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Information Notice No. 92-34: New Exposure Limits for Airborne Uranium and Thorium
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS WASHINGTON, D.C. 20555 May 6, 1992 Information Notice No. 92-34: NEW EXPOSURE LIMITS FOR AIRBORNE URANIUM AND THORIUM Addressees: All licensees whose operations can cause airborne concentrations of uranium and thorium. Purpose: The U.S. Nuclear Regulatory Commission is issuing this information notice to alert addressees of changes, in 10 CFR Part 20, governing airborne uranium and thorium exposures that may significantly affect exposure calculations and reporting requirements. It is expected that recipients will review this information for applicability to their facilities and consider actions, as appropriate, to avoid violations of the new Part 20. However, suggestions contained in this information notice are not new NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: The major revision of 10 CFR Part 20 was published on May 21, 1991 (56 FR 23360). This revision adopted the dose-assessment methodology recommended by the International Commission on Radiation Protection (ICRP). The new methodology significantly changes the occupational exposure limits for airborne uranium and thorium compounds. The current regulation requires licensees to implement the new Part 20 by January 1, 1993. However, licensees should note that the Commission is proposing to extend the implementation date to January 1, 1994. Discussion: Because NRC has adopted the dose-assessment methodology of ICRP 26 and 30, the new Part 20 contains two changes that can impact greatly on licensees that experience airborne concentrations of uranium and thorium compounds. These are changes in occupational exposure limits, and equivalence of internal and external dose. 9204300066 . IN 92-34 May 6, 1992 Page 2 of 3 As shown in the table below, the new Part 20 includes a reduction in occupational airborne concentrations of certain thorium and uranium compounds. However, the allowed concentrations of other nuclides have been relaxed. Although most changes have been made to reflect radiological concern, 10 CFR 20.1201 (e) limits intakes of soluble uranium to 10 milligrams in a week, in consideration of chemical toxicity, which is likely to be controlling at enrichments of 5 percent or less. Table 1: Old versus New Occupational Exposure Limits � Compound � Old Part 20 � New Part 20 � � �Appendix B, Table I, Col. 1�Appendix B, Table I, Col. 3� � Th-234, class W � 6E-8 uCi/ml � 8E-8 uCi/ml � � Th-234, class Y � 3E-8 uCi/ml � 6E-8 uCi/ml � � Th-232, class W � 3E-11 uCi/ml � 5E-13 uCi/ml � � Th-232, class Y � 3E-11 uCi/ml � 1E-12 uCi/ml � � Th-231 � 1E-6 uCi/ml � 3E-6 uCi/ml � � Th-230, class W � 2E-12 uCi/ml � 3E-12 uCi/ml � � Th-230, class Y � 1E-11 uCi/ml � 6E-12 uCi/ml � � Th-228, class W � 9E-12 uCi/ml � 4E-12 uCi/ml � � Th-228, class Y � 6E-12 uCi/ml � 7E-12 uCi/ml � � Th-227 � 2E-10 uCi/ml � 1E-10 uCi/ml � � U-238, class D � 7E-11 uCi/ml � 6E-10 uCi/ml � � U-238, class Y � 1E-10 uCi/ml � 2E-11 uCi/ml � � U-235, class D � 5E-10 uCi/ml � 6E-10 uCi/ml � � U-235, class Y � 1E-10 uCi/ml � 2E-11 uCi/ml � � U-234, class D � 6E-10 uCi/ml � 5E-10 uCi/ml � � U-234, class Y � 1E-10 uCi/ml � 2E-11 uCi/ml � The relative equivalence of internal and external dose means that exposures to airborne concentrations of radioactive particles must now be maintained as part of a worker's total occupational dose limit (10 CFR 20.1202). Under the old Part 20, internal and external doses had separate limits and were not combined. Section 20.1204 states, further, that internal exposure can be determined through air sampling in the work place or routine bioassay. If air sampling is chosen as the most accurate means of tracking dose, compliance with the new limits may be demonstrated through precise solubility, isotopic, and particle-size classifications, pursuant to Appendix B to 10 CFR 20.1001-20.2401. . IN 92-34 May 6, 1992 Page 3 of 3 The new revision to NRC Regulatory Guide 8.25, "Air Sampling In The Workplace," gives guidance for setting up an air-sampling program that can be used to estimate internal dose from airborne activity. The associated NUREG-1400 explains acceptable implementation of methods described in Regulatory Guide 8.25. In addition, Table 2 of Appendix B to 10 CFR 20.1001-20.2401 places much more stringent limits on effluent concentrations for soluble uranium and thorium in water, and for thorium and insoluble uranium in air. The reduction in the allowable effluent concentrations to about a hundredth of the former values may necessitate changes in procedures or monitoring methods, or may even necessitate installation of new effluent treatment systems requiring appreciable lead time to procure. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please call the technical contact listed below or the appropriate NRC regional office. Richard E. Cunningham, Director Division of Industrial and Medical Nuclear Safety Office of Nuclear Material Safety and Safeguards Technical contact: Edward Shum, NMSS (301) 504-2607 Attachments: 1. List of Recently Issued NMSS Information Notices 2. List of Recently Issued NRC Information Notices .
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