DOE Guidance for LEU/HALEU A1/A2 Calculations 
(effective date 8/25/2022 )

This guidance applies only to DOE elements or persons working under contract to DOE elements

DOE elements means programs, operations offices, field/site offices, and other organizational units of the Department of Energy, excluding those of the National Nuclear Security Administration.  The list of DOE elements is hereexternal (link to DOE Directives website).

On August 24 and 25, 2022 the DOE PCP Manager consulted with DOT and NRC regarding A2 calculations for high assay low enriched uranium (HALEU), which is currently defined as uranium enriched between 5% and 20%.  Note - DOT and NRC regulations currently do not define HALEU but it meets their definition for enriched uranium (i.e., uranium containing a greater mass percentage of uranium-235 than 0.72%).  In addition, the table of A1 and A2 values for radionuclides in §173.435 (and Appendix A  to Part 71, Table A-1 - A1 and A2 Values For Radionuclides) both list "U (enriched to 20% or less)" with unlimited A1 and A2 values with specific activity based on enrichment, and that "These values apply to unirradiated uranium only."

DOE PCP contacted DOT & NRC for clarification for the HALEU material regarding when it is appropriate to use the unlimited A2 value for U (enriched to 20% or less) or to calculate the A2 value for the mixture of isotopes in the composition of HALEU.  Since DOT is the US Competent Authority, NRC deferred to DOT.

DOT replied that if uranium is enriched from virgin/natural uranium (not down-blended or reprocessed), then the unlimited A2 value for “U (enriched to 20% or less)” is acceptable.  If the uranium is not natural, then it would be treated as a mixture and a sum of fractions approach in §173.433(d) would need to be taken for the different isotopes.  Both DOT and NRC agree that this clarification is consistent with statements in Advisory Material for the IAEA Regulations for the Safe Transport of Radioactive Material, SSG-26 (2012 edition) Appendix I, Paragraph I.68 [SSG-26 Rev. 1, (2018 Edition), Appendix I, Paragraph I.62].

DOE PCP issues the following guidance to implement this clarification:

  • For uranium enriched to less than or equal 20% from virgin/natural uranium, for LEU or HALEU, use the A1/A2 values (unlimited) in accordance with §173.435 for "U (enriched to 20% or less)", otherwise determine the A1/A2 value for the mixture in accordance with the §173.433(d).

  • Applicants to DOE PCP must provide empirical evidence (e.g., lab analysis, process specification, etc.) that the wt.% of all the uranium isotopes expected in LEU/HALEU (U-232, U-233, U-234, U235, U-236, and U-238), and other isotopes from material down-blended or reprocessed to make LEU/HALEU, to ensure all isotopes are accounted for in the mixture.  The application must also state how the LEU/HALEU material was sourced (e.g., unirradiated virgin/natural U, down-blended, or reprocessed). 

  • For questions or comments contact DOE PCP Manager, Dr. Shuler, (301) 903-5513,

    Office of Environmental Management

    1000 Independence Ave. SW
    Washington DC 20585

    Federal Government