Feasibility study on an upgraded future Monju core concept with extended operation cycle length of one year and increased fuel burnup

Kinjo, Hidehito*; Kageyama, Takeshi*; Kitano, Akihiro ; Usami, Shin 

A conceptual design study has been performed on upgrading the core performance of the Japanese FBR Monju. The main aim of this study is to investigate and demonstrate the feasibility of an upgraded core with an extended refueling interval of 365 EFPD and increased average fuel burnup of 150 GWd/t, which are expected in future commercial FBRs. Two design measures have been taken to accommodate the largely increased burnup reactivity for the longer cycle: (1) A modified fuel pin with increased pin diameter, pellet density and active core height has been introduced to improve the burnup reactivity, (2) The control rod specification has been modified to enhance the reactivity worth by increasing the B content to assure sufficient shutdown margin. The evaluation results show that even a medium sized core of about 2.5 m could achieve the target, without causing significant drawbacks to the core characteristics. The feasibility is thus demonstrated.