United States Nuclear Regulatory Commission - Protecting People and the Environment

Frequently Asked Questions About Liquid Radioactive Releases

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What is Tritium?

Tritium (H-3) is a weakly radioactive isotope of the element hydrogen that occurs both naturally and during the operation of nuclear power plants. Tritium has a half-life of 12.3 years and emits a weak beta particle. The most common form of tritium is in water, since tritium and normal hydrogen react with oxygen in the same way to form water. Tritium replaces one of the stable hydrogens in the water molecule, H2O, and creates tritiated water, which is colorless and odorless.

Tritium can be found in self-luminescent devices, such as exit signs in buildings, aircraft dials, gauges, luminous paints, and wristwatches. It is also used in life science research and in studies investigating the safety of potential new drugs.

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What is Strontium-90?

Strontium-90 (Sr-90) is a radioactive isotope that is produced in nuclear fission, the splitting of an atom's center that releases energy. Sr-90 has a half-life of about 29 years and emits a beta particle as it decays.

Sr-90 is used as a radioactive tracer in medical and agricultural studies. The heat generated as Sr-90 radioactively decays can be converted to electricity for long-lived, light-weight power supplies. Some examples are navigational beacons, weather stations, and space vehicles.

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Where do Tritium and Strontium-90 come from?

Tritium is produced naturally in the upper atmosphere when cosmic rays strike air molecules. It is also produced during nuclear weapons explosions, and commercially in nuclear reactors producing electricity.

Sr-90 comes from three sources:

  • fallout from above-ground explosions of nuclear weapons testing worldwide from 1963 to 1980;
  • radioactive releases from the 1986 Chernobyl nuclear power plant accident in the Ukraine; and
  • radioactive releases from nuclear power plants into the environment.

Approximately 99 percent of the Sr-90 in the environment comes from weapons testing fallout. Sr-90 takes about 29 years to lose half of its radioactivity. The fallout-based Sr-90 still remains in the environment at nominal levels because Sr-90 takes about 29 years to lose half of its radioactivity. Most of the remaining one percent of Sr-90 in the environment came from the Chernobyl accident. At individual U.S. nuclear power plants, the amount of Sr-90 released is so low that it is usually at or below the minimum detectable activity of sensitive detection equipment.

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How can Tritium and Strontium-90 affect me?

Exposure to very small amounts of ionizing radiation is thought to minimally increase the risk of developing cancer, and the risk increases as exposure increases.

Tritium is one of the least dangerous radionuclides because it emits very weak radiation and leaves the body relatively quick. Since tritium is almost always found as water, if ingested, it goes directly into soft tissues and organs. The dose to these tissues are generally uniform and dependent on the tissues' water content.

Sr-90, if ingested, tends to mimic calcium when it is in the body and therefore becomes concentrated in calcified tissues such as bones and teeth. If ingested in quantities that produce very large doses (about a thousand times higher than what we all receive from natural radiation), Sr-90 is known to increase the risk of bone cancer and leukemia in animals, and is presumed to do so in people. Below these doses, there is no evidence of excess cancer.

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What are normal amounts of tritium released from nuclear power plants?

Nuclear power plants release varying amounts of tritium, depending on the amount of liquid waste discharged via normal and abnormal release discharge paths and the type of reactor. In the United States, there are two basic types of operating reactors, a pressurized water reactor (PWR) and a boiling water reactor (BWR). PWRs typically have higher tritium releases than BWRs. In 2003, the average PWR released about 700 curies of tritium in liquid effluents and the average BWR released about 30 curies of tritium in liquid effluents.

Curies of Tritium Released in Liquid Effluents
Statistical Summary for 2003 PWR BWR
Total 40,600 665
Minimum 0.1 0
Maximum 2,080 174
Average 725 27.7
Number of Data 56 24

For information on plant-specific radioactive releases.

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What is the NRC doing about radiological leaks and spills?

The NRC has established a lessons learned task force to address inadvertent, unmonitored liquid radioactive releases from U.S. commercial nuclear power plants. This task force will review previous incidents and identify lessons learned from these events and determine what, if any changes are needed to the regulatory program. The NRC will enter the findings from the lessons learned task force into its formal agency lessons learned program.

The NRC licensing process for nuclear power plants includes a thorough review of all the plant's radioactive, gaseous, liquid, and solid waste systems, components, and programs to ensure that radioactive material is safely controlled in accordance with NRC regulations. The licensing process, evaluated the plant’s ability to safely handle, store, monitor, and discharge radioactive effluents in accordance with NRC requirements. These requirements include safety limits on radiation dose to plant workers and members of the public. During operation of the plant, the NRC continuously inspects licensee performance through the use of Resident Inspectors stationed at each plant and the use of technical specialist inspectors from the NRC Regional offices. If there is an abnormal situation at a plant, the Resident Inspector and Regional Specialists become involved to assess the licensee’s response to the situation to ensure NRC requirements are met.

As with any industrial facility, a nuclear power plant may deviate from normal operation with a spill or leak of liquid material. However, the design of the plant and the NRC inspection program provides reasonable assurance that even in abnormal situations, safety limits are met.

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Page Last Reviewed/Updated Friday, May 10, 2013