Negative reactivity caused by radial expansion of core is known as one of the inherent safety features in a sodium-cooled fast reactor (SFR). In order to validate the evaluation models of the reactivity feedback equipped in the in-house plant dynamics analysis code named Super-COPD, we have been conducting the benchmark analyses for the unprotected loss of heat sink (ULOHS) tests of BOP-302R and BOP-301 as one of the representative issues in EBR-II, a pool-type experimental SFR in the United States. During the transient of the ULOHS tests, the reactor power decreased to the decay heat level due to the negative reactivity caused by the radial expansion of the core. It is essential for the prediction of the plant behavior in unprotected events such as ULOHS events to develop the evaluation models of the reactivity feedback. By comparing the numerical results and the experimental data, the profiles of the increase of the core inlet temperature and the decrease of the reactor power calculated by Super-COPD were comparable with those of the experimental data. Applicability of the evaluation models for the reactivity feedback was indicated during the ULOHS event. The refinement of the plenum model of the cold pool by taking account of the thermal stratification was indicated for the future work in order to improve the profile of the core inlet temperature.

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