Carbon-14 production in nuclear reactors

Abstract

Quantities of '''C that may be formed in the fuel and core structural materials of light-water-cooled reactors (LWRs), in high-temperature gas-cooled reactors (HTGRs), and in liquid-metal-cooled fast breeder reactors (LMFBRs) have been calculated by use of the ORIGEN code.' Information supplied by five LWR-fuel manufacturers pertaining to nitride nitrogen and gaseous nitrogen in their fuels and fuel-rod void spaces was used in these calculations. Average nitride nitrogen values range from 3 to 50 ppm (by weight) in LWR fuels, whereas gaseous nitrogen in one case is equivalent to an additional 10 to 16 ppm. Nitride nitrogen concentrations in fast-flux test facility (FFTF) fuels are 10 to 20 ppm. The principal reactions that produce '''C involve '''N, ' O, and (in the HTGR) "C. Reference reactor burnups are 27,500 MWd per metric ton of uranium (MTU) for boiling water reactors (BWRs), 33,000 MWd for pressurized water reactors (PWRs), about 95,000 MWd per metric ton of heavy metal (MTHM) for HTGRs, and 24,800 MWd/ MTHM for an LMFBR with nuclear parameters that pertain to the Clinch River Breeder Reactor. Nitride nitrogen, at a median concentration of 25 ppm, contributes 14, 15, and 6 Ci of "C/GW(e)-yr to BWR, PWR, and LMFBR fuels, respectively. The contribution of "O in BWR and PWR fuels is 3.3 and 3.5 Ci of "C/GW(e)-yr, respectively, but it is less than 0.2 Ci/GW(e)-yr, in blended LMFBR fuel. In the HTGR fuel particles (UCj or ThO;), 10 Ci of "C/GW(e)-yr will be formed from 25 ppm of nitrogen, whereas "O in the ThO: will contribute an additional 2 Ci/GW(e)-yr. All '^C contained in the fuels may be released in a gas mixture (CO2, CO, CH4, etc.) during fuel dissolution at the fuel reprocessing plants. However, some small fraction may remain in aqueous raffinates and will not be released until these are converted to solids. The gases would be released from the plant unless special equipment is installed to retain the '''C-bearing gases.Cladding metals and other core hardware will contain significant quantities of '^C. Very little of this will be released from BWR, PWR, and LMFBR hardware at fuel reprocessing plants; instead, the contained '""C, 30 to 60 Ci/GW(e)-yr for LWRs and about 13 Ci/GW(e)-yr for a CRBR, will remain within the metal, which will be retained on site or in a Federal repository. The only core structural material of HTGRs will be graphite, which will contain 37 to 190 Ci of '''C/GW(e)-yr, exclusive of that in the fuel particles, if the graphite (fuel block and reflector block) initially contains 0 to 30 ppm of nitrogen. All of this is available for release at a fuel reprocessing plant if the graphite is burned to release the fuel particles for further processing. Special equipment could be installed to retain the ''C-bearing gases.

Strange bedfellows: The curious case of STAR and Moata

“…Reactions (4) and (5) are highly endothermic and were assigned a cross section of 0 for thermal reactors in [6]. For an Argonaut class reactor, the first three reactions are important for the production of 14 C in graphite and concrete, with reaction (1) expected to dominate due to the large neutron cross section and the abundance of 14 N. Activation estimates were undertaken for the reactor of the University of Strasbourg (RUS), a 100 kW Argonaut reactor [7].…”

Diffusion-type model of the global carbon cycle for the estimation of dose to the world population from releases of carbon-14 to the atmosphere

“…The identification of C as a significant radiological effluent from nuclear power facilities has prompted a renewed interest in the assessment of its behavior in the environment and resultant radiation dose to man. Light-water-cooled reactors (LHRs) 1* produce C in their fuel and coolant; current estimates of the total production rate are in the range of 20 to 40 curies per GWe-yr (Davis 1977). At present it can be assumed that essentially all of that C will be released to the atmosphere either at the reactor (i 20-30%) or at the fuel reprocessing plant C^ 70-80*).…”

Comparative Biokinetics of Radiocarbon Ingested as Compounds or Foods in Rats

“…The estimated releases of 14 C from presently operating nuclear power facilities are still quite small comparing to naturally occurring 14 C, which is produced by cosmic ray interaction in the upper atmosphere. However, its potential long-term hazard as a source of human exposure has been of concern in a number of assessments of existing and proposed nuclear fuel cycles and facilities (Veluri et al 1976;Hayes and MacMurdo 1977;Davis 1977;Liepins and Thomas 1988;NCRP 1985).…”