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Interpretation Response #02-0047 ([RWE Solutions] [Stanley H. Hodges])

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: RWE Solutions

Individual Name: Stanley H. Hodges

Location State: SC Country: US

View the Interpretation Document

Response text:

May 10, 2002

Mr. Stanley H. Hodges                   Reference No. 02-0047
RWE Solutions
3800 Fernandina Road
Suite 200
Columbia, SC 29210-3854

Dear Mr. Hodges:

This is in response to your letter dated January 25, 2002, requesting clarification of the provisions in § 173.435 regarding the proper methodology and A2 values that should be utilized for transport calculations for uranium radioisotopes under the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180).

Q1: When calculating transport parameters for waste materials that contain uranium isotopes, when should we utilize the individual radionuclide A2 values vs. the A2 values delineated for the uranium on an enrichment basis [e.g. natural uranium, enriched uranium < 5%) or depleted uranium)?

A1: In § 173.403, Natural uranium (U(nat)) is defined as "uranium with the naturally occurring distribution of uranium isotopes." Depleted uranium (U(depleted)) is "uranium containing less uranium-235 (U-235) than the naturally occurring distribution of uranium isotopes." Similarly, enriched uranium (U(enriched)) contains more U-235 than the naturally occurring distribution of uranium isotopes.  Not said, but implied, is that U(depleted) or U(enriched) are uranium with the natural occurring distribution of uranium isotopes that has then been processed to reduce or increase the amount of U-235.  This process will also gradually change the fractions of other uranium isotopes present, as higher enrichments are reached.

Because of the above definitions, whenever radioisotopes of other elements are present in the material to be transported, the A2 value to be used to determine the appropriate packaging requirements is the effective A2 value for the mixture, using the formula in § 173.433(d)(2) and using as input for that formula the fractional activities and the A2 values of the individual nuclides present.

In general, that includes the A2 values of the various uranium isotopes which may be present.  An exception may be made if it is clear from process knowledge that none of the uranium in the waste material came from uranium. enriched to greater than 5% by mass of U-235, and that none of the uranium present had previously been irradiated (reprocessed).  In that case, when applying the mixture formula, an unlimited A2 value may be assumed for all isotopes of uranium present.

Q2: Since my waste does not contain U-230, U-232 and U-233, would these isotopes also be treated in a similar manner, if they were present?

A2: No. Since these isotopes are not normally present in measurable quantities in natural uranium or    uranium enriched to less than 5% by mass of U-235, if they are detected, the fractional activity of each, divided by each respective A2 value, should be used in the mixture formula.

Q3: If analytical data are not available for the individual uranium radionuclides, can we use the values based on enrichment or do we need to obtain additional analytical data to determine the uranium isotopic distribution in the package waste?

A3: If it is known that all uranium in the waste had the same enrichment, standard activity ratios for each of the uranium isotopes present for that enrichment may be assumed.  If uranium of more than one level of enrichment is present in the waste, it is preferable to determine these ratios experimentally.

I hope this information is helpful.


Hattie L. Mitchell, Chief
Regulatory Review and Reinvention
Office of Hazardous Materials Standards


Regulation Sections

Section Subject
173.435 Table of A1 and A2 values for radionuclides