September 27, 2024
Department of Energy (DOE) contractor personnel periodically test safety systems in defense nuclear facilities to ensure that the systems can perform their safety functions when needed. These periodic tests are called surveillance requirements. The DOE-approved safety basis for a facility specifies and documents the frequency for surveillance requirements and the basis for the surveillance frequency.
As safety systems age, they can become less reliable. Adjusting surveillance frequencies is a best practice to ensure early detection of safety system failures. No DOE regulation, directive, or standard requires reassessment of surveillance frequencies due to system age or observed failures. Although not required, Y-12 National Security Complex (Y-12) personnel increased surveillance frequencies (i.e., decreased the period between surveillances) for safety systems after systems failed surveillance requirements. Two examples of this best practice are briefly highlighted below:
- The criticality accident alarm system at Y-12 is credited with detecting a criticality accident and sounding an alarm. Upon hearing the alarm, facility workers are trained to protect themselves by exiting the area. Y-12 personnel observed excessive calibration drift in the system’s detectors (Figure 1). As a compensatory action, they increased the surveillance requirement frequency from 13 to 7 months for detector calibration until empirical data supported restoring the original frequency.
Figure 1. A Nuclear Measurements Corporation Radiation Detector.- The wet vacuum system (Figure 2) in Building 9212 is credited with protecting facility workers by preventing an accumulation of fissile material that could cause a criticality accident. In the spring and summer of 2021, the system failed multiple surveillance requirements. In response, Y-12 personnel implemented additional monthly surveillances to enable earlier detection of future failures. Y-12 personnel also replaced components and performed a system reliability study that recommended continued replacement of aged components.
Figure 2. A portion of the wet Vacuum system in Building 9212 at Y-12.