Fission Product Release from a Pressurized Water Reactor Defective Fuel Rod: Effect of Thermal Cycling

Abstract

The emission of fission gases and iodines by a pressurized water reactor fuel rod containing a defect when it is initially put in the reactor is studied experimentally using a pressurized water loop in the Siloe reactor at Grenoble. The initial leakage is simulated by making a small hole near the upper end of the rod. The rare gases and iodines are continuously analyzed, and the source terms of fission products are expressed as the ratio of the release rate of a given isotope from the defective fuel rod to the birth rate of this isotope.

The release fractions of rare gases and iodines have been determined in different conditions: steady power level between 120 and 700 W·cm⁻¹, power cycling in the range 200 to 400 W·cm⁻¹, and in the range 120 to 400 W·cm⁻¹ At steady power level, the amounts of radioactive gases escaped from the rod are 100 times higher than those emitted by a sound fuel submitted to a similar power level. The power cycling favors the emission of all iodines whose release rate is 10 to 20 times higher than at the maximum steady power level.