Determination of Temperature Feedback Coefficients for OPR-1000 Fuel Assembly Using Adjusted Cross Section Libraries

An important source of reactivity variation in an operating reactor is the change in the temperature of the system. This change affects the criticality of the reactor and is expressed by the temperature reactivity coefficients. The most important feedback coefficients are those caused specifically by fuel and by moderator temperature changes. In this paper, temperature reactivity feedback coefficients are calculated for two assemblies solid 16×16 and annular 12×12, designed for OPR-1000 reactor. Feedback coefficients calculated are the fuel temperature coefficient, moderator temperature coefficient, prompt reactivity coefficient and power coefficient. A thermal resistance model was adapted to solid and annular fuel and was used to calculate the power coefficient. MCNP6 code was used to determine the multiplication factor, and hence the feedback coefficients. Temperature adjusted libraries were produced using MAKXSF utility program, associated with MCNP6 code. The difference between the use of regular library and temperature adjusted one is clarified. It was assumed that both reactors, with either fuel assembly type, operate at 100% power. The results showed that both designs gave close values with better results of annular fuel for the prompt reactivity and power coefficients.