Negative power coefficient on PHWRs with CARA fuel

•A PHWR fuel was optimized to obtain a negative power coefficient.•Fuel cost, being a measure of design investment efficiency, was optimized.•Influence on power coefficient of geometrical and economical parameters’ was studied.•Different neutronic absorbers were studied; pure absorbers can be used.•Thermal and economical models were developed to complement neutronic assessment.

A study of power coefficient of reactivity in heavy water reactors is made analyzing the reactivity components of fuels with several modifications oriented at reducing the coefficient. A cell model is used for neutronics calculations; a non-linear two dimensional model is used to evaluate the thermal changes that follow a power change; and a levelized unit energy cost model is used to assess the economical feasibility of the design changes introduced to reduce power coefficient.The necessity of modelling all the aforementioned quantities in a coupled scheme is stressed, as a strong interdependence was found. A series of design changes complied with a negative power coefficient of reactivity, with a feasible power radial distribution and with low refuelling cost. Some investigation lines that exceed the fuel cell study and deal with the plant operation are marked as potentially addressing the stable operation of big heavy water reactors.