Study on improvement of reactor physics analysis method for FBRs with various core concept (2)

Takeda, Toshikazu*; Tagawa, Akihiro ; not registered; Kitada, Takanori*; not registered

Investigation was made on the following three themes as a part of the improvement of reactor physics analysis method for FBR with various core concepts. [Part 1: Investigations on Improvement of Neutron Spectrum Evaluation by the Use of Co-variance Matrices and Bias Corrections] In order to improve the neutron spectrum unfolding method used in the experimental fast reactor JOYO, investigation was made on the bias corrections to the initial neutron spectrum and error evaluation of nuclear data with the co-variance matrices. The error estimation was done by accumulating each bias correction factor and the co-variance matrix. It was concluded that the accumulated error for the initial neutron spectrum is relatively small, and a considerable improvement was achieved by the use of bias corrections. [Part 2: Evaluation of Neutron Streaming in Gas Cooled Fast Reactors by the use of Monte Carlo Method] As a part of investigations on the evaluation of the anisotropic diffusion coefficients for gas cooled fast reactors, a new tally function was added to a Monte Carlo code so that the neutron streaming can be calculated with heterogeneous core configurations. It was found that the neutron streaming becomes larger when the heterogeneous model was used. The tendency was more distinct in lower energy range. The same types of comparison was also done for the difference of core calculation models and the transport/diffusion theory. The final result shows that the transport/diffusion error has positive values in higher energy range, and the heterogeneous/homogeneous error has negative values in lower energy range. [Part 3: Investigation on the Calculation Method for Nuclear Converters with Neutron Moderators] A new calculation system which can deals with the target assemblies with neutron moderators was proposed. This concept has been investigated as a device to achieve high conversion rate for long life fission products. It was concluded that the characteristics method is ideal, wh