Neutronic properties of spectral shift light water reactors with thorium fuel

Cell calculations of a Th-fueled PWR are carried out to discuss the burnup characteristics, coolant void reactivity coefficients, and the effectiveness of the mechanical spectrum shift control method by fertile rod insertion. Four combinations of fissile and fertile materials were examined; 235U+238U, 233U+238U, 235U+Th and 233U+Th. The following conclusions were obtained: (1)A high burnup core requires a high fissile concentration. The necessary increase of the fissile concentration from 30 to 60GWD/t discharged burnup is 62% in the case of the U fuel, whereas it is only 36% in the case of the Th fuel. (2)Thorium makes the coolant void coefficient more negative, while the fissile 233U tends to make the void coefficient less negative. (3)The fertile rods are effective in the Th cores, where the heavy water has a small reactivity worth. (author). 4 refs., 5 figs., 6 tabs