RELAP5 and TRACE assessment of the Achilles natural reflood experiment

The RELAP5 computer code was one of the most used best-estimate system codes in the international community for performing nuclear power plant safety analysis. At present time, the development of the U.S. Nuclear Regulatory Commission RELAP5 has been ceased in favor of the newer TRACE best-estimate system code. Thus, the importance of validation and assessment of the TRACE code becomes evident. The present work presents the assessment of the Achilles natural reflood experiment with the RELAP5/MOD3.3 Patch 4 and TRACE V5.0 Patch 1 and Patch 3. The TRACE input deck has been obtained by conversion of the already existing RELAP5 input deck. The results of the RELAP5/MOD3.3 Patch 4, TRACE V5.0 Patch 1 and Patch 3 calculations of the Achilles natural reflood were compared against the experimental data. The results show that both TRACE and RELAP5 are capable of reproducing the reflood phenomena at a satisfactory level. However, some discrepancies between the predicted variables and the experimental data suggest further investigation of the TRACE reflood model.