Carbon-14 (C-14) is a naturally occurring isotope of carbon produced by cosmic radiation interactions in the upper atmosphere. Nuclear weapons testing in the 1950s and 1960s significantly increased the amount of C-14 in the atmosphere. C-14 is also produced in commercial nuclear reactors, but the amounts produced are much less than those produced naturally or from weapons testing. C-14 is released through permitted effluent pathways of a nuclear power plant. This report provides the current industry best practices for the estimation of site-specific dose to the public from C-14 in nuclear power plant gaseous effluents.

Background

Improvements in nuclear power plant effluent management practices have resulted in a decrease in the concentration and a change in the distribution of gaseous radionuclides released to the environment. The latest revision of U.S. Nuclear Regulatory Commission Regulatory Guide 1.21 defines a principal nuclide as "any radionuclide whose concentration exceeds 1% of the total release," stating that the released quantity must be included in the annual radioactivity discharge report. In 2010 and 2011, EPRI developed technical guidance and bases for estimating the amount of C-14 released in nuclear power plant effluents.

Objective

The objective of this report is to present current industry best practices, based on existing regulatory guidance and state of knowledge, for estimating site-specific dose to the public from C-14 released through nuclear power plant gaseous effluents.

Approach

Approach A review was conducted of the applicable regulatory guidance and industry practices in the United States supporting the calculation of the radiological dose from C-14 from nuclear power plants. Based on this review, best practices for site-specific estimation of dose to the public from C-14 were identified. Existing practice was obtained by interviews with industry personnel responsible for such calculations and by a limited review of the literature based on these interviews.

Results

Each nuclear power plant site is unique as to its physical characteristics, the local climate and weather, and the presence of critical receptors as determined by the land use survey. Individual sites have developed assumptions that support and refine their dose calculations. Some of the observed methods are considered good practices, such as limiting batch releases to periods when photosynthesis is not occurring. Important information continues to develop in some areas, such as the discharge rates and the chemical form of C-14 during the fuel cycle and during refueling operations.

Application, Value and Use

This report describes several areas in which important data and experiences continue to evolve. The fraction of CO2 is an important consideration to C-14 doses from ingestion. An improved understanding of the fraction of CO2 and the timing of releases during the fuel cycle and refueling outages may be important to further refinement of the C-14 source term and the resulting dose calculations.