Achieving Leak Tightness in New Savannah River Site Saltstone Disposal Units - 17454

Saltstone Disposal Unit (SDU) 6 is a new disposal unit at the Department of Energy's Savannah River Site Saltstone Disposal Facility. The Saltstone Facility is part of the site's overarching waste management and disposal system. It receives the low-level waste stream and will immobilize in grout more than 90 percent of the liquid volume generated during treatment of the site's liquid high level waste. SDU-6 is the first in a series of large disposal units to be constructed on site. Its internal diameter and height are 114 m (375 ft) and 13.1 m (43 ft), respectively. It uses a cylindrical wire-wrapped concrete water tank design (AWWA D110, Type I), and at 121 ML (32 Mgal), it is one of the largest structures of its kind in the country. Because of its size, SDU-6's base slab was placed in ten sections. Earlier placed sections restrained newer adjacent sections, resulting in shrinkage cracking. Visible cracks were repaired with epoxy. However, the SDU basemat leaked at less than an estimated 4 L/min rate during its first full-height hydrostatic test (2015). The project baseline was to install a coating system to chemically protect the concrete from the high-pH, high-sulfate Saltstone solutions. The coating was not installed during the first hydrostatic test, and subsequently, an adhered elastomeric liner system was chosen to provide higher assurance of bridging floor cracks and preventing leakage. A robust process was used to select and install a liner that will not only provide chemical protection but also achieve leak tightness, which was successfully demonstrated in a second hydrostatic test late in 2016. (authors)