Energywise contributions of Th, Pu and U isotopes to the reactivity feedbacks of (Th-LEU) fuelled AHWR

Advanced heavy water reactor (AHWR) has been designed with thorium based fuel cycle and boiling light water as coolant. The Coolant Void Reactivity (CVR) and Fuel Temperature Reactivity (FTR) are the main reactivity feedback mechanisms. In the present work, we have attempted to understand the physics behind CVR and FTR by estimating the energy wise isotopic contributions for AHWR fuelled with (Th, LEU) fuel. The normalised reaction rate approach was used to quantify the individual contributions from ²³²Th, U, Pu, H and other isotopes. It has been shown that ²³²Th captures plays a major role in making these coefficients negative. This led us to study the sensitivities of these isotopes to the reactivity coefficients to the basic nuclear cross section set. The sensitivity due to nuclear data to CVR and FTR from ENDF/B-VI.8 and JENDL 3.3 has been calculated. It is seen that FTR is less sensitive to the dataset whereas the CVR is 16% lower in the JENDL3.3 dataset as compared to the ENDF/B-VI.8. (author)