Study On Krylov Subspace Method And The Flux Mapping For Advanced Candu Reactor

Calculation method of harmonics is being widely studied due to its importance in the reactor physics area. Recently, Krylov subspace method is rapidly developed for solving the large-scale linear equation and eigen-value equation. In this paper, Implicitly Restarted Arnoldi Method (IRAM), one of the Krylov subspace method, is applied to solving the higher order harmonics. The numerical results demonstrate that while its accuracy is comparable with the conventional modified source iteration method (MSIM), IRAM method runs much faster than MSIM. Moreover, IRAM is very efficient to solve the duplicate eigenvalue problem, and has the capability of solving nonlinear eigenvalue problem.Online flux mapping is very important for the operation management of the heavy water reactor. Because the current flux mapping code POWERMAP relies on the previous information, so strictly speaking, it is not a online method. In order to map the neutron flux distribution online, it is necessary to fastly solve neutron diffusion equation. In this paper, three different methods, including the nonlinear iteration method, the coarse mesh and fine mesh alternate sweeping method, and the coarse mesh and fine mesh alternate sweeping method with albedo boundary condition, are investigated. Through the evaluation on the calculation precision and the CPU time, the last method can meet the requirement of the online flux mapping. Finally, a method of the online flux mapping is developped. Numerical results show that the method has the capability of remedying the calculated neutron flux distribution.