The Department of Energy's Office of Environmental Management (DOE) is responsible for the safe cleanup of sites used for nuclear weapons development and government-sponsored nuclear energy research. Low-level radioactive waste (LLW) is the most volumetrically significant waste stream generated by the DOE cleanup program. LLW is also generated through commercial activities such as nuclear power plant operations and medical treatments. The laws and regulations related to the disposal of LLW in the United States have evolved over time and across agencies and states, resulting in a complex regulatory structure. DOE asked the National Academies of Sciences, Engineering, and Medicine to organize a workshop to discuss approaches for the management and disposition of LLW. Participants explored the key physical, chemical, and radiological characteristics of low-level waste that govern its safe and secure management and disposal in aggregate and in individual waste streams, and how key characteristics of low level waste are incorporated into standards, orders, and regulations that govern the management and disposal of LLW in the United States and in other major waste-producing countries. This publication summarizes the presentations and discussions from the workshop.

Department of Energy (DOE) facilities, located at sites across the nation, generate large quantities and a wide variety of low-level radioactive waste (LLRW) from nuclear defense production and research and development activities. All DOE-generated LLRW is disposed of at DOE disposal sites. Most DOE waste generating sites do not have disposal facilities on site and so must ship their LLRW to one of six currently active DOE disposal locations. Four disposal sites are located in generally arid regions: the Hanford Reservation (HANF) in the state of Washington, the Nevada Test Site (NTS), the Idaho National Engineering Laboratory (INEL), and the Los Alamos National Laboratory (LANL) in New Mexico. The other two disposal sites are located in the humid southeast: The Savannah River Plant (SRP) in South Carolina and the Oak Ridge National Laboratory (ORNL) in Tennessee.

The US Department of Energy (DOE) and its contractors have long been pioneers in the field of radiological performance assessment (PA). Much effort has been expended in developing technology and acquiring data to facilitate the assessment process. This is reflected in DOE Order 5820.2A, Radioactive Waste Management Chapter III of the Order lists policy and requirements to manage the DOEs low-level waste; performance objectives for low-level waste management are stated to ensure the protection of public health and the environment. A radiological PA is also required to demonstrate compliance with the performance objectives. DOE Order 5820.2A further requires that an Oversight and Peer Review Panel be established to ensure consistency and technical quality around the DOE complex in the development and application of PA models that include site-specific geohydrology and waste composition. The DOE has also established a Performance Assessment Task Team (PATT) to integrate the activities of sites that are preparing PAs. The PATT's purpose is to recommend policy and guidance to DOE on issues that impact PAs so that the approaches taken are as consistent as possible across the DOE complex.

The United State Department of Energy (US DOE) disposes of low-level radioactive waste in near-surface disposal facilities. Safety of the disposal operations is evaluated for operational safety as well as long-term safety. Operational safety is evaluated based on the perceived level of hazard of the operation and may vary from a simple safety assessment to a safety analysis report. Long-term safety of all low-level waste disposal systems is evaluated through the conduct of a radiological performance assessment. The US DOE has established radiological performance objectives for disposal of low-level waste. They are to protect a member of the general public from receiving over 25 mrem/y, and an inadvertent intruder into the waste from receiving over 100 mrem/y continuous exposure or 400 mrem from a single exposure. For a disposal system to be acceptable, a performance assessment (PA) must be prepared which must be technically accurate and provide reasonable assurance that these performance objectives are met. Technical quality of the performance assessments is reviewed by a panel of experts. A number of lessons have been learned from conducting several preliminary reviews of performance assessments. These lessons are shared among the various US DOE sites to improve the process of evaluating low-level waste disposal sites for long-term performance.