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
