United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

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

HPPOS-081 PDR-9111210220

Title: Low-Level Radioactive Waste Scaling Factors, 10 CFR

Part 61

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 Thursday, March 29, 2012