9+ years of disposal experience at the Waste Isolation Pilot Plant (WIPP)

With almost a decade of operating experience, the Waste Isolation Pilot Plant (WIPP) has established an enviable record by clearly demonstrating that a deep geologic repository for unconditioned radioactive waste in rock salt can be operated safely and in compliance with very complex regulations. WIPP has disposed of contact-handled transuranic (TRU) waste since 1999 and remote-handled TRU waste since 2007. Emplacement methods range from directly stacking unshielded 0.21-4.5 m3 containers inside disposal rooms to remotely inserting highly radioactive 0.89 m3 canisters into horizontally drilled holes (shield plugs placed in front of canisters protect workers inside active disposal rooms). More than 100 000 waste containers have been emplaced, and one-third of WIPP's authorized repository capacity of 175,000 m3 has already been consumed. Principal surface operations are conducted in the waste handling building, which is divided into CH and RH waste handling areas. Four vertical shafts extend from the surface to the disposal horizon, 655 m below the surface in a 1000 m thick sequence of Permian bedded salt. The waste disposal area of about 0.5 km2 is divided into ten panels, each consisting of seven rooms. Vertical closure (creep) rates in disposal rooms range up to 10 cm per year. While one panel is being filled with waste, the next one is being mined. Mined salt is raised to the surface in the salt shaft, and waste is lowered down the waste shaft. Both of these shafts also serve as principal access for personnel and materials. Underground ventilation is divided into separate flow paths, allowing simultaneous mining and disposal. A filter building near the exhaust shaft provides the capability to filter the exhaust air (in reduced ventilation mode) through HEPA filters before release to the atmosphere. WIPP operations have not exposed employees or the public to radiation doses beyond natural background variability. They consistently meet or exceed regulatory standards and expectations. Process improvements continuously reduce cycle times and costs. During the past few years, regulators have approved configuration changes that eliminated some unnecessary tests and activities. Many more could be targeted to further reduce vulnerability, while maintaining and even enhancing safety. While WIPP is licensed to dispose of only defense-related TRU waste, past experiments and performance assessments have shown that heat-generating high-activity waste could also be safely isolated in salt (and without prior vitrification). Thus, beyond its current restrictions, WIPP helps pave the way toward permanent isolation of all categories of radioactive waste. (author)