【国外标准】 Standard Practice for Sampling of C-14 in Gaseous Effluents

5.1 This practice was developed4 for the purpose of sampling gaseous effluent streams from a facility that releases 14C in either organic or inorganic forms.5.1.1 For many years 14C was not included in gaseous and liquid effluent measurements used for effluent dose calculations at nuclear power facilities. U.S. NRC Regulatory Guide 1.21 now requires 14C analysis (either estimated by calculation or actual measurement) and its impact on annual dose in the environs of nuclear plants be evaluated. Based on the revisions to the Regulatory Guide and NRC guidance to licensees, 14C activity will need to be reported and evaluated for dose contribution based on the activity concentration and chemical form of the 14C in the release.5.2 While 14C releases may be estimated, the measurement of actual 14C emissions provides a more reliable and accurate means of reporting emissions. The chemical form of 14C that yields the greatest dose significance due to uptake by living organisms is the inorganic form. Thus the distribution of 14C chemical forms in plant effluents is important in assessing the overall dose impact.5.3 Use of this sampling practice has identified that for pressurized water reactors (PWRs) >90 % of all 14C released may be in the organic form during operation, and for boiling water reactors (BWRs) <30 % of all 14C released may be in the organic form during operation.5.3.1 Some power plants have catalytic hydrogen recombiners in the waste gas processing system. These can also oxidize organic carbon to CO2, increasing the percentage of 14CO2 in the effluent release.5.3.2 During refueling outages, oxidizing conditions exist in the reactor cavity due to air saturation and radiolytic reactions by the nuclear fuel. The combination of these two effects has been shown to increase the 14CO2 content of the sampled atmosphere inside the containment building.5.4 The sampling methodology described in this practice is not capable of discriminating between different organic forms of 14C.1.1 The intended use of this practice is for sampling of gasses containing 14C in inorganic, organic or particulate forms. This sampling practice captures the 14C in a media that can be submitted to a laboratory for analysis, typically by liquid scintillation counting (LSC)1.2 This practice does not include the needed steps for the liberation of 14C from the media on which it was adsorbed or those for the preparation for LSC sample preparation in the laboratory prior to liquid scintillation analysis. This practice does not include the methodology used to analyze the prepared samples by LSC.1.3 The overall 14C analytical detection capability is impacted by a number of factors including the volume sampled, the method used to desorb the 14C from the media, and the analytical method used the measure 14C from the media. This practice only directly addresses the volume of the gas stream from which any present 14C would be adsorbed.1.4 The values stated in pCi units are to be regarded as standard given the reporting requirements of the U.S. NRC Regulatory Guide 1.21. The Bq values given in parenthesis are mathematical conversions to SI units that are provided for information only and are not considered standard. Other values stated in SI units are to be regarded as standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.