|Fig. 1: Three Mile Island Accident Sign. (Source: Wikimedia Commons)|
The main risk of nuclear power is radiation and the negative health effects caused by radiation. The radiation associated with nuclear power is made up of subatomic particles traveling near the speed of light. Particles traveling this fast can easily enter the human body and damage biological cells, imitating cancer.  If these particles were to attack sex cells, they could cause genetic diseases in the offspring of the patient.
Radioactive materials are produced from nuclear power technology. These materials actively release radiation. There are many ways in which these materials can come in contact with humans especially those who work in nuclear power plants. They include: small radiation releases during routine plant operations, accidents in nuclear power plants, accidents transportation radioactive materials, and through the escape of radioactive wastes through confinement systems.
As summarized in Three Mile Accident Sign (Fig. 1), on March 28, 1979, the Three Mile Island Unit 2 (TMI-2) reactor near Middletown, Pennslyvania partially melted down.  The meltdown was caused by worker error, design deficiencies, and component failures. This was the most serious accident in the United States commercial nuclear power plant operating history. Though the meltdown released small amounts of radiation, there were no detected health effects on the plant workers or the public. From studies conducted by the Nuclear Regulatory Commission (NRC), the Environmental Protection Agency (EPA), and other government departments, it was found that about 2 million people who were around TMI-2 during the accident were estimated to have received a radiation dosage that was 1 millirem above the usual radiation dosage received from the background. 
In 1986, the NRC issued a policy statement establishing safety goals that would address risks to public health and safety from nuclear power plants. They addressed the risk associated with cancer in their policy stating, "the risk of cancer fatalities to the population near a nuclear power plant should not exceed 0.1% of the sum of cancer fatality risks from all other causes."  In August 1995, the NRC issued a policy statement on the use of probabilistic risk assessment (PRA) methods in nuclear regulatory activities. The PRA methodology provides a structured analytical process of assessing the likelihoods and consequences of nuclear reactor accidents.
The four basic elements of the policy are:
The use of PRA technology should be increased in all regulatory matters in a manner that complements the NRC's traditional defense-in-depth philosophy.
PRA and associated analysis should be used to reduce unnecessary conservatism associated with current regulatory requirements and guides, license commitments, and staff practices.
PRA evaluations in support of regulatory decisions should be as realistic as practicable and appropriate supporting data should be publicly available for review.
The NRC staff developed a PRA Implementation Plan which is updated semi-annually. 
© Charles Akin-David. 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.
 R. Bertell, No Immediate Danger: Nuclear Radiation and Its Biological Effects (Canadian Scholars Press, 1986), pp. 15-60.
 "Backgrounder: Three Mile Island Accident," U.S. Nuclear Regulatory Commission, February 2013.
 "Fact Sheet: Nuclear Reactor Risk," U.S. Nuclear Regulatory Commission, November 2011.