Standard Practice for Sampling of C-14 in Gaseous Effluents

Importancia y uso:

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.

Subcomité:

D19.04

Volúmen:

11.02

Número ICS:

13.040.40 (Stationary source emissions)

Palabras clave:

C-14; gaseous effuents; inorganic ¹⁴C; organic ¹⁴C;