Projects & Programs
Nuclear Reactor Disablement
Pacific Northwest National Laboratory (PNNL) researchers successfully developed the technology and associated equipment to neutronically poison and permanently disable a graphite moderated reactor, as illustrated in Figure 1. The project required that the poison delivery system be fast, low-cost, and safe and result in a reactor poisoning that was resistant to countermeasures. The system had to be deployed from the reactor charge face through available stand pipes. An additional requirement was that the disablement approach could not interfere with subsequent verification activities.
Figure 1. Typical Graphite Moderated Reactor shown with PNNL designed poisoning system.
Radiological Materials & Technology Development Staff characterized target graphite materials and developed poisoning methods/delivery approaches. RMTD staff then designed and tested two delivery systems were selected for development. The primary poisoning method uses a pressurized injection system to forcibly inject a neutron-absorbing solution into the reactor’s graphite core (Figure 2). A secondary, simple plug and fill (SPAF) system was also developed as a backup to the pressure injection system.
Figure 2. PNNL researchers inserting pressurized injection head into a graphite block and testing the injection control system.
Both systems were designed, fabricated, and successfully tested in full-scale exercises. The exercises included assembling a full height graphite fuel channel and associated reactor core internals that simulated the expected in-field configuration. This included the graphite column (encased in PVC pipe for safety), a section of the reactor charge face, a simulated stand pipe, and a simulated section of the reactor charge pan all assembled in a ~70 ft training tower as shown in Figure 3. Once the testing facilities were assembled, a team of PNNL scientists including several RMTD staff conducted exercises which served to demonstrate the system viability and effectiveness as well as train the deployment team. Subsequent testing of the graphite blocks verified that required quantity of neutron-absorbing solution was consistently injected into the target locations of the graphite column and that the proposed poisoning plan was a viable approach to permanently disable a graphite moderated reactor.
Figure 3. Building the graphite column for full height exercise.