Influence of Zinc Injection on Dose Rate from Primary System Loops for PWR Units and Predictive Assessments for VVER-1000

Abstract

The paper analyzed the advisability of zinc injection into the VVER primary system coolant in order to minimize radioactive fields of equipment. In the western NPPs with PWR, zinc injection into the coolant leads to permanent decrease of dose rates caused by radioactive cobalt. Zinc is introduced into the oxide film on the primary system equipment surfaces to form the most stable zinc spinel, which prevents the further introduction of radioactive cobalt in the oxide film. Predictive assessments for VVER-1000 show that under the zinc concentration of µg/dm3 in the coolant, cation vacancies in the spinel lattice will be occupied mostly by zinc, preventing the penetration of cobalt in the spinel and increase of radioactive fields of equipment.