Comparison of reactivity feedback models for the FFTF passive safety tests

The FFTF Loss-of-Flow-Without-Scram Test from 50% power to natural circulation flow was analyzed with the SASSYS code using both the SASSYS reactivity feedback models and the semiempirical reactivity feedback equations for the FFTF oxide-fuel core. The experimental data for primary loop flow and reactor power were used as inputs to obtain the same fuel, sodium, and structure temperatures for both sets of reactivity feedbacks. A detailed comparison was made for each of the reactivity feedbacks: Doppler, sodium density, control rod expansion, axial fuel expansion, radial expansion, and bowing. The major differences between the SASSYS reactivity models and the FFTF reactivity equations were in the radial expansion and bowing feedback. The sensitivity of the results to the input for the SASSYS radial expansion and bowing model was investigated