United States Nuclear Regulatory Commission - Protecting People and the Environment

Low-Level Radioactive Waste Scaling Factors, 10 CFR Part 61

HPPOS-081 PDR-9111210220

See IE Information Notice No. 86-20 entitled as above and dated March 28, 1986.

Attachment 1 to this Information Notice is entitled "Discussion of Scaling Factor Methodology Problem." These documents alert licensees that scaling factors derived from generic data and applied to specific plant data have caused radionuclide concentration underestimates by factors as high as 10,000 from actual facility samples. Guidance is provided on the appropriate use of scaling factors.

The health physics position was written in the context of 10 CFR 20.311, but it also applies to "new" 10 CFR 20.2006. HPPOS-290 and HPPOS-291 contain related topics.

NRC inspections have identified a poor correlation between generic radionuclide concentration data, used to classify waste, and actual radionuclide sample data at some nuclear power plants. These inspections determined that some plants with multiple waste streams had been using one set of scaling factors to classify waste from all their waste streams, despite significant differences in radionuclide concentrations. Such practices may have led to a significant under-estimation of certain radionuclides, directly affecting health and safety, as well as significant over estimates that led to limited disposal capacity and increased costs.

Any licensee who transfers radioactive waste to a land disposal facility or to a licensed waste collector or processor is required by 10 CFR 20.311 (d) (1) [or 10 CFR 20.2006 (d)] to classify the waste according to 10 CFR 61.55. The three LLW classes (A, B, and C) defined in 10 CFR 61.55 (a) (2)- (a) (7) describe how the classification is computed, based on concentrations of certain radionuclides within the waste. Because some of these radionuclides may be difficult to routinely measure using counting equipment normally found at power reactor facilities, 10 CFR 61.55 (a) (8) permits use of indirect methods such as scaling factors. Indirect methods can be used to determine concentrations of difficult-to-measure radionuclides provided the measurements correlate with actual measurements.

On May 11, 1983, the NRC's Division of Waste Management forwarded a technical position (TP) paper on waste classification to all licensees that described acceptable procedures for determining the presence and concentration of radionuclides listed in 10 CFR 61.55. The TP states that scaling factors should be developed on a facility and waste-stream specific basis. It also stated that the NRC staff recommended the estimated radionuclide concentration derived from scaling methods and that actually measured be precise to within a factor of 10. Scaling factors based on a single set of detailed sample analysis results were acceptable provided assurances were given that they were representative of all samples. [Note: The May 1983 Technical Position on Waste Classification has been revised. See HPPOS-290 and HPPOS-291.] The use of generic data (derived from similar waste streams from several other facilities) combined with actual plant sample data to derive facility scaling factors offers a limited number of facility waste stream samples.

Difficulties arise when scaling factors derived from the mix of generic and facility-specific data are under-conservative and differ from the actual facility samples by factors greater than 10. Use of scaling factors that produce estimates of radionuclide concentrations differing from the most recent actual measurement by factors greater than 10 may constitute noncompliance with 10 CFR 61.55 (a) (8) because the reasonable assurance of the correlation standard can not be met. When these discrepancies are observed, either the scaling factors need to be adjusted to agree with the most recent analysis of that waste stream, or the waste stream needs to be resampled.

As histories of sample analysis facility waste streams are compiled, licensees may determine new scaling factors based on the most recent sample analysis or refine currently used scaling factors by combining the latest analysis with those previously obtained. Licensees may also benefit by identifying individual facility waste streams and determining unique scaling factors for each. Facilities that have more than one operating unit will need separate scaling factors for each waste stream unique to the unit. One set of scaling factors would be appropriate for wastes produced by systems shared by two or more units.

Regulatory references: 10 CFR 20.311, 10 CFR 20.2006, 10 CFR 61.55

Subject codes: 9.0, 9.4, 9.6

Applicability: Reactors

Page Last Reviewed/Updated Monday, June 08, 2015