14C Produced by Nuclear Power Reactors - Generation and Characterization of Gaseous, Liquid and Solid Waste
Sammanfattning: This thesis presents the results from studies on carbon-14 produced by nuclear power reactors. Radioactive 14C enters the carbon cycle and can be taken up by humans, where it will constitute a potential health hazard. Therefore, the main focus of this thesis was to provide new data and knowledge necessary for the implementation of appropriate nuclear waste management strategies. Such data have previously been very limited or non-existent. The studies presented describe the characterization and mapping of 14C from the source of production, through various waste and release streams, to its final destination; here being the sea, the terrestrial environment and a national disposal facility. The reactor units investigated comprise Swedish BWRs and PWRs (boiling- and pressurized-water reactors, respectively), as well as two power plants located in Lithuania and Romania. In this thesis, a new method of separately quantifying organic and inorganic 14C in radioactive liquid, gaseous and solid samples was developed and applied to samples from waste and releases streams in Swedish BWRs and PWRs. Based on the results, mass balance assessments of the 14C produced in the reactor coolant were made. The assessments showed that the amount of 14C released to the sea in liquid discharges constituted only a minor fraction (<1%) of the amount originally produced in the coolant. The fraction of 14C ending up in the solid waste stream, which is dominated by 14C adsorbed on ion-exchange resins, was found to be 0.5?10%, depending on the reactor type. The remaining fraction is released as gaseous compounds to the air. Since the dominating fraction of the 14C activity in the Swedish waste repository is expected to be that contained in the spent ion-exchange resins, the total 14C inventory at the time of repository closure was also estimated and found to be 5.0 TBq; the present disposal limit being 7.2 TBq. However, these studies showed that the approach used by the operator of the repository to estimate the inventory suffers from significant uncertainties. Therefore, an alternative approach is suggested in this thesis. The studies related to the non-Swedish power plants showed enhanced 14C levels in plants and trees growing close to the power plants. The most interesting finding was that a few samples contained a 14C excess of up to 2000% above the contemporary background, which is thought to be the result of releases of particulate material.
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