DEVELOPMENT OF A COMPUTER CODE TO ESTIMATE THE FUEL-ROD FAILURE USINGPRIMARY COOLANT ACTIVITIES OF OPERATING PWRS

A Windows computer code entitled as ''CAAP (Coolant Activity Analysis Program)'' has been developed to evaluate the number,;he degree of fai lures, and the location of failed fuel rods using primary coolant radi oactivity data obtained from operating PWRS. New models are developed and incorporated into the CAAP program to improve some of the drawback s of existing computer codes. The iodine and noble gas activities obta ined by grab sampling and that obtained from the primary coolant radio activity monitoring system can be used to estimate fuel rod failures w ith CAAP. For an on-line evaluation of the number of failed fuel rods and the degree of failures, CAAP has been combined with the primary co olant radioactivity monitoring system at Kori 3 & 4 operating nuclear power plants. The validity of the computational models of CAAP has bee n examined using nuclear power plant data collected. For 29 cycles of PWRs for which ultrasonic inspections were performed at the end of fue l cycles, the number of failed fuel rods has been estimated with CAAP and compared with the ultrasonic inspection results. The results show that CAAP gives a better agreement with the ultrasonic test data than existing models. In addition, CAAP calculations performed to estimate the region and the burnup of the failed fuel rods for 2 cycles, whose locations of failed fuel rods were known, show that CAAP can predict b oth the region and the burnup of the failed fuel rods accurately. (C) 1998 Elsevier Science Ltd.