclear power plants use nuclear energy to produce steam and thus to generate electricity. Radioactive elements like Uranium and Plutonium are mainly used as nuclear fuels. These fuels are bombarded with neutrons ( a subatomic particle found inside the nucleus ) and they eventually split into fragments of intermediate mass along with the release of a massive amount of energy ( in the order of 200 mega electron volt ). This process is called Nuclear fission. The energy formed during this process is transferred to the surrounding matter as heat, and is used to produce electricity.
The nuclear reactors contain:
- Nuclear fuel – Uranium is the basic fuel.
- Moderators – Heavy water or graphite are used to slow down the neutrons released from fission.
- Control rods – Cadmium is generally used to absorb the neutrons.
- Coolant – water is generally used as coolant to transfer the heat from the core.
- Containment – They are a meter thick, concrete or steel structures to ensure that the radiation is contained even if a serious malfunction occurs inside.
1986, APRIL 25
Before the routine shutdown process, certain experiments were conducted in the 4th reactor of the Chernobyl power plant to check whether the reactor could supply some electricity required for the basic functioning of the power plant even if the reactor had to stop functioning. For this, reactors were made to work under critical conditions. Several safety measures were discarded for creating an abnormal environment. The reactors were RBMK reactors which used water as coolant and graphite as moderator. The experiment went out of hand and the reactor shot up. This made the rest of the water ( coolant ) to transform to heat.The steam of high pressure resulted in the destruction of the containment of the reactor, reacted with graphite at high temperature and formed hydrogen gas. This in turn led to another explosion. Disputes exist among experts regarding the characteristics of this second explosion. It is estimated that radioactive waste 50 times than that from the bomb dropped in Hiroshima, was released to hte environment
Two workers died at the time of the explosion. Around 28 people died within a few weeks, as a result of Acute Radiation Syndrome (ARS). 200 – 300 tonnes of water was pumped to the half of the reactor which was intact. 5000 tonnes of Boron, sand, clay etc were dropped onto the burning core to limit the release of radioactive particles. The radionuclides iodine-131 and caesium-137 were significant among the radiation doses delivered to the public. Around 116000 people living within a 30 km radius were evacuated and then relocated. Reports concluded that apart from 5000 thyroid cancer, there is no evidence for major health impact due to this disaster 20 years after the incident. A report from UNSCEAR in 2018 suggests that 20000 thyroid cancer was diagnosed in patients who were 18 and below at the time of the accident.
Major economic and social disruptions occurred to the population of Belarus, Ukraine and Russia. Around 200000 people from all over the Soviet Union were involved in the cleaning and recovering process. They received high doses of radiation averaging around 100 mSv.
The construction of reactor no:5 and 6 were cancelled after the accident, and the second reactor was shut down permanently in 1991. In 2013, the plant operators announced that units 1- 3 were fully defuelled and entered the decommissioning phase in 2015. In this phase, the contaminated equipment will be removed. And it is expected to be completed by 2065. For this ongoing decommissioning process, a large workforce is employed at the powerplant. As a part of the 2022 Ukraine invasion, the Chernobyl plant was occupied from 24th February to 31st March,2022.
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The Number Four RBMK reactor at the nuclear power plant at Chernobyl, Ukraine, went out of control during a test at low-power, leading to an explosion and fire that demolished the reactor building and released large amounts of radiation into the atmosphere.
- Nuclear fuel – Uranium is the basic fuel.
- Moderators – Heavy water or graphite are used to slow down the neutrons released from fission.
- Control rods – Cadmium is generally used to absorb the neutrons.
- Coolant – water is generally used as coolant to transfer the heat from the core.
- Containment – They are a meter thick, concrete or steel structures to ensure that the radiation is contained even if a serious malfunction occurs inside.