Improvement of calculational accuracy of coolant void reactivity by using WIMS-ATR code

Fukumura, Nobuo*; not registered; not registered

Improvement of calculational accuracy of ATR coolant void reactivity has been tried by using the more detailed calculational method as for the derivation of diffusion constant. The former calculational method of deriving the diffusion constant in WIMS-ATR code is the followings: (1)Calculation of collision probability with use of the model dividing the cell into three region (fuel, air gap and moderator). (2)Calculation of diffusion constant according to Bonalmi theory with use of the above calculated collision probability values. The present method is the one which calculates the collision probability more accurately by using multi region model including fuel, coolant, pressure tube and so on. For calculation of collision probability the CLUP code was used. By using the present code with the new calculational model of diffusion constant the coolant void reactivity were calculated. The following results were obtained: (1)The value of the diffusion constant is larger than the former one. This fact is more remarkable in the high voidage core and in the fast neutron energy region. (2)The present calculation accuracies of coolant void reactivity are 0.2%k for the DCA core and 0.07%k for the FUGEN core. These values are a half of the former ones. From the above results it is concluded that the present calculation model of the diffusion constant is effective for improvement of calculational accuracy of coolant void reactivity in ATR.