Evaluation of sodium radioactivity in the primary system of the prototype fast reactor Monju

Mori, Tetsuya ; Ohgama, Kazuya   ; Hazama, Taira 

In this study, the sodium radioactivity of Na and Na in the primary system measured in the prototype fast breeder reactor Monju was evaluated, and the reliability of measurements and calculations was examined. The calculated-to-experiment (C/E) values and their uncertainties for Na and Na radioactivities were 0.97-1.07 and 8.1%-11.0% and 1.03-1.16 and 23.3%-24.1%, respectively, using JENDL-4.0 nuclear data library. The Na radioactivity calculated with ENDF/B-VIII.0 was larger by 40% than those calculated with JENDL-4.0 and JEFF-3.3 due to the Na(n,2n) cross-section discrepancy. The importance of the Na neutron capture effect was also confirmed herein for the accurate evaluation of the Na radioactivity. The experimental data was judged to be useful for validating the calculation method for improving the reliability of the future designs of sodium-cooled fast reactors.