Document: NRC Regulatory Guide
Document ID: 96baa826-d3bb-478b-8f38-e74500f6d433
Document Type: regulatory_guide
Title: 06/2009 (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0911/ML091170109.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.21
CFR Part: 
CFR Title: 

Content:
is used, principal radionuclides should be determined based on an evaluation over a time period that includes a refueling outage (e.g., one fuel cycle). A periodic reevaluation should be performed to determine whether the radionuclide mix has changed and/or to identify new principal radionuclides. If a risk-informed approach is applied to the determination of principal radionuclides, the ODCM becomes the controlling document and specifies the list of principal radionuclides. If adopting this method, the ODCM should be updated with the list of principal radionuclides within 1 year of their identification. Licensees are allowed to revise the ODCM in accordance with the ODCM change process as described in the plant’s technical specifications (which includes documented evaluations of such changes). The concept of “principal radionuclides” does not reduce the requirement for reporting radionuclides detected in effluents. In addition to principal radionuclides, other radionuclides detected during routine monitoring of release points should be reported in the radioactive effluent release report and included in dose assessments to members of the public. 1.9 Carbon-14 Carbon-14 (C-14) is a naturally occurring isotope of carbon. Nuclear weapons testing in the 1950s and 1960s significantly increased the amount of C-14 in the atmosphere. C-14 is also produced in commercial nuclear reactors, but the amounts produced are much less than those produced naturally or from weapons testing. Since the NRC published Regulatory Guide 1.21, Revision 1, in 1974, the analytical methods for determining C-14 have improved. Coincidentally the radioactive effluents from commercial nuclear power plants over the same period have decreased to the point that C-14 is likely to be a principal radionuclide (as defined in this document) in gaseous effluents. Rev. 2 of RG 1.21, Page 16 C-14 releases in PWRs occur primarily as a mix of organic carbon and carbon dioxide released from the waste gas