|Fig. 1:The inner parts of a heavy water reactor. (Source: Wikimedia Commons)|
India has welcomed nuclear energy as a long term sustainable solution in creating electrical energy. However, this adoption is a double-sided solution, as nuclear energy does create energy efficiently, however with dangerous, radioactive materials. Like many other nations with nuclear reactors, India has also encountered an accident at Kalpakkam in 1999. Although not as large or catastrophic as Chernobyl, the incident at Kalpakkam shifted attention to the health of the plant workers.
To understand the accident, it is essential to first look at how heavy water reactors function. Heavy water reactors (See Fig. 1) contain water with the hydrogen replaced by deuterium, a heavier isotope of hydrogen. The heavy water is used in two ways: as a moderator to slow down neutrons emitted during fission so that they have a higher chance of being captured by other fissile nuclei and as a coolant to carry away the heat produced.  In the process, fission creates radioactive isotopes such as Cs-137 and Sr-90 which is mainly fatal if ingested, but uranium isotopes such as U-232 emitting gamma rays are also produced, creating heat and direct radiation upon decay in high-level waste. [2,3]
Since Kalpakkam Atomic Reprocessing Plant is a fuel reprocessing plant, there are chemical processes to extract plutonium and uranium from spent fuel that has been exposed to radiation in the reactors.  Throughout the functioning of this process, large quantities of radioactive waste are produced and are categorized into low, medium and high level radioactive concentrations. Due to the leak, high level waste had penetrated into a tank designated for low-level waste, resulting in large radiation doses to many of the workers. 
For Kalpakkam, the incident arose when workers were inspecting tubes within the reactor, which had cracks and vibration issues.  In the process, a valve came undone suddenly and a large amount of the radioactive heavy water leaked out. 42 workers were reportedly in charge of cleaning up the spilt heavy water. It has been disclosed that the radiation doses to the workers were higher than the annual limit, but lower than the lifetime dose, but the exact amount was not disclosed. To put into context, the amount of exposure is somewhere in between 30 mSv, the annual dose limit, and a cumulative dose of 100 mSv, within a 5-year radiation exposure span.  The final result was that 7 workers were not able to work in radioactive environments in the future due to the immense exposure and most of the other workers that helped clean the spill were limited in how long they could work in radioactive zones. Even after the incident had been resolved, there were many lingering effects on the surrounding environment. The exposure to the spill gave workers an increased chance at developing thyroid disease and thyroid cancer later in life. As a result, there was a rapid increase of autoimmune thyroid diseases and cancer in the surrounding villages. [5,6] The dangers remain as radiation is released into plants that are subsequently eaten by animals that are then eaten by humans. 
© Udit Goyal. 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.
 M. V. Ramana and A. Kumar, "Safety First? Kaiga and Other Nuclear Stories," Economic and Political Weekly 45, No. 7, 47 (2010).
 "Radioactive Waste," U.S. Nuclear Regulatory Commission, April 2015.
 J. Kang and F. N. von Hippel, "U-232 and the Proliferation-Resistance of U-233 in Spent Fuel," Sci. Global Secur. 9, 1 (2001).
 S. Anand, "India's Worst Radiation Accident," Outlook India, 28 Jul 03.
 K. Majumder, "The Lessons from the Kalpakkam Nuclear Facility," Tehelka Magazine, 11 Sep 10.
 H. Shimp, "Effects to the Human Body From Nuclear Fallout," Physics 241, Stanford University, Winter 2017.