ML22069A335
| ML22069A335 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 12/06/2021 |
| From: | ZionSolutions |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML22069A328 | List: |
| References | |
| ZS-2022-005 ZS-LT-07, Rev 1 | |
| Download: ML22069A335 (25) | |
Text
ZS-LT-07 Revision 1 D&D Procedure Cover Page CHARACTERIZATION/LICENSE TERMINATION PROCEDURE SURVEY PLAN FOR DISCRETE RADIOACTIVE PARTICLE IDENTIFICATION AND REMEDIATION ZS-LT-07 Revision No. 1 Preparer: (Print name / sign): ________________________________________________Date:_________________
Robert Yetter III Secondary Reviewer: (Print name / sign): ______________________________________Date: _________________
Robert Yetter VP Regulatory Affairs or Designee has reviewed and determined required program & regulatory reviews (*new procedures only*): SIGNATURE__ N/A_______________________________________DATE:___________
Regulatory Required Reviews (per AD-Part 72 ISFSI Impact License: 10 CFR 72.48 YES NO Part 50 License: 10 CFR 50.59 and 50.90 YES NO Fire Protection: 10 CFR 50.48(f)
YES NO Conditions of License: E-Plan: 10 CFR 50.54(q)
YES NO QA Review Required?
YES NO QA Reviewer: N/A DATE:____________
Print Name / Signature Technical Review Required?
YES NO Technical Reviewer: _ N/A ____________________________________________DATE:____________
Print Name / Signature Technical Reviewer: ____N/A______________________________________________DATE:____________
Print Name / Signature Approval Section DEPARTMENT MANAGER: Sarah Roberts DATE:____________
Print Name / Signature DECOMMISSIONING PLANT MANAGER*:_ N/A ____________________________________________DATE:___________
Print Name / Signature
- Required for Technical Reviews only Verification of Required Reviews Per MDI Completed:
DOCUMENT CONTROL:___________________________________________________DATE:___________
Print Name / Signature Effective Date:________________
sroberts Digitally signed by Robert F Yetter III DN: C=US, O=EnergySolutions, CN=Robert F Yetter III, E=rfyetteriii@energysolutions.com Reason: I am the author of this document Location: your signing location here Date: 2021-12-06 13:19:45 Foxit PhantomPDF Version: 9.7.0 Robert F Yetter III Digitally signed by Sarah Roberts DN: OU=VP Rad Programs, O=ES, CN=Sarah Roberts, E=sroberts@energysolutions.com Reason: I am the author of this document Location: your signing location here Date: 2021-12-07 12:34:19 Foxit PhantomPDF Version: 9.7.2 Sarah Roberts
ZS-LT-07 Revision 1 2
Summary of Changes in this Revision:
Rev. 0 Initial Issue Rev. 1 Added Section 3.1, Data Quality Objectives Overview; 3.3
-related 3.4.1: addition of language concerning areas inaccessible to hand scanning, and addition of more detail on the calibration and MDA calculations; 3.3.2: removed requirement for instrument headphones; 3.4.3 / 3.4.4 / 3.6: clarified the types of particles that will be sent for analysis and what type of analysis will be performed
ZS-LT-07 Revision 1 3
- 1.
INTRODUCTION.............................................................................................................................................. 5 1.1.
PURPOSE...................................................................................................................................................... 5 1.2.
SCOPE.......................................................................................................................................................... 5
- 2.
BACKGROUND................................................................................................................................................ 5
- 3.
REQUIREMENTS AND GUIDANCE............................................................................................................. 7 3.1.
DATA QUALITY OBJECTIVES OVERVIEW..................................................................................................... 7 3.2.
SURVEY UNITS IN THE SCOPE OF THE SURVEY PLAN................................................................................... 9 3.3.
RADIONUCLIDES OF CONCERN.................................................................................................................. 13 3.4. DESCRIPTION OF PLANNED DRP SURVEY ACTIVITIES............................................................................... 14 3.4.1 Gamma Scan Survey with Towed Array............................................................................................. 14 3.4.2 Gamma Scan Survey with Hand-Held Detectors................................................................................. 17 3.4.3 Scan Investigations.............................................................................................................................. 18 3.4.4 Systematic Soil Sampling.................................................................................................................... 19 3.4.5 Sample Investigations.......................................................................................................................... 21 3.4.6 Sample Analysis Requirements........................................................................................................... 23 3.4.7 Quality Control.................................................................................................................................... 23 3.4.8 Survey Documentation........................................................................................................................ 23 3.5.
DATA VALIDATION................................................................................................................................... 23 3.6.
DATA EVALUATION................................................................................................................................... 24 3.7.
SURVEY REPORTING.................................................................................................................................. 24
- 4.
REFERENCES................................................................................................................................................. 25
ZS-LT-07 Revision 1 4
ABBREVIATIONS CCDD clean concrete demolition debris DQO data quality objective DRP discrete radioactive particle FSS final status survey HTD hard-to-detect IMU inertial measurement unit LTP license termination plan MARSSIM Multi-Agency Radiation Survey and Site Investigation Manual MDA minimum detectable activity MDCR minimum detectable count rate NRC U.S. Nuclear Regulatory Commission ORISE Oak Ridge Institute for Science and Education QC quality control RAI request for additional information ROC radionuclides of concern TSD technical support document UTV utility terrain vehicle VSP Visual Sample Plan ZSRP Zion Station Restoration Project
ZS-LT-07 Revision 1 5
- 1.
Introduction 1.1.
Purpose This document establishes a survey plan for discrete radioactive particle (DRP) identification and remediation at the Zion Station Restoration Project (ZSRP), to support partial U.S. Nuclear Regulatory Commission (NRC) license termination of the Zion Nuclear Power Station (Zion) site in compliance with applicable NRC requirements. This survey plan has been prepared in accordance with industry best practices and in response to the NRC letter received August 26, 2021, which details the draft request for additional information (RAI)-10.
In addition to identifying and retrieving DRPs, this survey will provide an estimate of the number of hypothetical DRPs that may still remain on the site as well as any hypothetical dose consequences if the DRP were encountered in the future.
1.2.
Scope The survey aims to identify and eliminate the presence of DRPs at the site, especially in survey units where clean concrete demolition debris (CCDD) was temporarily stored or transported through, waste loadout areas, and areas of elevated activity identified during the April 2021 inspection survey or during the most recent reperformance of final status survey (FSS) in some survey units. Additionally, other areas (e.g., survey units 10214, 10213, 10212) are included in the scope of this survey in order to bound Class 1 survey units where particles or elevated areas were previously identified to ensure that the particles did not spread outside of the Class 1 survey units. Although CCDD was stored in survey units 12205A through 12205E, these survey units are not included in the scope of this survey, because FSS was successfully reperformed after removal of the CCDD and no areas of elevated activity were identified by the Oak Ridge Institute for Science and Education (ORISE) in their independent verification survey in 2020.
This plan also describes the data quality objectives (DQOs) for the radiological evaluation of the survey units of interest. The areas within the scope of this survey will be expanded as needed as a result of investigations performed to bound areas of elevated radioactivity, or as a result of remediation.
- 2.
Background
Approximately 290 DRPs have been detected during the course of the ZSRP. Primarily, two events and one operational function potentially contributed to the presence of particles around several areas of the site. DRPs were first identified outside of structures after a spread of contamination event in September 2014. In this case, containers (8-120 liners) loaded with debris from the reactor internals segmentation project, were temporarily stored in a shielded array in the lower south lot present in survey units 10221A, 10221B, and 10221C. The cause of the contamination spread was inserting an 8-120 liner into its overpack outside. DRPs were again identified in June 2015 during down-posting of a Radiological Material Area outside of the Unit 2 Containment Building that previously contained pieces of the Steam Generators. The most likely
ZS-LT-07 Revision 1 6
cause for the DRPs identified was wind entrainment of DRPs inside of each Containment Building into the immediate vicinity of the Containment construction openings, as well as the movement of potentially contaminated equipment through the construction openings. Lastly, DRPs generated during demolition of interior containment concrete structures (i.e., under vessel or bioshield) were likely introduced into the soil during waste handling operations. DRPs from these origins ultimately migrated to other areas of the site by way of surface water flow and/or heavy equipment and vehicle movement.
In immediate response to the events described above, and in response to the detection of DRPs at any time during decommissioning, biased surveys were conducted and the DRPs were successfully remediated. While this was the case, DRPs were still intermittently detected throughout decommissioning at different stages, during radiological assessments, FSS, or even after FSS. The most recent example of the detection of DRPs after FSS completion is the April 2021 inspection survey conducted by ORISE, in which eight DRPs were identified. Because the DRPs were identified post-FSS and, in some cases, their radiological characteristics differed from the historical DRPs discovered at the site, the NRC determined (as described in RAI-10) that a survey plan was needed to address the presence of DRPs on-site 10 CFR Part 50 license can be amended.
The April 2021 inspection survey revealed seven elevated areas, in which eight DRPs (S0112A, S0116, S0120, S0124, S0126, S204AEu, S203B, 5271-S-203ATh) were found.
According to the ORISE report, 5271-SR-09-0 [1], three DRPs collected during the confirmatory survey are consistent with previously collected DRPs from past confirmatory surveys, both in terms of the radionuclides present and total activity.
Three particles (S0120, S0126, and S0204A) contain radionuclides that are not consistent with the historical radionuclide contributions typically found in DRPs. DRPs S0120 and S204AEu contain Eu-152, Eu-154, and Ba-133, which are neutron activation products typically located within the bioshield. DRP S0126 contains a mixture of transuranics (Am-241, Cm-241, Pu-238, Np-237, and Pu-239/240) and fission products (Cs-137, Sr-90, Eu-154, and Eu-155). Based on the radionuclides present, the reactor fuel is the most likely source of DRP S0126.
Particles S203A and S203B exhibited radionuclides unlike any other particle identified during this survey or previous surveys. Particle S203A contained elevated activities of Th-232, Th-228, and Ra-228. Elevated activities of natural U-238 and U-234 also were reported in this sample. The elevated Ra-228 activity relative to Th-232 indicates that the material within the sample is not natural and the material has received some form of processing. Laboratory staff were able to determine an activity concentration of particle S203ATh (concentration values are not presented). The activity concentration was used to estimate the total activity of the particles comprising S203B based on the total mass of the particles. The origin of these samples could not be determined based on the available data.
Table 1 below, recreated from Table 5.2 of 5271-SR-09-0, summarizes the total DRP
ZS-LT-07 Revision 1 7
activities. Table 2, recreated from Table 5.3 of 5271-SR-09-0, summarizes the total thorium particle activities.
Table 1 - Summary of Particle Total Activities (pCi)a Sample ID Am-241 Ba-133 Cm-244 Co-60 Cs-134 Cs-137 Eu-152 Eu-154 Eu-155 Np-237 Pu-238 Pu-239b Sr-90 S0112A 0.04 10 0
48400 36
-27
-20
-40 27 0
0 0.059
-0.21 S0116 0.019
-8 0.038 18400 22
-4
-28 0
48 0
0 0.041
-0.34 S0120 0.033 11 0.011 378 11 0.6 20000 1100 13
-0.011 0.043 0.063 0.83 S0124 0.12
-300 0.06 1508000 1200 1000
-500 2000
-10 0.02 0.14 0.079 0.49 S0126 79900
-11 14800 62 12 98900
-70 2920 838 3.9c 26188 7540 157043 S204AEu 0.028 1520 30000 344000 16200
-0.028
-0.028 16.6 0.8 a: Bolded values indicate the 95% uncertainty interval did not include zero.
b: Pu-239 value includes contributions from Pu-240.
c: Result is statistically positive; however, review of the alpha spectrum indicated that the alpha emissions were likely the result of Pu-242.
Table 2 Summary of Thorium Particle Total Activities (pCi)a Sample ID Ra-228 Th-228 Th-230 Th-232 U-234 U-238 S203Bb 16800 10850 1180 7350 1170 1070 5271-S-203ATh 37000 23900 2600 16170 2570 2360 a: Bolded values indicate the 95% uncertainty interval did not include zero.
b: Total activity of the particles was estimated based on the concentration of S203ATh and the sample mass of the particles (concentration values are not provided).
- 3.
Requirements and Guidance 3.1.
Data Quality Objectives Overview The following is an overview of the DQOs that are detailed in various sections throughout this survey plan.
1.)
The problem: The problem associated with this plan is to determine if DRPs remain at the site, and if so, how does their presence affect public health and safety and the
, as discussed in Section 2 of this plan.
Stakeholders: The primary stakeholders interested in the answer to this problem are ZionSolutions, Exelon Nuclear Generation, and the NRC.
2.)
Decision: If the results of the survey are inadequate to demonstrate that the site is sufficiently free of DRPs or that the presence of DRPs would pose no threat to public health and safety, then NRC staff will not be able to terminate the Zion 10 CFR Part 50 license without further actions.
3.)
Information Needed: Sections 1 and 2 present the scope and background information pertinent to this survey plan.
ZS-LT-07 Revision 1 8
Prior Radiological Data: Prior radiological data collected by ZionSolutions related to DRPs has been summarized within or provided to the NRC through the RAI process.
DRPs identified by ZionSolutions did not undergo detailed analysis; rather, the DRPs were treated as source term and remediated regardless of radionuclide profile. However, qualitative gamma spectroscopy measurements indicated that the DRPs identified by ZionSolutions consisted of only Co-60. The most recent data concerning DRPs was collected by ORISE and the NRC during the April 2021 inspection survey, the results of which are summarized in Section 2.
Radionuclides of Concern: Section 3.3 presents the radionuclides of concern.
Basis for Scan Measurements: Scan measurements will be performed to identify elevated areas that potentially contain DRPs. Sections 3.4.1 and 3.4.2 detail the scan processes under this survey plan.
Basis for Quality Control (QC) Measurements: QC replicate scan measurements, as detailed in Section 3.4.7, will be performed to ensure that data collected are of good quality and reproducible.
Sampling and Analysis Methods to Meet the Data Requirements: As discussed in systematic soil samples will be utilized for this survey plan. 775 soil samples from 155 systematically-located grid cells will be screened by hand scanning and portable gamma spectroscopy for DRPs. Soil samples will be collected systematically to assess the potential for DRPs to exist in soil down to a depth of 12 inches.
If DRPs are identified during any portion of the survey (large area scanning or presence/absence sampling), the radionuclide contents of the DRP will be identified using portable gamma spectroscopy. As discussed in Section 3.6, samples containing any non-Co-60 particles will be sent to the off-site laboratory for full suite radionuclide analysis.
Investigation Levels: Sections 3.4.1 and 3.4.2 present the investigation level for the towed array scanning system and hand scanning, respectively. Sections 3.4.3 and 3.4.5 present the investigation protocol for the towed array system/hand scanning and the systematic sampling process, respectively.
4.)
Boundaries of the Survey: Section 1.2 defines the scope of this survey plan. Section 2 details the survey units within the scope of this plan and the justifications for including them in the scope of the plan. The areas within the scope of the survey will be expanded as needed as a result of investigations performed to bound areas of elevated radioactivity or as a result of remediation. The rationale for areas not included in the scope of this plan is that based on process knowledge and the results of previous radiological surveys, including successful performance in FSS and ORISE confirmatory surveys, there is a low potential for the presence of DRPs.
5.)
ZS-LT-07 Revision 1 9
Decision Rule: If a DRP is identified, then remediate the DRP. Further, if the remediated DRP contains non-Co-60 radionuclides, then send the sample containing the DRP to the off-site laboratory for full suite radionuclide analysis.
Pertaining to presence/absence sampling, if no more than 0.5% of the grid cells in the population are unacceptable, then there will be no more than a 0.8% probability of concluding that the population is unacceptable (i.e., observing more than 3 unacceptable grid cells in the sample size of 155), as discussed in Section 3.4.4.
6.)
Uncertainty: Analytical uncertainty is controlled by using appropriate instrumentation, methods, techniques, training, and QC. Uncertainty in the calculation of the hypothetical number of particles to remain on-site after survey completion is controlled by the number of grid cells defined for systematic sampling.
Hypothesis Testing and Decision Errors: Section 3.4.4 details a statistical method in the form of presence/absence sampling for assessing soil up to a depth of 12 inches. For the presence/absence survey, the Type I error (
is less than 0.5 and the 0.786. See Figure 2 for the VSP inputs and outputs that detail these decision errors.
7.)
Survey Design: The detailed survey design aspects are provided in the following sections.
3.2.
Survey Units in the Scope of the Survey Plan A list of the survey units (36 in total), their classifications and sizes, and the justification for their inclusion into the scope of this survey plan are provided below in Table 3. The total surface area for the survey units of interest is 103,476 m2 (25.57 acres). A map showing the survey units of interest is provided as Figure 1.
Table 3 Survey Units and Justification SU Class sq. m acres Justification 12110 1
1,740 0.43 Unit 1 loadout tent area 12111 1
1,964 0.49 Unit 1 loadout tent area 12112 1
1,693 0.42 CCDD was stored in the survey units after FSS, and FSS was not re-performed 12113 1
1,658 0.41 CCDD was stored in the survey units after FSS, and FSS was not re-performed 10203A 1
1,999 0.49 Travel path for CCDD to loadout areas in 10206B and 10214B 10204B 1
1,549 0.38 Travel path for CCDD to loadout areas in 10206B and 10214B; Elevated areas were identified by ORISE/NRC 10204C 1
1,547 0.38 Travel path for CCDD to loadout areas in 10206B and 10214B
ZS-LT-07 Revision 1 10 SU Class sq. m acres Justification 10204D 1
1,545 0.38 Travel path for CCDD to loadout areas in 10206B and 10214B 10206A 1
2,844 0.45 Travel path for CCDD 10206B 1
1,837 0.45 CCDD loadout area 10206C 1
1,833 0.45 Travel path for CCDD to loadout areas in 10206B and 10214B 10206D 1
1,829 0.45 Travel path for CCDD to loadout areas in 10206B and 10214B 10206E 1
1,825 0.45 Travel path for CCDD to loadout areas in 10206B and 10214B 10207E 1
1,731 0.43 Travel path for CCDD to loadout areas in 10206B and 10214B 10208D 1
1,827 0.45 Travel path for CCDD to loadout areas in 10206B and 10214B 10209E 1
1,560 0.39 Elevated areas were identified by ORISE/NRC 10212A 2
9,550 2.36 Bounding Class 2 buffering Class 1 10213A 2
5,730 1.42 Bounding Class 2 buffering Class 1 10214A 2
8,542 2.11 Bounding Class 2 buffering Class 1 10214B 2
7,372 1.82 CCDD loadout area; Bounding Class 2 buffering Class 1 10214C 2
7,579 1.87 Travel path for CCDD to loadout areas in 10206B and 10214B; Bounding Class 2 buffering Class 1 10214D 2
8,946 2.21 Bounding Class 2 buffering Class 1 10220I 1
2,060 0.51 Elevated areas were identified by ORISE/NRC 12109 1
1,931 0.48 Unit 1 loadout tent area 12201A 1
1,992 0.49 Unit 2 loadout tent area 12201B 1
1,995 0.49 Unit 2 loadout tent area; Elevated areas were identified by ORISE/NRC 12202A 1
1,988 0.49 Travel path for CCDD to loadout areas in 10206B and 10214B 12202B 1
1,999 0.49 Travel path for CCDD to loadout areas in 10206B and 10214B 12202C 1
1,894 0.47 Travel path for CCDD to loadout areas in 10206B and 10214B 12202D 1
1,650 0.41 Travel path for CCDD to loadout areas in 10206B and 10214B; Unit 1 loadout tent area 12202E 1
1,845 0.46 Travel path for CCDD to loadout areas in 10206B and 10214B 12202F 1
1,858 0.46 Travel path for CCDD to loadout areas in 10206B and 10214B 12203A 1
1,988 0.49 CCDD was stored in the survey units after FSS, and FSS was not re-performed; Elevated areas were
ZS-LT-07 Revision 1 11 SU Class sq. m acres Justification identified by ORISE/NRC; Travel path for CCDD to loadout areas in 10206B and 10214B 12203B 1
1,989 0.49 CCDD was stored in the survey units after FSS, and FSS was not re-performed 12203C 1
1,955 0.48 CCDD was stored in the survey units after FSS, and FSS was not re-performed 12203D 1
1,637 0.40 CCDD was stored in the survey units after FSS, and FSS was not re-performed; Elevated areas were identified by ORISE/NRC; Travel path for CCDD to loadout areas in 10206B and 10214B
ZS-LT-07 Revision 1 12 Figure 1 - Map of Survey Units of Interest
ZS-LT-07 Revision 1 13 3.3.
Radionuclides of Concern ZionSolutions technical support document (TSD)11-001, Radionuclides of
[2] establishes the basis for an initial suite of potential radionuclides of concern (ROC) of distributed contamination for the decommissioning. Industry guidance was reviewed as well as the analytical results from the sampling of various media from past plant operations. Based on the elimination of some of the theoretical neutron activation products, noble gases, and radionuclides with a half-life less than two years, an initial suite of potential ROC for the decommissioning of the ZNPS was prepared based on characterization samples of basement concrete surfaces. The only radionuclides identified in characterization soil samples were Cs-137 and Co-60 at low levels. Thus, concrete ROCs and their surrogate ratios were used for soil. The initial suite of potential ROC is provided in Table 4 below, which is recreated from Table 5-1 of the Zion LTP.
Table 4 Initial Suite of Radionuclides Radionuclide Half Life (years)
Radionuclide Half Life (years)
Radionuclide Half Life (years)
H-3 1.24E+01 Tc-99 2.13E+05 Np-237 2.14E+06 C-14 5.73E+03 Ag-108m 1.27E+02 Pu-238 8.77E+01 Fe-55 2.70E+00 Sb-125 2.77E+00 Pu-239/240 2.41E+04 Ni-59 7.50E+04 Cs-134 2.06E+00 Pu-241 1.44E+01 Co-60 5.27E+00 Cs-137 3.00E+01 Am-241 4.32E+02 Ni-63 9.60E+01 Eu-152 1.33E+01 Am-243 7.38E+03 Sr-90 2.91E+01 Eu-154 8.80E+00 Cm-243/244 1.81E+01 Nb-94 2.03E+04 Eu-155 4.96E+00 Section 6.5.2 of the LTP discusses the process used to derive the ROC for the decommissioning of ZNPS, including the elimination of insignificant dose contributors from the initial suite consistent with the guidance in Section 3.3 of NUREG-1757, Volume 2 oning Guidance Characterization, Survey, and
[3]. Based upon the analysis of the mixture in Table 19 of TSD 14-019, Source Ter
[4], it was determined that Co-60, Ni-63, Sr-90, Cs-134, and Cs-137 accounted for 99.5% of all dose in the contaminated concrete mixes. For activated concrete, H-3, Eu-152, and Eu-154, in addition to the five aforementioned nuclides, accounted for 99% of the dose.
Table 5 below (recreated from Table 5-2 of the LTP) presents the ROC for the decommissioning of ZNPS and the normalized mixture fractions based on the radionuclide mixture presented for the Auxiliary Building and Containment in TSD 14-019, Table 19.
ZS-LT-07 Revision 1 14 Table 5 Dose Significant Radionuclides and Mixture Radionuclide Containment Auxiliary Building (2)
% of Total Activity (normalized)(1)
% of Total Activity (normalized)(1)
H-3 0.08%
NA Co-60 4.72%
0.92%
Ni-63 26.50%
23.71%
Sr-90 0.03%
0.05%
Cs-134 0.01%
0.01%
Cs-137 68.17%
75.32%
Eu-152 0.44%
NA Eu-154 0.06%
NA (1) Based on maximum percent of total activity from Table 20 of TSD 14-019, normalized to one for the dose significant radionuclides.
(2) Does not include dose significant radionuclides for activated concrete (H-3, Eu-152, Eu-154).
The radionuclides positively identified, as indicated in bold in Table 1, during the April 2021 inspection survey are of particular concern in this survey plan.
ant-radionuclides, within the context of this plan, refer to the gamma-emitting radionuclides Cs-137, Co-60, Eu-152, Eu-154, Fe-59, Am-241, Nb-94, Mn-54, and Ba-133.
3.4.
Description of Planned DRP Survey Activities 3.4.1 100% of the accessible surface area of the survey units listed in Table 3 will be scanned using a towed 62 inch-wide array of six Ludlum Model 44-mounted on a utility terrain vehicle (UTV) attached to a Ludlum Model 4612, a 12-channel counter data logger. The unit will also be equipped with a single Trimble GA810 GPS receiver and antenna combined with a high-accuracy inertial measurement unit (IMU). The Ludlum Model 4612, Trimble GPS receiver, and the IMU are integrated using an on-board tablet or laptop computer (control computer) running the scanning software. Collimators will not be used on the towed array detectors. Areas inaccessible to this towed array will be surveyed using hand-scanning methods. Areas inaccessible for hand scanning will be evaluated by the Director Radiological Site Closure to determine path forward. These areas will be documented in the field notes and with the survey results.
Use of the towed array scanning system is in accordance with procedure ZS-LT-300-001-
-10
[5]. Details of system calibration and the sensitivity and performance assessments are provided in TSD 21-Particle Detection Sensitivity and Performance Assessment for a Ludlum 44-10 Six-
[6].
ZS-LT-07 Revision 1 15 TSD 21-001 includes an evaluation of the system performance in several aspects. The first is a probabilistic analysis of the minimum detectable activity (MDA) to DRPs with consideration of the random variables that impact the relative positions of potential DRPs to the detectors during scanning operations. This probabilistic analysis represents a hybrid between an a priori and a posteriori estimate of the MDA distribution since the measurement distribution was used as a probabilistic parameter along with the MARSSIM scan MDA expression. The second aspect is an estimate of the system sensitivity based on post-processing all of the scan data against a 7-sigma exceedance criteria applied to 20 ft x 20 ft fishnet analysis across the towed array survey areas. The third aspect is an empirical test of the towed array using three DRPs found during FSS activities at the site with the particles placed on the ground surface. A summary of the results of these are provided in the following table.
Table 6 Summary of Towed Array Sensitivity Tests Methodology Co-60 Sensitivity (µCi)
Cs-137 Sensitivity (µCi)
Probabilistic Model, 50th Percentile 0.063 0.15 Post-Process data Assessment, 7 sigma 0.115 0.26 Array Drive-Over 0.12 0.231 As this table shows, the sensitivity using the probabilistic model suggests values that are approximately a factor of two lower than the other methods for both Co-60 and Cs-137.
This is primarily caused by the z-score value applied to the MARSSIM MDA equation (a value of 3.28) as compared to the z-score value used in the initial post processing process of 7.
The dose analysis, provided in response to RAI 10 (Specific Consideration 3b) includes an ingestion dose analysis, based on particle size estimates, using the post-process sensitivities (0.115 and 0.26 µCi for Co-60 and Cs-137, respectively) for the mixture of These doses are 1.33 mrem and 37.6 mrem for the highest activated metal and the irradiated fuel particles, respectively. These doses are well below the 100 mrem dose applicable to a less likely but plausible exposure scenario.
The ingestion doses calculated from these hypothetical particles are largely from the particles as they travel through the GI tract where the dose model makes conservative assumptions on the distribution of radioactivity and the mean residence time for each portion of the GI tract. These assumptions also do not account for the self-absorption of low penetrating radiations (alpha and beta) within the particles given their calculated sizes. Therefore, the ingested doses shown above represent a conservative estimate and any actual exposure would result in lower doses.
In developing the probabilistic MDA model, a detailed calibration of each detector was performed by RSCS, accredited through ISO 17025. The first step of the calibration process was determining the high-voltage (HV) settings to be used for each individual detector. An HV plateau was performed for each detector using Cs-137 to determine the optimal operating voltage. The Ludlum 4612 Counter software HV Plateau utility was utilized to collect the data for this process. A figure of merit (S2/B) analysis was performed to optimize the efficiency of each detector using the guidance provided in
ZS-LT-07 Revision 1 16 Knoll [7]
other than the one with the highest S2/B were considered and selected when deemed appropriate. These resulting HV settings were then programmed into the Ludlum 4612 Counter using the latest version of the Ludlum 4612 Counter software (V 2.3.3).
Because the isotopes of interest are Cs-137 and Co-60, the LLD for each detector was then set using a Co-57 source to discriminate gamma/X-ray energies below those of Co-57 (122 and 136 keV). This was accomplished by setting the LLD at a point where the observed count rate for Co-57 was approximately the same as the detector background.
The upper-level discriminator was set to 3300 mV (maximum allowed by the Ludlum software) in order to ensure the high energy photons from Co-60 were included in the count rate.
The next step in the calibration process was to measure the detector response as a function of distance from a source of known radioactivity. Two NIST traceable sources were used: a Cs-137 button source (SN: 14290) and a Co-60 button source (SN: 2006-63-3). The decay corrected activity of each source was 0.7695 µCi for the Cs-137 source and 0.6056 µCi for the Co-60 source.
Each of the 44-10 detectors were centered on the source and the Ludlum 4612 software was set for 1 minute count times to obtain to obtain the total number of counts during the counting interval. The distance from the source to the end of the detector casing was varied from one inch up to a maximum of 18 inches. The center of the NaI detector was added to the detector to source distance to compensate for the offset. A ten-minute background count was also performed for each detector. The net count rates are then determined by subtracting the background count rate from the gross count rate for each radionuclide and detector. Lastly, the detection efficiency, E(c/d), is determined by the ratio of the net count rate (cpm) to the source 4 pi activity emission rate (dpm).
TSD 21-001 further describes the system setup and initial performance testing using NIST-traceable sources.
For scanning with the towed array attached to the UTV, a scan speed of approximately 0.22 m/sec (0.5 mph) will be applied. However, we expect that this speed will vary and the variability is accounted for by setting this parameter to a probabilistic variable.
Survey staff will ensure that the proper overlap between the detectors field of view is maintained to ensure that gaps in scan coverage are not created.
During the survey process, the system displays live-time data on a 2-dimensional map of the site showing each 1-second measurement on a color-coded scale. Once 1-day of measurement data is completed, the data (GPS Coordinates and 2 measurement quantities) is post-processed using off-the-shelf ESRI ARCMap 10.8 GIS software. The two measurement quantities are the ratemeter count rate data and integrated scaler data.
The evaluation described below uses built-in tools within the ARC-GIS software platform with no customization. The objective is to identify scan measurement locations that warrant additional field investigations.
The workspace within ARCMap is set to
ZS-LT-07 Revision 1 17 NAD_1983_NSRS2007_StatePlane_Illinois_East_FIPS_1201_Ft_US. The daily files are imported and merged into a master shapefile each datapoint is then assigned the appropriate Survey unit number.
A digital fishnet grid will be overlayed onto the survey units with a general alignment to the north-south alignment of most of the survey unit boundaries.
The fishnet grid will use a size of 20 foot on a side resulting in approximately 300 to 1,500 measurements in each fishnet grid. This will produce approximately 3,100 grids across the survey units.
For each grid, at a minimum the following statistical parameters will be determined:
mean, standard deviation, minimum, maximum detector logged count rates.
For each grid, each data point (detector response, R) will be assigned a unique color based on its magnitude using the following initial criteria:
o 2 R <=
o 3 R <=
o 4 R <=
o 5 R <=
o 6 R <=
o R >
Once assigned to each category, the data will be visually inspected to identify measurements containing the highest values absent a cluster of elevated values that would be indicative of a homogeneous distribution rather than DRPs. This process will identify the GPS locations corresponding to these elevated and isolated discrete measurements for further field investigations. These identified locations will be uploaded to the ESRI Field maps app to allow them to be viewed and found in the field with a GPS.
The process would then select the next highest criteria using the same process.
Once approximately 30 locations are identified across the site in this manner, further data analysis may proceed (i.e. selecting a lower sigma criteria) if DRPs are identified.
Additional ARC-GIS tools (or equivalent) such as tests for outliers and clusters may be used to help gain insights into the variability and distributions of measurement scan data across the site. To further eliminate or include data investigations.
This data evaluation process will provide the ability to identify potential DRPs even in the presence of substantial variations in site background radiation levels.
3.4.2 As a supplement to the towed array gamma scanning, scanning in the traditional method, using hand-held sodium-iodide detectors, will be utilized for detailed
ZS-LT-07 Revision 1 18 investigations that require a human element (i.e., the ability to listen to variations in detector audio output and slow the scan accordingly). Hand scanning will also be performed in areas that are inaccessible with the towed array. The following protocol will be followed for hand-held gamma scanning:
Technicians will scan slowly (0.25 m/sec or slower) in a serpentine fashion while maintaining the detector end cap no more than 2 Collimators will not be utilized.
Technicians will pause during the survey when the audible output signal from the detector indicates the presence of suspect DRPs.
The investigation level for hand-held scanning is minimum detectable count rate (MDCR) plus background, but this investigation level is a second stage to the monitoring for variation of detector audio output.
Hand-held detectors will also be used to scan the systematically-collected soil samples (see Section 3.4.4).
3.4.3 Detailed investigation will be performed any time the investigation level is exceeded during the scan survey. The protocols for performing the investigation are as follows:
Scan the elevated area using the hand-held NaI detector to locate the precise area of the elevated activity. Mark the location in the field with a flag or similar. If the area of elevated activity cannot be duplicated, then make a notation in the field notes and no further actions are necessary.
Obtain a qualitative measurement using a portable gamma spectroscopy instrument and utilizing a 10-minute count.
If a plant-related radionuclide is identified, collect a soil sample in the location down to a depth of 12 inches, capturing at least 2 liters of soil. This will effectively remediate the potential DRP.
If the sample has been detected in an area of elevated background, notify the radiological engineer to consider moving the sample to an area of lower background for further analysis.
Spread the soil sample out into a pan or other appropriate container to an approximate 1-inch thickness. Use the hand-held NaI detector to try to isolate a potential DRP.
o If no DRP is identified, denote as such in the field notes. No further action is required.
o If a DRP is identified but only Co-60 is identified, capture the DRP and archive the sample. No further action is required.
o If a DRP is identified and any non-Co-60 plant-related radionuclide is identified, then capture the DRP and send the sample to GEL Laboratories for
ZS-LT-07 Revision 1 19 full suite radionuclide (Table 4) analysis.
If a DRP was captured in an investigative soil sample, rescan the sample void using the hand-held NaI detector to verify that the location has been successfully remediated.
o If additional elevated readings are encountered, collect additional samples for screening, as necessary.
3.4.4 compliance sampling survey design for the collection of systematic soil samples will be utilized for this survey plan. The objective of this design is to demonstrate, with high probability (approximately 95%), that a high percentage (95%) of the decision area is acceptable (i.e., grid cell does not contain DRPs), where a small number of the observed samples may be unacceptable (i.e., grid cell does contain DRPs). Visual Sample Plan (VSP), a software tool for survey design and data assessment developed by the Pacific Northwest National Laboratory, was used to design the survey.
The area of interest (survey units denoted in Figure 1) was divided into 103,529 grid cells 1 m2 in size. Grid cell sizes for presence/absence survey design should correspond to the footprint of the sampling methodology; in this case, the sampling footprint is the 1 m2 area where 5 total soil samples will be collected. For each grid cell, 1 sample will be collected at the center of the grid cell and 4 samples will be collected at each of the cardinal directions (N, S, E, W) 0.5 m equidistant from the center sample.
VSP determined that if 155 of the 103,529 grid cells are sampled and 3 or fewer of the 155 sampled grid cells are unacceptable, then there will be at least a 95.4% confidence that at least 95% of the grid cells are acceptable. Additionally, if no more than 0.5% of the grid cells in the population are unacceptable, then there will be no more than a 0.8%
probability of concluding that the population is unacceptable (i.e., observing more than 3 unacceptable grid cells in the sample size of 155). The VSP inputs and outputs are presented in Figure 2.
ZS-LT-07 Revision 1 20 Figure 2 VSP Inputs and Outputs for Presence/Absence Compliance Sampling Thus, 775 soil samples will be collected (5 in each of 155 grid cells) for this survey design. Grid cells for assessment were selected systematically by VSP using a triangular grid pattern with a random start. Figure 3 shows the center coordinate of the grid cell locations.
Systematic soil samples will be collected to a depth of 12 inches, and approximately 2 liters of material will be collected at each sample location. The following process will be used to screen the systematic soil samples in the field:
Spread the soil sample out an approximate 1-inch thickness around each sample location while keeping the five piles segregated from each other (this is to help identify the exact sample that may contain a particle). Use the hand-held NaI detector (with the protocols outlined in Section 3.4.2) to try to isolate a potential DRP.
If no elevated area/potential DRP is identified, denote as such in the field notes.
Then place the soil back in the hole, and no further action is required.
If an elevated area/potential DRP is identified, obtain a qualitative measurement using a portable gamma spectroscopy instrument and utilizing a 10-minute count.
o If plant-related radionuclides are not identified, denote the naturally occurring radioactive material radionuclides in the field notes. No further action is required. The soil may be placed back into the hole.
o If the portable gamma spectroscopy instrument identifies plant-related radionuclides, then collect the soil in an appropriate container, effectively remediating the potential DRP.
If only Co-60 is identified by the portable gamma spectroscopy instrument, denote as such in the field notes and archive the sample.
ZS-LT-07 Revision 1 21 If any non-Co-60 plant-related radionuclide identified by the portable gamma spectroscopy instrument, the sample will be sent to GEL Laboratories for full suite radionuclide (Table 4) analysis.
If a DRP was captured in a soil sample, rescan the sample void using the hand-held NaI detector to verify that the location has been successfully remediated.
o If additional elevated readings are encountered, collect additional soil material for screening, as necessary.
3.4.5 If at any time during the systematic sampling process one of the samples is found to be unacceptable (i.e., a DRP is identified in the sample), geospatial investigational sampling will be implemented. A soil sample, down to 12 inches, will be collected at each cardinal direction 0.5 m equidistant to the unacceptable sample. The investigational samples will be processed and screened in the same fashion as the systematic samples described in Section 3.4.4. If additional samples are found to be unacceptable during these investigations, the investigation process outlined in this section will repeat.
ZS-LT-07 Revision 1 22 Figure 3 - Presence/Absence Survey Design Grid Cell Locations
ZS-LT-07 Revision 1 23 3.4.6 Because this survey plan is designed to identify and retrieve DRPs, determining the concentrations of radioactivity in each sample is not required. However, if a DRP is identified that contains any non-Co-60 plant-related radionuclide, the sample containing the DRP will be sent to GEL for full suite radionuclide (Table 4) analysis.
Additional samples may be sent to GEL for analysis as directed by radiological engineering.
3.4.7 5% of the systematic grid cells (155) in the presence/absence survey design will be selected at random for QC replicate scan measurements. The QC replicate scan will be performed on all 5 sample locations within the grid cell using a different technician and different NaI detector from the original scan.
If the same conclusion is reached with the QC replicate scan as the original scan (i.e., a particle is identified or not), the results are in agreement. If QC agreement is not achieved, further evaluations will be performed.
3.4.8 Detailed field notes must be maintained for the survey. The field notes should include as a minimum:
date, time, and description of activities, actions, observations, and obstructions a description of the physical conditions encountered observed background as well as obvious sources contributing to background from adjacent areas instruments and detectors used, serial numbers, and calibration dates changes in measurement/sample locations due to encountered obstacles or physical constraints a description of locations surveyed where the applicable investigation levels were exceeded, the results of any investigations, and any actions taken as a result 3.5.
Data Validation Survey measurement and/or analysis results are reviewed to ensure that the survey is complete, fully documented, and technically acceptable. Validation ensures that the data set is comprised of qualified measurement results collected in accordance with the survey design. The review criteria for data acceptability includes the following items as a minimum:
Compliance with survey instructions as specified in the survey plan.
Showing that MDCs were appropriate for the instruments and techniques used to
ZS-LT-07 Revision 1 24 perform the survey.
The instrument calibration was current and traceable to NIST standards.
The field instruments were source checked with satisfactory results before and after use each day that the data was collected, or if unsatisfactory, data obtained with that instrument since its previous acceptable performance check was evaluated for acceptability.
The survey methods used to collect data were proper for the types of radiation involved and for the media being surveyed.
The data set is comprised of qualified measurement results collected in accordance with the survey design, which accurately reflects the radiological status of the survey unit.
The data has been properly recorded.
If the data review criteria are not met, then the radiological engineer is informed.
The discrepancy is then reviewed and the decision to accept or reject the data is documented.
3.6.
Data Evaluation As stated in Section 3.4.6, determining the concentrations of radioactivity in each sample is not required, because the objective of this survey plan is to identify and retrieve DRPs. As such, data comparisons to a dose-based criterion (i.e., derived concentration guideline levels) will not be performed. However, as explained in Sections 3.4.3 and 3.4.4, if a suspected non-Co-60 particle is identified, the sample will be sent to GEL Laboratories for full suite radionuclide analysis.
Based on the actual number of unacceptable grid cells identified during the presence/absence compliance sampling, the a posteriori confidence level and percentage for grid cell acceptance will be calculated in VSP.
3.7.
Survey Reporting A report containing the results of the survey will be generated in the form of a TSD and submitted to the NRC. The survey report will include, as a minimum, the following information (taken from Specific Consideration No. 5 from RAI-10):
The number of discrete radioactive particles detected during the survey activities and their location.
The radionuclide composition and activity of the collected non-Co-60 particles, along with a description of the laboratory analyses performed, as required in Sections 3.4.3 and 3.4.4.
An estimate of the number of discrete radioactive particles that may remain at the Zion site after the survey is completed (i.e., discrete radioactive particles either missed or below the MDA).
ZS-LT-07 Revision 1 25 An estimate of the radiation dose from the particles that may remain at the Zion site after the survey is completed.
- 4.
References
[1] Oak Ridge Institute for Science and Education, 5271-SR-09-0, Independent Confirmatory Survey Summary and Results Assessing the Presence of Residual Radioactivity and Radioactive Particles within Select Land Areas at the Zion Nuclear Power Station.
[2] TSD 11-
[3] NUREG-Characterization,
[4] TSD 14-
[5] ZS-LT-300-001-Ludlum 44-
[6] TSD 21-itivity and Performance Assessment for a Ludlum 44-10 Six-
[7]
Second Edition, Glenn Knoll; John Wiley & Sons, 1989, p.94.