Preliminary evaluation of liquid integrity monitoring methods for gunite and associated tanks at the Oak Ridge National Laboratory, Oak Ridge, Tennessee

The Gunite and Associated Tanks (GAAT) are inactive, liquid low-level waste (LLLW) tanks located in and around the North and South Tank Farms (NTF and STF) at Oak Ridge National Laboratory (ORNL). These tanks, which contain a supernatant over a layer of radioactive sludge, are the subject of an ongoing treatability study that will determine the best way to remove the sludge and remediate the tanks. As part of this study, a preliminary assessment of liquid integrity (or ``tightness``) monitoring methods for the Gunite tanks has been conducted. Both an external and an internal liquid integrity monitoring method were evaluated, and a preliminary assessment of the liquid integrity of eight Gunite tanks was made with the internal method. The work presented in this report shows that six of the eight GAAT considered here are liquid tight and that, in the case of the other two, data quality was too poor to allow a conclusive decision. The analysis indicates that when the release detection approach described in this report is used during the upcoming treatability study, it will function as a sensitive and robust integrity monitoring system. Integrity assessments based on both the internal and external methods can be used as a means of documenting the integrity of the tanks before the initiation of in-tank operations. Assessments based on the external method can be used during these operations as a means of providing a nearly immediate indication of a release, should one occur. The external method of release detection measures the electrical conductivity of the water found in the dry wells associated with each of the tanks. This method is based on the fact that the conductivity of the liquid in the GAAT is very high, while the conductivity of the groundwater in the dry wells and the underdrain system for the GAAT is very low