Savannah River Remediation Begins Testing for Liquid Tightness of Saltstone Disposal Unit 6

Savannah River Remediation (SRR) will be performing a liquid tightness test this month on Saltstone Disposal Unit 6 (SDU 6), the first 30-million gallon, mega-volume salt waste disposal unit constructed at the Savannah River Site (SRS). SRR is the Liquid Waste Contractor for the U.S. Department of Energy at SRS.

The purpose of the liquid tightness test is to qualify the newly constructed SDU 6 for use, and, therefore, will be safe to store solidified decontaminated salt waste at SRS. During the test, SDU 6 will be filled with water to check for potential leakage outside of the unit.

A permanent disposal unit for Saltstone, SDU 6 is a cylindrical concrete unit that is based on a design used commercially for storage of water and other liquids.

SRR began filling SDU 6 with water on October 12, 2015. The volume of water that will be put into SDU 6 is equivalent to the amount of water that would fill 55 Olympic-sized swimming pools. During the approximately 22-day water fill activity, the unit will be continuously checked for any signs of leakage visible on the exterior. If any damp spots are detected, they will be immediately repaired.

Once the water fill is complete, the liquid tightness test will be performed. This test will use both qualitative and quantitative means to demonstrate the unit is liquid tight.

After the liquid tightness test is complete, which is expected to be in November, a dye/tracer will be introduced to the water in SDU 6. Approximately 332 gallons of Rhodamine WT will be introduced into the unit and mixed using submersible pumps. The bright, fluorescent red dye is certified by NSF International (the Public Health and Safety Organization) for use in drinking water and is commonly used in dye/tracer tests. The dye is being added as an additional means to confirm liquid tightness.

Finally, SDU 6 will be drained. The water will be pumped from SDU 6 to on-site drainage basins for a controlled discharge that will ultimately enter the Savannah River.

While this dye in the water may not visible to the naked eye, it may be detectable using black light. Because this dye is environmentally friendly, there are no health, safety, or environmental concerns with discharging this dyed water in the SRS ecosystem or the Savannah River.