The Chernobyl Disaster

Marc Joshua
May 29, 2018

Submitted as coursework for PH241, Stanford University, Winter 2018


Fig. 1: Chernobyl reactor after the disaster. (Source: Wikimedia Commons)

On April 25th, 1986 the Chernobyl Nuclear Power Plant in Pripyat, Ukraine malfunctioned, resulting in one of the largest unintentional releases of radioactivity to date. [1] As a result, the explosion and acute radiation poisoning caused the deaths of 30 people within the next couple weeks. [1] The radioactive materials released into the atmosphere caused the entire city to evacuate immediately.


Chernobyl's operators ran the nuclear power plant very carelessly, refusing to take safety precautions and communicating procedures with safety personnel. [2] On April 25th, 1986 before a routine shutdown, the crew for the 4th reactor was testing the quality of its turbines and the amount of supply power that could be transferred to the main circulating pumps. [2] In order to run through the test, numerous operator actions such as disabling the automatic shutdown mechanism had to take place. Once the operator decided to shut down the reactor, Xenon-135 poisoning began to occur on the fuel rods and the thermal power of the plant continued to decrease. [3] In order to return the thermal power and fuel rods to safe conditions, the control rods were removed, causing thermo-hydraulic instability in the reactor. After removing the control rods, only 4 of the 8 water pumps that supplied cooling water to the reactor were working. [3] The increase of steam voids in the cooling water caused increased reactivity. This eventually led to the burning of the Xenon-135 and an uncontrollable surge in thermal power, which reached 30 000 MW. [3] The nuclear chain reaction caused the entire reactor to explode. Fig. 1 shows the aftermath.

Effects on Humans

The result of the Chernobyl Disaster and the radiation that comes with it proves to have long-lasting effects on humans. Approximately 400 000 Ukrainians were forced to relocate because of the poor conditions in the contaminated area, affecting civilians social networks, economic stability, and emotional well-being. [4] The radioactivity didnt only have an impact on many peoples living situation but on their long-term health as well. Studies have shown that there was a large increase of thyroid cancer, due to the radioactive iodine released by the nuclear power plant, among children and adolescents who lived in the contaminated areas after the accident. [4] In fact, around 600 cases of thyroid cancer have been determined in civilians who were under the age of 18 at the time of the accident. The Chernobyl liquidators who were exposed to high radiation doses were affected the worst. 28 of the 134 liquidators died due to acute radiation sickness. [1] Recent studies show that the victims of Chernobyl are not at a higher risk of getting leukemia. [1] The majority of the civilians living in Chernobyl were exposed to relatively low radiation doses, which means the radiation won't have a negative effect on fertility or any pregnancy outcomes.

© Marc Joshua. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] Y. Socol, "Reconsidering Health Consequences of the Chernobyl Accident," Dose Response 13, 1 (2015).

[2] V. Kortov and Yu. Ustyantsev, "Chernobyl Accident: Causes, Consequences and Problems of Radiation Measurements," Radiat. Meas. 55, 12 (2013).

[3] K. Alnoaimi, Xenon-135 Reactor Poisoning, Physics 241, Stanford University, Winter 2014.

[4] D. L. Henshaw, "Chernobyl 10 Years On: Thyroid Cancer May Be The Only Measurable Health Effect," Brit. Med. J. , 1052 (1996).