Underground Pipes at Nuclear Reactors

Background

In the past, minor 

corrosion caused leaks in 

underground or buried pipes 

and related systems at several 

U.S. nuclear power plants, 

contaminating groundwater 

with minor levels of 

radioactive material. The 

plants’ safety systems still 

function properly despite these 

leaks. The types and amounts 

of radioactive material 

involved in the leaks fall short 

of the limits the NRC sets to 

maintain public health and 

safety, so the leaks do not 

present a risk to the public.

The most recent buried pipe leaks have mainly involved water with above-normal levels of 

tritium, a mildly radioactive isotope of hydrogen normally measured in picocuries (trillionths of a curie) 

per liter. The NRC reviews affected plants’ groundwater monitoring programs to confirm the leaks do 

not affect public health and safety and the environment. The NRC’s oversight of the buried pipe issue as 

a whole focuses on ensuring nuclear power plant operators properly monitor and, when necessary, repair 

the pipes. 

NRC Response

The NRC’s regulations focus on systems necessary to safely operate the plant or safely shut it 

down in case of an emergency. These safety systems’ buried piping is subject to inspection and testing 

requirements laid out in agency regulations and standards from the American Society of Mechanical 

Engineers. These standards call for regular flow testing and other examination of buried safety-related 

pipes, and NRC reviews have confirmed nuclear plants perform these tests several times every year. If 

leaks are detected, they must be repaired, although the repairs can be postponed up to 24 months if 

circumstances permit. NRC regulations also require plants to ensure procedures and resources are in 

place to prevent potential leaks from exceeding limits on radioactive material releases and public 

radiation doses. The agency’s resident inspectors, who are stationed full time at U.S. nuclear power 
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plants, regularly monitor all these activities. Any deficiencies can trigger additional NRC oversight of 

buried piping issues.

Industry Response

Following increased NRC inspections, industry groups have begun examining the issue as well. 

The Institute for Nuclear Power Operations has studied buried piping degradation and maintenance for 

several years, including individual plant efforts in this area. A non-nuclear industry group, NACE 

International (formerly the National Association of Corrosion Engineers), formed a “Nuclear Buried 

Piping” group to examine how its standards can be put to use at nuclear power plants. The Electric 

Power Research Institute (EPRI) produced recommendations for controlling buried pipe decay and other 

degradation, based on NACE standards. In addition, the nuclear power industry worked with EPRI to 

develop further guidance for buried piping repairs. The Nuclear Energy Institute issued guidance in 

2012 and 2015. The NRC continues to observe the initiative to determine if any further inspections or 

other oversight are called for.

License Renewal

When a nuclear plant licensee wants to renew a plant’s operating license, the licensee must show 

it can account for the effects of aging on a plant’s systems. Some categories of buried piping fall under 

these requirements. The NRC judges a plant’s Aging Management Programs against examples in the 

agency’s Generic Aging Lessons Learned (GALL) report, which includes information on the aging of 

both interior and exterior surfaces of buried pipes. Several recent license renewal applications have 

included terms for additional buried pipe inspections and replacement programs to account for recent 

operating plant experience. The NRC revised the GALL report in 2016, incorporating new information 

on managing buried piping. The agency also issued revised guidance for staff conducting license 

renewal inspections and reviews.

New Reactors

Applications for new nuclear power plants must show that the proposed reactor meets the same 

buried piping requirements current plants follow. The nuclear power industry and NRC staff are 

working with ASME to develop design requirements that use alternative materials to ensure stronger, 

more long-lived buried piping. Applicants for design certifications and new reactor licenses must also 

describe how their designs and operational procedures will ease eventual decommissioning by 

minimizing any contamination of the facility and environment, as well as the creation of radioactive 

waste. The NRC staff will incorporate current operating reactor experience as they review and evaluate 

measures applied by new reactor applicants to confirm they will minimize contamination. To date, many 

applications describe using fewer buried piping systems for fluids contaminated with radioactive 

material. 

More information on buried piping, including links to industry and NRC guidance, is available 

on the NRC website.

June 2018