Isothermal Temperature Coefficient Evaluation for the Monju Restart Core

The present technical note describes the evaluation of the isothermal temperature coefficient data obtained in the Monju restart core. As in the preceding evaluations on the criticality and the control rod worth, the best-estimate value and its uncertainty are evaluated as accurately as possible. Data obtained in the previous test are evaluated in the same level of detail.

The measured data show that the fuel composition change from the previous test decreases the magnitude of the temperature coefficient by [approximately]8%. Through a sensitivity analysis, it is confirmed that the decrease is mainly brought by the composition of ²⁴¹Pu and ²⁴¹Am.

The best calculation accuracy within the experimental uncertainty of 2% is attained with JENDL-4.0 for the previous core; however, such a good accuracy is not achieved for the restart core. A further experimental investigation is required to solve the dependence of calculation accuracy on the core configurations.