From 1943 until the late 1980s, the Hanford Site in Hanford, Washington, produced plutonium for the U. S. nuclear arsenal. The production of high-level nuclear waste during plutonium production was transferred to 177 underground storage tanks on the Hanford plateau. These underground tanks were first produced with a single steel shell (single-shell tanks, surrounded by concrete) and then with double steel shells (double-shell tanks, surrounded by concrete). Single-shell tanks were first produced in the late 1940s during the height of the Cold War. The waste in the tanks is scheduled to be encapsulated into glass (a vitrification process) produced at a plant under construction by Bechtel Corporation (Hanford Tank Waste Treatment and Immobilization Plant (WTP)).
Washington River Protection Solutions (WRPS) approached CTLGroup to evaluate the concrete surrounding these waste containment tanks. The program was part of an investigation into the structural integrity of the tanks, particularly the concrete’s structural soundness. Because the waste in the tanks is highly radioactive and reached high temperatures during disposal (up to 600°F during initial disposal), there was concern that the concrete could have been damaged over time. Further, the concrete would also be radioactively contaminated, or radioactivity could be induced in the concrete. Single-shelled tanks are known to have “leaked” waste into the surrounding groundwater (the contents of single-shelled tanks have since been transferred to the newer double-shelled tanks and “dewatered”).
The WRPS project consisted of two phases. The first phase was the extraction of cores from a top “plug” of a waste containment tank; WRPS extracted fourteen 4 ¼-inch-diameter cores, which were sent to CTLGroup for examination.
As these concrete cores were considered radioactively contaminated, CTLGroup’s radiation safety officer, Dr. Eli Port of Radiation Safety Services, Inc. (RSSI), evaluated all of the concrete before CTLGroup testing. Testing consisted of compressive strength testing, modulus of elasticity testing, frequency evaluations (NDT), and petrographic (microscopic) evaluations. As these tests were destructive, RSSI required continuous monitoring during testing to detect fugitive particle contamination in the laboratory or on CTLGroup personnel.
The second phase of the project consisted of extracting a 39-foot-long, approximately 3 ¼-inch-diameter core from the sidewall of a concrete tank.
The 39-foot-long core was sent to CTLGroup (RSSI) in 10 sections. Again, testing of the sections consisted of the same physical testing, NDT, and petrographic evaluations.
The evaluations from CTLGroup showed that the concrete structure was structurally sound (of the tank evaluated), and CTLGroup test data were used in the structural evaluations subsequently performed by WRPS for other structures.
