Kinetic simulation of fission product activity in primary coolant of typical PWRs under power perturbations

Kinetic simulations of fission product activity in primary circuits of a typical PWR under power transients, has been performed. A detailed two-stage model-based methodology has been developed and implemented in a computer coder FPCART which uses LEOPARD and ODMUG codes as subroutines. For normal constant power operation, results for over 39 fission products show that the activity due to fission products in fuel region of PWRs is dominated by 134I which is followed by 134Te and 133I. The value of the total fission product activity in fuel region predicted by FPCART code has been found to agree with-in 0.36% range with the corresponding values found by using the ORIGEN-2.0 code. The predictions of FPCART code have also been found in good agreement with the corresponding values found in ANS-18.1 Standard as well as with some available power-plant operation data with 2.4% deviation in the value of specific activity of the dominating fission product 134I. The saturation value of the fission product activity in coolant depends strongly on the fuel-clad gap escape rate coefficient (ɛ) and approaches a maximum value with increasing value of ɛ. During power transients, the FPCART predictions have been found in good agreement with the corresponding experimental measurements of 131I specific activity for Beznau and Surry PWRs.