Development of Hexagonal-Z Geometry Capability in RAST-K for Fast Reactor Analysis

Abstract

Recently, sodium-cooled fast reactor developments have been active with experimental and research reactors. It is considered as one of promising reactor types that can meet the Generation IV International Forum (GIF) goals. The three-dimensional (3D) two-group nodal diffusion code RAST-K v2.0 has been developed by the COmputational Reactor physics and Experiment laboratory (CORE) of Ulsan National Institute of Science and Technology (UNIST) with the initial application goal to Light Water Reactors (LWRs). It was successfully verified and validated that it can provide results in good agreement with measured data of LWRs. In other to use it for Sodium cooled Fast Reactor (SFR) cores, the RAST-K code is under further development for the hexagonal-z geometry (RASTK-HEX) including the extension of twogroup rectangular solver to multi-group hexagonal solver and the update of thermal-physical properties of fast reactor core materials in the internal thermal-hydraulic solver. To solve the multi-group neutron diffusion equation in the 3D hexagonal-z geometry, the triangle-based polynomial expansion nodal (TPEN) method is implemented in the RASTK-HEX code. The capability of RASK-HEX to perform steady state analyses of SFR cores is demonstrated in this paper using benchmarks of sodium-cooled fast reactor cores with various fuel types and core sizes (MOX-3600, CAR-3600, MET-1000, MOX-1000). The effective neutron multiplication factor (𝑘𝑒𝑓𝑓), control rod worth (𝜌𝐶𝑅), Doppler constant (𝐾𝐷) , sodium void worth (∆𝜌𝑁𝑎) values and power distribution are obtained by using RASTK-HEX and PARCS diffusion codes. The comparison between RASTK-HEX and PARCS results show good agreement in overall. This study demonstrates that the methodology implemented in the RASTK-HEX solver is correct. The and it can be used to analyze for fast reactor. The two-step code MCSXS/RASTK-HEX was used to obtain the effective neutron multiplication factor for 3D MET1000 and MOX-3600 cores. The comparison with continuous energy MCS code shows good agreement with just small differences, 109 pcm and 97 pcm for MET-1000 and MOX-3600 cores, respectively. It is also demonstrated that the two-step code MCS-XS/RASTK-HEX is a potential code system for FR analysis and design.