Assessment of contamination distribution of "Monju", 8; Assessment of activation of around the reactor with revised elemental composition and libraries

Kinoshita, Takuma*; Kato, Mitsuaki*; Kishimoto, Yasufumi*; Mashimo, Ryutaro; Nanri, Tomohiro ; Hayashi, Hirokazu 

Disassembling in a radiation-controlled area is planned for Phase 3 of the Monju decommissioning program, and improving evaluation accuracy remains a key objective. This time, the internal structures of the Monju reactor were evaluated using elemental composition data based on analysis results and the latest library (ActLib-J5) to confirm changes in radioactivity concentration. The revised elemental composition lowered overall radioactivity within the reactor; however, increased radioactivity was observed in the upper section. The impact of the library updates on evaluation results was minor. We will continue to improve the reliability of our evaluations by reviewing conditions and incorporating the latest findings. Furthermore, we will confirm the validity of the evaluation by collecting and analyzing neutron shield materials.