KARATE-1200: An enhanced neutron transport code for VVER-1200 reactor physics calculations

Comprehensive safety analysis is crucial for the deployment of new reactor designs. It requires accurate prediction of reactivity caused by temperature, boron concentration changes or control rod movement, as well as the 3D power, temperature, and burnup distributions during the cycle. Moreover, the reactor’s behavior under accident conditions has to be assessed. This necessitates advanced neutron transport codes capable of detailed modeling of heterogeneous core structures. It uses detailed meshing to model inhomogeneous structures, following the latest VVER core, and enables accurate prediction of reactor parameters during the burnup. One possible solution is to develop further a neutron code that has already been proven in practice for similar tasks.

This article presents the capabilities and performance of KARATE-1200, an in-house developed deterministic neutron transport code designed for third-generation VVER reactors. Building upon the 40-year legacy of the KARATE code used at VVER-440 NPPs, KARATE-1200 incorporates significant enhancements to improve VVER modeling from pin-cell to coarse-mesh levels, achieving good agreement with reference data. The KARATE-1200 code package, incorporating MULTICELL for group constant generation and GLOBUSKA-1200 for criticality calculations, has been verified against benchmark solutions and validated against published measurements. Safety-related parameters of the VVER-1200 core, based on data from the Novovoronezh II NPP, were calculated. Simulated reactivity coefficients using KARATE-1200 show agreement within ± 3 % of published measurements, depending on the coefficient type. Furthermore, key safety parameters, such as the isothermal re-criticality temperature, also demonstrate good agreement with literature values.