Simulation of air oxidation during a reactor accident sequence: Part 2 – Analysis of PARAMETER-SF4 air ingress experiment using RELAP5/SCDAPSIM

A new model, primarily aimed at air oxidation has been recently developed at PSI, assessed against separate effects tests data and implemented into a developmental version of RELAP5/SCDAPSIM. Oxygen is treated as an active species and nitrogen as a catalyst that promotes breakaway, so that the essential feature of the model is the transition from parabolic to breakaway oxidation. As part of the second stage of the model assessment, analysis is performed of the air ingress bundle experiment PARAMETER-SF4 which comprised pre-oxidation in steam, a period of air ingress, and reflood. The analysis focuses on the thermal response and possible breakaway during, the oxygen consumption. Of particular interest is the effect of oxygen starvation on the oxidation excursion during the subsequent reflood.

► A new oxidation model for steam and air with N2 as a catalyst has been assessed at PSI. ► It recognises breakway transition to linear from parabolic kinetics. ► It was successfully implemented in RELAP5/SCDAPSIM/Mod3.5. ► It was tested against PARAMETER-SF4 experimental data. ► The model successfully calculated the SF4 air ingress scenario.