The Oregon State TRIGA reactor is licensed to operate at a steady state power of 1.1 megawatts (MW) and can pulse to 2,500 MW with a peak steady-state thermal flux of about 1013 neutrons per square centimeter per second (n/cm2-s) in the B1 position. The reactor was originally fueled with a 70 percent enriched UZrHx fuel with a 1.6 weight percent erbium burnable absorber. The reactor was converted to a 19.75 percent enriched UZrHx fuel with a 1.1 weight percent erbium burnable absorber.

This reactor has a lifetime core, and it was important to the reactor operator to maintain a full grid of fuel assemblies in the converted core to maintain flexibility for conducting irradiation experiments. However, maintaining a full core reduced the shutdown margin (i. e., raised the excess reactivity) at the beginning of life of the new reactor core. Adjusting the erbium burnable poison to 1.1 percent in the converted core restored the shutdown margin and maintained the longevity of the core (Figure 2-4).