Research on the Expected Carbon-14 Production and Discharge in Pressurized Water Reactors

Abstract

Carbon-14 is one of the most important radionuclides discharged to the environment from pressurized water reactors due to its long half-life and its important role in the biological chain. Carbon-14 is the largest contributor of the dose rate to the public from all radionuclides discharged to the environment during the normal operation of pressurized water reactors, and thus the production and discharge of Carbon-14 have been focused on in the industry in recent years. Based on the generation mechanism in pressurized water reactor, one theoretical model of Carbon-14 generation has been established and the nitrogen concentration of all chemical species in the primary loops has been determined according to the measured ammonium. It predicts that the annual Carbon-14 generation in the primary loops is proportional to annual electricity output and the typical normalized Carbon-14 is 2.9E+02 GBq/GWe/yr. The theoretical model has been verified by the statistical analysis of annual Carbon-14 discharges from French PWR units. In addition, the quantity of Carbon-14 in radioactive solid waste has been estimated in these PWR units. It shows the generation of Carbon-14 in PWR cannot be effectively minimized because O-17 atoms, the predominant origin of Carbon-14, exist naturally in the primary loops during long-term operation. This approach can be applied to analyze the Carbon-14 production and discharges in operating pressurized water reactors and in the assessment of source term of the new pressurized water reactors.