United States Nuclear Regulatory Commission - Protecting People and the Environment

Buried Piping Activities

Nuclear power plants have extensive piping systems. Some of these pipes are buried. Cooling water is the most common material transported in buried pipe. Cooling water is generally taken from a lake or river and, except for a slight increase in temperature, is returned unchanged to the same body of water. Generally, this water contains only naturally occurring, background, levels of radioactive materials. Some buried piping also transports smaller amounts of water that may contain slightly elevated levels of radioactive isotopes, most commonly tritium. A few buried pipes may contain materials other than water. Diesel fuel is the most significant of these materials.

The NRC defines buried piping as piping which is in contact with soil. The NRC recognizes that other structures and components exist in nuclear power plants which are beneath the surface of the earth but do not meet the definition of buried piping and are not included in the NRC's buried piping activities. These other structures and components include piping enclosed in trenches or vaults. The NRC distinguishes between buried piping and other structures and components beneath the surface of the earth because they are exposed to different environments, they corrode by different mechanisms, and they are protected from corrosion differently.

At nuclear power plants, the buried piping systems are comparable to those used in other industries such as public water supply and oil and gas transmission. Preventative measures are taken for piping which may corrode, such as coating piping with corrosion resistant material. While buried piping is normally reliable, damage to the corrosion resistant coatings can lead to small leaks.

As a result of this type of corrosion, several leaks in buried pipes have occurred recently. These leaks have not created safety hazards at the plants because, in spite of the leak, the pipe was still carrying more than enough water to cool the plant. While some of these leaks did introduce slightly elevated levels of radiation into the ground water, they did not result in the exposure of any member of the public or power plant employee to radiation beyond regulatory limits.

While these incidents have not jeopardized public health and safety, the NRC and the nuclear power industry as a whole are reexamining the issue of buried piping to determine whether any changes are required in the current approach to the design, maintenance, and inspection of buried piping. Current NRC activities and some industry activities are described in the linked documents below. The NRC anticipates that, in the short term, the increase in excavation and inspection could increase the frequency of discovery of degraded buried piping.

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Page Last Reviewed/Updated Friday, April 15, 2016