1. Lisa Edwards Sr. Program Manager LLW Forum April 13-14, 2016
Development of Generic Scaling Factors for Technetium-99 and Iodine-129 in Low and Intermediate Level Waste
Lisa Edwards
Sr. Program Manager
LLW Forum April 13-14, 2016
2/7/2016. Revision 2.

2. Project Purpose, Scope, and Benefit
Objective:
Develop generic scaling factors for estimating the concentration of Tc-99 and I-129 in low and intermediate level waste (LILW).
Scope:
Validate Pacific Northwest National Laboratory datasets for Tc-99 and I-129 for use in development of generic scaling factors.
Develop generic scaling factors.
Validate generic scaling factors using calculations and/or other independent data.
Benefits & Applicability:
More accurate estimation of Tc-99 and I-129 in LILW and radwaste disposal sites.
In the U.S., guidance for implementing an indirect method to estimate Tc-99 and I consistent with NRC Regulatory Information Summary “Reporting of H-3, C-14, Tc-99, and I-129 on the Uniform Waste Manifest”
May be useful for international nuclear power plants wastes where generic scaling factors are commonly used.
Published EPRI Report
Implementation Category
EPRI Nuclear
Reference
Technical Basis

3. Industry Challenge
The accurate estimation of these mobile radionuclides is important for LILW characterization, classification, and disposal.
Use of non-positive LLD values (or scaling factors derived from LLD values) would result in manifested activity for Tc-99 and I-129 that are 100-1,000 times higher than actual.
Multiple references have documented the positive bias in using scaling factors derived from LLD values, a few are listed here:
NUREG-1418 “Roles Report”, 1990
DOE/EH-0332P, LLW & MW Disposal During 1990, 1993
NUREG/CR-6567, LLW Classification, Characterization and Assessment, 2000
NCRP 152, LLW Performance Assessment, 2005
EPRI , LLW Disposal Practices, 2009
ML13260A075, EPRI Letter to Staff, August 1, 2013

4. Scaling Factor Development - Approach
Mass spectrometry analyses performed by Pacific Northwest National Laboratory (PNNL) on NPP LILW between 1990 and 2000 (NUREG/CR-6576.)
Mass spectroscopy sample results from NUREG/CR-6567 Table 7.8 for 99Tc and 129I were evaluated for use in developing generic scaling factors.
Statistical methods were applied to develop scaling factors for 99Tc and 129I from easy to detect radionuclides, 137Cs or 60Co.
The sources of the 99Tc and 129I, whether fission product (fuel gap release or tramp fuel) and/or decay product of activated materials of construction, were considered.
A basic summary of the approach used to evaluate a proper treatment method of the data form PNNL and published in NUREG / CR 6567 is described in this slide.
As a general background, when this data was initially analyzed, a linear relationship didn’t appear to fit well. However, it should be understood that the apparent absence of a linear relationship is not uncommon with natural processes.  Similar to other scaling factor data that spans several orders of magnitude and appears non-linear in normal space may prove to be linear in log space if a normal distribution of the log transformed data is present --also known as a log-normal distribution.
To develop the log normal distribution, the direct measurements of the PNNL data and related ratios were transformed to their natural log values. The resulting data was checked for normality using 3 standard tests including a histogram, a Q-Q plot and a diagnostic residual plot. Once the data quality was determined to be acceptable, the data was evaluated for determination of scaling factors taking into account fuel condition as determined by the Cs/Co ratio.
So for I-129, the PNNL direct measurements of and Cs-137 and their relative ratio were transformed to their natural log values. The result was then validated using the 3 standard test just described.

5. Results – 99Tc/60Co or 99Tc/137Cs
Two scaling factors for 99Tc emerged from this analysis:
The 137Cs/60Co ratio describes the dominant 99Tc production mechanism as either decay of activated of corrosion products or fission products.
99Tc is scaled to the activated corrosion product 60Co when 137Cs/60Co <10 using a value of 1.3E-06.
All Rx/60Co value chosen for conservatism
99Tc is scaled to the fission product 137Cs when 137Cs/60Co >10 using a value of 2.5E-08.
All Rx/60Co
BWR/60Co
PWR/60Co
All Rx/60Co Cs/Co <10
All Rx/137Cs Cs/Co >10
Sample Count 31 10 21
Geometric Mean
1.26E-06
1.18E-06
1.29E-06
7.19E-07
2.53E-08
LMD 68%
6.36
6.31
6.67
5.46
4.35
LMD 80%
10.7
10.57
11.3
8.79
6.56
LMD 90%
21.1
22.1
24.2
16.5
11.30
LMD 95%
37.5
37.0
41.2
27.9
17.82
So, the preliminary conclusion of this research is that I should be scaled to cesium.
If a scaling factor of 1.2E-7 is used, based on this data set, you would be within a factor of 10 at the 80% confidence level.
Although a slightly better confidence level could be achieved thru the use of one scaling factor for when the Cs/Co ratio is <10 and another scaling factor when the Cs/Co ratio is >10, the recommended value for the entire data set is more conservative that either of the alternatives.
I expect the this analysis to be subjected to debate and independent scrutiny as all good science is. I recognize that a larger data set would be more ideal and that higher confidence level would be more appealing, however, I am comfortable in making this preliminary recommendation based on its alignment with other calculations that are described in the work, but for the sake of time not presented today.
In addition, if the aim here is for accurate reporting, one must consider the potential shortcomings of this approach in comparison to the shortcomings of using LLD values which are known to grossly over report the presence of Iodine.

6. Results – 129I/137Cs or 129I/60Co
129I/137Cs
129I/60Co
129I should be scaled to 137Cs when present using scaling factor of 2.00E-07.
This value is within a factor of 10 at the 80% confidence interval
This value for optimal fuel clad conditions is the most conservative and it bounds the “all fuel clad integrity” data by a factor of ~2 and the “poor fuel clad integrity” data by a factor of ~5
129I should be scaled to 60Co when 137Cs is not present in waste using the factor 3.20E-08.
May be needed due to improving fuel integrity.
Especially true for dry wastes and filters that do not concentrate soluble radionuclides.
There is no direct correlation between 129I and 60Co.
As such, this method to scale 129I to 60Co in the absence of 137Cs looks at the relationship between 99Tc and 129I originating from fission.
Makes the bounding, conservative assumption that, for the purposes of developing a 129I/60Co scaling factor, the 99Tc in the waste originates from fission of tramp fuel.
 129I/137Cs
All Rx/137Cs where 137Cs/60Co >10
All Rx/137Cs
All Rx/137Cs where 137Cs/60Co <10
Sample Count 13 45 32
Geometric Mean
3.48E-08
1.21E-07
2.01E-07
LMD 68%
5.62
6.03
4.89
LMD 80%
9.11
9.98
7.62
LMD 90%
17.3
19.4
13.7
LMD 95%
29.5
33.9
22.4

7. Scaling Factor Conclusion
The PNNL mass spec datasets for 99Tc and 129I in LILW:
Provide a reasonable basis for generic scaling factors, the data fits well and has been verified using independent calculation methods
Proposed Indirect Method (RIS *)
Perform analysis for 99Tc and 129I in waste to required sensitivity (1% Table 1 a-priori at a minimum)
When 99Tc and/or 129I results are not positive use a scaling factor from this research to calculate a value as applicable and treat as a positive measurement.
International members should review data and results provided in this report for applicability to their LILW.
Hard-to-Detect
Condition
Easy-to-Detect
Scaling Factor
129I
When 137Cs is detected
Should be scaled to 137Cs
2.00E-07
When 137Cs is not detected
Should be scaled to 60Co
3.20E-08
99Tc
When the 137Cs/ 60Co <10
1.30E-06
When the 137Cs/ 60Co >10
2.50E-08
In conclusion, the PNNL mass spec measurements make sense and demonstrate good fit that form the basis for reasonable scaling factors with a sufficient level of confidence.
While additional mass spec analyses are welcome and will always serve to refine the central tendency of the datasets - additional mass spec analyses are really not necessary to use the existing data generically in lieu of using LLD values.
Generic scaling factors were conservatively derived from this EPRI analysis that were mathematically validated. These generic scaling factors provide a reasonable assurance of accuracy and are far better used than an LLD result that is know to be high by a factor of 100 to 1,000 or even 10,000 times actual.
What EPRI proposes is that NRC licensees that choose to use the scaling factors from this work continue to perform radiochemistry analysis for 99Tc and 129I at a minimum in accordance with the sensitivity requirements of the 1983 BTP but when the results of those measurements do not detect any activity or LLD, a generic scaling factor be used from this work in lieu of manifesting an LLD value as real.
*U.S. NRC Regulatory Information Summary “Reporting of H-3, C-14, Tc-99, and I-129 on the Uniform Waste Manifest”