Investigation of flapper valve malfunction in Tehran Research Reactor with porous media model

Abstract

In the majority of research reactors, the core cooling is a combination of forced and Natural Circulation (NC). Typically, in normal operation the generated heat is removed by forced convection whilst the NC prepares residual decay heat removal. In this study, the focus is on evaluation of Tehran Research Reactor (TRR) core in failure of the natural cooling system. In present work, the integrity of hot fuel plate in the NC cooling process of the TRR, with flapper valve (FV) malfunction has been analyzed. In this way, for evaluation of the incore Thermal-Hydraulics (TH) the COBRA-EN code is enhanced, numerically. A finite element solver for plate type fuels is included and the appropriate heat transfer correlations in laminar and turbulent flow are added. For CFD study of the pool, regarding the fluid-solid domain in the TRR, the porous media model has been applied and the resistance coefficients for porous media model are extracted. The CFD streamlines have been used in COBRA-EN for TH study of hot and normal plates in inversions. In this analysis, the flow patterns in reactor core and pool for normal operation of the FV and its stuck in opening during NC are evaluated. The analysis shows that clad temporarily exceeds from allowable temperature for 74% opening of the FV and remains for seconds. In following, for 56% of opening the void generation is seemed in addition to permanent clad temperature exceeding. Therefore, the 56% of the FV opening due to failure is introduced as criteria for core and fuel plate damage.