Sandia recently upgraded the critical assembly (a small nuclear reactor) in Tech Area 5 to permit a new class of experiments as part of the development of a reactor experiments training course for NNSA. Hardware was designed and installed that allows experiments to safely approach critical conditions by varying the amount of water in the assembly. This provides the capability to simulate a critically accident caused by flooding, something that is at the heart of many safety analyses for the storage of nuclear material across the DOE enterprise.
About the photo:
The upgraded hardware (the large black cylinder to the right) that permits criticality experiments by varying the amount of water in the reactor is shown installed on the Sandia critical assembly in Tech Area 5.