Abstract
Negative reactivity caused by radial expansion of the core is known as one of the inherent safety features in a sodium-cooled fast reactor (SFR). In this paper, the numerical results of the benchmark analyses for the unprotected loss of heat sink (ULOHS) tests in the pool-type experimental SFR in the United States, EBR-II (BOP-302R and BOP-301) are discussed in order to validate the evaluation method of the reactivity feedback equipped in the in-house plant dynamics analysis code named Super-COPD. During the transient of the ULOHS tests as one of the representative issues, the reactor power decreased to the decay heat level due to the negative reactivity caused by the radial expansion of the core. 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 method 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.
