Fuel assembly design for the demonstration advanced thermal reactor

In the demonstration advanced thermal reactor, in order to heighten the core performance, the development of improved fuel containing gadolinia and having axial multiple enrichment regions has been carried out. In the thermal design of fuel, from the viewpoint of ensuring the thermal soundness, the design improvement such as the optimization of spacer positions was carried out, and the applicability of the correlation equation for critical heat flux to the improved fuel was confirmed based on the test results at an actual scale loop. In the manufacture of fuel, the fuel parts for preceding irradiation fuel for confirming the soundness at the time of irradiation were made, and the fuel using these parts is being irradiated now in the prototype reactor 'Fugen'. The concept of the fuel aiming at higher burnup has been investigated, and the development of the detailed analysis technique supporting it is advanced. The technique of evaluating the thermal soundness in the demonstration advanced thermal reactor, the features of the improved fuel, the ensuring of thermal soundness for the improved fuel, the verification of the thermal design technique based on test data and the ensuring the soundness at the time of irradiation are reported. (K.I.)