Evaluation of moderator temperature coefficient of reactivity for the 1000 MWe PWR nuclear plant

Passive and inherent safety improvement have become important factors in reactor safety. One of the inherent safety parameters in the power reactors is the coefficient of reactivity. It will be classified has an inherent safety if the reactor has a negative reactivity coefficient. This paper describes the evaluation of the moderator temperature coefficient of reactivity (MTC) of PWR with 1000 MWe (electric), the AP1000 reactor designed by Westinghouse. The objective of this research to evaluate the designed MTC of AP1000 reactor with a focus on the effect of boron concentration on the MTC without water density changes. The MTC calculations have been carried out by modeling the AP1000 core in 3-dimension geometry model with a neutron diffusion method code, BATAN-3DIFF. The evaluated water temperatures are 20 °C, 50 °C, 100 °C, 200 °C and 300 °C with three boron concentration levels, 0 ppm, 827 ppm and 1574 ppm. The calculation results showed that the value of the MTC of AP1000 reactor is strongly influenced by the boron concentration, the higher boron concentration could cause the value of the MTC to be 0 (positive). The calculation results also showed that MTC is positive in the low temperature (50 °C) for the boron concentration of 1875 ppm. However this condition is unattainable because the designed maximum boron concentration is 1574 ppm. This research also showed that the stability of the AP1000 reactor at high power (or nominal power) is guaranteed because the MTC is negative. (author)