Document: NRC Regulatory Guide
Document ID: 535957c7-1203-410d-b709-8e4d381f00de
Document Type: regulatory_guide
Title: Measurements of Radionuclides in the Environment, Analysis of I-131 in Milk
Source: NRC Regulatory Guide Division 4
Source URL: https://www.nrc.gov/docs/ML1335/ML13350A246.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-4.3
CFR Part: 
CFR Title: 

Content:
cts 3. Fuels and Materlals Facilites 4. Environmental and Siting 6. Materialk and Plant Protection B. Products 7. Transportation a. Occupational Heahh 9. Antitrust Review 10. General necessary in some instances to measure 1-131 in tile presence of i-129 2-as Well as other radioisotopes of iodine; since the usual beta counting methods are nonspecific, provisions for the resolution of such a potential mixt'jre of isotopes should be included in the procedure. In most instances, however, radioisotopes of iodine other than 1-131 and possibly 1-129 are not expected to be of significance in the milk pathway because of their short half-lives. Also, under normal operating conditions of nuclear power plants, the contribution from 1-129 will be negligible, the potential significance of 1.129 being associated primarily with fuel .reprocessing plant:i. It is probable, therefore, that any radioiodine detected in milk sampled from the environs of nuclear power plants will be primarily 1-131. Nevertheless, because of the nonspecificity of heta counting methods, as a minimum. decay checks should be performed. A simple check for isolopic purity can be performed by recounting the sample for radioactive decay. A half.time of 8 days would be a good indication that the activity is due to 1-131. However, since it is not practical to attempt to monitor decay half-times when the sample net counting rate is less titan about 0.3 cpm. it would be 'A regulatory guide for the analysis of 1-129 in milk is in preparation. .worthwhile to do ,this only, wihen the net count. is more than about 0.3 cpm. If, after the second count, it is determined that the activity is not decaying with a half-time of about 8 days, a third count made 4-5 days after the second count can provide the basis for a rough graphical resolution of 1-131 activity. In any case, it would be desirable to hold the sample for at least a year to permit possible identification of the long-lived component should the need arise. C.