Answer to Question #6532 Submitted to "Ask the Experts"

Category: Radioactive Waste Disposal — Disposal

The following question was answered by an expert in the appropriate field:

Q

We are an environmental company and have been requested to coordinate testing and disposal of decomissioned boilers that were found to contain low-level radioactive material. What is the standard testing protocol for unknown radionuclide mixtures? Would gross alpha-, beta-, and gamma-activity counts per surface area unit satisfy a disposal facility's requirements for testing?

A

The most authoritative response to your question would be to directly access the disposal facility's waste acceptance criteria (WAC). For example, you can access the WAC for the EnergySolutions disposal facility in Clive, Utah. Most disposal facilities require the waste generator to provide information about the waste, such as the process that generated the waste, waste material physical composition and characteristics, radiological and chemical characterization method, and basis for determining manifested radionuclide concentrations. This information is necessary to provide an understanding of the radionuclides and their concentrations likely to be present in the waste. The Clive, Utah, WAC states that "the waste must be characterized via gamma spectroscopy, liquid scintillation, or other standard radiochemistry methods to determine the radionuclide concentrations in the waste. Indirect measurements such as dose-to-curie or use of scaling factors may also be used if the process has been validated with direct measurements. Non-gamma emitting radionuclides, such as 55Fe and 63Ni, may be scaled from the gamma spectral analysis obtained from testing the material if the waste generator has specific process knowledge of the material being profiled (10 CFR Part 61 analyses)."

The Nevada Test Site WAC also supports the use of scaling factors to relate gross radiation measurements to the activity concentration of a waste stream. The radiological characterization methods in Appendix E specify that "generators using gross radiation measurements shall ensure that measurements correlate with activity concentration on a consistent basis. Radionuclide distributions in the waste stream shall be initially determined and periodically verified through direct measurements or sampling and analysis. When developing scaling factors, generators must consider the waste package and detector geometry, shielding and attenuation effects, self-absorption, and the energy spectra and decay schemes of radionuclides in the waste."

Based on this information, it seems possible that gross alpha-, beta-, and gamma-activity counts per surface area unit would satisfy the disposal facility's requirements, provided that these measurement data are used with technically defensible scaling factors to determine the radionuclide concentrations in the waste. In other words, a combination of gamma spectroscopy, liquid scintillation, or other standard radiochemistry methods in conjunction with direct surface activity measurements that serve as surrogates for specific radionuclides might suffice. Again, ultimate approval of the proposed radiological characterization methods for WAC compliance should be obtained from the disposal facility.

Eric W. Abelquist, PhD, CHP

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