Thermal hydraulic analysis of a pebble-bed modular high temperature gas-cooled reactor with ATTICA3D and THERMIX codes

Abstract Along with the further ongoing design procedures of a large demonstration power plant of Chinese 200 MWe high temperature gas-cooled reactor pebble-bed module (HTR-PM), three-dimensional (3-D) analysis is necessary for studying the reactor characteristics under some special unsymmetrical conditions. Compared with the well established two-dimensional thermal-hydraulics code THERMIX, a new three-dimensional system analysis code ATTICA3D (Advanced Thermal hydraulics Tool for In-vessel & Core Analysis in 3D), developed by IKE of University of Stuttgart on the basis of TH3D, is used to perform the steady state calculation and transient analysis of a depressurized loss of coolant accident (DLOCA) for the HTR-PM. After a brief introduction of the reactor primary circuit, the above two codes, including correlative typical parameters and relevant formulae are described in detail. Then an ATTICA3D model, which keeps consistent with the THERMIX model as much as possible, is constructed according to the preliminary design of the HTR-PM. Based on the cylindrically symmetrical power distribution, the comparisons of the two-dimensional calculations between ATTICA3D and THERMIX indicate, that the main results including pressure drop and temperature distribution show good agreement. Furthermore, considering one set of small absorber spheres (SAS) dropping into the side reflectors resulting in an asymmetric distribution of the nuclear power, a three-dimensional calculation for the steady state is implemented to basically show the good 3-D simulation capabilities of ATTICA3D, which will be helpful to the next refined design stage for the HTR-PM project. It should be pointed out that the current 3-D simulation results illustrated in this paper are still preliminary, and more research work, e.g., comparison with experimental data or with some commercial CFD codes, needs to be carried out in order to further validate the ATTICA3D code and study the special 3-D characteristics of the HTR-PM in the future.