ASTM D7938-21

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Designation: D7938 − 15 D7938 − 21
Standard Practice for
Sampling of C-14 in Gaseous Effluents
This standard is issued under the fixed designation D7938; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 The intended use of this practice is for sampling of gasses containing C in inorganic, organic or particulate forms. This
sampling practice captures the C 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 C 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 C analytical detection capability is impacted by a number of factors including the volume sampled, the method
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used to desorb the C from the media, and the analytical method used the measure C from the media. This practice only directly
addresses the volume of the gas stream from which any present C 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.
2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D7282 Practice for Set-up, Calibration, and Quality Control of Instruments Used for Radioactivity Measurements
D7902 Terminology for Radiochemical Analyses
2.2 U.S. NRC Publications:
U.S. NRC Regulatory Guide 1.21 “Measuring, Evaluating, and Reporting Radioactive Material in Liquid and Gaseous Effluents
and Solid Waste,” revision 2, June 2009
This practice is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.04 on Methods of Radiochemical Analysis.
Current edition approved Dec. 15, 2015Dec. 15, 2021. Published February 2016February 2022. Originally approved in 2015. Last previous edition approved in 2015 as
D7938 – 15. DOI: 10.1520/D7938-15.10.1520/D7938-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, http://www.nrc.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7938 − 21
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this standard, refer to Terminologies D1129 and D7902.
3.2 Definitions of Terms Specific to This Standard:
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3.2.1 organic C, n—any gaseous, chemical C form (including CO) that is not particulate and not CO .
3.2.1.1 Discussion—
Although no specific organic form is determined, the major contributors are likely to be CH , C H , C H , CO, and C H .
4 2 6 2 4 2 2
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3.2.2 inorganic C, n—the gaseous, chemical form of C as CO .
3.2.2.1 Discussion—
These chemical form categorizations are based on U.S. NRC Regulatory Guide 1.21.
4. Summary of Practice
4.1 A sample of a flowing gaseous stream is extracted at a flow rate of 30 to 3000 mL/min. The sample is filtered,filtered and split
into two parallel flow paths. One flow path is passed through a furnace to convert all carbon to CO . This will yield a total C
content of the sample. The other flow path collects only the CO fraction of the gaseous stream. This yields the inorganic C
content of the gaseous stream. The calculated difference between the measured total and inorganic carbon content is the organic
content (U.S. NRC Regulatory Guide 1.21). The concentration of C in the particulate matter may also be determined.
5. Significance and Use
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5.1 This practice was developed for the purpose of sampling gaseous effluent streams from a facility that releases C in either
organic or inorganic forms.
5.1.1 For many years C 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 C 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, C activity will need to be reported and evaluated for dose contribution based
on the activity concentration and chemical form of the C in the release.
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5.2 While C releases may be estimated, the measurement of actual C emissions provides a more reliable and accurate means
of reporting emissions. The chemical form of C that yields the greatest dose significance due to uptake by living organisms is
the inorganic form. Thus the distribution of C 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 C released may be in
the organic form during operation, and for boiling water reactors (BWRs) <30 % of all C 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 CO , increasing the percentage of CO in the effluent release.
2 2
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 CO 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 C.
6. Interferences
6.1 Based on the chemical methodology used in this sampling practice, interference from non-volatile radionuclides is eliminated.
Holtzclaw, J., “Sample and Analysis Protocol for C in Gaseous Effluents,” Radioactive Effluent Technical Specifications (RETS) and Radiological Environmental
Monitoring Programs (REMP) Workshop, San Jose, CA, June 28–30, 2010.
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222 220 219
However, the radon progeny of the uranium ( Rn), thorium ( Rn), and actinium ( Rn) series may be possible interferences.
Their contribution to the liquid scintillation activity of the samples should be assessed by an independent radiological method (for
example, gamma ray gamma-ray spectrometry, or monitoring the liquid scintillation region above the C window).
6.2 Gaseous flow paths with carbon dioxide concentrations greater than those found in routine atmospheric samples may raise the
detection limit for C. This would require a lower sample volume ensuring that the adsorbent does not become saturated with
stable CO , allowing bypass of the CO .
2 2
6.3 Tritium can interfere with the analysis of C by LSC. Tritium (when present as part of a water molecule) is effectively
removed during the sampling collection process using a desiccant upstream of the carbon dioxide trap.
6.3.1 Tritium removal can also be accomplished during the sample preparation step in the laboratory by using a water trap with
HCl prior to the final carbon dioxide trap (see Fig. X1.1).
6.4 High levels of moisture in the gaseous effluent would limit the sample volume raising the detection limit. A method of
monitoring the level of depletion of the desiccant material should be employed in this method.
7. Apparatus
7.1 Combustion Furnace—Capable of attaining at least 600°C with the air flow at a maximum of 3000 mL/min.
7.1.1 The performance of the converter was determined by independent laboratory tests by measuring the conversion efficiency
of methane to CO . The conversion efficiency was found to be >95 % over a sample flow rate of 300 to 3000 mL per minute. No
reduction in conversion efficiency was observed as a function of methane concentration or flow rate.
7.2 Air Sampling Pump—Capacity in the range of 30 to 3,0003000 mL/min.
7.3 Two Flow Monitors—Calibrated for air flow in the desired flow range.
7.4 Particulate Filter Holder—Normally sized for a 47–mm diameter filter but may be sized to fit the sample flow.
7.5 Desiccant Tube—Sized for the amount of desiccant needed for the volume of air to be sampled.
8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without increasing the background of the measurement.
8.1.1 Some chemicals, even of high purity, contain naturally occurring radioactive elements, for example, uranium, actinium,
thorium, rare earths and potassium compounds. Also, some chemical reagents, including organic compounds, have been found to
be contaminated with artificially produced radionuclides. Consequently, when carrier chemicals are used in the analysis of
low-radioactivity samples, the radioactivity of the carriers shall be determined under identical analytical conditions as used for the
sample. The radioactivity of the reagents may be considered as background and subtracted from the test sample counting rate. This
increased background reduces the sensitivity of the measurement.
8.2 Ascarite II, commercially available solid material for adsorption of CO .
Reagent Chemicals, American Society Specifications,ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials,
American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed by the American Chemical Society, see ‘AnalaR’Analar Standards for
Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National Formulary, U.S. PharmaceuticalPharmacopeial Convention, Inc.
(USPC), Rockville, MD.
The sole source of supply of the apparatus known to the committee at this time is Arthur H. Thomas Company in Swedesboro, NJ, 08085. If you are aware of alternative
suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical
committee, which you may attend.
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8.2.1 The use of another material which will trap carbon dioxide will be acceptable. However, validation of the mediums’ ability
ability of the medium to retain carbon dioxide should be verified.
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