ML23310A312
| ML23310A312 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 11/08/2023 |
| From: | Shaun Anderson Reactor Decommissioning Branch |
| To: | Zion Restoration Project, ZionSolutions |
| Shared Package | |
| ML23310A311 | List: |
| References | |
| EPID L-2017-DTP-0006, EPID L-2017-DTP-0007 | |
| Download: ML23310A312 (1) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 U.S. NUCLEAR REGULATORY COMMISSION EVALUATION BY THE OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS RELATED TO THE FINAL STATUS SURVEY REPORTS, ZIONSOLUTIONS, LLC ZION NUCLEAR POWER STATION DOCKET NO. 50-295 AND 50-304 1 INTRODUCTION The Final Status Survey Reports (FSSRs) were submitted by ZionSolutions, LLC (the licensee or ZS) by letters dated November 1, 2018 (Phase 1) (Agencywide Documents Access and Management System (ADAMS) Accession No. Main Library (ML) ML18331A016 Pkg); June 21, 2019 (Phase I, Revision) (ML19178A109 Pkg); March 11, 2019 (Phase 2, Part 1)(ML19077A095 Pkg); September 30, 2019 (Phase 2) (ML19295G627 Pkg); November 25, 2019 (Phase 2, Part 2) (ML19338B809 Pkg); December 30, 2019 (Phase 3)(ML20009E643 Pkg); February 29, 2020 (Zion Station Restoration Project Final Status Survey Final Report -
Phase 1, Rev 2) (ML20073F671), April 30, 2020 (For four Phase 3 Survey Units (SUs),
Revision) (ML20147A092 Pkg); and May 1, 2020 (Phase 4) (ML20133J976 Pkg), as supplemented by letters dated May 15, 2020 (request for additional information (RAI) Response for Phases 2a, 2b, and 3) (ML20147A128); June 4, 2020 (RAI Responses for Phases 2a, 2b, and 3) (ML20167A280); November 11, 2020 (RAI Response for Phases and Revised Phase 2, Part 2) (ML20351A154 Pkg); February 10, 2021 (Revised RAI Responses addressing sequencing of actions, clarifications, survey completion, Oak Ridge Institute for Science and Education (ORISE) findings on confirmatory survey, controls post survey, corrective actions, condition reports, and discrete particles) (ML21067A225 Pkg); April 2, 2021 (RAI Response)
(ML21103A229 Pkg); April 15, 2021 (RAI Response, Switchyard not included in Radiological Restricted Area (ML21112A166)); May 11, 2021 (Clarification on the Independent Spent Fuel Storage Installation (ISFSI) Controlled Area Boundary (CAB)) (ML21131A072); August 4, 2022 (Revised Survey Units (ML22224A002 Pkg); September 30, 2022 (Final Status Survey Final Report - Phase 3 FSSR Rev. 1 and Final Status Survey Final Report - Phase 4 FSSR Rev. 2 (ML22279A984 Pkg); and October 27, 2023 (Further clarification on ISFSI CAB (ML23303A090).
These submittals, identified above, support the ZS Partial Site Release (PSR) request received on June 5, 2020 (ML20164A096), as supplemented on March 3, 2021 (ML21102A397) which would remove a 112 acre portion of the site from the Zion Nuclear Power Station, Units No. 1 and No. 2 (ZNPS or Zion) Facility Operating License Demonstration Power Reactor (DPR)-39 and DPR-48. These licenses were issued pursuant to Part 50, Domestic Licensing of Production and Utilization Facilities, of Title 10 of the Code of Federal Regulations (10 CFR).
Enclosure
Previously, the Nuclear Regulatory Commission (NRC) approved the PSR of approximately 214 acres of non-impacted land from the 10 CFR Part 50 licenses by letter dated March 31, 2016 (ML16053A257 Pkg). The proposed action would effectively terminate the Zion 10 CFR Part 50 licenses outside the on-site ISFSI boundary.
Specifically, ZS proposes to remove an area consisting of seven basement SUs and 116 land SUs (including three below grade excavation SUs), and five buried piping SUs. This action will represent the completion of decommissioning activities at the Zion site outside the on-site ISFSI boundary, until such time as the ISFSI is no longer needed for the storage of spent fuel and subsequently decommissioned. The FSSR is the documentation that ZS submits to demonstrate completion of the activities described in the Zion License Termination Plan (LTP).
The Zion LTP was submitted by letter dated December 19, 2014 (ML15005A330), as supplemented by letters dated February 26, 2015 (ML15061A230), November 12, 2015 (ML15344A344), March 8, 2016 (ML16081A010), July 20, 2016 (ML16211A199), February 27, 2017 (ML17208A121), and July 20, 2017 (ML17215A098). Revision 2 of the LTP was submitted February 7, 2018 (ML18052A857 and ML18052A530), and supplemented by letters dated April 10, 2018 (ML18103A016), and August 28, 2018 (ML18242A082). The Zion LTP was approved by the NRC on September 28, 2018 as documented in the NRC staffs Safety Evaluation Report (SER)(ML18164A222).
The LTP provides the summary of the site characterization, as well as plans for identifying, and remediating the remaining residual radioactivity at the Zion site to a level that would allow the site to be released for unrestricted use. The LTP also describes how ZS plans to confirm the extent and success of remediation through radiological surveys, as captured in the FSSRs, provides financial assurance to complete decommissioning, and ensures the environmental impacts of the decommissioning activities would be within the scope originally envisioned in the associated environmental documents. The NRC staff compared ZSs FSSRs to the LTP in its evaluation to determine whether ZS followed its LTP.
The NRC staff has completed its review of the Zion FSSRs to ensure that the removal of these 128 SUs from the Zion Part 50 licenses demonstrates the ability of the site, in aggregate, to meet the criteria for unrestricted release contained in Subpart E, Radiological Criteria for License Termination and Subpart F, Surveys and Monitoring of 10 CFR Part 20, Standards for Protection Against Radiation. The NRC staffs safety evaluation is described below.
2 BACKGROUND The Zion is located near the city of Zion in northeast Illinois on the west shore of Lake Michigan.
The site is approximately 40 miles north of Chicago, Illinois and 42 miles south of Milwaukee, Wisconsin. In September 1996, Zion Unit No. 2 was permanently shutdown after approximately 23 years of operation. In February 1997, Zion Unit No. 1, was permanently shut down after approximately 24 years of operation.
For a history of the permanent cession of operations and the license transfer and pending
license transfers upon completion of decommissioning outside the ISFSI boundary, refer to the SER for the PSR of the Zion site outside the boundary of the ISFSI (ML23286A304 Pkg).
During reviews of FSS and 2021 confirmatory survey data for the Zion site, and RAI Responses, the NRC staff learned that decommissioning activities performed at the Zion site from 2012 to 2018 resulted in discrete radioactive particles (DRPs) becoming airborne and being transported outside the Unit No. 1 and Unit No. 2 Containments and Fuel Handling Building to the local on-site environment. Multiple operational events occurred during the performance of decommissioning activities that led to releases of DRPs with potentially different activity levels and sizes. ZS contamination control and corrective actions alone were unable to fully resolve the release of the DRPs such that DRPs were being sporadically identified by ZS during FSSs and later during confirmatory surveys in 2021 and 2023. The NRC inspectors issued a non-cited Severity Level IV violation of 10 CFR 20.1501 regarding the inadequate surveys because DRPs were being identified by the NRC after the licensee had conducted its FSSs (ML23024A208).
Because there was an apparent DRP contamination issue and no NRC guidance for DRP surveying, significant delays were incurred while the NRC staff and ZS evaluated the situation.
Eventually, after considering estimated scanning sensitivities for DRPs (ML22304A137) and the potential dose from exposure to DRPs (ML23136A178), NRC staff determined that performance of hand scanning while progressing as low to the surface and as slowly as practicable should provide adequate sensitivity for identifying DRPs of concern in the environment. ZS had already modified its scanning techniques and Data Quality Objectives (DQOs) to reflect this and reperformed multiple FSSs using the appropriate techniques, as well as completed the remaining FSSs. On October 17, 2022, ZS stated (ML22293A644 Pkg) it had completed its FSSs. On May 4, 2023, ZS stated that all known DRPs had been removed from the site and it had provided reasonable assurance that the Zion site meets the regulatory requirements for unrestricted release (ML23167A069).
In 2023, the NRC asked its contractor, ORISE, to return to the site to perform a confirmatory survey involving extensive hand scanning over areas where DRPs had been found in the past and assess if DRPs were likely present in subsurface soil. The NRCs goal was to verify that ZS identification and the remediation of the DRPs was effective and to also verify that the FSSs were compliant with the LTP. In the process, the NRC staff was also able to independently collect subsurface data for its independent analyses. For more details on the history of DRPs at the Zion site and the DRP assessment, refer to Attachment A and Attachment B, respectively, of the SER for the PSR of the Zion site outside the boundaries of the ISFSI (ML23286A304 Pkg).
Eventually through a combination of the FSSs, confirmatory surveys, and ZS extent of condition survey (ML23251A071), the NRC has reasonable assurance that all DRPs were identified, removed, and dispositioned as waste.
2.1 Area to be Released The area ZS intends to release consists of 128 SUs, which encompass 112 acres (approximately 34 percent) of the original licensed site area of 331 acres, leaving only the land
area associated with the ISFSI within the 10 CFR Part 50 Licenses (approximately 5 acres). An FSS was performed for each of these impacted SUs in accordance with the Zion LTP, Multi-Agency Radiation Survey and Site Investigation Manual, NUREG-1575, Rev. 1 (MARSSIM)
(ML003761476 Pkg), and Zion implementing procedures. ZS stated that an FSS Release Record was prepared for each SU to provide complete and unambiguous records of the as-left radiological status. During the review, the NRC staff determined that the release records for certain areas did not contain sufficient data and information to assess the as-left radiological status. However, the release records, as supplemented by the responses to the RAIs, and the NRCs additional inspection and confirmatory surveys enable an independent evaluation of both the survey activities and the derived results.
Figure 2-1, Zion Land Survey Areas below shows the Zion Land Survey Areas. The shaded areas in green, depicted in this figure, are non-impacted and were released with the PSR on March 31, 2016 (ML16053A257 Pkg). The shaded area in dark purple, depicted in this figure, is the land area associated with the ISFSI that will remain under the 10 CFR Part 50 licenses. The pink, orange, yellow and blue shaded areas, depicted in this figure, are parts of this PSR.
Figure 2-1, Zion Land Survey Areas ZS developed the FSSRs consistent with the guidance provided in NUREG-1700, Revision 2, "Standard Review Plan for Evaluating Nuclear Power Reactor License Termination Plans,"
dated April 2018 (ML18116A124), and provided its FSSRs to the NRC in four phases. The FSSRs were prepared by ZS after each separate phase (Phases 1-4) of the site remediation work was complete. Phases 1, 3, and four addresses open land areas of the Zion site with Phase 4 also addressing groundwater. Phase 2 was submitted in two parts (two separate FSSRs) and addresses the structures/embedded piping and buried piping remaining on-site.
Each FSSR is evaluated in a separate section of this SER.
2.2 Applicable Requirements 10 CFR 20.1402, Radiological criteria for unrestricted use, states in part: A site will be considered acceptable for unrestricted use if the residual radioactivity that is distinguishable from background radiation results in a TEDE [Total Effective Dose Equivalent] to an average member of the critical group that does not exceed 25 mrem (0.25 mSv) per year, including that
from groundwater sources of drinking water, and the residual radioactivity has been reduced to levels that are as low as reasonably achievable (ALARA). 10 CFR 20, Subpart F, Surveys and Monitoring further states that each licensee shall make or cause to be made, surveys of areas, including the subsurface, that (1) May be necessary for the licensee to comply with the regulations in this part; and (2) Are reasonable under the circumstances to evaluate: (i) The magnitude and extent of radiation levels; and (ii) Concentrations or quantities of residual radioactivity; and (iii) The potential radiological hazards of the radiation levels and residual radioactivity detected. ZS documented its proposed approach for meeting these requirements and for documenting the results of its surveys in its approved LTP (ML18164A223 Pkg).
Section 5.11, Final Status Survey (FSS) Reporting, of the Zion LTP describes ZS approach to license termination and FSSR documentation. Specifically, ZS specifies that documentation of the FSSs are contained in two types of reports consistent with Section 8.6, Documentation, of MARSSIM. ZS prepared an FSS Release Record to provide a complete record of the as-left radiological status of an individual SU, relative to the specified release criteria. ZS made the SU Release Records available to the NRC for review as appendices to the appropriate FSS Final Report. ZS provided to the NRC, a FSS Final Report, to provides a summary of the survey results and its overall conclusions to demonstrate that the site, or portions of the site, meets the radiological criteria for unrestricted use including the ALARA criterion.
In Chapter 6, of its approved LTP, ZS provided site-specific derived concentration guideline level (DCGL)1 values that correspond to a dose of 25 mrem/yr for each radionuclide of concern (ROC) and each potentially contaminated media expected to remain at the time of license termination. ZS states in the LTP that dose from multiple radionuclides would be accounted for using the sum of fractions (SOF) approach. ZS further states in the LTP that the dose summation for compliance to account for the multiple source terms present on-site would be conducted after FSS using the below equation.
= ( BASEMENT + +
+ ) x 25 mrem/yr On March 31, 2016 (ML16053A257), the NRC approved the PSR of approximately 214 acres of non-impacted land from the Zion 10 CFR Part 50 licenses, leaving approximately 117 acres of the original 331 acres under the current Zion licenses. The PSR SER (ML23286A304 Pkg) also considers the results of the previous PSR.
2.3 NRC Review Approach The NRC staff evaluated the Zion FSSR against the information contained in the Zion LTP, 1 DCGL (derived concentration guideline level): As defined in MARSSIM, a derived, radionuclide-specific activity concentration within a survey unit corresponding to the release criterion. The DCGL is based on the spatial distribution of the contaminant and hence is derived differently for the nonparametric statistical test (DCGLW) and the Elevated Measurement Comparison (DCGLEMC). DCGL's are derived from activity/dose relationships through various exposure pathway scenarios.
Revision 2, to ensure that ZS decommissioning and FSS activities were consistent with, or comparable to, the NRCs applicable decommissioning guidance. The guidance that NRC staff used for this evaluation includes: MARSSIM; NUREG-1507, Minimum Detectable Concentrations with Typical Radiation Survey Instruments for Various Contaminants and Field Conditions, Revision 0, dated June 1998 (ML003676046); NUREG-1700, Standard Review Plan for Evaluating Nuclear Power Reactor License Termination Plans, Revision 2, dated April 2018 (ML18116A124); and NUREG-1757, Volumes 1 and 2, Consolidated Decommissioning Guidance, (ML063000243 and ML22194A859, respectively) in order to ultimately ensure that ZS met the radiological criteria for unrestricted use as specified in 10 CFR 20.1402, Radiological criteria for unrestricted use. The NRC staff provide evaluations regarding the FSS strategies and final dose for each Phase as follows.
3 OPEN LAND AREAS As previously mentioned in Section 2.3 of this SER, the site was addressed for FSS in four phases. Phases 1, 3, and 4 address open land areas of the site. The Phase 1 Zion FSSR was submitted on November 1, 2018 (ML18331A015) and includes eight Class 3 open land SUs.
The NRC staff responded on March 22, 2019 (ML19079A359). On May 14, 2019 (ML19136A045), ZS provided a response to the issues identified by the NRC. Phase 1 was revised and resubmitted on June 21, 2019 (ML19178A106). By letter dated October 9, 2019 (ML19277E336), the NRC responded to the revised Phase 1 FSSR, finding the release records acceptable, but with specific comments regarding SU 10223. On March 3, 2020 (ML20073G099), ZS submitted the revised release record for SU 10223 and the revised FSS Final Report for Phase 1.
The Phase 3 FSSR was submitted on December 30, 2019 (ML20009E615) and included 41 open land area SUs, all of which are Class 1. The NRC submitted an RAI on both Phase 2 and Phase 3 on April 20, 2020 (ML20108E992). ZS responded to the RAI on May 15, 2020 (ML20147A128), along with revisions to 11 of the Phase 2 and Phase 3 release records (ML20167A279). ZS supplemented that response on June 4, 2020 (ML20167A280), and submitted revisions to certain release records as noted above.
The Phase 4 FSSR was submitted on May 1, 2020 and included 67 open land area SUs. Of the 67 units, 60 are Class 1 SUs, six are Class 2 and one is Class 3. The Phase 4 FSSR also provided an overview of existing groundwater conditions and the methods used for calculating the dose from groundwater. In addition, the Phase 4 FSSR includes a description of how dose compliance is demonstrated through the summation of the five distinct source terms for the Zion end state (i.e., basements (including embedded piping and penetrations in basements), soil, buried piping, and groundwater), which demonstrates that the Zion site, as a whole, meets the 25 mrem/yr unrestricted release criterion established in 10 CFR 20.1402, Radiological criteria for unrestricted use.
The NRC submitted another set of RAIs on November 4, 2020, primarily on Phase 3 and Phase 4 release records (ML20303A207). ZS responded to the request on November 11, 2020
(ML20351A143), and submitted revisions to certain release records. The NRC staff provided comments on the response in letter dated December 17, 2020 (ML20345A303). ZS revised its response to RAIs in letter dated February 10, 2021 (ML21067A225). ZS provided supplemental information on April 2, 2021 (ML21103A229) and on April 15, 2021 (ML21112A166).
The following sections provide additional information on these submittals and NRC staffs review.
3.1 Radionuclides of Concern and DCGLs for Soil ROCs were identified as described in its LTP, Rev 2 (ML18052A851 Pkg). The initial list of potential ROCs was provided in Table 5-1 of the LTP. A final suite of ROCs was developed using the results of concrete core analyses from the Containment and Auxiliary Buildings, as was documented in Technical Support Document (TSD)14-019, Radionuclides of Concern for Soil and Basement Fill Model Source Terms. ZS determined several insignificant dose contributors based upon the guidance contained in Section 3.3 of NUREG-1757. The suite of dose significant ROCs for use in decommissioning was provided in Table 5-2 of the LTP (Table 3-1 in this SER).
ZS states in its FSSRs (e.g., ML22279A985) that Co-60, Cs-134, Cs-137, Ni-63, and Sr-90 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 radionuclides, accounted for 99% of the dose. Due to the assumption that all activated concrete will be removed and disposed of as waste, the final suite of ROC for all areas outside of the Containments does not include H-3, Eu-152, and Eu-154.
The release criteria for the FSS program will utilize concentration based DCGLs (e.g., pCi/g for land areas, pCi/m2 for basement surfaces, and disintegrations per minute (dpm)/100 cm2 for buried piping internal surfaces), with Base Case DCGLs calculated to demonstrate compliance with the 25 mrem/yr dose limit. DCGLs developed for soil were based on a resident farmer scenario. Surface soil DCGLs correspond to the top 0.15 m and subsurface soil DCGLs correspond to a depth of 0 to 1 m in soil. The NRC staff note that it would be conservative to utilize subsurface soil DCGLs on soil which has been covered with clean backfill. Tables 3-2 and 3-3 present the Operational and Base Case DCGLs for surface soil and subsurface soil.
ZS also calculated area factors for surface and subsurface soil for use in calculating the dose from hot spots in soil (areas where soil contamination exceeds the Base Case DCGLs). These area factors are in Tables 6-41 and 6-42 of the LTP (ML18052A958) but were not utilized in demonstrating compliance as ZS stated it had remediated any areas greater than the operational DCGLws which were a fraction of the Base Case DCGLs.
Table 3-1, Dose Significant Radionuclides and Mixture (recreated from LTP Table 5-2)
Containment(1) Auxiliary Building(2)
Radionuclide <%,of Total Activity % of Total Activity (normalized)(1) (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).
Table 3-2, Base Case and Operational DCGLs for Surface Soils [from Table 2-1 in the FSSR for Phase 3, which was compiled from Tables 5-5 and 5-7 of LTP, Chapter 5]
Radionuclide Base Case DCGL (pCi/g) Operational DCGL (pCi/g)
Co-60 4.26 1.091 Cs-134 6.77 1.733 Cs-137 14.18 3.630 Ni-63 3,572.10 914.458 Sr-90 12.09 3.095 Table 3-3, Base Case and Operational DCGLs for Subsurface Soils [from Table 2-1 in the FSSR for Phase 3, which was compiled from Tables 5-6 and 5-8 of LTP, Chapter 5]
Radionuclide Base Case DCGL (pCi/g) Operational DCGL (pCi/g)
Co-60 3.44 0.881 Cs-134 4.44 1.137 Cs-137 7.75 1.984 Ni-63 763.02 195.333 During FSSs, ZS inferred that Ni-63 and Sr-90 concentrations were in samples used to demonstrate compliance. The ratios used were the maximum surrogate ratios based on characterization as documented in the LTP. As stated in the Phase 3 FSSR, The mean, maximum and 95% Upper Confidence Level (UCL) of the surrogate ratios for concrete core samples taken in the Auxiliary Building basement were calculated in ZS Technical Support Document (TSD)-14-019, Radionuclides of Concern for Soil and
Basement Fill Model Source Terms and are presented in Table 4-1. The maximum ratios are used in the surrogate calculations during FSS unless area specific ratios are determined by continuing characterization. Table 5 of the LTP, showing the values taken from ZS TSD-14-019 Table 4-1, is recreated in Table 3-4 below.
Table 3-4, Surrogate Ratios [from Table 5 of the FSSR for Phase 3]
Ratios Auxiliary Building Mean Max 95% UCL Ni-63/Co-60 44.143 180.450 154.632 Sr-90/Cs-137 0.001 0.002 0.002 3.2 Overview of Final Status Survey Approach for Open Land SUs Each of the open land FSSRs submitted by ZS contains discussion of the survey quality objectives and planning requirements meant to be consistent with the LTP. The primary objective of the DQO process was to demonstrate that the level of residual radioactivity found in the soils in the land area SUs, including any areas of elevated activity, was equal to or below the site-specific DCGLs that correspond to the 25 mrem/yr release criterion.
The details for the FSS survey planning and survey techniques are provided in the LTP, Chapter 5, and in the FSSRs and release records for each survey unit. In simple terms, the process involved scanning of the SUs using gamma detectors and taking samples and having them analyzed to demonstrate whether the residual radioactivity is in compliance with the DCGLs/ Elevated Measurement Comparison (DCGLemc) and therefore the unrestricted release criteria. ZS developed procedures to implement the applicable commitments in the LTP.
The scanning was to demonstrate general homogeneity across the survey unit with elevations in measurements typically warranting investigation by sampling. Information obtained during the scanning survey was automatically logged by the instrument for review and analysis.
The sampling was conducted either to perform the aforementioned investigations (biased or judgmental sampling) or to assess the average concentrations of residual radioactivity in the survey unit (systematic sampling). The number of systematic samples collected in each survey unit was typically derived from the Sign Test statistical requirements given Type 1 and Type 2 error rates of 0.05 and a relative shift of 1.67. In some cases, such as when sampling identified elevations greater than the Operational Derived Concentration Guideline Levels (OpDCGLs),
additional remediation was performed, and the FSS was redone with a reduced relative shift caused by assuming an increased variability in the assumed distribution of data (the standard deviation of samples in the SUs was typically presumed to be 0.3 and was typically increased to 0.4 if additional remediation was performed). In other cases, such as where the survey unit size exceeded the recommendations in MARSSIM, the number of samples was increased so that the sample distribution/spacing would be consistent with the maximum spacing for the survey
unit size recommendations in MARSSIM. It is also noted that biased sampling may have been performed based on the judgment of personnel due to site history of areas of concern and, if any sample taken exceeded an investigation level (the OpDCGLs), then an investigation of the sample location would occur to ensure that an elevated area (hot spot) was not missed or to bound the area to be assessed as a hot spot.
Almost all sampling was of surface soil (~0-15 cm depth interval) although 10% of the sampling locations were randomly selected and subsurface sampling was also performed (~0-1 m depth interval). During the performance of FSS, if the analysis of a surface soil sample or the results of a surface gamma scan indicated the potential presence of residual radioactivity at a concentration of 75% of the subsurface soil OpDCGL, then a biased subsurface soil sample(s) would be required to the appropriate depth within the area of concern as part of the investigation.
All samples were analyzed by on-site gamma spectroscopy with 10% of the samples selected for hard-to-detect (HTD, Sr-90 and Ni-63) analysis. The concentrations of Sr-90 and Ni-63 were normally inferred for all samples using the maximum ratios of these radionuclides to Cs-137 and Co-60, respectively, based on concrete samples from the Auxiliary Building as shown in Table 3-4 of this SER. If a sample measurement exceeded an Operational Sum of Fractions (OpSOF) of 0.1, then it was analyzed off-site for HTDs. Approximately 5% of the samples were duplicated and analyzed with approximately 5% also being split and analyzed by an off-site laboratory for quality control purposes.
As previously stated, details of the survey planning and techniques employed are described in the LTP, Chapter 5, in each FSSR, and in each survey unit release record. Procedures were established to implement the FSS commitments and techniques. Variability in the survey design may occur amongst the SUs based on the survey unit classification (Class 1, 2, or 3), the size of the survey unit, the assumed standard deviation of samples in the survey unit, inaccessible areas within the survey unit, and the results of scans and investigations within the survey unit.
All surveys were designed to be generally consistent with guidance in MARSSIM and NUREG-1757, Vol 2.
3.3 Phase 1 Open Land Areas Phase 1, Rev. 2 of the FSS (ML20073F671) for the Zion site evaluated the potential dose from residual radioactivity in surface soils around the perimeter of the site. A total of eight open land SUs with an overall area of 197,091 m2 were included in Phase 1 (Figure 3.1 and Table 3 1).
The SUs in Phase 1 all had a final classification of Class 3 per MARSSIM.
Figure 3-1, Phase 1 SU Locations Table 3-5, Zion FSSR Phase 1 SUs (8 Total SUs)
SU Name Class Size (m2) 10205 Switchyard 3 54,573 10219A Area Far South of Switchyard (A) 3 2,433 10219B Area Far South of Switchyard (B) 3 7,516 10220C Adjacent to South Restricted Area - 3 27,870 Lakeshore 10222 North Beach Area 3 21,778 10223 Power Block Beach Area 3 12,371 10224 South Beach Area 3 14,608 10301 West Training Area 3 55,942
3.3.1 FSS Results for Phase 1 The NRC staff previously evaluated Phase 1 release records in letter dated October 9, 2019 (ML19277E336), approving the release records, but with specific comments regarding SU 10223. Note that while SUs 10212A and 10213A were originally part of Phase 1, ZS revised the release records for 10213 and 10212 because portions of these SUs were reclassified from Class 3 to Class 2 or Class 1. ZS resubmitted the revised release records for the 10213 and 10212 SUs as part of Phase 4; therefore, those survey results are separately evaluated in Phase 4. Given that the NRC staff previously evaluated and approved Phase 1, the discussion in this section is limited to SU 10233.
The previous NRC staff evaluation on Phase 1 states:
Based upon the licensees commitment in Section 5.7.1.6.2 of the LTP (Revision 2) to assess subsurface residual radioactivity when 75 percent of the subsurface OpDCGL is detected in a surface soil sample, it appears that samples in SU 10223 would have triggered this commitment for Sr-90, and a subsurface investigation should occur.
Specifically, three samples (L3-10223A-FRGS-003-SS (0.526 pCi/g), L3-10223A-FRGS-004-SS (0.984 pCi/g), L3-10223A-FRGS-005-SS (0.566 pCi/g)) were above Minimum Detectable Concentration (MDC) of about 0.4 pCi/g. The subsurface OpDCGL for Sr-90 is 0.425 pCi/g, and 75% of the OpDCGL is 0.319 pCi/g.
In accordance with the LTP Chapter 5, Section 5.7.1.6.2, No subsurface soil sample(s) will be taken as part of the survey design in Class 3 open land SUs. However, if during the performance of FSS, the analysis of a surface soil sample, or the results of a surface gamma scan indicated the potential presence of residual radioactivity at a concentration of 75% of the subsurface OpDCGL, then a biased subsurface soil sample(s) would have been taken to the appropriate depth within the area of concern as part of the investigation.
ZS submitted a revised release record for SU 10223 on March 3, 2020, with details on the subsurface investigation, along with the revised FSS Final Report for Phase 1. The NRC staff reviewed the revised release record for SU 10223 and the results of the subsurface investigation that ZS conducted. The results were all below the subsurface OpDCGLs; however, off-site analysis for HTD radionuclides positively identified Sr-90 above the MDC in one sample (L3-10223A-FRGS-003-SS). As an investigation to the anomalous Sr-90 identification, a smaller portion of the same sample was analyzed by the same off-site facility, which did not identify Sr-90 above the MDC.
To further investigate, a sample (L3-10223A-FRGS-004-SS) from an adjacent location was sent for off-site analysis and positively identified Sr-90 just above the MDC but within the range of uncertainty associated with the sample results. However, subsequent reanalysis of the same
sample did not identify Sr-90 greater than MDC.
A third sample (L3-10223A-FRGS-005-SS) also revealed Sr-90 just above the scan MDC but within the range of uncertainty associated with the sample results. Because this sample was not available for reanalysis, ZS collected two subsurface investigation samples in October 2019.
These investigational samples were collected at the closest accessible locations to the specified coordinates that had media available for sampling. The Sr-90 results for both investigational samples were less than MDC.
Figure 3-2, SU 10223 Final Status Survey Sample Locations
3.3.2 Phase 1 Confirmatory/Inspection Survey Results In April 2021, the NRC staff, with the support of ORISE, performed an inspection survey at the Zion site, primarily to survey for potential DRPs (ML21267A523). Portions of several SUs included in Phase 1 were surveyed as part of the inspection including the switchyard (SU10205), and several SUs along the beach (SU10222, SU10223, SU102240). Based on gamma walkover scans and subsequent investigations, eight DRPs were found. One of these samples (S0127) located within SU 10220C exhibited slightly elevated concentrations of Cs-137, Am-241, and Pu-239/240. More information on licensee action based on and NRC evaluation of these survey data are presented in Section 3.7 Discrete Radioactive Particles.
3.3.3 NRC Evaluation of Phase 1 Based on the historical operational history of the site, ZS would not expect Sr-90 to have been present in SU 10223. ZS concluded that the detections of Sr-90 in sample analyses were a result of false positives. ZS points to the reanalysis results being less than MDC for the two samples that were reanalyzed. However, the NRC staff note that the MDCs for the reanalysis of these samples were not low enough to detect the subsurface OpDCGL for Sr-90, and therefore not adequate to detect 75% of the subsurface OpDCGL. It appears that even after the NRC addressed that the MDCs were not low enough in its evaluation of Phase 1 (ML19277E336), ZS still did not meet the required MDC level in the reanalysis of the two samples for which off-site analysis positively identified Sr-90.
However, the MDC of the two additional investigational subsurface samples taken in October 2019 were sufficient to confirm that Sr-90 was not present above the MDC. Given that these samples were taken within the vicinity of the original sample, and that the MDC was sufficiently low enough on the analysis of these samples, this is an indication that the original result was a false positive.
The NRC staff agree that the operational history and the two additional investigations collected with the MDC adequate to detect 75% of the subsurface DCGLs which did not detect the presence of Sr-90 are sufficient to indicate the original results were most likely false positives and provide reasonable assurance that the approved LTP was met.
Figure 3-3, SU 10223 Location of Investigational Samples 3.4 Phase 3 Open Land Areas
In Phase 3 of the FSSR, ZS evaluated the potential dose from residual radioactivity in surface and subsurface soils. A total of 41 open land SUs with an overall area of 73,546 m2 were included in Phase 3 (Figure 3-4 and
SU Name Size (m2)
NE Corner of Restricted Area -
10201A 1,554 Lakeshore NE Corner of Restricted Area -
10201B 1,427 Lakeshore NE Corner of Restricted Area -
10201C 1,379 Lakeshore NE Corner of Restricted Area -
10201D 1,472 Lakeshore 10202A IRSF/Fire Training Area 1,757 10202B IRSF/Fire Training Area 1,711 10202C IRSF/Fire Training Area 1,696 10202D IRSF/Fire Training Area 1,680 10203D East Training Area 1,993 10203E East Training Area 1,886 10209A Restricted Area South of Gate House 1,966 10209B Restricted Area South of Gate House 1,977 10209D Restricted Area South of Gate House 1,586 10209E Restricted Area South of Gate House 1,560 10210A Restricted Area South of Turbine Building 1,788 10210B Restricted Area South of Turbine Building 1,913 10210C Restricted Area South of Turbine Building 1,893 10211A SE Corner of Restricted Area (Lakeshore) 1,536 10211B SE Corner of Restricted Area (Lakeshore) 1,663 10220B SE Corner of Exclusion Area - Inland 1,696 10220D SE Corner of Exclusion Area - Inland 1,475 10220E SE Corner of Exclusion Area - Inland 1,976 10220F SE Corner of Exclusion Area - Inland 1,578 10220G SE Corner of Exclusion Area - Inland 1,674 10220J SE Corner of Exclusion Area - Inland 2,030 10221B South of Protected Area - Inland 1,855 10221E South of Protected Area - Lakeshore 1,975 10221F South of Protected Area - Lakeshore 1,968 10221G South of Protected Area - Lakeshore 1,956 10221H South of Protected Area - Lakeshore 1,994 Waste Water Treatment Facility (WWTF) 12101 2,036 Sludge Drying Bed Area 12102 WWTF 2,024 12103 Unit No. 2 PWST/SST Area 2,034 12112 Unit No. 1 PWST/SST Area West 1,693 12113 Unit No. 1 PWST/SST Area West 1,658
Under Service Building and Southeast 12203B 1,989 Yard Under Service Building and Southeast 12203C 1,955 Yard Under Service Building and Southeast 12203D 1,635 Yard 12204A Crib House Area 1,943 12204B Crib House Area 1,971 12204C Crib House Area 1,994
). The SUs in Phase 3 all had a final classification of Class 1 per MARSSIM. The majority of the SUs in Phase 3 were originally classified as Class 2 or Class 3 SUs. However, ZS reclassified the Class 2 and Class 3 SUs to Class 1 prior to FSS which is a conservative measure not requiring NRC approval. According to ZS, this reclassification was due to changing radiological and operational conditions brought about by site decommissioning activities inside or adjacent to this area, survey. As described in Section 2 of this SER, a large number of particles were released and dispersed on the site during decommissioning activities, which resulted in the licensee reclassifying these SUs.
Figure 3-4, Phase 3 SU Locations (Based on Figure 1-1 in the Phase 3, Rev 0 FSSR)
Table 3-6, Zion FSSR Phase 3 SUs (41 Total Class 1 SUs)
SU Name Size (m2)
NE Corner of Restricted Area -
10201A 1,554 Lakeshore NE Corner of Restricted Area -
10201B 1,427 Lakeshore NE Corner of Restricted Area -
10201C 1,379 Lakeshore NE Corner of Restricted Area -
10201D 1,472 Lakeshore 10202A IRSF/Fire Training Area 1,757 10202B IRSF/Fire Training Area 1,711 10202C IRSF/Fire Training Area 1,696 10202D IRSF/Fire Training Area 1,680 10203D East Training Area 1,993 10203E East Training Area 1,886 10209A Restricted Area South of Gate House 1,966 10209B Restricted Area South of Gate House 1,977 10209D Restricted Area South of Gate House 1,586 10209E Restricted Area South of Gate House 1,560 10210A Restricted Area South of Turbine Building 1,788 10210B Restricted Area South of Turbine Building 1,913 10210C Restricted Area South of Turbine Building 1,893 10211A SE Corner of Restricted Area (Lakeshore) 1,536 10211B SE Corner of Restricted Area (Lakeshore) 1,663 10220B SE Corner of Exclusion Area - Inland 1,696 10220D SE Corner of Exclusion Area - Inland 1,475 10220E SE Corner of Exclusion Area - Inland 1,976 10220F SE Corner of Exclusion Area - Inland 1,578 10220G SE Corner of Exclusion Area - Inland 1,674 10220J SE Corner of Exclusion Area - Inland 2,030 10221B South of Protected Area - Inland 1,855 10221E South of Protected Area - Lakeshore 1,975 10221F South of Protected Area - Lakeshore 1,968 10221G South of Protected Area - Lakeshore 1,956 10221H South of Protected Area - Lakeshore 1,994 Waste Water Treatment Facility (WWTF) 12101 2,036 Sludge Drying Bed Area 12102 WWTF 2,024 12103 Unit No. 2 PWST/SST Area 2,034 12112 Unit No. 1 PWST/SST Area West 1,693 12113 Unit No. 1 PWST/SST Area West 1,658
Under Service Building and Southeast 12203B 1,989 Yard Under Service Building and Southeast 12203C 1,955 Yard Under Service Building and Southeast 12203D 1,635 Yard 12204A Crib House Area 1,943 12204B Crib House Area 1,971 12204C Crib House Area 1,994 The Phase 3 FSSR, Rev 1 (ML22279A984) incorporates the results from the release records for the 41 SUs included in Phase 3 (ML20009E643 Pkg). ZS provided updated release records for SUs 10209D, 10220J, 12101, and 12204B (ML20147A092 Pkg) to correct an error identified by ZS in the analysis of Sr-90. ZS also provided updated release records and supporting information for Phase 3 SUs in response to RAIs and other supplemental information requests (ML20147A128, ML20167A280, ML20351A154 Pkg, ML21067A225 Pkg, ML21103A229, ML21112A166, ML22224A002 Pkg, and ML22279A984 Pkg).
3.4.1 FSS Results for Phase 3 The results of the systematic surface soil samples were provided by ZS in Tables 5-1 and 5-2 in the Phase 3 FSSR, Rev 1 and are summarized below. ZS stated in its Phase 3 FSSR that several discrete elevated areas of contamination were identified in several Phase 3 SUs during FSS, but all residual radioactivity greater than OpDCGL concentrations were remediated prior to demonstrating compliance. ZS further stated that none of the systematic soil measurements exceeded an OpSOF of one for Phase 3 and that no Elevated Measurement Comparisons were used for the Phase 3 SUs. ZS identified the SU with the maximum average SU dose as SU10209D with a mean Base Case2 SOF of 0.022, which corresponds to a dose of 0.544 mrem/yr.
2 ZS use the terms Base Case for its compliance term and Operational for its administrative constraint.
Table 3-7, Phase 3 Systematic Sample Results (Adapted from Tables 9 and 10 in FSSR (ML22279A984))
Co-60 (pCi/g) Cs-137 (pCi/g) Mean Max Mean Dose SU Mean Max Mean Max OpSOF OpSOF BcSOF (mrem/yr) 10201A 2.39E-02 6.18E-02 3.00E-02 7.81E-02 0.047 0.080 0.012 0.299 10201B 2.47E-02 7.11E-02 3.32E-02 7.92E-02 0.047 0.097 0.012 0.303 10201C 5.48E-03 1.83E-02 3.44E-02 1.02E-01 0.023 0.058 0.006 0.146 10201D 6.22E-03 2.93E-02 2.79E-02 6.82E-02 0.023 0.057 0.006 0.148 10202A 3.22E-02 6.99E-02 4.12E-02 7.52E-02 0.055 0.100 0.014 0.354 10202B 2.57E-02 6.65E-02 4.38E-02 9.33E-02 0.046 0.085 0.012 0.292 10202C 7.27E-03 2.69E-02 1.32E-02 6.59e-2 0.017 0.040 0.004 0.109 10202D 5.97E-03 2.34E-02 1.70E-02 4.22E-02 0.021 0.069 0.005 0.133 10203D 2.33E-02 5.54E-02 3.43E-02 1.24E-01 0.041 0.122 0.011 0.263 10203E 2.99E-02 6.66E-02 3.90E-02 9.02E-02 0.050 0.106 0.013 0.323 10209A 2.19E-02 4.52E-02 2.87E-02 7.12E-02 0.041 0.077 0.011 0.264 10209B 2.39E-02 6.78E-02 3.78E-02 1.22E-01 0.047 0.090 0.012 0.304 10209D 3.62E-02 1.21E-01 1.26E-01 1.10E+00 0.085 0.458 0.022 0.544 10209E 2.46E-02 9.11E-02 4.49E-02 7.17E-02 0.050 0.109 0.013 0.318 10210A 3.03E-02 2.07E-01 5.03E-02 2.25E-01 0.056 0.243 0.014 0.361 10210B 3.17E-02 7.99E-02 2.90E-02 5.54E-02 0.057 0.141 0.015 0.365 10210C 2.24E-02 4.94E-02 3.21E-02 9.89E-02 0.045 0.090 0.012 0.287 10211A 1.44E-02 4.00E-02 2.61E-02 6.00E-02 0.029 0.056 0.008 0.189 10211B 2.73E-02 9.13E-02 3.17E-02 6.23E-02 0.050 0.125 0.013 0.321 10220B 2.43E-02 7.49E-02 3.27E-02 7.63E-02 0.047 0.111 0.012 0.302 10220D 8.91E-03 2.77E-02 2.58E-02 6.64E-02 0.027 0.061 0.007 0.173 10220E 1.48E-02 5.48E-02 2.21E-02 7.05E-02 0.031 0.081 0.008 0.196 10220F 1.94E-02 4.12E-02 3.06E-02 7.86E-02 0.037 0.084 0.009 0.233 10220G 2.35E-02 9.82E-02 2.76E-02 6.09E-02 0.042 0.150 0.011 0.270 10220J 2.10E-02 4.51E-02 3.05E-02 5.74E-02 0.045 0.082 0.012 0.289 10221B 1.99E-01 5.96E-02 3.27E-02 2.15E-01 0.038 0.116 0.010 0.245 10221E 2.90E-02 8.07E-02 4.56E-02 1.83E-01 0.055 0.109 0.014 0.353 10221F 2.76E-02 6.63E-02 6.25E-02 2.15E-01 0.052 0.114 0.013 0.331 10221G 1.80E-02 4.39E-02 3.52E-02 7.96E-02 0.036 0.065 0.009 0.233 10221H 1.24E-02 4.56E-02 1.95E-02 6.18E-02 0.025 0.096 0.007 0.163 12101 2.45E-02 1.07E-01 7.57E-02 2.83E-01 0.055 0.200 0.014 0.355 12102 8.56E-03 2.37E-02 1.03E-02 1.13E-01 0.020 0.058 0.005 0.125 12103 1.19E-02 3.92E-02 1.60E-02 5.07E-02 0.026 0.058 0.007 0.167 12112 1.37E-02 9.57E-02 1.10E-01 3.59E-01 0.055 0.144 0.014 0.353 12113 1.25E-02 5.23E-02 3.63E-02 1.04E-01 0.033 0.104 0.008 0.212 12203B 5.82E-03 2.62E-02 2.68E-02 1.05E-01 0.027 0.065 0.007 0.172 12203C 9.26E-03 3.25E-02 4.20E-02 2.12E-01 0.032 0.097 0.008 0.205 12203D 6.59E-03 3.90E-02 5.68E-02 2.92E-01 0.033 0.112 0.008 0.208 12204A 1.60E-02 4.45E-02 2.41E-02 4.84E-02 0.036 0.070 0.009 0.229 12204B 2.66E-02 9.18E-02 4.21E-02 1.04E-01 0.052 0.118 0.013 0.335 12204C 2.55E-02 5.77E-02 6.33E-02 4.58E-01 0.060 0.174 0.015 0.383 Shaded SU is highest dose in this Phase.
In accordance with the previously approved LTP, subsurface samples were also taken at 10%
of the systematic surface soil locations with the specific locations selected at random. The LTP also required biased subsurface samples to be taken in locations where the analysis of a surface soil sample or the results of a surface gamma scan indicated the potential presence of residual radioactivity at a concentration of 75% of the subsurface OpDCGL. According to the Phase 3 FSSR, this occurred in thirteen (13) of the forty-one (41) SUs in this Phase 3 FSSR (SUs 10202B, 10203E, 10209A, 10209D, 10209E, 10221B, 12102, 12103, and 12112, 12113, 12203B, 12203C, and 12203D). The Operational SOF values for these subsurface samples reported in the FSS release records were all less than 1.
Section 5.3 of the Phase 3 FSSR describes SUs in which the licensee identified anomalous data, had elevated scan results, or had investigations. According to the licensee, these SUs included SU 10202B, 10203D, 10203E, 10209A, 10209E, 10220B, 10221B, 10221H, 12102, 12103, 12112, 12113, 12203B, 12203C, 12203D. In the Phase 3 FSSR, the licensee reported that none of the Phase 3 SUs had elevated areas with concentrations corresponding to an Operational SOF value of greater than 1.
The licensee identified DRPs in several Phase 3 SUs. ORISE also identified DRPs in some of the Phase 3 SUs during its confirmatory surveys. DRPs are discussed in more detail in Section 3.7 of this SER.
3.4.2 Confirmatory/Inspection Survey Results Several of the ORISE confirmatory survey reports generated for the Zion site were, partially, related to Phase 4 open land area SUs. This includes the reports listed in the table below.
Table 3-8, Confirmatory Survey Reports for Phase 3 SUs Accession Report Date Title Number Oak Ridge Institute for Science & Education -
Submittal of Independent Confirmatory Survey ML19053A677 February 7, 2019 Summary and Results for the Waste Water Treatment Facility and Select Land Areas at the Zion Nuclear Power Station Independent Confirmatory Survey Summary ML20127H834 April 24, 2020 and Results of The Remaining Land Areas at the Zion Nuclear Power Station, Zion, Illinois ORISE Report of April 2021 Survey at Zion ML21267A523 September 2, 2021 Nuclear Power Station
Accession Report Date Title Number Zion Nuclear Generating Station, Units 1 and 2 ML23310A108 November 3, 2023
- Confirmatory Survey Report 2023 The confirmatory survey documented in the February 7, 2019, report included gamma surface scans and volumetric soil sampling from both random and judgmental locations in the land areas. Areas identified during the gamma scan as having a response that was audibly distinguishable from local background were further investigated with soil samples. ORISE reported that all of the confirmatory soil samples were well below the DCGL values. The ORISE report further concluded that there was no discernable bias between the ORISE and FSS laboratory measurements for these soil samples.
The confirmatory survey documented in the April 24, 2020, report included gamma walkover surface scans, gamma direct measurements, and soil sampling. The areas investigated included all or a portion of the follow areas that contain Phase 3 SUs 10201, 10202, 10203, 10209, 10211, 10220, 10221, 12102, 12103, 12112, 12113, 12203, and 12204. The gamma scans identified seven areas of elevated radiation that was distinguishable from background.
ORISE indicated that shine from the ISFSI was responsible for the elevated reading in three of these areas. ORISE also identified a DRP and a piece of concrete-like debris that were responsible for the elevated readings in two of these areas.
As described in more detail in Sections 2.2.2 and 3.7 of this SER, the September 2, 2021, Confirmatory Survey Report (ML21267A523), describes a limited scope survey for DRPs in portions of the site where the potential presence of DRPs was suspected based on site history and previous survey findings. The results of this survey and related DRP assessments are further discussed in Sections 2 and 3.7 of this SER.
In the confirmatory survey documented in the November 3, 2023 report (ML23310A108), ORISE was tasked by NRC with performing scanning surveys of both surface and subsurface soil for DRPs as well as confirming the FSSs conducted since the previous confirmatory surveys. After significant effort in scanning most of the restricted area of the site, ORISE identified and collected 12 DRPs from surface soil and did not identify any DRPs in a limited assessment of subsurface soil. The NRC staff evaluated the DRPs as a less likely but plausible consideration as discussed in Section 3.7 of this SER. The soil samples taken during the survey generally confirmed the FSS surveys performed by ZS although ORISE obtained notably higher results than obtained by ZS in two locations. In one instance, the ORISE sample results indicated that a subsurface hot spot was present which had not been identified by ZS. ORISE identified the sample location as being in SU 10224C at the border of SU 12112 and SU 10223. When NRC staff assessed the hot spot, an incremental dose for this hot spot was conservatively estimated to be between 4.1 mrem/yr and 8.4 mrem/yr (using area factors associated with a 3 m2 area and a 10 m2 area). ORISE estimated its elevated scanning measurements extended over a 5 m2
area. The sample location was very near the conjunction of three SUs (10224C, 12112, and 10223). The addition of 8.4 mrem/y to the previous dose estimates for soil in these SUs is a sizable increase. The NRC staff reviewed the other components of potential dose in these three SUs and found that the maximum dose would occur in SU 12112 which had a potential dose from exposure to residual radioactivity in soil (including consideration of an 8.4 mrem/y hot spot) as well as structural components remaining in the SU and groundwater totaling to 14.9 mrem/yr.
For this reason, the NRC staff maintains that there is reasonable assurance that no one would receive more than 25 mrem/y due to consideration of the hot spot indicated during the 2023 survey.
3.4.3 NRC Staff Evaluation of Phase 3 FSS The NRC staff reviewed the FSSR and associated release records and confirmed that the soil doses for the land SUs included in Phase 3 were generally much below the release criteria in 10 CFR 20.1402, Radiological Criteria for Unrestricted Use. As described in more detail in Section 7, the soil dose is combined with doses from other media to demonstrate the overall compliance of the site with the release criteria. As seen in Table 3-7, the maximum reported dose from diffuse contamination in any of the Phase 3 SUs was 0.544 mrem/yr. The NRC reviewed the release records and confirmed that they did not have any elevated areas that were identified by the licensee remaining at the time of license termination. However, ORISE identified an elevated area in a Phase 3 SU during a survey performed in 2023. As described above, the NRC staff performed an independent analysis of the dose considering this elevated area and found that the dose remains below the release criteria in 10 CFR 20.1402.
The NRC staff also reviewed the DCGLs used by the licensee in their survey design and concluded that they appropriately used the previously approved DCGL values in their survey design and they used the previously approved dose calculation methodology to determine the potential dose from the residual radioactivity present in the SUs. The NRC staff reviewed the analytical lab results in the release records to verify that the concentrations measured by the laboratory was correctly used in the calculations and found that this was done correctly and found that with the exception in minor errors in identifying values that were above the detection limit (i.e., values bolded in the summary tables), this was done correctly. The NRC staff also performed independent calculations of the survey unit average concentrations and resulting SOFs and doses and calculated comparable results to the licensee.
The NRC staff reviewed the survey methodology described in the release records to ensure that the surveys were performed in accordance with the commitments made in the LTP. The NRC staff found that the SUs either used the classification described in the LTP or were reclassed to a class requiring a more rigorous survey. The NRC finds that this reclassification is acceptable and appropriate because the licensee was allowed to reclassify the SUs to more restrictive classifications per their LTP and resulted in a more conservative survey being performed. In addition, the NRC staff agrees with the ZSs assessment that the reclassification was appropriate given the changing site conditions, such as the discovery of DRPs in the soil during decommissioning.
The NRC staff reviewed the release records and confirmed that ZS had adequate gamma scan coverage of these SUs. The NRC staff noted that there were a few areas of Class 1 SUs that were not surveyed 100% due to reported accessibility issues. The NRC staff finds that although 100% of these areas should have been scanned during FSS per guidance in MARSSIM, the NRC has reasonable assurance that these areas have been surveyed adequately through a combination of the FSS surveys, other surveys performed by the licensee, and surveys performed by ORISE. The NRC reviewed the number of systematic surface samples, subsurface samples, and quality assurance (QA) samples taken by ZS during FSS and found it was consistent with their LTP. As discussed in more detail in Section 3.5.3, NRC staff identified that the sample results from the off-site laboratory appeared to be consistently higher than the results from the on-site laboratory. The NRC also reviewed ZSs analysis of HTD radionuclides in FSS samples and found that the HTDs were less than the detection limit in all cases but one.
In one sample, Ni-63 was detected, but Co-60 was not, so the ratio could not be calculated.
Based on this information, the NRC staff concludes that the licensee adequately demonstrated that the ratios assumed in the LTP for the HTDs were appropriately applied for. As discussed in Section 3.7 of this SER and in Attachment A of the PSR SER (ML23286A304 Pkg), HTDs in higher amounts were detected in DRPs and were considered as part of the NRCs evaluation of DRPs.
The NRC staff reviewed the licensees descriptions of anomalies, investigations, and additional remediation in the release records and found that DRPs had been identified in several of the SUs. Although ZS found some DRPs during their FSSs, the NRC staff note that the FSS was not designed to account for the potential for DRPs to be present on the site and for this reason questioned whether the FSSs performed by ZS on their own were adequate to demonstrate that the site was surveyed adequately and that the residual radioactivity remaining on-site is consistent with the unrestricted release criteria. For this reason, the NRC staff is relying on a combination of the licensees FSS surveys, other surveys performed by the licensee using hand scanning techniques that are adequate to detect DRPs, and surveys performed by ORISE that were designed for DRPs. The NRCs evaluation of DRPs is described in more detail in Section 3.7 of this SER.
The NRC staff also reviewed the release records and subsequently information to confirm that the information provided in the FSSs represented an adequate assessment of the final radiological conditions present at the site. The NRC staff identified that there were some instances where isolation and control of the SUs does not appear to have been maintained after FSS and in some cases the results from the FSS did not appear to be representative of the final site conditions. The NRCs further evaluation of this is discussed in Section 3.6.
3.5 Phase 4 Open Land Areas ZS, in its Phase 4 of the FSSR for the Zion site (ML22279A986), evaluated the residual radioactivity in surface and subsurface soils as well as the potential dose resulting from unrestricted use of the area. A total of 67 open land SUs with an overall area of 178,182 m2
were included in Phase 4 (Figure 3-5 and Table 3-9). Sixty SUs in Phase 4 had a final classification of Class 1 per MARSSIM while six SUs were Class 2 and one was Class 3. The majority of the SUs in Phase 4 were originally classified as Class 2 or Class 3 SUs. However, many of the Class 2 and Class 3 SUs were reclassified by ZS to Class 1 prior to FSS and subdivided as indicated by a letter designator after the SU number. According to ZS, this reclassification typically occurred after evaluation of continuing characterization results or emergent data which indicated that a more restrictive classification was required. This was elaborated on by ZS in Section 3.3 of the FSSR as being a conservative measure due to the discrete particles of radioactive material being identified during the performance of operations surveys and Radiological Assessments (RAs) in and around the Class 2 and 3 SUs. As described in Section 2 of this SER, a large number of particles were released and dispersed on the site during decommissioning activities.
Figure 3-5, Phase 4 SU Locations (Replicated from Figure 1-1 in the Phase 4 Rev 2 Report)
Table 3-9, Zion FSSR Phase 4 SUs (67 Total SUs) (Replicated from Table 1-1 in the Phase 4 FSSR Report)
Size Size SU Name Class SU Name Class (m2) (m2)
Construction Parking 10203A East Training Area 1 1,999 10214E 1 1,989 Area Construction Parking 10203B East Training Area 1 1,977 10214F 1 1,661 Area SE Corner of Exclusion 10203C East Training Area 1 1,871 10220A 1 2,025 Area - Lakeshore SE Corner of Exclusion 10203F East Training Area 1 1,888 10220H 1 2,088 Area - Lakeshore SE Corner of Exclusion 10204A North Gate Area 1 2,231 10220I 1 2,060 Area - Lakeshore South of Protected Area -
10204B North Gate Area 1 1,549 10221A 1 1,976 Inland South of Protected Area -
10204C North Gate Area 1 1,547 10221C 1 1,959 Inland South of Protected Area -
10204D North Gate Area 1 1,545 10221D 1 1,697 Inland Station Construction North Half of Unit No. 2 10206A 1 2,844 12104 1 1,940 Area Containment Station Construction South Half of Unit No. 2 10206B 1 1,837 12105 1 1,938 Area Containment Station Construction North Half of Fuel &
10206C 1 1,833 12106 1 1,936 Area Auxiliary Buildings Station Construction South Half of Fuel &
10206D 1 1,829 12107 1 1,934 Area Auxiliary Buildings Station Construction North Half of Unit No. 1 10206E 1 1,825 12108 1 1,933 Area Containment South Half of Unit No. 1 10207A North Warehouse Area 1 2,675 12109 1 1,931 Containment Yard Between Unit No. 1 10207B North Warehouse Area 1 1,736 12110 1 1,740 Containment and Turbine South Yard Area 10207C North Warehouse Area 1 1,735 12111 1 1,964 Northeast of Gate House North Protected Area 10207D North Warehouse Area 1 1,733 12201A 1 1,992 Yard North Protected Area 10207E North Warehouse Area 1 1,731 12201B 1 1,995 Yard North Protected Area 10208A South Warehouse Area 1 2,460 12201C 1 1,968 Yard North Protected Area 10208B South Warehouse Area 1 1,835 12201D 1 1,842 Yard North Protected Area 10208C South Warehouse Area 1 1,868 12201E 1 1,902 Yard Gate House and 10208D South Warehouse Area 1 1,827 12202A 1 1,998 Southwest Yard Gate House and 10209C Restricted Area South of 1 1,970 12202B 1 1,999 Gate House Southwest Yard
Size Name Size SU Name Class SU Class (m2) (m2)
Gate House and 10212A NE Corner of Exclusion 2 9,550 12202C 1 1,894 Area - Lakeshore Southwest Yard Gate House and 10212B Vertical Concrete Cask 3 16,154 12202D 1 1,663 (VCC) Construction Area Southwest Yard Gate House and 10212C NE Corner of Exclusion 1 1,744 12202E 1 1,845 Area - Lakeshore Southwest Yard Gate House and 10212D NE Corner of Exclusion 1 1,490 12202F 1 1,858 Area - Lakeshore Southwest Yard Under Service Building 10213A NE Corner of Exclusion 2 5,730 12203A 1 1,988 Area and Southeast Yard Area Under the Turbine 10213B NE Corner of Exclusion 1 1,994 12205A 1 1,809 Area Building Area Under the Turbine 10213C NE Corner of Exclusion 1 1,934 12205B 1 1,814 Area Building Area Under the Turbine 10214A Construction Parking Area 2 8,542 12205C 1 1,818 Building Area Under the Turbine 10214B Construction Parking Area 2 7,372 12205D 1 1,821 Building Area Under the Turbine 10214C Construction Parking Area 2 7,579 12205E 1 1,825 Building 10214D Construction Parking Area 2 8,946 ZS, in its FSSR for Phase 4 (ML22279A986), explains the results from the release records for the 67 SUs included in Phase 4 (ML20133J975 Pkg). In the FSSR, ZS states:
Release Records are complete and unambiguous records of the as-left radiological status of each specific SU. Each Release Record contains sufficient information necessary to perform an independent review and evaluation of both the survey activities, the analytical results, and the final conclusion.
ZS provided updated release records for multiple SUs (ML22279A984 Pkg; ML22224A002, Pkg; and; ML22237A206 Pkg) to reflect updated site conditions after completion of the original FSS created by moving or adding soil to the SUs or concerns related to the storage and removal of clean concrete demolition debris (CCDD) in SUs after the initial FSS surveys had been performed.
3.5.1 FSS Results for Phase 4 All reported hypothetical doses from residual radioactivity in the Phase 4 SUs was less than 1 mrem/yr with the maximum hypothetical dose being estimated for SU 10213B (0.968 mrem/yr).
FSS surveys involved a combination of scanning and sampling. Scanning was performed consistent with Section 5.6.4.4 of the LTP in that a reasonable effort was made to perform 100 percent scanning of accessible soil surfaces in Class 1 SUs, between 10 and 100 percent of
accessible surfaces were surveyed in Class 2 areas, and judgmental scanning was performed in Class 3 SUs. This scanning effort led to investigations of those areas either greater than the MDC scan or the OpDCGL. Investigations typically involved sampling of the suspect area as documented in the individual SU release record and discussed in Section 5.3 of the FSSR which explains how ZS will address investigations, anomalies, and elevations exceeding the OpSOF identified during the surveys.
Of note in Section 5.3 of the FSSR, ZS found and removed several radioactive particles or objects identified during scanning from several SUs. Also, ZS noted that several instances of exceedance of the OpSOF occurred in various SUs. In each instance of elevated areas, the area was investigated, bounded, and then conservatively remediated and recharacterized. The FSSR hypothetical dose does not include the elevated area as a dose source term because that material was removed from the site as waste and backfilled with clean fill from off-site.
Of lesser concern, ZS noted in Section 5.3 of the FSSR that it also had instances of standing water or other obstructions that prevented scanning in areas and that some sample locations had to be adjusted due to obstructions. It was also noted by the NRC staff that in some of the larger Class 1 SUs, the required number of samples was increased in order to maintain the sample spacing established for a 2,000 m2 SU, which is a size limitation for Class 1 SUs in MARSSIM guidance.
In at least two instances (SU 10220A and SU 10221A), ZS elected to fail an initial survey primarily because the analytical data having variability that significantly exceeded that of the variability used to plan the survey. The survey was then reperformed taking more samples to reflect the increased variability in data after ZS elected to perform additional remediation in the area.
The results of the systematic surface soil samples are provided by ZS in Tables 5-1 and 5-2 in the Phase 4 FSSR and are summarized below. As previously mentioned, ZS noted that several discrete elevated areas of residual radioactivity were identified in some of the SUs, but all residual radioactivity greater than the OpDCGL values were remediated and elevated areas were not considered in the ZS hypothetical dose estimate because the material was removed. The SU with the maximum average SU dose was SU10213B with a dose of 0.968 mrem/yr.
Table 3-10, Phase 4 Systematic Sample Results (Adapted from Tables 5-1 and 5-2 in FSSR)
Co-60 Cs-137 OpSOF BcSOF Dose Mean Max Mean Max SU Mean Max Mean mrem/yr)
(pCi/g) (pCi/g) (pCi/g) (pCi/g) 10203A 6.95E-02 1.78E-02 9.90E-02 4.41E-02 0.038 0.092 0.010 0.244 10203B 6.48E-02 2.21E-02 2.18E-01 5.17E-02 0.050 0.127 0.013 0.321 10203C 5.00E-02 1.79E-02 8.18E-02 3.20E-02 0.037 0.090 0.010 0.238
Co-60 Cs-137 OpSOF BcSOF Dose Mean Max Mean Max SU Mean Max Mean mrem/yr)
(pCi/g) (pCi/g) (pCi/g) (pCi/g) 10203F 4.89E-02 1.55E-02 3.56E-02 1.02E-02 0.028 0.078 0.007 0.181 10204A 5.57E-02 2.29E-02 6.17E-02 2.45E-02 0.044 0.085 0.011 0.283 10204B 6.02E-02 1.77E-02 6.17E-02 2.94E-02 0.037 0.095 0.009 0.235 10204C 6.50E-02 3.52E-02 1.14E-01 3.73E-02 0.056 0.102 0.014 0.361 10204D 6.36E-02 2.37E-02 5.68E-02 2.48E-02 0.044 0.084 0.011 0.279 10206A 5.18E-02 2.11E-02 1.52E+00 9.90E-02 0.061 0.422 0.016 0.392 10206B 6.61E-02 2.64E-02 7.91E-02 3.97E-02 0.048 0.117 0.012 0.309 10206C 5.18E-02 2.70E-02 9.11E-02 5.55E-02 0.058 0.106 0.015 0.370 10206D 1.56E-01 3.99E-02 1.26E-01 6.45E-02 0.069 0.198 0.018 0.440 10206E 8.29E-02 1.73E-02 5.37E-02 1.70E-02 0.028 0.104 0.007 0.180 10207A 1.51E-01 3.31E-02 4.26E+00 3.14E-01 0.136 1.345 0.035 0.869 10207B 6.19E-02 2.05E-02 1.03E-01 3.65E-02 0.038 0.085 0.010 0.243 10207C 1.04E-01 3.87E-02 1.78E-01 6.00E-02 0.069 0.150 0.018 0.441 10207D 5.88E-02 2.59E-02 8.72E-02 4.06E-02 0.052 0.110 0.013 0.333 10207E 6.78E-02 2.65E-02 6.34E-02 3.34E-02 0.044 0.096 0.011 0.282 10208A 6.13E-02 2.71E-02 8.74E-02 3.43E-02 0.046 0.089 0.012 0.297 10208B 6.05E-02 2.67E-02 9.88E-02 3.76E-02 0.047 0.095 0.012 0.300 10208C 6.33E-02 2.58E-02 5.92E-02 2.27E-02 0.045 0.083 0.012 0.291 10208D 5.35E-02 2.44E-02 5.54E-02 2.37E-02 0.042 0.086 0.011 0.272 10209C 7.23E-02 3.19E-02 1.48E-01 6.04E-02 0.060 0.117 0.015 0.382 10212A 3.87E-02 2.01E-02 1.44E-01 5.54E-02 0.048 0.092 0.012 0.304 10212B 6.92E-02 2.19E-02 5.25E-02 2.35E-02 0.039 0.097 0.010 0.250 10212C 5.97E-02 2.00E-02 4.90E-01 9.46E-02 0.060 0.202 0.015 0.382 10212D 8.32E-02 2.53E-02 4.00E-01 1.60E-01 0.082 0.150 0.021 0.526 10213A 7.02E-02 2.76E-02 4.54E-01 1.55E-01 0.081 0.188 0.021 0.519 10213B 5.00E-02 2.27E-02 3.47E+00 4.31E-01 0.151 1.014 0.039 0.968 10213C 6.23E-02 2.93E-02 5.85E-01 1.90E-01 0.096 0.187 0.025 0.616 10214A 5.05E-02 1.84E-02 8.22E-02 2.41E-02 0.036 0.059 0.009 0.230 10214B 4.62E-02 2.00E-02 8.78E-02 2.65E-02 0.038 0.085 0.010 0.243 10214C 3.98E-02 1.78E-02 9.50E-02 1.96E-02 0.035 0.067 0.009 0.227 10214D 6.20E-02 1.59E-02 1.45E-01 3.44E-02 0.036 0.101 0.009 0.232 10214E 5.60E-02 1.50E-02 5.87E-02 2.05E-02 0.030 0.090 0.008 0.195 10214F 5.87E-02 2.05E-02 5.44E-02 2.16E-02 0.043 0.086 0.011 0.278 10220A 2.34E-01 3.36E-02 6.63E-02 3.40E-02 0.058 0.298 0.014 0.348 10220H 4.87E-02 2.47E-02 1.22E-01 4.83E-02 0.048 0.100 0.012 0.307 10220I 7.76E-02 2.00E-02 9.76E-02 3.30E-02 0.038 0.117 0.01 0.244
Co-60 Cs-137 OpSOF BcSOF Dose Mean Max Mean Max SU Mean Max Mean mrem/yr)
(pCi/g) (pCi/g) (pCi/g) (pCi/g) 10221A 8.32E-02 3.15E-02 3.81E-01 5.48E-02 0.059 0.189 0.015 0.379 10221C 1.05E-01 3.19E-02 4.32E-01 7.78E-02 0.067 0.262 0.017 0.427 10221D 4.45E-02 2.35E-02 2.28E-01 4.36E-02 0.045 0.110 0.011 0.286 12104 5.14E-02 1.89E-02 4.36E-02 1.55E-02 0.034 0.068 0.009 0.215 12105* 4.85E-02 1.91E-02 5.74E-02 1.03E-02 0.034 0.080 0.009 0.216 12106* 4.35E-02 1.83E-02 4.08E-02 1.28E-02 0.031 0.053 0.008 0.198 12107* 6.09E-02 2.54E-02 4.07E-02 1.16E-02 0.038 0.076 0.01 0.246 12108 3.33E-02 1.59E-02 1.35E-02 3.53E-03 0.027 0.046 0.007 0.17 12109 9.77E-02 2.43E-02 3.78E-02 1.01E-02 0.037 0.131 0.009 0.236 12110 7.99E-02 3.78E-02 2.84E-02 7.66E-03 0.053 0.114 0.014 0.34 12111 4.82E-02 1.76E-02 2.82E-02 7.52E-03 0.031 0.061 0.008 0.197 12201A 4.61E-02 2.12E-02 4.45E-02 1.25E-02 0.035 0.077 0.009 0.223 12201B 5.15E-02 1.61E-02 3.61E-02 1.12E-02 0.030 0.068 0.008 0.19 12201C 1.75E-02 6.54E-03 6.60E-02 1.34E-02 0.016 0.036 0.004 0.103 12201D 1.80E-02 4.09E-03 5.38E-02 1.21E-02 0.015 0.037 0.004 0.098 12201E 2.79E-02 5.79E-03 8.12E-02 1.17E-02 0.003 0.039 0.003 0.085 12202A 8.10E-02 2.09E-02 4.75E-02 7.12E-03 0.032 0.094 0.008 0.206 12202B 4.86E-02 2.04E-02 4.24E-02 7.50E-03 0.032 0.072 0.008 0.202 12202C 4.79E-02 2.47E-02 5.65E-02 1.14E-02 0.039 0.091 0.01 0.248 12202D 7.43E-02 2.50E-02 4.37E-02 1.65E-02 0.039 0.092 0.01 0.252 12202E 3.23E-02 1.28E-02 4.05E-02 1.32E-02 0.024 0.046 0.006 0.156 12202F 5.52E-02 2.11E-02 6.61E-02 2.31E-02 0.039 0.074 0.01 0.248 12203A 5.22E-02 1.12E-02 1.71E-01 4.21E-02 0.037 0.078 0.009 0.237 12205A 4.01E-02 6.37E-03 1.73E-02 4.38E-03 0.016 0.046 0.004 0.104 12205B 3.90E-02 1.32E-02 3.56E-02 5.50E-03 0.023 0.055 0.006 0.15 12205C 6.51E-02 2.12E-02 4.53E-02 1.35E-02 0.034 0.092 0.009 0.22 12205D 6.71E-02 2.01E-02 2.09E-02 4.67E-03 0.031 0.075 0.008 0.199 12205E 5.87E-02 1.88E-02 3.59E-02 4.09E-03 0.033 0.083 0.008 0.211
- The NRC staff note that this table does not include the subsurface survey results for these SUs designated as 12105K, 12106K, and 12107K which are included as addendums in the SU release records.
Shaded SU is highest dose in this Phase.
All dose estimates should be multiplied by a factor of 1.91 to account for potential bias from the Zion on-site measurement laboratory.
Discussed in the FSSR, but not reflected in the table above, are the FSSs taken of the excavation performed to expose the remaining foundation of the Fuel Handling Building and Car Shed. This excavation included the west half of SUs 12105, 12106, and 12107. A FSS was performed in each of these SUs prior to backfilling the excavation. The SUs were designated
12105K, 12106K, and 12107K and the survey results included as addendums to the release records for SUs 12105, 12106, and 12107, respectively. ZS noted that all samples obtained in the excavation met the release criteria the highest sample having a OpSOF of 0.453 and the highest mean OpSOF being 0.155 prior to being backfilled with clean fill.
The FSSR also discusses subsurface sampling around the Containment basement foundation and Auxiliary Building basement floor slab. The objective was to assess the radiological contamination of subsurface soils adjacent to and below these basement slabs. Section 5.3.4.4 of LTP Chapter 5 also states that attempts shall be made to acquire soil samples from beneath each basement floor slab and around each foundation from grade to the floor slab depth or refusal, whichever was less.
Many attempts were made to acquire these samples following the demolition of all above grade structures. As part of this effort, one (1) subsurface soil sample was taken in SU 12109 along the west side of the Auxiliary Building to a depth of 52 feet below grade, where refusal was met.
Several attempts were made to acquire samples at a deeper depth and below the basement slab in SU 12109. However, except for a sample acquired under the Auxiliary Building, the mud-mat placed around the Containment basement exterior during construction obstructed the GeoProbe from acquiring samples at a deeper depth. For the sample acquired in SU 12109, the probe was able to punch through the mud-mat and acquire a sample at a sub-basement slab depth. Twelve (12) additional samples were taken adjacent to the foundations of both Unit No. 1 and Unit No. 2 Containment Buildings and the Auxiliary Building to a depth of 32 feet to 48 feet.
All deep subsurface soil samples were analyzed by the on-site gamma spectroscopy system.
No ROCs were positively detected in any of these samples except for one sample taken along the foundation of Unit No. 2 Containment where Cs-137 was positively detected at a concentration of 0.095 pCi/g which is below the action level that would require an investigation.
Finally, the LTP required subsurface soil samples be taken at 10% of the systematic surface soil sample locations in Class 1 SUs. If during the performance of FSS, an indication of residual radioactivity at a subsurface OpSOF of 0.75 or greater is identified, then additional biased subsurface soil samples will be taken in the area of concern as part of the investigation. In Class 2 or 3 SUs, biased subsurface samples were to be taken if indications of residual radioactivity in excess of a subsurface OpSOF of 0.75 were identified. As previously mentioned, investigations were summarized in Section 5.3 of the FSSR. No subsurface soil samples were noted by ZS as exceeding the subsurface OpSOF of unity. In Section 2.5 of the FSSR, ZS discusses the Quality Assurance and Quality Control Measures employed throughout the FSS process to ensure that all decisions were based on data of acceptable quality.
3.5.2 Confirmatory/Inspection Survey Results Several of the ORISE confirmatory survey reports generated for the Zion site were, at least partially, related to Phase 4 open land area SUs. The applicable confirmatory survey reports are listed in the table below.
Table 3-11, Confirmatory Survey Reports for Phase 4 SUs Accession Report Date Title Number Report dated August 5, 2016, from Kaitlin M.
Engel, Oak Ridge Associated Universities (ORAU), to John Hickman, U.S. NRC, ML18240A035 August 5, 2016 regarding Independent Confirmatory Survey of the Turbine Building Basement and Open Land Areas at the Zion Nuclear Power Station Oak Ridge Institute for Science & Education -
Submittal of Independent Confirmatory Survey ML19053A677 February 7, 2019 Summary and Results for the Waste Water Treatment Facility and Select Land Areas at the Zion Nuclear Power Station Oak Ridge Institute for Science & Education -
Transmittal of Independent Confirmatory Survey Summary and Results for the ML20034D661 January 31, 2020 Subsurface Soils Associated With the Sacrificial Barrier at the Zion Nuclear Power Station Independent Confirmatory Survey Summary ML20127H834 April 24, 2020 and Results of The Remaining Land Areas at the Zion Nuclear Power Station, Zion, Illinois ORISE Report of April 2021 Survey at Zion ML21267A523 September 2, 2021 Nuclear Power Station ML23310A108 November 3, 2023 ORISE DRP surveys and open land areas The August 5, 2016, Confirmatory Survey Report (ML18240A035) noted three samples were taken in SU 10213A. Only low concentrations of Cs-137 were detected above the respective MDC. All other ROCs were less than the MDC. Ni-63 was not reported but, consistent with the LTP, is typically inferred from the Co-60 concentrations. Given the reported Co-60 was less than its MDC, Ni-63 concentrations would not have been expected to a significant fraction of the applicable DCGL.
In the February 7, 2019, Confirmatory Survey Report (ML19053A677), overburden soil from two excavations were sampled (referred to as land areas 6 and 7) which were contained in SUs 10209E, 10204B&C, 10206D&E, and 10207D&E. In general, land area 7 was scanned and elevated areas investigated by sampling while land area 6 was evaluated only through sampling. The confirmatory soil sample results from both land areas were all below their respective OpDCGL and, therefore, are also below the Base Case DCGL (BcDCGL). ORISE
concluded that there was not a discernable bias between the ORISE and FSS laboratory measurement system for the collected samples.
In the January 31, 2020, Confirmatory Survey Report (ML20034D661), ORISE evaluated the subsurface soil associated with the sacrificial soil placed to facilitate building demolition by performing an independent confirmatory survey consisting of gamma walkover surface scans and soil sampling in the power block area of the site (comprised of SUs 10203, 12201A through C, 12202A through F, and 12104 through 12111). This effort was comprised of two site visits.
The first was suspended by licensee request after ORISE identified several anomalies during its walkover survey and collected several judgmental samples. ORISE identified three DRPs in 16 judgmental samples it collected. Other than the DRPs, the soil met the OpDCGLs. When ORISE returned 3 months later to reperform its survey, after ZS completed its evaluations and corrective actions for the subject soil, twenty-one judgmental samples were collected. ORISE found two DRPs of Co-60 and one sample had Cs-137 at levels exceeding an OpSOF of unity but less than the BcSOF of unity. All other samples were less than the OpSOF of unity. ORISE concluded only that this portion of the site does contain residual radioactivity.
In the April 24, 2020, Confirmatory Survey Report (ML20127H834), ORISE investigated all or a portion of survey areas 10150, 10201, 10202, 10203, 10206, 10207, 10208, 10209, 10211, 10213, 10214, 10219, 10220, 10221, 12102, 12103, 12112, 12113, 12201, 12203, 12204, and 12205. Seven locations were identified during surface soil scans as distinguishable from background and were marked for investigation. A total of 37 soil samples were collected: 30 random samples, three judgmental samples, and four rainwater catch basin drain sediment samples. Of the seven identified areas with elevated gamma radiation levels, three were judgmentally selected for sampling. One of the judgmentally-sampled areas contained a piece of concrete-like debris, which was left with site personnel, while the soil from around the concrete was collected as a confirmatory soil sample. Three of the areas identified with elevated gamma radiation were investigated by the site, as directed by the NRC staff. One of these areas had a discrete radioactive particle. ORISE had no information on the other 2 areas that the site investigated. ORISE noted that other than the particle turned over to the site and the unknown status of the other 2 anomalous areas, the collected confirmatory survey data did not present any anomalous issues that would preclude the FSS data from demonstrating compliance with the release criterion.
In the September 2, 2021, Confirmatory Survey Report (ML21267A523), the NRC staff asked ORISE to concentrate on a limited assessment of a portion of the site for DRPs given the now suspected commonality of these particles identified during previous FSSs and confirmatory surveys. The results of this survey and related DRP assessments are further discussed in Sections 2.2.2 and 3.7 of this SER.
In the November 3, 2023, Confirmatory Survey Report (ML23310A108), ORISE was tasked with performing scanning surveys of both surface and subsurface soil for DRPs as well as confirming the FSSs conducted since the previous confirmatory surveys. After significant effort in scanning most of the restricted area of the site, ORISE identified and collected 12 DRPs from surface soil
and did not identify any DRPs in a limited survey of subsurface soil. The NRC staff evaluated the DRPs as a less likely but plausible (LLBP) consideration to inform its decision regarding unrestricted release of the Zite site outside the ISFSI boundary (not a compliance evaluation) as discussed in Section 3.7 of this SER. The soil samples taken generally confirmed the surveys performed by ZS in the Phase 4 section of the site.
3.5.3 NRC Staff Evaluation of Phase 4 FSS The NRC staff reviewed the FSSR for the Phase 4 open land areas and found that, generally, it appears as though the site met the release criteria by a considerable margin (the largest reported hypothetical dose was less than 1 mrem/yr). To facilitate a technical review and verify that the surveys accurately reflect the site conditions and provide reasonable assurance that the potential dose is less than the unrestricted release criterion (25 mrem/y plus ALARA), the NRC staff selected the release records for SUs 10206A, 10206D, 10207A, 10212B, 10213B, 10220A, 10221A, and 10221C for detailed review. The NRC staff verified a random selection of data to verify transposition of the analytically reported data to the summary tables in the release records. The NRC staff calculated the OpSOF and Base Case SOF (BcSOF) for samples to verify the calculations. The NRC staff verified the reported potential dose calculation based solely on the systematically collected surface soil samples average activity. In addition, the NRC staff reviewed the scanning survey summaries to verify that a reasonable effort was made to survey ~100% of the Class 1 SUs and the survey planning sheets to verify that an appropriate number of samples were collected. The NRC staff reviewed the ROC sample analyses tables containing analytical results for all ROCs to verify the surrogate ratios used to infer HTD ROCs were conservative as well as the subsurface sample results to verify that there was no apparent indication that residual radioactivity increased with depth below the surface. Finally, the NRC staff reviewed the release records for SUs 12105, 12106, and 12107 to assess the impact of the reported surveys of the excavation surface vs the surveys of the clean fill which were tabulated in the FSSR. The following paragraphs discuss items of concern the NRC staff had and how the concerns were assessed.
The NRC staff reviewed the release records for SUs 12105, 12106, and 12107 as these SUs addressed an area of excavation which was then backfilled and surveyed for final status as discussed in the FSSR. Each SU was surveyed prior to backfilling with clean soil; the survey report of the excavation surface was included as an addendum in each release record and referred to as 12105K, 12106K, and 12107K. The backfilled SUs were then surveyed and reported in the summary tables as shown in Section 3.5.1 of this SER. As both surveys were included in the release record, the NRC staff reviewed each and noted that the excavation surfaces were generally considered to have a higher dose potential than the clean backfill material. When evaluated using the subsurface Base Case DCGLs, the excavation of these SUs had a potential dose ranging from 0.51 mrem/yr to 1.02 mrem/yr. The reported surface surveys of backfill had a potential dose ranging from 0.20 mrem/yr to 0.25 mrem/yr. The NRC staff do not have much concern in surveys of clean backfill material and would prefer to consider the residual radioactivity present upon conclusion of the remediation of an area, prior to backfill. While the potential dose is up to a factor of five greater than what was reported by ZS
in these SUs, the maximum dose is still only slightly higher than 1 mrem/yr and there is significant safety margin remaining to meet the dose criterion of 25 mrem/yr. This is especially true when considering that the subsurface DCGLs applied to the excavation surface assume direct exposure is possible (DCGLs assumed a surface to 1 meter depth increment) when, in actuality, the excavation surface is covered by backfill so that the potential dose for the excavation surface is conservatively overestimated. If exhumed and brought to the surface, the excavated soil would be expected to be mixed with the clean backfill material and be diluted so that a lesser dose would occur than is estimated for the soil prior to backfilling. This concern was communicated to ZS who considered it appropriate to designate survey unit 12106K as having the highest dose potential of all land SUs when evaluating its compliance dose (see Section 7.1 of this SER). It was further noted that, in response to RAI 15d (ML21067A178), ZS recognized a bias present between the on-site gamma spectroscopy results and the off-site gamma spectroscopy results. A factor of 1.91 was derived to correct for a potential non-conservative impact caused by this bias. ZS stated it would apply this factor to the final dose calculated using the on-site gamma spectroscopy results such that the results for survey unit 12106K would become 1.95 mrem/yr.
The NRC staff verified, during review of the release records, that ZS inferred the residual radioactivity concentrations of Ni-63 and Sr-90 in each SU consistent with the LTP maximum ratios of 180.45 (Ni-63/Co-60) and 0.002 (Sr-90/Cs-137). While reviewing the analytical HTD data in the release records, the NRC staff noted that the inferred Ni-63 concentrations generally appeared to be conservative while the inferred Sr-90 concentrations appeared non-conservative. To evaluate this discrepancy, the NRC staff considered the analytical data for SU 10213B. Even though there were no Sr-90 detects greater than the MDC in these samples, MARSSIM guidance implies that the measured result is still the best estimate of the true value even if less than the detection limit and, if a significant population of data is present, measured results can be used to determine a reasonable estimate of the true mean. SU 10213B had 31 samples analyzed for all ROCs so the NRC staff calculated the Sr-90/Cs-137 ratio for each sample and then determined the average ratio. The average ratio for this data was 0.24 whereas the ratio that ZS used to infer Sr-90 was 0.002. The NRC staff believe this discrepancy was caused by ZS using ratios established from characterization data and considered only significantly contaminated materials as the data can also be utilized to estimate and characterize waste generated during remediation. Sr-90 was a much less common site than Cs-137; however, both Cs-137 and Sr-90 may be present in background to some extent as they would originate from the same events (i.e., historic atmospheric bomb testing). After remediation, both these radionuclides are more likely to be present at levels approaching what the background ratio would be which could be significantly greater than that established during characterization for site contaminants. This was somewhat confirmed by data from the confirmation survey performed in 2023. One sample collected during the confirmation survey had detectable Sr-90 and Cs-137 at relatively low levels. The ratio of Sr-90/Cs-137 in that sample was 0.2 although there was still relatively significant uncertainty reported for the Sr-90 result in that sample. The NRC staff believe that, while ZS non-conservatively underestimated Sr-90 concentrations after site remediation activities were complete by approximately two orders of magnitude, it primarily underestimated the concentration and impact of background Sr-90 at
the site which is not a regulatory consideration for meeting the unrestricted site release criteria and would not have made a significant difference in the potential dose estimate for a SU.
Human errors in the reported data were noted in two instances during review of the release records. While reviewing the release record for SU 10220A, the NRC staff note that the Cs-137 concentration in one of the investigative samples was reported incorrectly. It was apparent that the error was a result of not correctly transposing data from the analytical report as the value in the report summary table was that of the entry immediately below that of the Cs-137 result in the analytical report. Both values were very small compared to the DCGL and of the same order of magnitude. Also, the error occurred in the reported results for an investigative sample so there was no impact to the assessment of the SU. A human error was also noted in the evaluation of the subsurface sample data in the same SU, in this case, ZS switched between evaluating the results of the samples using the surface Operational DCGLs and the subsurface Operational DCGLs when only the subsurface DCGLs should have been applied. The NRC staff conclude that all subsurface sample results were of very low concentrations and so that the SOF in the samples was only slightly underestimated and this caused no impact to the evaluation of the SU.
The NRC staff identified that there were some instances where isolation and control of the SUs does not appear to have been maintained after FSS and, in some cases, the results from the FSS did not appear to be representative of the final site conditions. The NRCs further evaluation of this is discussed in Section 3.6.
The NRC staff conclude that: (1) the FSSs were effectively conducted in accordance with the LTP; (2) the FSSR and release records contain the information identified in NUREG-1757, Vol 2, Section 4.5; and (3) the FSS results demonstrate that the residual radioactivity in soil in each of the 67 Phase 4 SUs meet the radiological criteria for unrestricted release identified in the LTP. The NRC staff independently evaluated data in the FSSR and individual SU release records and found the data adequate even though ZS failed to utilize a conservative ratio for inferred Sr-90 when evaluating SUs; reported and prioritized surveys of clean backfill over surveys of excavation soil after remediation in the FSSR (but not in the compliance dose demonstration); and made insignificant human errors in some release records. In addition, significant effort was made to ensure no dose significant DRPs remain in the SUs. The NRC staffs conclusion is based on its review of ZS FSSRs, SU release records, and the results of confirmatory surveys conducted by ORISE.
3.6 Isolation and Control of SUs Post-FSS The LTP outlines ZS strategy and commitments to control the spread of radioactivity and prevent recontamination of areas that had received FSS. Specifically, ZS states in Section 5.12 of the LTP Isolation and control measures will be implemented in accordance with ZionSolutions site procedures as described in Section 5.6.3. Isolation and control measures will remain in
force throughout FSS activities and until there is no risk of recontamination from decommissioning or the survey area has been released from the license. In the event that isolation and control measures established for a given survey unit are compromised, evaluations will be performed and documented to confirm that no radioactive material was introduced into the area that would affect the results of the FSS.
The LTP allowed ZS to reuse the clean concrete as backfill in certain basements. In certain areas, as noted in the above section on decommissioning history and reuse of concrete debris, ZS stored concrete debris on SUs that had already received FSS and did not re-perform FSS.
Given that these areas may not have been properly surveyed after potentially contaminated debris was stored on them, there was potential for some concrete debris to remain on the site.
Refer to Phase 3 and Phase 4 for more details.
ZS committed to not stockpile and store excavated soil for reuse as backfill in the basements.
ZS was permitted to remove overburden soils, scanning the soil as it is excavated to access and remove buried components and then replace it. The LTP, Section 5.7.1.7, Reuse of Excavated Soils ZS commits to the following:
ZSRP will not stockpile and store excavated soil for reuse as backfill in basements.
However, overburden soils will be created to expose buried components (e.g., concrete pads, buried pipe, buried conduit, etc. ) that will be removed and disposed of as waste or, to install a new buried system. In these cases, the overburden soil will be removed, the component will be removed or installed, and the overburden soil will be replaced back into the excavation. In these cases, a RA will be performed. The footprint of the excavation, and areas adjacent to the excavation where the soil will be staged, will be scanned prior to the excavation. In addition, periodic scans will be performed on the soil as it is excavated and the exposed surfaces of the excavated soil will be scanned after it is piled next to the excavation for reuse. Scanning will be performed in accordance with Section 5.7.1.5.1. A soil sample will be acquired at any scan location that indicates activity in excess of 50% of the soil Operational DCGL. Any soil confirmed as containing residual radioactivity at concentrations exceeding 50% of the soil Operational DCGL will not be used to backfill the excavation and will be disposed of as waste.
3.6.1 Control of Radioactivity After FSS During the winter of 2019, potentially contaminated concrete demolition debris (referred to by the site as CCDD from the Containment Buildings) was stockpiled on SUs that had previously had an FSS completed on them during Phase 3. The stockpiling of this material on these SUs was initially identified during an NRC inspection (ML20080J249). According to ZS in its RAI response dated February 10, 2021 (ML21067A225 Pkg), SUs 12112, 12113, 12203B, 12203C, and 12203D had concrete demolition debris placed on them after FSS was completed.
ZS also indicated in its RAI response that the Phase 4 SU 12203A also had concrete demolition debris placed on it after FSS. The release records initially submitted by ZS did not include a discussion of this event and FSS was not reperformed on these SUs. As described below, ZS
did perform some surveillance surveys on these SUs after the concrete debris was removed, though this information was also not initially provided in the release records.
ZS also placed the concrete debris on some additional Phase 4 SUs after FSS was conducted (SUs 12205A, 12205B, 12205C, 12205D, and 12205E). However, FSS was redone for these SUs. The release records for these SUs each state After completion of the FSS in January of 2019, Clean Concrete Demolition Debris (CCDD) from the demolition of the Containment Buildings was stored in the area. After the CCDD was removed in the summer of 2019, the area needed to be backfilled again to an elevation of 591-foot elevation over the basements due to a significant amount of soil being removed along with the CCDD. Since this action significantly changed the end state of the SU, it was decided to perform the FSS again. The RAI response (ML21067A225 Pkg) further states that walkdowns and inspections performed in SUs 12205A, 12205B, 12205C, 12205D, and 12205E noted significant intermixing and deep settling of the CCDD in the SU footprints.
In response to NRCs RAI (ML21067A225 Pkg), ZS stated that this concrete was surveyed in accordance with the MARSAME-based unconditional release survey procedures. ZS further stated that they previously provided the NRC with two TSDs documenting the results: TSD 17-007, Evaluation of Static Measurements Performed for Unconditional Release Surveys of Building Materials Used for Backfill at the Zion Decommissioning Project, Revision 1 (ML18052A529), and TSD 17-010, Final Report -Unconditional Release Surveys at the Zion.
ZS also stated that the CCDD placed in SUs in SUs 12112, 12113, 12203A, 12203B, 12203C, and 12203D was comprised of concrete originating from the exterior of the Containment Buildings (i.e., concrete on the outside of the 1/2-inch stainless steel liner) and was therefore, in its view, considered to be low risk with respect to plant-originated contamination. However, as noted in the NRC RAI (ML21231A187), it appears that plant-derived radioactivity above background was found during these surveys. The NRC staff is basing this conclusion on the reported scan alarms, smear samples greater than the minimum detectable activity (MDA), and the remediation of areas of the Zion containment structure concrete performed by the licensee as a result of the 2018 Unconditional Release Survey (URS) survey results.
A detailed timeline of the events related to the surveys, demolition, movement, storage, and disposition of the concrete debris from the demolition of the Unit No. 1 and Unit No. 2 Containment Structures was provided in the response to RAI 9a (ZS-2021-0001)
(ML21067A225 Pkg). In this RAI response, ZS also reported that it performed surveillances after FSS to determine if the radiological conditions of the SUs remained the same. These surveillances consisted of surveys of portions of the SU and some biased soil samples. ZS also ultimately reperformed FSS in all of the SUs in which the concrete material was placed.
As documented in the first quarterly 2020 inspection report, NRC inspectors identified a Severity Level (SL) IV, Non-Cited Violation (NCV) of License Condition 2.C.(17) for failing to implement and maintain in effect all provisions of the approved LTP. Specifically, ZS placed contaminated concrete debris in an area under FSS controls which is inconsistent with LTP Section 5.6.3 to
implement controls throughout FSS activities until there is no risk of recontamination from decommissioning or the survey area has been released from the licenses (ML20080J249).
Portions of the Zion site were also regraded after FSS was completed. ZS reported that Final grading of the power block area started in June of 2019 and was completed by August of 2019 and that final site grading and scarification of the rest of the site commenced on August 31, 2020, and was completed on September 23, 2020 (ML22293A432). ZS provided additional details on the final site grading in the document Final Site Grading and Seeding Timeline with Maps" (ML22069A332).
3.6.2 NRC Conclusions on Isolation and Control of SUs Post-FSS The NRC reviewed the isolation and control of the SUs after the time of FSS and concludes that there were instances where isolation and control appeared to have not been maintained and where the FSS release records initially provided to the NRC did not appear to reflect the final site conditions. For example, ZS placed potentially contaminated concrete on areas that had been previously surveyed for FSS reporting. ZS provided the NRC with surveys of the concrete that were performed before demolition. However, there was enough uncertainty within the survey DQOs to preclude concluding the material was unimpacted and was not recontaminated during the course of decommissioning operations. In addition, discrete pieces of activated concrete was discovered during the April 2021 NRC confirmatory survey in units where CCDD had been placed. For this reason, the NRC was not able to rely on this information alone as justification that the concrete material had not potentially introduced contamination into the affected SUs after FSS. In addition, the NRC staff reviewed the information provided by the licensee about the special surveillances that they performed after FSS. The NRC staff conclude that these surveillances are a useful spot check to determine if there have been unexpected changes to the radiological conditions of a survey unit, but these surveillances alone are not detailed or extensive enough for the NRC to rely on for the purposes of having reasonable assurance that the radiological conditions are consistent with the NRC regulations in cases where there had been movement of soil or concrete material onto or off of the SU. ZS subsequently reperformed FSS in these soil SUs to address the concern about the radiological conditions of these SUs potentially being affected by the placement of the concrete debris on them. The NRC concludes that the reperforming of FSS in these areas was appropriate to demonstrate compliance and was consistent with the LTP and with MARSSIM. The NRC staff concludes that this rework of the FSSs in those SUs ensured that the FSS represented the site conditions after the concrete material was removed.
It also appears that ZS performed regrading of portions of the site after FSS was completed.
This regrading could have resulted in potentially radiologically contaminated material (from those areas before FSS resurvey) being moved between different SUs and could have resulted the destination FSS units being inconsistent with the final site conditions as documented in their FSS reports. The NRC concludes that for diffuse contamination, there was only one elevated area (evaluated in Section 3.4.2 of this SER) and that the soil concentrations were below the unrestricted release criteria by a wide margin. For this reason, for the diffuse contamination, the
NRC concludes that even if contaminated material was moved between SUs, it would not affect the overall conclusion that the level of diffuse contamination is consistent with the unrestricted release criteria. Therefore, the NRC concludes that although isolation and control does not appear to have been fully maintained after FSS was performed, the NRC is able to use the previously collected data for the affected SUs in Phases 3 and 4 as its basis for evaluating whether the average SU concentrations are consistent with the DCGLs. The NRC staff notes that the regrading of the site did add complication to its FSS review though and does not consider this regrading to be a best practice.
With respect to DRPs, the movement of soil on the site after FSS did introduce significant uncertainty into the origin and transport of DRPs and the adequacy of surveys for DRPs. For this reason, the NRC staff directed its contractor to perform extensive surveys for DRPs on the site. DRPs at ZS are described in more detail in the next section.
3.7 Discrete Radioactive Particles DRPs are described in MARSSIM, Rev. 2 Draft for Public Comment (ML21008A572) as small (usually on the order of millimeters or micrometers), distinct, highly radioactive particles capable of delivering extremely high doses to a localized area in a short period of time. Neither MARSSIM, Rev. 1 nor NUREG-1757 and its associated technical documents provide guidance on how to appropriately survey for or assess the dose from exposure to DRPs with respect to public exposures. The NRC staff reviewed previous site release documentation for several sites where DRPs were of concern and found that there was inconsistency in how DRPs were assessed and addressed. This caused delays while NRC staff and ZS assessed DRP surveying techniques and methods. The NRCs Office of Nuclear Regulatory Research contracted with a qualified contractor to develop DRP dose coefficients (ML23136A178) for the most likely contaminants anticipated for nuclear power plants and routes of potential exposure for the public. The same contractor provided a report of the ulceration threshold, a potential deterministic effect, should a DRP be inhaled or ingested (ML23136A207). ORISE, another NRC contractor who authored much of the surveying guidance in MARSSIM, was contracted by NRC to develop a method to evaluate the sensitivity of scanning for DRPs. ORISE documented and utilized this methodology to assess scanning for Cs-137 and Co-60 as point sources instead of area sources (ML22304A137). The NRC staff were eventually able to use the information provided in these reports, along with information provided by ZS in response to RAIs and results of the 2023 NRC Confirmatory Surveys, to assess the potential risk from DRPs found at the ZS site if, in the very unlikely event, they had not been removed.
As previously stated in this SER, extensive surveying of the site has been conducted by both ORISE, NRCs contractor, and ZS so that there are no DRPs known to remain at the site for license termination. However, the NRC staff evaluated the DRPs collected during the 2023 confirmatory survey to assess the potential impact should similar DRPs have been missed due to human error or other extenuating circumstances and the public be potentially exposed to one after license termination as discussed in Attachment A of the PSR SER (ML23286A304 Pkg.)
NRC contractors and ZS used appropriate hand scanning techniques for DRPs over a majority of the site such that only DRPs that may have been missed during multiple extensive scanning efforts could remain. The NRC staff believe the probability of encountering a DRP at the Zion site is very unlikely. Because all calculated EDE/CEDE3 hypothetical doses were less than 100 mrem/yr TEDE (the public dose limit), and other hypothetical dose estimates (shallow dose equivalent (SDE) and localized dose equivalent (LDE)) were much less than what would be considered exceedance of any deterministic threshold, the NRC staff believe that there is reasonable assurance that, in the very unlikely event that exposure to DRPs could occur at the Zion site, any exposure would be consistent with the less likely but plausible (LLBP) category of hypothetical considerations consistent with guidance in NUREG-1757, Vol 2, Rev. 2 Consolidated Decommissioning Guidance, Characterization, Survey, and Determination of Radiological Criteria, Table 5.1, Comparison and Description of Scenario Terms Used in this Guidance (ML22194A859). As such, the assessed dose from potential interaction with a DRP is only considered to risk inform the decision for license termination due to its very unlikely occurrence.
This LLBP conclusion, combined with the fact that a significant effort has been made by the NRC, its contractors, and ZS to identify and remove DRPs from the site, demonstrate to the NRC staff that ALARA of residual radioactivity and DRPs was achieved. Also, because the primary ROCs for exposure to DRPs are Co-60 and Eu-152/154, the activity of any remaining DRPs, if present, will reduce over time consistent with the relatively short half-lives of these radionuclides (Co-60 half-life is 5.27 years, Eu-152 half-life is 13.5 years, and Eu-154 half-life is 8.59 years). Thus, the potential dose should one encounter a DRP at the site will diminish with time.
3.8 NRC Evaluation of Open Land Area Final Status Surveys As discussed in more detail in in the previous sections, the NRC evaluated the FSSRs provided by ZS for the Phase 1, 3, and 4 Open Land Areas and concluded that the open land areas have been surveyed adequately, through a combination of ZS surveys and NRC confirmatory surveys, to evaluate the magnitude and extent of radiation levels, the concentrations or quantities of residual radioactivity, and the potential radiological hazards of the radiation levels and residual radioactivity detected. For this reason, the NRC staff concludes that there is reasonable assurance that the criteria of 10 CFR 20 Subpart F have been met.
The maximum reported SOF for the land SUs was 0.078 for SU 12106K, which corresponds to a dose of 1.95 mrem/y (see Section 3.5.3). The NRC staff therefore agrees with ZS use of the value 0.078 for the parameter Max BcSOFSOIL in the overall compliance equation.
3 EDE is the effective dose equivalent from external exposure assuming a DRP is in contact with an individuals upper torso. It is a component of the TEDE dose which has a public dose limit of 100 mrem/yr.
CEDE is the committed effective dose equivalent from internal exposure assuming a particle is ingested and passes through the Gastrointestinal (GI) tract consistent with reference man models (note: particles were considered to be insoluble). CEDE is a component of TEDE which has a public dose limit of 100 mrem/yr.
The NRC performed independent dose analyses of an elevated area identified by ORISE (see Section 3.4.2) and DRPs that could hypothetically exist on-site (see Section 3.7) to risk inform its conclusions. The NRC staff concluded that the potential dose from the elevated area is consistent with the unrestricted release criteria in 10 CFR 20.1402. The NRC staff concluded that the potential dose from a hypothetical DRP, in the unlikely event that a DRP remains on-site and an individual is exposed to it, is less than the public dose limit.
4 BASEMENT STRUCTURES, EMBEDDED PIPING, AND PENETRATIONS Phase 2 FSSRs were separated into two parts. The Phase 2, Part 1, Rev 1 FSSR was submitted on March 11, 2019 (ML19077A095), and includes seven basement SUs (Unit No. 1 Containment, Unit No. 2 Containment, Auxiliary Building, SFP/Transfer Canal, Turbine Building, Crib House/Forebay and Wastewater Treatment Facility. The Phase 2, Part 1, Rev 1 was submitted on June 30, 2020 as part of the RAI Responses (ML20167A279). Note, the seven basement SUs are further delineated into 31 dose components to separate surveys of the penetrations and embedded pipping from the wall surface surveys within a given basement. In November 2020, Phase 2, Part 1, Rev 2 was submitted (ML21067A204). This submittal included survey results and overall conclusions in order to demonstrate compliance with radiological criteria for unrestricted release for basement structures, embedded piping, and penetrations.
Section 5 of this SER discusses NRCs evaluation of the Phase 2, Part 2 FSSR submitted on November 25, 2019 (ML19338B809) that contains five buried pipe SUs. The NRC submitted RAIs on both Phase 2 and Phase 3 on April 20, 2020 (ML20108E992). ZS responded to RAIs on May 15, 2020 (ML20147A128), along with revisions to 11 of the Phase 2 and Phase 3 release records (ML20167A279). ZS supplemented that response on June 4, 2020 (ML20167A280), and submitted revisions to certain release records as noted above. On June 30, 2020, Phase 2, Part 2 Rev 1 was submitted (ML20167A282).
4.1 FSS Results for Phase 2, Part 1 4.1.1 Description of SUs As summarized in the Section 1.1 of the Phase 2, Part 1 FSSR, The Phase 2 FSS Final Report encompasses the below grade basement structures for the Unit 1 and Unit 2 Containments, Turbine Building, Auxiliary Building, Spent Fuel Pool (SFP)/Transfer Canal, Forebay, Crib House, and the Wastewater Treatment Facility (WWTF).
These seven basements were divided up into 31 separate SUs as depicted in Figure 4-1 below.
Figure 4-1, Phase 2, Part 1 Basement Structures The SUs associated with Phase 2, Part 1 are listed in below.
Table 4-1, Zion FSSR Phase 2, Part 1 SUs (7 Basements (31 SUs))
SU Name Class(6) Size (m2) 01100(1) Unit No. 1 Containment above 565 ft. 1 2,465 01110(1) Unit No. 1 Containment Under Vessel Area 1 294 01111 Unit No. 1 Containment Incore-Sump Drain 1 0.86 01112 Unit No. 1 Containment Penetrations 1 242 02100(2) Unit No. 2 Containment above 565 ft 1 2,465 02110(2) Unit No. 2 Containment Under Vessel Area 1 294 02112 Unit No. 2 Containment Penetrations 1 242 03202 SFP/Transfer Canal 1 723 05100 Auxiliary Building 542 ft. Floor and Walls 1 7,226 05119 Auxiliary Building Embedded Floor Drains 1 294 05120 Auxiliary Building Penetrations 1 949 06100(3) Turbine Building Basement and Steam Tunnels 3 27,135 06105A(3) Circulating Water Discharge Pipe 3 1,075 09200(4) Unit Nos. 1 & Unit 2 Circulating Water Discharge Tunnels 3 4,868 06105B(4) Turbine Building Embedded Pipe 3 238 06107(4) Unit No. 1 Turbine Building Buttress Pit 3 1,596 06108(4) Unit No. 2 Turbine Building Buttress Pit 3 1,596 06201(4) Unit No. 1 Turbine Building 570 Diesel Fuel Storage 1 813 06202(4) Unit No. 2 Turbine Building 570 Diesel Fuel Storage 1 813 06209(4) Unit No. 1 Steam Tunnel Floor Drain 3 47 06210(4) Unit No. 2 Steam Tunnel Floor Drain 3 46 06211(4) Unit No. 1 Tendon Tunnel Floor Drain 3 51 06212(4) Unit No. 2 Tendon Tunnel Floor Drain 3 42 06213(4) Unit No. 1 Steam Tunnel East Valve House 1 304 06214(4) Unit No. 1 Steam Tunnel West Valve House 1 304 06215(4) Unit No. 2 Steam Tunnel East Valve House 3 240 06216(4) Unit No. 2 Steam Tunnel West Valve House 3 240 08100(5) Crib House 3 8,435 08401(5) Forebay 3 5,407 08102A&B(5) Unit No. 1 and Unit No. 2 Circulating Water Intake Pipes 3 4,412 09100 Waste Water Treatment Facility 1 1,124 (1) Both SUs included in Release Record for Unit No.1 Containment (2) Both SUs included in Release Record for Unit No. 2 Containment (3) The Release Record for the Turbine Building basement also includes the surface area of the Unit 1 and Unit 2 Steam Tunnels, the Unit No.1 and Unit No.2 Circulating Water Discharge pipe and the Unit No. 1 and Unit No.2 Circulating Water Discharge Tunnels (4) Included as an Appendixes to the Turbine Building basement Release Record (5) The Release Record for the Crib House also includes the FSS for the Forebay and the Unit No. 1 and Unit No.2 Circulating Water Intake Pipes.
(6) Denote Final SU Classification SUs associated with Unit No. 1 and Unit No. 2 Containment, SFP/Transfer Canal, WWTF and
the Auxiliary Building were designated as Class 1, while those associated with the Turbine Building, Crib House, Forebay, and Valve Houses were Class 3.
Figure 4-2, Phase 2 SU Release Record Designation Section 3.5.5.1 of the NRC Final SER for the LTP (ML18164A222) and Section 5.5 of the LTP covers the FSS of Basement Structures. The LTP details how ZS planned to conduct FSSs of the basements, including instrument use, classification of SUs, determination of sample size, statistical tests, and methods for evaluating elevated areas.
For the below grade structures, compliance with the unrestricted release criteria was demonstrated mainly using Canberra In-Situ Object Counting System (ISOCS) for direct measurements of building surfaces, hand-held instruments for scans/static measurements of penetrations, and pipe survey instruments for embedded piping.
ZS committed to using an OpDCGL for survey planning and implementation. This OpDCGL value represents a fraction of the Base Case DCGL (BcDCGL), which correlates to a TEDE of 25 mrem per year to an average member of the critical group (AMCG). The fraction of the BcDCGL that ZS assigned to the basement surfaces is described in Chapter 6 of the LTP and in TSD 17-004, Operational Derived Concentration Guideline Levels for Final Status Survey.
4.1.2 Radionuclides of Concern and DCGLs Section 5.1 of the LTP discusses ZS anticipated ROC and mixture fractures applicable to basement structures, embedded piping, and penetrations. ZS 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 4-2, Table 4-3, and Table 4-4 can be used to help orient the reader to the Base Case and Operational DCGLs for each ROC for basement structures, embedded piping, and penetrations, respectively.
Table 4-2, Base DCGLs for Basements (reproduced from LTP Table 5-3)
Auxiliary SFP/ Turbine Crib House CTMT Transfer WWTF Building Building /Forebay ROC Canal (1)
H-3 5.30E+08 2.38E+08 2.38E+08 1.29E+08 1.93E+08 1.71E+07 Co- 3.04E+08 1.57E+08 1.57E+08 7.03E+07 5.52E+07 2.83E+07 60 Ni- 1.15E+10 4.02E+09 4.02E+09 2.18E+09 3.25E+09 2.89E+08 63 Sr- 9.98E+06 1.43E+06 1.43E+06 7.74E+05 1.16E+06 1.03E+05 90 Cs- 2.11E+08 3.01E+07 3.01E+07 1.59E+07 2.13E+07 2.31E+06 134 Cs- 1.11E+08 3.94E+07 3.94E+07 2.11E+07 2.96E+07 2.93E+06 137 Eu- 6.47E+08 3.66E+08 3.66E+08 1.62E+08 1.23E+08 7.55E+07 152 Eu- 5.83E+08 3.19E+08 3.19E+08 1.43E+08 1.12E+08 5.74E+07 154 (1) The BcDCGL for the SFP/Transfer Canal set equal to the lower of either the Auxiliary Building or Containment BcDCGL.
The Containment BcDCGLSs were lower for all ROC, therefore the SFP/Transfer Canal BcDCGLs were set equal to Containment BcDCGLs.
Table 4-3, Base Case DCGLs for Embedded Pipe (reproduced from LTP Table 5-12)
Unit No. 1 & Unit No. 1 &
Auxiliary Turbine Bldg. Unit No. 1 &
Unit No. 2 Unit No. 2 Bldg. Basement Unit No. 2 Containment Steam Basement Embedded Tendon Tunnel ROC Incore Sump Tunnel Embedded Floor Embedded Floor Drains Embedded Embedded Floor Drains Drains Drain Pipe Floor Drains (pCi/m2) (pCi/m2) (pCi/m2) (pCi/m2) (pCi/m2)
H-3 N/A N/A 8.28E+09 N/A 1.61E+10 Co-60 7.33E+09 6.31E+09 5.47E+09 4.07E+10 1.06E+10 Ni-63 2.78E+11 1.96E+11 1.40E+11 1.26E+12 2.72E+11 Sr-90 2.41E+08 6.94E+07 4.98E+07 4.48E+08 9.70E+07 Cs-134 5.10E+09 1.43E+09 1.05E+09 9.22E+09 2.04E+09 Cs-137 2.68E+09 1.89E+09 1.37E+09 1.22E+10 2.67E+09
Unit No. 1 & Unit No. 1 &
Auxiliary Turbine Bldg. Unit No. 1 &
Unit No. 2 Unit No. 2 Bldg. Basement Unit No. 2 Containment Steam Basement Embedded Tendon Tunnel ROC Incore Sump Tunnel Embedded Floor Embedded Floor Drains Embedded Embedded Floor Drains Drains Drain Pipe Floor Drains (pCi/m2) (pCi/m2) (pCi/m2) (pCi/m2) (pCi/m2)
Eu-152 N/A N/A 1.28E+10 N/A 2.48E+10 Eu-154 N/A N/A 1.11E+10 N/A 2.16E+10 Table 4-4, Base Case DCGLs for Penetrations (reproduced from LTP Table 5-13)
SFP/ Crib Auxiliary U1/U2 Turbine Transfer House/ WWTF (1)
Radionuclide Bldg Containment Bldg Canal Forebay (1)
(pCi/m2) (pCi/m2) (pCi/m2) (pCi/m2) (pCi/m2) (pCi/m2)
H-3 3.99E+09 3.42E+09 4.84E+16 3.23E+09 N/A N/A Co-60 8.82E+07 2.26E+09 4.45E+08 1.76E+09 N/A N/A Ni-63 6.79E+10 5.78E+10 1.86E+14 5.48E+10 N/A N/A Sr-90 2.41E+07 2.06E+07 9.26E+10 1.94E+07 N/A N/A Cs-134 3.28E+08 4.32E+08 7.48E+08 4.00E+08 N/A N/A Cs-137 6.17E+08 5.66E+08 1.46E+09 5.29E+08 N/A N/A Eu-152 3.29E+08 5.26E+09 9.44E+08 4.06E+09 N/A N/A Eu-154 2.33E+08 4.58E+09 8.53E+08 3.58E+09 N/A N/A 4.1.3 FSS Results for Phase 2 Part 1 Table 4-5, below, has been reproduced from Table 5-1 Basic Statistical Properties of Phase 2, Part 1 SU Non-Parametric Measurements from the Phase 2 Part 1 Rev. 2 FSSR.
Table 4-5, Phase 2 Part 1 FSS Results
- of # Dose To Mean Max Mean SU Name Class Measure- OpSOF> SU OpSOF OpSOF BcSOF ments 1 (Mrem/yr)
Unit No. 1 CTMT above 01100 565 foot 1 173 0.124 1.156 1 0.019 0.463 Unit No. 1 CTMT Under 01110 Vessel 1 63 0.532 0.738 0 0.196 4.888 Unit No. 1 CTMT Incore 01111 Sump Drain 1 25 0.363 5.793 1 0.049 1.221 Unit No. 1 CTMT 01112 Penetrations 1 369 0.661 10.082 45 0.101 2.537 Unit No. 2 CTMT above 02100 565 foot 1 173 0.063 0.985 0 0.009 0.219 Unit No. 2 CTMT Under 02110 Vessel Area 1 57 0.147 0.457 0 0.106 2.650
- of # Dose To Mean Max Mean SU Name Class Measure- OpSOF> SU OpSOF OpSOF BcSOF ments 1 (Mrem/yr)
Unit 2 CTMT 02112 Penetrations 1 369 0.142 0.803 0 0.010 0.260 03202 SFP/Transfer Canal 1 80 0.139 1.843 2 0.033 0.829 Auxiliary Building 05100 Basement 1 453 0.143 2.189 16 0.075 1.868 Auxiliary Building Embedded Floor 05119 Drains 1 2816 0.170 0.839 0 0.007 0.170 Auxiliary Building 05120 Penetrations 1 730 0.405 10.082 45 0.037 0.927 Turbine Building 06100 Basement 3 55 0.245 1.346 1 0.022 0.539 Circulating Water 06105A Discharge Pipe 3 4 0.146 0.417 0 0.012 0.310 Unit Nos. 1 & 2 Circulating Water 09200 Discharge Tunnels 3 17 0.285 2.252 2 0.241 6.025 Turbine Building 06105B Embedded Pipe 3 148 0.011 0.028 0 0.001 0.011 Unit No. 1 Turbine 06107 Building Buttress Pit 2 8 0.011 0.034 0 0.001 0.023 Unit No. 2 Turbine 06108 Building Buttress Pit 2 7 0.010 0.022 0 0.001 0.021 Unit No. 1 Turbine Building 570 Diesel 06201 Fuel Storage 1 54 0.054 0.177 0 0.004 0.102 Unit No. 2 Turbine Building 570 Diesel 06202 Fuel Storage 1 54 0.043 0.228 0 0.004 0.091 Unit No. 1 Steam 06209 Tunnel Floor Drain 3 72 0.007 0.018 0 0.001 0.020 Unit No. 2 Steam 06210 Tunnel Floor Drain 3 63 0.002 0.003 0 0.000 0.006 Unit No. 1 Tendon 06211 Tunnel Floor Drain 3 61 0.018 0.074 0 0.000 0.009 Unit No. 2 Tendon 06212 Tunnel Floor Drain 3 47 0.014 0.016 0 0.000 0.007 Unit No. 1 Steam Tunnel East Valve 06213 House 1 28 0.448 4.213 2 0.051 1.285 Unit No. 1 Steam Tunnel West Valve 06214 House 1 28 0.239 1.817 1 0.033 0.816 Unit No. 2 Steam Tunnel East Valve 06215 House 3 21 0.096 0.327 0 0.008 0.205
- of # Dose To Mean Max Mean SU Name Class Measure- OpSOF> SU OpSOF OpSOF BcSOF ments 1 (Mrem/yr)
Unit No. 2 Steam Tunnel West Valve 06216 House 3 21 0.109 0.304 0 0.009 0.231 08100 Crib House 3 15 0.000 0.000 0 0.000 0.000 08401 Forebay 3 15 0.053 0.064 0 0.020 0.503 Unit Nos. 1 & 2 Circulating Water 08102 Intake Pipes 3 5 0.002 0.006 0 0.001 0.018 Waste Water Treatment Facility 09100 (WWTF) 1 74 0.013 0.236 0 0.013 0.335 Table 4-6, below, (reproduced from Phase 2, Part 1 FSSR, Rev 2, Table 5-4) presents the values for dose for surface, penetrations, embedded pipe and clean fill and the derived value for each basement. Section 4.3.9 of this SER discusses this table in further detail. The maximum basement dose was for the Unit No. 1 Containment; therefore, this value was used in the total compliance equation.
Table 4-6, Adjusted Basement Surface Areas for Area-Weighted SOF Calculation Basement BcSOFB BcSOFEP BcSOFPN BcSOFCF BcSOFBASEMEN Dose (mrem/yr)
T Unit No.1 Containment 0.222 0.049 0.102 0.071 0.443 11.11 Unit No. 2 Containment 0.122 0.000 0.010 0.071 0.203 5.071 Auxiliary Building 0.078 0.007 0.044 0.040 0.169 4.218 SFP/Transfer Canal 0.033 0.000 0.000 0.006 0.039 0.979 Turbine Building 0.068 0.001 0.002 0.063 0.134 3.340 Crib House/Forebay 0.006 0.000 0.000 0.063 0.069 1.723 WWTF 0.013 0.000 0.000 0.256 0.269 6.725 BcSOFBASEMENT = BcSOF (mean of FSS systematic results plus the dose from any identified elevated areas) for backfilled basements BcSOFB = BcSOF for structural SU(s) within the basement BcSOFEP = BcSOF for embedded pipe SU(s) within the basement BcSOFPN = BcSOF for penetration SU(s) within the basement BcSOFCF = BcSOF for clean concrete fill (if applicable) based on maximum MDC during URS 4.2 Phase 2 Part 1 Confirmatory/Inspection Survey Results From April 2016 through July 2018, the NRC staff, with support from the ORISE, performed
independent confirmatory surveys in the Turbine Building Basement, Waste Water Treatment Facility, Select Penetrations and Buried Piping, Containment and Auxiliary Buildings, Spent Fuel Pool, and Transfer Canal in support of Phase 2 Part 1 decommissioning.
4.2.1 Turbine Building Basement Confirmatory Survey, April 2016 In April 2016, NRC staff, with the support of ORISE, performed independent confirmatory surveys for the Turbine Building (TB) basement at Zion (ML18240A035). This surveying effort included gamma surface scans and in-situ gamma spectroscopy measurements of the TB basement. ORISE submitted their final summary report to the NRC in August 2016. Based on the results of the confirmatory survey, NRC issued RAIs to ZS. NRC concluded that the confirmatory survey did not identify issues that would preclude the FSS data for demonstrating compliance with the release criteria for these areas.
ORISE performed low-density gamma radiation scans of the accessible lower surfaces (floors and lower walls) inside the TB basement and in low-lying regions/accumulation points (i.e.,
sumps). Additionally, quantitative gamma radiation measurements collected during the surface scans inside the TB basement were used to select six judgmental and eleven random in-situ gamma spectroscopy measurement locations. Most of the TB basement gamma surface scans were not distinguishable from background. None of the randomly collected in-situ measurements identified ROCs above the MDC. Two judgmental in-situ measurements identified Cs-137 at concentrations which are a small fraction of the inventory limit.
Three sediment samples were collected at two elevations from locations exhibiting elevated detector response near the fire sump. Analysis showed that the samples exhibited Cs-137 and Co-60 concentrations above the analytical MDC. However, at the time of the surveys, the Zion LTP had not yet been approved. Therefore, there was not an applicable DCGL for direct comparison against the results of the sediment samples. In May 2020, ZS responded to NRC issued RAI-5c with explanatory information about this elevated sample. According to the analysis, one explanation for the Cs-137 concentration was that the radionuclide originated from embedded piping located close to the sample location. This section of piping was inaccessible at the time of surveying. In the RAI response, ZS stated that this elevated sample and the survey data for the accessible portions of the buried pipe have been accounted for in the final dose calculations and are consistent with the grouting criteria in the LTP.
Section 4.3.5 Turbine Sump Sediment Dose and Section 4.3.7 Commitment to Grout Embedded Piping and Penetrations of this SER provide more detail on NRCs evaluation of these elevated survey results.
4.2.2 Waste Water Treatment Facility, September 2018 In September 2018, the NRC staff, with the support of ORISE, performed independent confirmatory surveys for the Waste Water Treatment Facility (WWTF) at Zion (ML19053A677).
This surveying effort included volumetric concrete sampling. ORISE submitted its final summary
report to the NRC in February 2019. NRC agrees with ORISEs conclusion that confirmatory survey data did not identify issues that would preclude the FSS data for demonstrating compliance with the release criteria for these areas.
ORISE took 16 volumetric concrete samples in the WWTF. Concrete samples were collected from randomly and judgmentally selected locations using an electric concrete coring machine to a depth of up to 15 cm (6 inches), or until refusal. The samples were analyzed by gamma spectrometry for gamma-emitting fission and activation products based on a sample depth of 5.08cm. Eight of the 16 samples were randomly selected and analyzed for HTD radionuclides (Sr-90 and Ni-63).
Only one sample result identified had Cs-137 concentration above the analytical MDC, and further analysis of the other sections of the core (deeper than 5.08cm) yielded a result below the MDC. ORISE concluded that all individual confirmatory samples collected from the WWTF were below their respective Operational DCGL and, therefore, are also below the Base Case DCGL.
NRC agrees with ORISEs conclusion that additional investigation is unnecessary provided the overall magnitude of the confirmatory survey results.
4.2.3 Containment Buildings and Auxiliary Building, April 2018 In April 2018, the NRC staff, with the support of ORISE, performed independent confirmatory surveys for the remaining structures in the Containment Buildings and Auxiliary Building at Zion (ML18285A143). This surveying effort included surface scans, in-situ gamma spectrometry measurements, volumetric concrete sampling, and water and sediment sampling. ORISE submitted its final summary report to the NRC in October 2018 detailing the results of the survey.
In the Containment Buildings, surface scans were performed, and ISOCS measurements concrete samples were taken at random and judgmental locations. All individual in-situ measurements taken at all locations within the Containment Buildings were less than the Operational DCGL. For the Unit No. 1 Undervessel Area and Unit No. 2 Undervessel Area, ORISE found elevated H-3 levels via concrete sampling. The concrete samples were taken analyzed by gamma spectrometry for gamma-emitting fission and activation products. Certain concrete samples were processed and analyzed for Sr-90, Ni-63, and H-3. For the Unit No. 1 Undervessel Area, all individual ROC concrete sample concentrations were less than the Operational DCGL, with the exception of H-3. Three samples exceeded the Base Case DCGL for H-3. ORISE recommended that NRC evaluate the potential for tritium contamination greater than six inches in the Undervessel Area concrete. For the Unit No. 2 Undervessel Area, one sample indicated H-3 levels above the Operational DCGL.
NRC agrees with ORISEs conclusion that, based on the results of the confirmatory survey, no issues were identified that would preclude FSS data from demonstrating compliance with the release criteria for all radionuclides analyzed, except H-3. ORISE recommended that NRC
evaluate the potential for tritium contamination greater than six inches in the Undervessel Area concrete.
In the Auxiliary Building, ORISE performed scans (high- and medium-density scan coverage) and took nine random and six judgmental volumetric concrete samples of the remaining basement floor and the west wall near the former Hold-up Tank cubicle. The survey results indicated Cs-137 exceeding the Base Case DCGL at two locations. The ISOCS FSS measurements were less than the Operational DCGL. ORISE attributed this difference to the much larger area represented by the gamma spectrometry measurement relative to the concrete sample. The resulting upper bound of confirmatory gamma-emitting ROC SOF for the Auxiliary Building Floor was a small fraction relative to the DCGLs. Six samples were selected for HTD analysis to evaluate the surrogate ratios specified in the LTP; the analysis did not indicate that the approved ratios presented in the LTP were non-conservative.
The results from water and sediment sampling indicated that there was mobile radioactivity present in the Auxiliary Building basement. There was sand/sediment on top of the concrete near Sump Pit B. One DRP was identified and removed from a judgmental sediment sample that was on top of the concrete floor of the Auxiliary Building. The surveyor noted that the sediment material was fine and resuspendable in water. ORISE was unable to confirm the source of the contamination present in the sump where the samples were collected.
As a result of these confirmatory survey results, the NRC staff issued RAIs to request more information on possible H-3 contamination in the Containment Buildings and Auxiliary Building.
ZS provided additional information on its foundation and subsurface soil sampling effort. One sample identified H-3 at 8.51 pCi/g which did not trigger reassessment of insignificant radionuclide contribution per LTP Section 5.1. The RAI Responses also indicated that ZS calculation to estimate the actual insignificant radionuclide contribution demonstrated that the insignificant radionuclide contribution (IC) dose contribution was not exceeded (1.25 mrem/yr for all basement structures other than Containment Buildings, and 2.5 mrem/yr for Containment Buildings and soils).
Based on the risk significance of the elevated samples and ZS RAI response, NRC concludes that the confirmatory survey did not identify issues that would preclude the FSS data for demonstrating compliance with the release criteria for these areas.
4.2.4 Penetrations and Buried Piping, June 2018 In June 2018, the NRC staff, with the support of ORISE, performed independent confirmatory surveys for select penetrations and embedded piping in the Containment and Auxiliary Buildings at Zion (ML20029D896). This surveying effort included gamma surface scans, direct gamma measurements, and additional sampling inside penetrations and embedded piping. ORISE submitted its final summary report to the NRC in January 2020 detailing the results of the survey. NRC agrees with ORISEs conclusion that, based on the results of the confirmatory survey, no issues were identified that would preclude FSS data from demonstrating compliance
with the release criteria.
The penetrations selected during the confirmatory survey effort were based on the highest FSS SOF results of penetrations that will remain on-site. Table 4-7 below (reproduced from ORISE Confirmatory Survey Report Table 3.4) contains the penetrations selected for survey.
Table 4-7, Penetrations Selected for Confirmatory Survey Unit No.1 Containment Unit No. 2 Containment Auxiliary Building P035 Recirculating Sump Suction P235 Recirculating Sump Suction A011 Waste Disposal P036 Cavity Flood Sump Suction P236 Cavity Flood Sump Suction A023 Waste Disposal P037 Cavity Flood Sump Suction P237 Cavity Flood Sump Suction P123 Recirculating Sump Suction P323 Recirculating Sump Suction P124 Recirculating Sump Suction P324 Recirculating Sump Suction P125a In-Core Sump Discharge Pipe P325a,b In-Core Sump Discharge Pipe a Classified as embedded piping and, thus, DCGLs in Table 3.2 apply.
b This piping was removed during remediation and was not available for confirmatory survey.
Cesium iodide (CsI) and Sodium Iodide (NaI) pipe detectors were used to evaluate direct gamma radiation levels on interior penetration surfaces. Surface activity measurements were collected from both randomly and judgmentally selected locations. None of the piping or penetration interior direct measurements exceeded the most restrictive Base Case DCGL in any of the areas investigated.
A miscellaneous sample of residual material was collected from penetration P035 in Unit No. 1 Containment. The sample was collected by wiping a cloth over the bottom portion of the penetration interior totaling approximately 0.25 m2. The sample was analyzed by high-resolution gamma spectrometry for gamma-emitting Cs-134/137, Co-60, and Eu-152/154 and revealed the presence of Am-241. The sample was subsequently analyzed by alpha spectrometry for Am-241 after chemical separation. Am-241 had been deselected from FSS analysis based on an insignificant dose contribution. The Am-241 activity on the wipe, which represents the removable ROC portion, was at least an order of magnitude less than the more predominant gamma-emitters, Cs-137 and Co-60.
When performing surveys in Unit No. 2 Containment, ORISE noted that the measurement pairs trend similarly between the FSS and confirmatory measurements throughout the length of the penetration, except for P323. The confirmatory measurement data set is missing a peak at Location 1 that is present in the FSS data set. ORISE staff noted that there appeared to be loose concrete rubble in several of the survey locations. A possible explanation for the mismatched pair between the data sets is that loose concrete rubble containing contamination inside P323 was removed prior to the confirmatory survey.
Based on the results of the confirmatory survey, no issues were identified that would preclude FSS data from demonstrating compliance with the release criteria.
4.2.5 Spent Fuel Pool and Transfer Canal, July 2018 In July 2018, the NRC staff, with the support of ORISE, performed independent confirmatory surveys of the remaining structures and surfaces of the Spent Fuel Pool (SPF) and Transfer Canal at Zion (ML20027A238). This surveying effort included surface scans, in-situ gamma spectrometry measurements, and volumetric concrete sampling. ORISE submitted its final summary report to the NRC in January 2020 detailing the results of the survey. NRC agrees with ORISEs conclusion that, based on the results of the confirmatory survey, no issues were identified that would preclude FSS data from demonstrating compliance with the release criteria.
ORISE took 14 random and two judgmental in-situ measurements from the SPF. The only gamma-emitting radionuclides identified above their respective MDCs were Cs-137 and Co-60. All individual confirmatory in-situ measurements were below the applicable Operational DCGL and therefore, the applicable Base Case DCGL. Eight concrete core samples were taken from randomly selected in-situ gamma spectroscopy measurement locations. Concrete samples were segmented into 5cm increments and analyzed by gamma spectrometry for gamma-emitting fission and activation products. Portions of each concrete sample were then processed and analyzed for Sr-90, Ni-63, and H-3. None of the individual ROC concentrations were above their respective Operational DCGL and therefore, the applicable Base Case DCGL.
Based on the results of the confirmatory survey, no issues were identified that would preclude FSS data from demonstrating compliance with the release criteria.
4.3 NRC Staff Evaluation of Phase 2 Part 1 This section summarizes the major issues that were part of the NRC staffs RAIs for Phase 2, Part 1. These issues include assessment of concrete debris reuse as basement fill material, quality control samples, the process for investigation and reclassification, dose associated with the turbine sump sediment, verification of surrogate ratios and insignificant contributor dose, commitment to grout embedded piping and penetrations, and DCGLs applied for Zion Unit No. 1 and Unit No. 2 Containment Penetration grouting action levels.
4.3.1 Concrete Debris Reuse as Basement Backfill As part of decommissioning activities, ZS demolished all above grade buildings, and all foundations were either completely removed or demolished and removed to a depth of 3 feet below grade. ZS reused concrete debris from certain structures as backfill in basements.
As summarized in the LTP SER, In Section 5.7.1.12 of the LTP ZS discusses the intentions to reuse concrete from several demolished structures on-site and notes that prior to demolition the materials will be surveyed using the site unconditional release program with surveys that meet the statistical rigor and quality of MARSSIM. Section 5.7.1.12 of the LTP further notes that if the unconditional release surveys positively detect plant-derived radionuclides in any
concentration, then the concrete will not be used as clean fill, and in this case, it will be segregated, packaged and disposed of as low level radioactive waste.
The LTP, Chapter 3, describes ZS methodology for demolition of buildings that included the following:
- Prior to open-air demolition, ZS completed unconditional release surveys (URSs) of each structure in accordance with surveys as documented in (TSD)17-010, Rev. 1 Final Report - Unconditional Release Surveys at the Zion Station Restoration Project (ML18052A529 Pkg). For radiologically impacted structures, ZS performed Contamination Verification Surveys to verify that the radiological conditions of the structures met the criteria for open-air demolition as presented in TSD 10-002, Technical Basis for Radiological Limits for Structure/Building Open Air Demolition (ML15344A388).
- Concrete debris was processed to remove all exposed rebar and to ensure that individual debris pieces were smaller than 10 inches in diameter. The processed concrete debris was transported to a designated storage area where it was stockpiled for use as potential backfill material.
As part of the URS surveys, the surfaces were assigned a classification category commensurate with the standard MARSSIM classifications. Class 1 surfaces received a 100%
scan and Class 2 and Class 3 surveys received a scan coverage commensurate with Table 2 of TSD 17-010, Rev 1. The action level for the URS scan was based on the detector background plus the scan minimum detectable count rate (MDCR) of the instrument. Background was typically determined as the mean of five measurements taken within the survey area or taken of a representative non-radioactive reference material. The instrument alarm setpoint was set to the action level. When the action level was exceeded, an investigation was performed, which generally consisted of a portable gamma spectroscopy measurement (Canberra Inspector-1000 LaBr Detector) to qualify the activity.
As documented in TSD 17-010, the following structures were unconditionally released, and the concrete, following the structures demolition, was potential to be utilized as backfill:
- Chlorination/De-chlorination Buildings (North and South)
- Contractor Break Building
- Crib House
- East/West Service Building
- Engineering and Construction (ENC)
- Fire Training Buildings
- Interim Radwaste Storage Facility (IRSF)
- Mechanical Maintenance Training Center (MMTC)
- Nuclear General Employee Training (NGET)
- Old Gatehouse
- Old Sewage Lift Station
- South Gatehouse
- Turbine Building
- Unit No. 1 Containment Building (Exterior)
- Unit No. 2 Containment Building (Exterior)
- Vertical Concrete Cask (VCC) Pad The URS results for the 16 areas listed above (consisting of 115 SUs) are summarized in TSD 17-010, along with detailed records of the surveys in the Attachments.
The following seven basement structures received the debris as fill:
- TB Basement
- Auxiliary Building Basement
- Spent Fuel Pool (SFP)/Transfer Canal
- Crib House/Forebay
- WWTF
- Unit No. 1 Containment Basement
- Unit No. 2 Containment Basement After the basements were backfilled to the 588-foot elevation level, ZS committed to emplacing 3 feet of clean soil on top of the hard concrete debris fill. Chapter 5 of the LTP states, The structural surfaces that will remain at ZNPS following the termination of the license are constructed of solid steel and concrete which will be covered by at least three (3) feet of soil and physically altered to a condition which would not allow the remaining structural surfaces, if excavated, to be realistically occupied. As another example, Section 3.3.2 of the LTP states, The Turbine Building void was backfilled using concrete debris suitable for reuse as clean hard fill and/or clean fill to the original site grade and contours, with at least the top 3 feet as soil only.
The top 3 feet of fill will be soil only (i.e., concrete clean hard fill was only utilized as fill up to the 588 foot elevation).
The NRC staff note that the dose associated with concrete fill in basement excavations is derived directly from the detection limit associated with each backfilled basement. When the FSS of the TB occurred in March of 2016, it was performed at risk in accordance with Rev. 0 of the LTP, which was not approved. The survey designed included in Rev. 0 included Basement Investigations Levels (BILs) that were much higher than the conservative Operational DCGLs for basement structures that were included in the approved LTP (Rev. 2). When compared against the BILs, all measurements taken for the FSS of these SUs were less than a SOF of 0.5 and decommissioning decisions were made based upon those results. However, when compared to the Operational DCGLs in the approved LTP, five measurements taken during the FSS of the TB in 2016 exceeded 50% of the OpDCGL. No measurements exceeded the Base Case DCGLs. Additionally, the approved LTP included other commitments, such as the requirement to acquire concrete core samples for HTD ROC analysis. However, because the basement had already been backfilled before the LTP was approved, ZS did not perform
investigations nor assess if reclassification was required. By the time the discrepancy was identified, the TB basement had already been backfilled, and additional investigations were not possible. The NRC staff note that two measurements taken in the Unit No. 2 Circulating Water Discharge Tunnel were above the Operational SOF of one.
As a result, ZS assigned a dose value to backfill using the basement volumes and maximum allowable MDC of (5000 dpm/100cm2) during performance of URS. The doses assigned to the fill in the basements are documented in Table 4-8 (reproduced from Chapter 5, Table 5-21 of the LTP).
Table 4-8, Dose Assigned to Concrete Debris Fill Basement Structure Dose for Concrete Fill (mrem/yr)
Auxiliary Building 0.99 Unit No. 1 Containment 1.77 Unit No. 2 Containment 1.77 SFP/Transfer Canal 0.15 TB 1.58 Crib House/Forebay 1.57 WWTF 6.40 The concrete debris from Unit No. 1 containment exterior was stored in multiple locations across the site, including in some SUs where FSS had been completed. The concrete debris from Unit No. 1 and Unit No. 2 containment exterior was stored in certain SUs at the site during decommissioning. For SUs 12205A-E, the concrete debris was stored, removed, and then an FSS was reperformed on those SUs. In the response to RAIs, ZS indicated that SUs 12112, 12113, 12203A, 12203B, 12203C, and 12203D had debris temporarily placed in them, or transported through them, after FSS was completed. ZS, stated that the debris that was temporarily placed in SUs 12112, 12113, 12203A, 12203B, 12203C, and 12203D was comprised of concrete originating from the exterior of the Containment Buildings and was therefore considered low risk (ML21067A225). ZS reperformed FSS in those SUs that had concrete debris stored in them after their initial FSS. The NRC staffs evaluation of ZS isolation and control practices are discussed in further detail in Section 3.6 Isolation and Control of SUs Post-FSS.
4.3.2 Quality Control Samples In the LTP, ZS made commitments regarding quality control samples taken during FSS. The commitments outlined in Section 5.9 of the LTP, and the Quality Assurance Project Plan (QAPP) are summarized in the RAIs dated November 5, 2020 (ML20303A207). In summary, the LTP and QAPP contained commitments to perform quality control samples but lacked clarity on the type of quality sample (replicate versus duplicate samples) that measurements acquired with ISOCS or most pipe detector systems would be interpreted as. Also, although the QAPP and LTP did not discuss the potential use of K-40, ZS regularly compared results of K-40 for quality control samples when Cs-137 was either not present or not in agreement. Therefore, quality control was a subject of a RAI.
In the RAIs dated November 4, 2020 (ML20303A207), the NRC staff asked ZS how quality control (QC) ISOCS measurements were assessed, how the approach was in compliance with the QAPP, and to check for consistency in use of the resolution table from NRC Inspection Procedure (IP) 84750, Radioactive Waste Treatment, and Effluent and Environmental Monitoring (specifically reference QAPP sections 4.1.1 and 4.1.2 and 6.2.2.1 - uncertainty).
In the RAI response, dated November 11, 2020 (ML20351A143), ZS, while acknowledging that an ISOCS measurement is essentially a timed static measurement, claimed that since it also assesses the volumetric residual radioactivity concentrations in the media measured, that it was addressed similarly to duplicate and split samples in QAPP Section 4.2 and LTP Section 5.9.3.2 instead of a replicate measurement. In the QAPP, dated 09/24/19, duplicate and split samples are assessed using IP 84750, Revision dated March 1994, by applying the resolution table within it to assess adequacy of QC measurement agreement.
The NRC staff make the following observations regarding the QC measurements:
- It is more appropriate to define ISOCS measurements as replicate measurements versus duplicate or split samples, because they are taken with the same instrument, same settings, and same location (even if the instrument is calibrated to measure some assumed amount of volumetric contamination). Duplicate samples are two separate physical volumetric samples taken side by side using the same procedures and analyzed separately, while a split sample is one physical volumetric sample that is split and then analyzed separately.
- IP 84750 was rewritten in November 2019 (ML19270D639), and again underwent major revision in November 2020 (ML20290A843). Neither of these revisions contain the resolution table that ZS applied. Still, the NRC staff note that ZS QAPP predates the publication of the November 2019 revision, and no guidance on how to assess ISOCS quality control measurements had been issued at the time of the LTP given the relative newness of the technology.
- In the response to RAIs, ZS also provided a supplementary comparison that applied a
+/- 20% criteria to the (ISOCS) ISOCs QC measurements. Applying a straight +/- 20%
comparison criteria is not necessarily more or less appropriate than the resolution table; it is instead seen as another comparison that can be used to inform the decision. NRC staff note that in several of the instances where there was inadequate resolution or unacceptable agreement using the resolution table, the two measurements were within the +/-20% range. For those instances where the +/- 20% criteria nor the resolution table criteria were met, the results in almost every case were very close to or overlapping MDCs considering uncertainty.
- Absent specific guidance on how ISOCS quality control measurements should be assessed, ZS applied the 1994 version of IP 84750, interpreting ISOCS to be duplicate samples. In addition, ZS supplemented the information using a commonly applied criteria for comparing replicate measurements of +/-20%. Although ZS approach of using the outdated resolution tables for evaluating ISOCs QC measurements is
adequate in this case, it does not apply to all sites and may not be applicable to future sites.
- The NRC staff notes that updated guidance on this topic has been provided in Inspection Procedure 84750, Radioactive Waste Treatment and Effluent and Environmental Monitoring, dated November 5, 2020, with an effective date of January 1, 2021 (ML20290A843). This guidance states that results of the licensees inter-laboratory comparison programs should be reviewed to verify the adequacy of environmental sample analyses performed by ZS. Regulatory Guides 1.33 Quality Assurance Program Requirements (Operation), 1.21 Measuring, Evaluating, and Reporting Radioactive Material in Liquid and Gaseous Effluents and Solid Waste, and 4.15 Quality Assurance for Radiological Monitoring Programs (Inception through Normal Operations to License Termination) -- Effluent Streams and the Environment provide guidance for licensees participating in an intra-laboratory and inter-laboratory comparison program to verify the quality of analyses.
- Regarding the use of K-40 to compare quality control samples in the FSS reports, ZS explained its QC results by referencing K-40 values in the absence of positive concentrations of plant-derived radionuclides, without discussing additional aspects of their QA plan. The NRC staff note that the use of K-40 was not discussed in ZS approved QA plan. The QA plan is expected to be capable of measuring low levels of residual radioactivity in the presence of natural background and identifying the absence of residual radioactivity. Furthermore, a comparison of K-40 values alone is not an acceptable QC analysis for the lower energy radionuclides of interest. In the RAI response, ZS provided additional information on how quality assurance protocols were followed during collection and analysis of the samples, and further interpreted the data.
The NRC staff find the QC samples acceptable upon review of this additional information because quality assurance protocols were followed, and ZS explanation of why the QC checks failed the acceptance criteria for sample results greater than MDC.
4.3.3 Investigation Process Section 5.6.4.6 of the LTP states that areas exceeding investigation levels will be addressed by further biased sampling as necessary according to the investigation levels in Table 5-25. For Class 1 and Class 2 areas, the direct investigation level is greater than the Operational DCGL (OpDCGL). For Class 3 areas, the direct investigation level is greater than 50% of the OpDCGL.
During the review, the NRC staff identified that for some of the basement SUs in Phase 2, Part 1, ZS did not follow the process of investigations as outlined in the approved LTP.
In the RAIs, the NRC staff identified sample results that exceeded the investigation levels, but where no investigation had been conducted, for several of the SUs in Phase 2, Part 1, as described in Table 4-9 below. In the RAI response, ZS provided an evaluation of the potential dose impacts of areas that should have been investigated per LTP Section 5.6.4.6 but were not investigated.
Table 4-9, SUs Where Samples Exceeded Investigation Levels OpSOF of Samples Description/ Dose SU Exceeding Licensee Evaluation Classification Impacts Investigation Levels 06100B TB Steam OpSOF of 1.346 on Licensee assumed an 0.012 Tunnels/Class the floor in the Unit elevated area of 140.52 m.2 mrem/yr 3 No. 1 Steam Tunnel at the entrance to the East Valve House 06100 TB Valve Pit OpSOF of 0.941 at Licensee assumed the whole 0.005 and Fire the 510-foot Valve FOV was elevated which mrem/yr Sump/Class 3 Pit encompassed the 510-foot Valve Pit of 4.65 m2 was OpSOF of 0.891 in elevated.
the Floor Drain Sump Licensee assumed whole FOV was elevated which encompassed the entire area of the Floor Drain Sump of 18.58 m2 was elevated.
06213 TB Unit No. 1 4.213 As 100% areal coverage was None Steam Tunnel achieved with the FSS, the East Valve 1.515 elevated area was adequately House/Class 1 bounded to the area of the ISOCS FOV.
1100 Unit No. 1 1.156 As 100% areal coverage was None Containment achieved with the FSS, the Basement elevated area was adequately above 565 ft bounded to the area of the elevation/ ISOCS FOV.
Class 1 3202 Spent Fuel 1.356 As 100% areal coverage was None Pool Transfer achieved with the FSS, the Canal/Class 1 1.843 elevated area was adequately bounded to the area of the ISOCS FOV.
9200 Unit No. 1 and 2.252 Licensee assumed the 240.98 3.037 Unit No. 2 m2 of the floor area was mrem/yr Circulating 1.641 elevated.
Water Licensee assumed 694.58 m2 Discharge of the walls and ceiling were Tunnels (part elevated.
of TB Basement)/
Class 3
OpSOF of Samples Description/ Dose SU Exceeding Licensee Evaluation Classification Impacts Investigation Levels 5100 Auxiliary 16 measurements As 100% areal coverage was None Building resulted in an achieved with the FSS, the Basement OpSOF greater than elevated area was adequately Surfaces/ one, with a maximum bounded to the area of the Class 1 value of 2.19 ISOCS FOV.
For the Class 3 TB basement ZS applied FSS criteria associated with the Rev. 0 of LTP because the FSS was completed at risk in 2016 prior to Rev. 2 of the LTP being approved in September 2018. By the time ZS identified that investigations should have been triggered, the TB basement void had been completely backfilled and additional investigations were not possible. To compensate for this, ZS estimated the potential bounding dose for elevated areas and added it to the TB structure.
In the Class 1 basements (Unit No. 1 Containment, SPF Pool, and Auxiliary basement structures), ZS reason for not performing investigations was different. ZS performed FSS on the Class 1 using the final approved criteria. Elevated measurements were obtained but ZS did not conduct additional investigations because a Class 1 area received 100% coverage with the ISOCS measurements. Therefore, ZS concluded that all activity had been captured. The NRC staff note that if ZS did not intend to investigate areas above the investigation level in Class 1 basement structures where ISOCs measurements were used, this approach to investigations should have been part the review and approval of the LTP. Also, this lack of investigation represents a departure from typical MARSSIM approach.
For the Class 1 SUs, ZS stated in the RAI response that elevated areas identified in structural survey areas were bounded by the FOV of the ISOCS measurement as well as the ISOCS measurements taken adjacent to the elevated area. The ISOCS measurements did have sufficient overlap to adequately cover 100% of the SU. Therefore, any activity present would have been seen by one or more of the ISOCS measurements. However, the activity is averaged over the entire FOV in an ISOCS measurement. So, it is possible that there were smaller areas of activity within the FOV with higher concentrations.
The NRC LTP SER Section 3.5.5.9.1 (ML18164A222) highlighted this point stating:
The NRC notes that ISOCS should not arbitrarily be considered as a replacement for gamma scanning to locate elevated areas of activity. This is because ISOCS results represent an average of all detectable radioactivity within the instruments field of view, which can present challenges in delineating small areas of elevated activity within a relatively large field of view.
The LTP SER stressed the importance of ZS additional scan surveys as part of the overall FSS approach:
The licensee commits to using additional scan surveys and investigations to inform the FSS, and has noted in Section 5.5.2 of the LTP that characterization data, radiological surveys performed to support commodity removal and surveys performed to support structural remediation for open air demolition have and will continue to be used to verify that the contamination potential within each FSS unit is reasonably uniform throughout all walls and floor surfaces. As such, the NRC staff considers the additional scan surveys as a necessary part of the overall FSS process.
In the RAI response, ZS claims that no additional bounding measurements (investigations) would have been required per LTP Chapter 5, Section 5.6.4.6. While additional ISOCS shots may not have provided any additional useful information in terms of total activity present in Class 1 areas, the NRC staff disagree that any type of investigation was not required per the LTP. Section 5.6.4.6 of the LTP states that the suspect areas will be addressed by further biased surveys and sampling as necessary according to the approved investigation levels. For the areas that were above the OpDCGL, ZS could have performed additional scans of the area as an investigation. However, as outlined in TSD 14-022 - Use of In-Situ Gamma Spectroscopy for Final Status Survey of End State Structures, Revision 1, the location(s) of small isolated spots, if any, in contaminated areas such as the Auxiliary basement should be well known through the results of the scan surveys that will be performed to identify areas exceeding the 2 mR/hr open-air demolition criteria, and that after remediation of these areas additional scan surveys will be conducted to ensure that the remediation was successful providing additional information in regards to the potential for elevated areas at the time of FSS. In this instance, while investigations were required per the LTP, scans were conducted prior to FSS as per TSD 14-022, and therefore, significantly elevated areas would have been identified and remediated prior to FSS.
The NRC staff performed an independent evaluation of potential dose impact of the areas where ZS did not provide a potential dose impact. The evaluation assumed that the activity in the FOV was hypothetically concentrated in various sized areas smaller than the FOV and applied Equation 5-5 to estimate potential impact on dose. Because of the way in which Equation 5-5 weights dose by the elevated area by size, any increase in concentration is equally compensated by decrease in elevated area size. So, in these hypothetical scenarios, the potential added dose due to the elevated areas did not change the overall dose assigned to the SU. ZS had committed to remediating any localized areas that were above the Base Case DCGLs. Given the measurement values, all the activity in the ISOCs measurement would have had to have been limited to a small fraction of the FOV for the concentration to be above the Base Case DCGLs. If this had been the case, it would have been identified by the scans performed prior to FSS as per TSD 14-022.
The NRC staff finds that the incremental dose added to Class 3 SUs in the TB is adequate to bound the elevated areas and compensate for the inability to perform investigational measurements as required by the LTP. For the Class 1 SUs, NRC staff conclude that the LTP required investigations when investigation levels were triggered. However, ZS conducted scans of the surfaces prior to FSS which would have aided in identifying significantly concentrated
areas.
4.3.4 Reclassification In the LTP, Section 5.6.4.6.1, Remediation, Reclassification, and Resurvey discusses criteria for when a SU might be reclassified. In the RAI response, licensee clarified that actions in Table 5-26 of the LTP are only required when the statistical test fails or when an investigation confirms residual radioactivity in excess of 50 percent of the OpDCGL. The ambiguous language in the LTP regarding the use of Table 5-26 muddles the understanding of how it was intended to be implemented. For example, if the table were only intended to be implemented after an investigation confirmed residual radioactivity in excess of 50 percent of the OpDCGL, then the row indicating reclassification based on samples between 1% but below 50% would not be necessary. Given the ambiguity surrounding the intent of Table 5-26, the NRC staff independently assessed the potential reclassification of SUs following the typical MARSSIM approach.
Given that one measurement of the Turbine Basement Unit No. 1 Steam Tunnel was above 50% of the OpDCGL, ZS should have investigated that measurement and determined whether reclassification was appropriate, as per Section 5.6.4.1 of the LTP. As described above, ZS did not investigate that measurement because they were applying criteria from Rev. 0 of the draft LTP, which were greater than the ultimately approved criteria in Rev. 2 of the LTP. However, the elevated measurement associated with the Steam Tunnel was at the entrance to the East Valve House, and the East Valve House was appropriately reclassified to Class 1. The Turbine Basement FSS was conducted in April 2016, but demolition of the steam tunnel valve houses occurred nearly two years after the Turbine basement structure. When ZS began the FSS of the East and West Steam Tunnel Valve Houses, they identified several areas where measurements exceeded 50% of the OpDCGLs. So, according to the reclassification process in Table 5-26 of the LTP, the Unit No. 1 East and West Steam Tunnel Valve Houses, SUs 06213 and 06214, were reclassified from Class 3 to Class 1, and the FSS was redesigned accordingly. Therefore, the NRC staff finds the classification level of the Turbine Basement Steam Tunnel reasonable given that there was only a single measurement that exceeded 50% of the OpDCGL, and it was at the entrance to the East Valve House which was Class 1.
Similarly, according to the LTP, ZS should have investigated whether reclassification of other portions of the TB (i.e., Valve Pit, Fire Sump, and the Circulating Water Discharge Tunnel) was appropriate given that some measurements were above 50% of the OpDCGL. The Valve Pit and Fire Sump are relatively small areas that received adequate coverage from the FOV of the judgmental ISOCs measurements, thereby providing a level of coverage that is akin to Class 1 area.
The Circulating Water Discharge Tunnels were the main authorized effluent release pathway for the discharge of treated and filtered radioactive liquid effluent to Lake Michigan. The release of effluent during decommissioning occurred at the west end of the Unit No. 2 Discharge Tunnel in the steel lined area under the 12-foot diameter down-comer pipes. Judgmental measurements
B3-09200B-FRFC-005-GD and B3-09200BFRCC-008-GD were taken on the floor under the Unit No. 2 down-comer pipe where the effluent was released during decommissioning. For the Circulating Water Discharge Tunnels, all FSS ISOCS measurements were less than an OpSOF of 0.5 with the exception of the area under the Unit No. 2 down-comer pipe. As shown in Figure 4-3, fourteen (14) judgmental ISOCS measurements were taken within the Unit No. 1 and Unit No. 2 Circulating Water Discharge Tunnels, which equated to 392 m2 or 3% of coverage of the entire surface area of the tunnels (4,868 m2). While the OpSOF was greater than one for the measurement near the Unit No. 2 down-comer pipe, the BcSOF was less than one for these two measurements, so remediation was not required. Given that the contamination was localized below the Unit No. 2 down-comer pipe and since ZS bounded the potential elevated area and dose from this localized area, the NRC staff finds ZS failure to investigate and potentially reclassify the Circulating Discharge Tunnels acceptable.
Figure 4-3, Unit No. 1 and Unit No. 2 Circulating Water Discharge Tunnels Judgmental Measurements
Figure 4-4, Unit No. 2 Circulating Water Discharge Tunnel Judgmental Sample Locations and Elevated Area Bounded Locations 4.3.5 Turbine Sump Sediment Dose The ORISE confirmatory survey of the TB states that all three samples from the TB basement fire sump exhibited detectable concentrations of Co-60 and Cs-137 in the sediment. The maximum concentration in the sediment was 34.5 pCi/g for Cs-137 and 0.181 for Co-60. Also, the report states that survey measurements at the 10-foot elevation of the fire sump (24,000 cpm) were elevated in comparison to background count rates (5,000 to 7,000 cpm).
In response RAIs (ML20147A128), ZS calculated the potential dose impact to an inadvertent intruder (well-driller scenario) upon the TB fire sump. This evaluation included a justification for why it is or is not ALARA to not have further remediated the sediment from the sump.
Specifically, ZS added 0.18 mrem/yr to the total dose of the Turbine basement (SU 6100). ZS described the worker safety and confined spaces considerations that made further remediation beyond the 2 inches that remained post remediation not practical. The NRC staff reviewed the dose calculation and ALARA justification and finds it acceptable.
4.3.6 Surrogate Ratios and Insignificant Radionuclide Contribution (IC)
In the response to RAIs (ML20147A128), ZS provided additional information on their commitments in LTP Section 5.1 for analyzing 10% of all media samples, collected during continuing characterization, for the full initial suite of radionuclides to verify the IC dose and HTD ratios. The NRC staff reviewed ZS calculations to estimate the actual IC dose for each continuing characterization sample result to verify that the calculations demonstrate that the IC dose contribution was not exceeded (1.25 mrem/yr for all basement structures other than Containment Buildings, and 2.5 mrem/yr for Containment Buildings and soils).
In the response to RAIs (ML20147A128), ZS provided additional justification for why the applied HTD surrogate ratios are representative, for those SUs where the commitment to analyze samples for the HTD ROCs (Sr-90 and Ni-63) in 10% of the samples was not consistently followed.
In the response to RAIs, ZS acknowledged that a specific requirement in Revision 2 of the LTP was not followed, given that the TB FSS was performed under Revision 0 of the LTP.
Specifically, ZS did not collect concrete cores at 10% of the measurement locations during the FSS of the TB and Crib House. To address this discrepancy, ZS retrieved two concrete cores from the sample archive that were taken in the TB (concrete core B2-06207-CJFC-002-CV and B2-06104-CJFC-003-CV) and sent them to Eberline Analytical for full-suite analysis. In the response, ZS stated that the only plant-derived radionuclides detected in concrete core samples B2-06207-CJFC-002-CV were residual concentrations of H-3 and Cs-137. In sample B2-06104-CJFC-003-CV, both Np-237 and Cm-243/244 were positively detected at residual concentrations; however, the residual detectable concentrations had no consequence on mixture, IC dose adjustments, or ratios. NRC reviewed the Eberline Analytical data and IC dose calculations. The NRC staff note that Tc-99 was also positively identified. However, the positive detects above MDC in many cases would be negative considering the uncertainty. Therefore, there was still no consequence on the IC dose adjustments or ratios.
4.3.7 Commitment to Grout Embedded Piping and Penetrations In the RAIs, the NRC staff noted that ZS did not consistently implement the commitment in Section 5.5.5 of the LTP to grout embedded piping or penetrations that meet specific survey data criteria. In response, ZS, provided an estimated dose consequence attributable to not grouting the embedded piping or penetration where the commitment was not followed. The two pipes in question were the Unit No. 1 Equipment Drain Sump, pipe #3, position 0, and TB Floor Drain Sump, pipe #5, position 2. As a result, ZS added a dose of 0.083 mrem/yr to the mean dose for the TB for two of its pipes that should have been grouted but were not. The Release Record for the TB (SU 06100) was revised accordingly. The NRC staff reviewed the dose assessed for these two pipes and verified the calculation.
The confirmatory survey performed by ORISE on the TB basement indicated slightly elevated radiation levels at the ISOCS-J-03 location. Further investigation with a Nal detector revealed that the source of the direct gamma radiation was originating from two pipes in the floor. Further discussions with ZS and ORISE during the review process revealed that these pipes were only 1-2 inches in diameter and therefore could not be part of a process system. The piping was most likely electrical conduit piping. The only embedded piping that remained in the TB at the time of FSS were equipment or floor drain piping that were 4 or 6 in diameter. ZS attributed the slightly elevated readings to dirt and debris that concentrated around the conduit openings. The NRC staff finds this explanation reasonable given conversations with the ORAU technician regarding the size of the piping. Furthermore, the ISOCS measurement taken directly over the elevated readings identified ROC at less than 1% of the OpDCGLB (basement) for the Turbine floor and walls.
4.3.8 Comparison to DCGLs for Unit No. 1 and Unit No. 2 Containment Penetrations As part of the review, the NRC staff noted that ZS compared survey data to Containment DCGLs for Unit No. 1 and Unit No. 2 containment penetrations, which is not consistent with ZS
commitment to compare survey data to the most limiting DCGL of the two basement surfaces that interface with the penetration. Therefore, the NRC staff asked ZS to re-evaluate the remediation and grouting action levels by applying the lesser Base Case DCGLPN (Pentrations) for each ROC of the two basements and the most limiting Operational DCGLB of the two basements for each ROC where a penetrations interface.
In the revised approach that reflects LTP commitments, slightly more dose is assigned to the Containments and less to the Auxiliary Building and Turbine Building. The most limiting basement structure for the compliance equation remains the Unit No. 1 Containment.
In Unit No. 1 Containment and Unit No. 2 Containment, there were 4 and 3 respective additional penetrations that would have required grouting when compared to the most limiting OpDCGLB.
However, following FSS, all these penetrations were physically removed in their entirety. In the Auxiliary Building and TB, no additional penetrations would have required grouting when compared to the most limiting OpDCGLB. The NRC staff reviewed ZS reevaluation of grouting requirements and finds ZS actions acceptable given that all the penetrations that would have required grouting were physically removed.
4.3.9 Apparent Transcription Error Related to Maximum Dose in Final Status Survey Report The FSSR for Phase 2, Part 1 Rev. 2 (ML21067A204) presents the Adjusted Basement Surface Areas for Area-Weighted SOF Calculation for total compliance dose from all media, recreated as Table 4-6 in Section 4.1.3 of this SER. Based on this table, the Base Case SOF value for the Unit 1 Containment basement is 0.443, equating to a dose of 11.080 mrem/yr. However, Section 14 of the Release Record for the Unit 1 Containment SUs 01100 and 01110 (ML20167A285) reports the Base Case SOF value for the Unit 1 Containment as 0.444, equating to a dose of 11.105 mrem/yr.
NRC staff believe this discrepancy to be an apparent transcription error and subsequent quality control error between the release record and Phase 2, Part 1 FSSR. This survey unit is of particular importance because it is the Maximum SOF for a backfilled Basement FSS unit (including surface, embedded pipe, penetrations, and fill), and therefore will be used in the total compliance dose calculation.
Because these values are only slightly different and there is almost no impact to the overall dose, NRC staff will use the higher of the two values, namely the Base Case SOF of 0.444, for the Unit 1 Containment Survey Unit dose as the highest dose to basement structures.
Therefore, this value will be used to evaluate the total compliance dose for the Zion site as it relates to the 25 mrem/yr dose limit required by 10 CFR 20.1402. See Section 7.4 for NRC staffs evaluation of final compliance dose.
4.4 Summary of Conclusions for FSS Phase 2 Part 1 The FSS results demonstrated that any residual radioactivity remaining in the SUs addressed by the Phase 2, Part 1 Final Report resulted in a TEDE to an AMCG that does not exceed 25 mrem per year, and the residual radioactivity has been reduced to levels that are ALARA, which correspond to the release criterion for license termination for unrestricted use specified in 10 CFR 20.1402, Radiological criteria for unrestricted use and support the release of these areas from the 10 CFR 50 license.
The NRC staff noted multiple instances where ZS did not follow requirements approved in the LTP. ZS did not perform additional investigations in areas where surveys exceeded investigation levels in Class 1 areas for several SUs in the TB, Unit No. 1 Containment Building, SPF Pool Transfer Canal, and Auxiliary Building. ZS did not collect concrete cores at 10% of the measurement locations during the FSS of the Turbine Building and Crib House. ZS did not consistently implement the commitment to grout embedded piping or penetrations that meet specific survey data criteria. However, NRC has determined that the SUs in FSSR Phase 2 Part 1 meet the criteria for unrestricted release because ZS demonstrated, and the NRC staff independently confirmed, that each SU was below 25 mrem/yr plus ALARA.
Most contaminated and non-contaminated systems were disassembled, removed, packaged, and shipped off-site as waste. A contamination verification survey was performed to identify areas requiring remediation to meet the open-air demolition limits prior to demolition.
Additionally, concrete inside the liner above the 565-foot elevation containing all activated and contaminated concrete was removed from the interiors of both Containment Buildings prior to demolition. Because the vast majority of residual radioactivity remaining in the structures after open-air demolition and concrete removal from the Containment basements was located in the 542-foot elevation floor of the Auxiliary Building, ZSs ALARA assessment focused on this area.
NRC staff agree that FSS activities performed in relation to the release of SUs in Phase 2, Part 1 meet the requirements to reduce residual radioactivity to levels that are ALARA. See Section 7.3 of this SER for more detailed ALARA evaluation.
Because of the aforementioned apparent transcription error between the FSSR for Phase 2, Part 1 (ML21067A204) and the Unit 1 Containment Release Record (ML20167A285), NRC used the higher SOF associated with the reported data. The Maximum SOF of 0.444 for backfilled basements including basement surfaces, embedded piping, penetrations, and fill was for Unit No. 1 Containment which equated to a dose of 11.1 mrem/yr. The NRC staff note that the dose from basement substructures is the highest dose contribution of any individual source but is still below the regulatory limit of 25 mrem/yr TEDE from all dose contributions. Therefore, the SUs in Phase 2, Part 1 are acceptable for unrestricted release.
5 BURIED PIPING In June 2020, ZS submitted Revision 1 of FSSR Phase 2 Part 2 (ML20167A282). This submittal included survey results and overall conclusions in order to demonstrate compliance with
radiological criteria for unrestricted release for buried piping.
This section of the SER will discuss the contents of the submission as well as the NRC staffs independent review for compliance with radiological criteria for PSR.
5.1 FSS Results for Phase 2, Part 2 5.1.1 Description of SUs Section 5 of the LTP indicates that certain below-ground structures, such as buried pipes, will remain on-site at the time of license termination, and will require a FSS. Buried piping is pipe that runs through soil. Buried pipe SUs consisted of various pipe lengths and sizes, ranging from 4.5-inch to 20-inch inside diameters. The residual radioactivity in buried piping located below the 588-foot grade that was scheduled to remain on-site and require FSSs is discussed in LTP Chapter 2, Section 2.3.3.7, and Attachment F to ZS TSD 14-016, Description of Embedded Pipe, Penetrations, and Buried Pipe to Remain in Zion End State. TSD 14-016 lists buried pipe systems, along with their anticipated end state condition at the time of license termination and noted that no additional buried pipes were intended to be added to the list.
Since the issuance of TSD 14-016, several buried pipe sections that were anticipated to remain on-site were removed and disposed during decommissioning activities. The buried pipes that remain on-site are addressed in this section of the SER. These buried pipe systems are shown below in Figure 5-1 (copied from the Phase 2, Part 2 Final Report).
Figure 5-1, Buried Piping Systems
A total of five buried piping systems were identified by ZS. These systems are the Condensate Feedwater Supply and Recirculation, Primary Water Supply Header, Diesel Generator Heat Exchangers Service Water Supply and Service Water Return, Service Water Supply Header, and North Yard Storm Drain. Table 5-1 provides the SU number, SU classification, area of pipe within each SU, and the corresponding pipe identification number.
Table 5-1, Zion FSSR Phase 2, Part 2 SUs Area SU Name Class(1) Pipe ID (m2)
Condensate Feed Water Supply and T-103, T-105, 00101A 3 228 Recirculation Buried Pipe and T-106 Primary Water Supply Header T-095 00101B 2 29 T-095 and T-102 and T-102 Buried Pipe AO-27, AO-28, Diesel Generator Heat Exchangers AO-30, AO-31, 00101F Service Water Supply and Service 3 89 TO-32, and Water Return Buried Pipe TO-33 Service Water Supply Header CO-26 00101H 3 489 CO-26 and CO-29 and CO-29 Buried Pipe North Yard Storm Drain Buried 00150A/B&C 2 203 NA Piping ZS changed the initial designation of the buried piping system from one large SU, 00101A, to eight different piping systems, 00101A through 00101H, to improve the distinction between these piping systems in the FSS database. Table 5-2 references the survey design and the number of FSS measurements for each of the buried piping systems (reproduced from Tables 4-4 and 5-1 of the FSSR for Phase 2, Part 2 (ML20167A282).
Table 5-2, Survey Design and Results Summary SU No. 00101A 00101B 00101F 00101H 00150A/B&C Diesel Generator Condensate Heat Exchangers Primary Feed Water Service Water Service Water North Yard Water Supply SU Name Supply and Header Supply and Supply Header Storm Drain Recirculation Service Water Buried Pipe Buried Piping Buried Pipe Buried Pipe Return Buried Pipe AO-27, AO-28, T-103, T-105, AO-30, AO-31, CO-26 and CO-Pipe ID No. T-106 T-095, T-102 29 NA TO-32, TO-33 Surface Area 288 29 89 489 203 (m2)
SU No. 00101A 00101B 00101F 00101H 00150A/B&C Number of Measurements 257/18/275 253/17/270 256/17/273 132/7/139 272/18/290 (Static/ QC/
Total)
One One One One One measurement measurement measurement measurement measurement every foot of Spacing every foot of every foot of every 2 feet of every 2 feet of accessible accessible pipe accessible pipe accessible pipe accessible pipe pipe One Sufficient Sufficient Sufficient Sufficient measurement measurements measurements measurements measurements Scan every foot of for 10% areal for 10% areal for 10% areal for 10% areal Coverage accessible coverage coverage coverage coverage pipe Classification Non-(Initial/Final) 3/3 3/2 3/3 3/3 Impacted/2 Gross Investigation Gross Gamma
> 0.5 OpDCGL Gamma > 0.5 OpDCGL > 0.5 OpDCGL Level OpDCGL OpDCGL 5.1.2 Radionuclides of Concern and DCGLs Section 5.1 of the LTP discusses ZS anticipated ROC and mixture fractures applicable to buried pipe systems. The final suite of ROCs was developed using results of concrete core analyses from the Containment and Auxiliary Building, as documented in TSD 14-019, Radionuclides of Concern for Soil and Basement Fill Model Source Terms. Section 5.2.11 of the LTP notes that the final ROCs are Co-60, Cs-134 and Cs-137, Ni-63 and Sr-90 but that Eu-152, Eu-154, and H-3 are not applicable to buried pipes. Table 5-3 lists the ROCs (reproduced from Table 5-2 of the LTP).
Table 5-3, Radionuclides of Concern for Buried Piping Dose Significant Radionuclides and Mixture Radionuclide Percent of Total Activity Co-60 0.92%
Cs-134 0.01%
Cs-137 75.32%
Ni-63 23.71%
Sr-90 0.05%
Continuing characterization was expected to occur in potentially contaminated buried pipe systems that would remain on-site after the license is terminated. ZS verified the fractions by performing a continuing characterization process during decommissioning, as described in Section 5.3.4.4 of the LTP. In a letter dated May 15, 2020, ZS provided additional information on the continuing characterization using a sediment sample collected from the North End Storm
Drain buried piping system (ML20147A128). The sediment sample (L2-10214C-RJGS-001-SM-A) was sent to an off-site radioanalytical laboratory (Eberline Analytical) for an analysis of the full-suite HTD radionuclides. The results of the report indicate that surrogate ratios do not require adjustment, per Section 5.1 of the LTP. No other samples for continuing characterization of buried piping systems were available because the piping systems were flushed to remove sediment and debris before FSS were performed. Characterization surveys were not performed in any of the buried piping systems because no sediment samples were available. Also, ZS stated in its response that scan surveys of pipe openings indicated that minimal residual radioactivity was present in the buried piping systems.
For decommissioning of the Zion facility, demonstration of compliance is accomplished through summation of doses from buried pipes, basements, soils, and groundwater source terms. The NRC evaluation of and independent analysis of buried piping DCGLs is contained in Section 3.6.5.3 of the NRC staffs SER for the LTP. The NRC staff found the exposure scenarios (excavation, in-situ unsaturated and in-situ saturated), input parameters, and uncertainties in the modeling analysis acceptable for developing the buried piping DCGLs.
The Operational DCGL for buried piping was based on assigning an a priori fraction of 0.256 of the dose limit. The Base Case and Operational DCGLs are summarized in Table 5-4 below (reproduced from Table 5-9 of LTP).
Table 5-4, Base Case and Operational DCGLs for Buried Piping (dpm/100cm2)
Radionuclide Base Case Operational Co-60 2.64E+04 6.76E+03 Cs-134 4.54E+04 1.16E+04 Cs-137 1.01E+05 2.59E+04 Ni-63 4.89E+07 1.25E+07 Sr-90 4.50E+04 1.15E+04 During FSSs, ZS inferred the concentrations of the HTD radionuclides by using Cs-137 as the principle surrogate radionuclide for Sr-90, and Co-60 as the principle surrogate radionuclide for Ni-63. The mean, maximum and 95% UCL of the surrogate ratios calculated in TSD 14-019 are presented in Table 5-5 below.
Table 5-5, Surrogate Ratios for Buried Piping Ratio Mean Max 95% UCL Ni-63/Co-60 44.143 180.450 154.632 Sr-90/Cs-137 0.001 0.002 0.002 The maximum ratios were used in the surrogate calculations during buried piping FSSs. The surrogate Base Case DCGLs and surrogate Operational DCGLs for buried piping are summarized in Table 5-6 below.
Table 5-6, Surrogate DCGLs for Buried Piping (dpm/100cm2)
Radionuclide Base Case Operational Co-60 2.41E+04 6.16E+03 Cs-134 4.54E+04 1.16E+04 Cs-137 1.01E+05 2.58E+04 Using the surrogate DCGLs listed in Table 5-6 and applying the gamma radionuclide mixture from TSD-14-019, ZS calculated an adjusted gross gamma Operational DCGL of 2.49E+04 dpm/100cm2 for the FSSs of buried pipe systems.
ZS applied a SOF approach to evaluate whether the total dose from all radionuclides will be less than 25 mrem/yr and thus meet the unrestricted release criterion. Since several ROCs were identified for buried pipe systems, a SOF approach was used to account for dose contributions from each ROC and ensure the total dose from all ROC did not exceed the dose criterion. The SOF was applied for survey data evaluation and statistical tests since multiple radionuclide-specific measurements were performed or the concentrations inferred based on mixture ratios.
For buried pipes, areas of elevated activity are defined in this context as any area identified by measurement/sample (systematic or judgmental) that exceeds the Operational DCGL but is less than the Base Case DCGL. The SOF (when using the Operational DCGL) for a systematic or judgmental measurement/sample may exceed one without remediation as long as the SU passes the Sign Test and the mean SOF (when using the Operational DCGL) for the SU does not exceed one. For buried pipes, if the SOF for a sample/measurement(s) exceeds one when using Base Case DCGLs, then remediation is required.
5.1.3 FSS Results for Phase 2, Part 2 Table 5-7 below has been reproduced from Table 5-1 Basic Statistical Properties of Phase 2, Part 2 Survey Unit Non-Parametric Measurements from the Phase 2 Part 2 FSSR.
Table 5-7, Phase 2, Part 2 FSS Results
- of Mean Max # Mean Dose To SU Name Class Measure- OpSOF OpSOF OpSOF BcSOF SU ments >1 (Mrem/yr)
Condensate 275 0.320 0.493 0 0.082 2.052 Feed Water 00101 Supply and 3 A
Recirculation Buried Pipe Primary 270 0.784 1.506 53 0.227 5.674 Water Supply 00101 Header T-095 2 B
and T-102 Buried Pipe 00101 Diesel 3 273 0.144 0.488 0 0.037 0.922
- of Mean Max # Mean Dose To SU Name Class Measure- OpSOF OpSOF OpSOF BcSOF SU ments >1 (Mrem/yr)
F Generator Heat Exchangers Service Water Supply and Service Water Return Buried Pipe Service Water 139 0.127 0.288 0 0.033 0.814 Supply 00101 Header CO- 3 H
26 and CO-29 Buried Pipe North Yard 290 0.017 0.276 0 0.027 0.683 00150A Storm Drain 2
/B&C Buried Piping After the FSS was completed in May 2017, ZS assessed the survey data and determined that survey measurements were higher than expected in multiple SUs, based on process knowledge of this piping system. ZS decided to perform an additional study to determine whether another source of radiation was present and possibly contributed to ambient radiation levels during the FSS. In August 2019, ZS surveyed clean sections of pipe to obtain a new ambient background level after radioactive commodities were removed from the Unit No. 2 Containment and Auxiliary Building and staged near the FSS location. This subsequent survey determined that ambient radiation levels were elevated in the vicinity where the FSS was performed in May 2017, and that the ambient radiation levels were significantly lower in the same site location two years later.
The FSS Release Record was unclear whether ZS took credit for the reduced background radiation levels measured in August 2019 in its assignment of dose from this SU. In response to an RAI by the NRC staff on April 20, 2020, ZS clarified that background data was included in the release record as information only and was not used to demonstrate compliance for this SU (RAI number 8; May 15, 2020 letter; ML20147A128). ZS submitted a revised release record for this SU as an attachment to its letter.
In SU 00101F, Diesel Generator Heat Exchangers Service Water Supply and Service Water Return, seventeen replicate measurements were acquired, in addition to the 256 systematic measurements. Two of the replicate measurements were not within the acceptance criteria for a static measurement, which is 20 percent of the original measurement value. One measurement was approximately 40 percent less than the original measurement, and one measurement was 20.3 percent greater than the original measurement. All measurements were below 50 percent of the DCGL, and ZS determined that no further action was necessary. The NRC staff noted that there was an electronic malfunction of the survey instrument that prevented the survey
instrument from downloading stored survey data. However, data was manually recorded during the performance of the FSS and was used to document survey results. The survey instrument passed the post-use operation checks. ZS determined that this malfunction did not contribute to the two replicate measurement exceedances. Also, the two replicate measurements that did not meet the 20 percent acceptance criteria were in different pipe sections, and one replicate measurement exceeded the acceptance criterion by a small margin of 0.3 percent. In addition, ZS acquired significantly more measurements in this SU than were necessary for a Class 3 survey.
In SU 00150A/B&C, North Yard Storm Drain, an additional 18 replicate measurements were acquired for quality control purposes. Two replicate measurements did not fall within 20 percent of the original measurement. One replicate measurement from the 8-inch ID pipe between CB-4 and CB-5 at the 20-foot measurement location was approximately 32 percent less than the original measurement. One replicate measurement in the 12-inch ID pipe at CB-7 at the 8-foot measurement location was approximately 31 percent less than the original measurement. ZS verified that the survey instruments used in the survey passed the post-use response check.
The NRC staff notes that all measurements taken in this SU were below 50 percent of the DCGL.
All measurements taken in SUs 00101A, 00101F, 00101H, and 00150A/B&C were below an Operational SOF of one. For the Primary Water Supply Header SU 00101B, the average Operational SOF for this was 0.784. The measurements that exceeded an Operational SOF of one were added to the mean Base Case SOF for compliance. The dose assigned to the SU was 5.674 mrem/yr, based on the average of the systematic measurements, adjusted for the dose contribution of elevated areas.
5.2 Phase 2 Part 2 Confirmatory/Inspection Survey Results 5.2.1 Turbine Building Basement Confirmatory Survey, April 2016 As referenced in Section 4.3.1 of this SER, the NRC contractor ORISE performed independent confirmatory surveys for the TB basement at Zion in April 2016. This surveying effort included gamma surface scans and in-situ gamma spectroscopy measurements of the TB basement.
The majority of the confirmatory gamma scan results of the TB basement exhibited radiation levels within the detector background range. However, some embedded piping had elevated readings above background. A judgmental measurement was taken on the floor of the TB, and Cs-137 was identified in the measurement spectrum. Further investigation identified the source of the direct gamma radiation was originating from two embedded pipes in the floor.
According to ORISE analysis, one explanation for the Cs-137 concentration was that the radionuclide originated from embedded piping located close to the sample location. This section of piping was inaccessible at the time of surveying. In the RAI response, ZS stated that this elevated sample and the survey data for the accessible portions of the buried pipe have been
accounted for in the final dose calculations and are consistent with the grouting criteria in the LTP.
5.2.2 Containment Buildings and Auxiliary Building, April 2018 As referenced in Section 4.3.3 of this SER, the NRC contractor ORISE performed independent confirmatory surveys for the remaining structures in the Containment Buildings and Auxiliary Building at Zion in April 2018. This surveying effort included surface scans, in-situ gamma spectrometry measurements, volumetric concrete sampling, and water and sediment sampling ORISE noted several embedded piping/penetrations in the Auxiliary Building floor and sump that were previously grouted and exhibited relatively high direct gamma radiation. Because these locations were assessed as part of the sites FSS of embedded piping/penetrations prior to grouting, they were excluded from further ORISE confirmatory assessment.
5.2.3 Penetrations and Buried Piping, June 2018 As referenced in Section 4.3.4 of this SER, the NRC contractor ORISE performed independent confirmatory surveys for select penetrations and embedded piping in the Containment and Auxiliary Buildings at Zion in June 2018. This surveying effort included gamma surface scans, direct gamma measurements, and additional sampling inside penetrations and embedded piping.
None of the piping/penetration interior direct measurements exceeded the most restrictive Base Case DCGL. NRC agrees with ORISEs conclusion that, based on the results of the confirmatory survey, no issues were identified that would preclude FSS data from demonstrating compliance with the release criteria.
5.3 NRC Staff Evaluation of Phase 2, Part 2 The survey methods used to measure residual radioactivity in buried piping systems were consistent with information contained in Sections 5.7.1.9 of the LTP and Section 3.5.5.9.3 of the NRC Final SER for the LTP (ML18164A222) that approved the FSSs approaches for buried piping. Prior to performing FSS, the interior of three buried piping systems were flushed to remove sediment and debris and reduce the level of residual radioactivity. Also, to the extent practical, ZS disassembled and removed sections of buried piping systems for off-site disposal.
In addition to FSSs planned for the buried piping systems, ZS performed radiological surveys in sections of two of the five SUs (Service Water and Condensate Piping systems) to support segmentation and removal of associated piping systems. Scan surveys were performed on those piping sections and were found to be consistent with ambient background radiation levels.
FSSs of buried piping systems were conducted from May 2017 through August 2019. ZS submitted five release records for the five FSS units that comprised buried piping systems. For those sections of buried piping systems that were obstructed by groundwater intrusion, ZS surveyed other sections of the same buried piping system with similar radiological
characteristics to obtain a sufficient number of measurements to meet the objectives of the survey design. The NRC staff agrees that residual radioactivity characteristics and levels are expected to be consistent within the same buried piping system. The NRC staff notes that survey measurements were obtained from the bottom of the piping interior. Survey measurements from this location within the pipe represent the most likely pipe area impacted by operations and is expected to bound residual radioactivity on other portions of the piping.
The NRC staff reviewed each release record for the five SUs of buried piping systems were accomplished by taking static measurements with a radiation detector that was calibrated for the pipe interior dimensions, consistent with information contained in LTP Section 5.7.1.9.
Modification to survey plans for specific pipe sections and conditions encountered during the conduct of the FSSs are considered acceptable. In its review of the release records, the NRC staff verified the MDC for the instruments, number of required measurements for the survey, survey results, and conversion to DCGL units. The NRC staff finds the methods used during the FSS of the buried piping systems to be adequate and to have demonstrated reasonable assurance of meeting the DCGL values as presented in the LTP.
The following subsections summarize the major topic areas that the NRC staff issued RAIs to address for Phase 2 Part 2. These questions include flooding of pipes with groundwater during the performance of decommissioning activities, inconsistent information on the size of pipes within a SU, and reclassification of SUs.
5.3.1 Flooding of Buried Piping Systems Sections of buried piping in three of the five SUs became inaccessible for FSSs due to groundwater intrusion. The flooding occurred after pipes were segmented in the TB basement.
The piping was not capped or isolated after it was cut, which allowed groundwater to enter the pipes. A summary of the three flooding occurrences is provided below.
The Condensate Feed Water Supply and Recirculation Buried Pipe (Pipe IDs T-103, T-105 and T-106) in SU 00101A were located below the level of groundwater. The only pipe remaining from this system is the pipe under the road which penetrated the east A wall of the TB and ran under the TB floor. The condensate pipes were cut inside the TB basement before demolition and backfill. These pipes were not capped or isolated, which allowed unobstructed groundwater to enter each pipe. The T-105 section was accessible for survey measurements, but the T-103 and T-106 sections could not be surveyed due to groundwater intrusion. The three sections of pipe (T-103, T-105 and T-106) were part of the same system and were determined by ZS to have similar radiological characteristics. Pipe sections T-103 and T-106 could not be removed for surveys. ZS was able to remove and cut sections of the T-105 piping above ground for measurement. A Ludlum Model 2350-1 was coupled with Ludlum Model 44-162 sodium iodide (Nal) gamma detector to perform the survey of pipe section T-105. A one-minute static measurement was acquired at one-foot intervals throughout 257 feet of the interior of the 20-inch outside diameter (OD) pipe. This represents approximately 50 percent coverage of the total internal surface area. ZS considered the sections of T-105 pipe surveyed representative of radiological conditions within the T-103 and T-106 pipe sections that were obstructed by
groundwater intrusion.
Sections of the Primary Water Supply Header Buried Pipe (Pipe IDs T-095 and T-102) in SU 00101B were flooded with groundwater because those sections were not capped or isolated after segmentation inside the TB basement. This buried piping system consists of two sections of 6-inch ID pipe under the TB basement. After flooding of the pipe occurred, ZS cut and surveyed sections of the T-095 and T-102 pipes above ground. ZS made 1-minute static measurements with a Ludlum Model 2350-1 Data Logger paired with a Ludlum Model 44-157 Nal gamma detector that had a calculated field of view of 1.57 square feet. The areal coverage of the survey was determined to be approximately 50 percent of the interior pipe surface area.
ZS considered the sections of pipe surveyed representative of radiological conditions within the two pipe sections that were obstructed by groundwater intrusion.
SU 00101F consisted of approximately 304 linear feet of 12-inch ID pipe in the Diesel Generator Heat Exchanger Service Water Supply (Pipe IDs A0-27, AO-28, AO-30, A0-31) and 367 linear feet of 15-inch ID pipe in the Service Water Return Buried Pipe (Pipe IDs TO-32, and TO-33).
The latter two sections of the return piping were cut on the TB floor opening, which allowed groundwater to intrude into the pipes. ZS acquired measurements from the supply piping (Pipe IDs AO-27, AO-28, AO-30, and AO-31) with a Ludlum Model 2350-1 Data Logger and Ludlum Model 44-10 Nal detector calibrated for a Cs-137 energy window. One-minute static measurements were taken with a calculated FOV of 3.14 square feet for the 12-inch ID pipe.
The total length of the piping in this SU was approximately 672 linear feet. ZS considered the radiological conditions in the Diesel Generator Heat Exchanger Service Water Supply pipes to be representative of the entire piping system in SU 00101F because all pipes were part of the same system.
5.3.2 Inconsistent Reporting of Buried Pipe Diameters In the release record for the Condensate Feed Water Supply and Recirculation Buried Pipe (SU 00101A), the pipe diameters reported were inconsistent throughout the report. The NRC staff requested additional information on the diameters of buried pipe sections T-103, T-105 and T-106. In a letter dated May 15, 2020, (ML20147A128), ZS clarified that section T-103 is a 20-inch diameter pipe that is 226 linear feet long; TD-105 is a 4.5-inch diameter pipe that is 221 long; and T-106 is a 12.75-inch diameter pipe that is 21 feet long. The designation of the T-105 as a 20-inch diameter pipe that received FSS was incorrect. ZS corrected the information in the release record by stating FSS was performed in the T-103 section, which was representative of the T-105 and T-106 sections of buried pipe that were obstructed by groundwater intrusion.
5.3.3 Reclassification of SUs Characterization surveys were not performed in any of the SUs that comprised buried piping systems because most pipe interiors were not accessible until after commencement of decommissioning activities. Information contained in the Zion Station Historical Site Assessment (HSA) did not identify radioactivity levels in buried piping systems that would require a SU
classification of Class 1.
Four of the five buried piping systems were initially determined to be Class 2 and 3 SUs per MARSSIM guidance. A fifth buried piping system, the North Yard Storm Drain, was initially classified as non-impacted based on information contained in the HSA, and therefore was not included in Attachment F to ZS TSD 14-016. In May 2019, the results of an above ground (open land) FSS in SU 10205 identified Cs-137 an Co-60 in sediment collected from buried pipes within the North Yard Storm Drain. LTP Section 5 states that no additional piping will be added to the impacted piping list as identified in Attachment F of TSD 14-016. However, identification of Cs-137 an Co-60 prompted a change of classification from non-impacted to Class 2 and a compliance demonstration, as required by LTP Chapter 5, Section 5.7.1.9, and ZS procedure ZS-LT-300-001-002, Survey Unit Classification. After reclassification of the North Yard Storm Drain SU, ZS determined that leaving this buried pipe system did not adversely impact the release of the impacted area and revised the LTP and TSD 14-016 to account for reclassification of this buried piping system.
SU 00101B for the Primary Water Supply Header Buried Pipe (Pipe IDs T-095 and T-102) was initially classified as a Class 3 in accordance with Attachment F of TSD-14-016. This SU was reclassified as Class 2 in response to the identification of detectable residual radioactivity during the removal of the Primary Water Storage Tank, which was serviced by the Primary Water Supply Header pipe. The concentrations of residual radioactivity within the pipe were expected to be less than the Operational DCGL, which formed the basis for the reclassifying this piping system as a Class 2 SU in accordance with procedure ZS-LT-300-001-002, Survey Unit Classification.
5.4 Summary of Conclusions for FSS Phase 2 Part 2 The survey data for all Phase 2, Part 2 SUs demonstrate that the dose from residual radioactivity is less than the maximum annual dose which corresponds to the release criterion for license termination for unrestricted use specified in 10 CFR 20.1402, Radiological criteria for unrestricted use and support the release of these areas from the 10 CFR 50 licenses.
NRC has determined that the SUs comprising FSSR Phase 2, Part 2 meet the criteria for unrestricted release because ZS demonstrated, and the NRC staff independently confirmed, that each SU was below 25 mrem/yr plus ALARA.
FSS activities were performed in accordance with the LTP, and any deviations from the actions approved in the LTP have been dispositioned in a risk-informed manner. In this way, the residual radioactivity in SUs associated with Phase 2, Part 2 have been reduced to levels ALARA. Most contaminated and non-contaminated systems were disassembled, removed, packaged, and shipped off-site as waste. The remaining structural surfaces were remediated to or below the removable contamination levels and contact exposure rates as necessary to meet the open-air demolition criteria. Typically, buried pipe interiors were remediate to levels less than the Operational DCGLs for buried piping. FSS activities performed in relation to the release
of SUs in Phase 2, Part 2 meet the requirements to reduce residual radioactivity to levels that are ALARA. See Section 7.3 of this SER for more detailed ALARA evaluation.
The Maximum SOF of 0.227 for embedded piping was for the Primary Water Supply Header SU 00101B which equated to a dose of 5.674 mrem/yr.
6 GROUNDWATER DOSE In the Zion LTP, ZS stated that the dose from existing residual radioactivity in groundwater is expected to be diminutive. However, if groundwater contamination is identified during decommissioning, the dose will be calculated using the Groundwater Exposure Factors presented in Chapter 6, (reproduced as Table 6-1 in this SER). Also, that assessments of any residual radioactivity in groundwater at the site will be via groundwater monitoring wells installed at ZNPS.
Table 6-1, Groundwater Exposure Factors (reproduced from Table 6-18 in the LTP)
GW Exposure Factor Radionuclide (mrem/yr per pCi/L)
Co-60 2.50E-02 Cs-134 8.75E-02 Cs-137 6.94E-02 Eu-152 3.62E-03 Eu-154 5.26E-03 H-3 4.43E-05 Ni-63 9.78E-04 Sr-90 1.09E-01 6.1 Summary of Licensee Submittals on Groundwater Dose In the approved LTP, ZS claimed that, based on the HSA and results of the ongoing groundwater monitoring program, there has been no groundwater contamination identified by the groundwater monitoring program at ZNPS. The monitoring program and results are described in TSD 14-003. ZS noted the very low potential for groundwater contamination but still included groundwater dose conversion factors in the Basement Fill Model.
By letter dated October 9, 2019 (ML19288A067), ZS requested concurrence from the U.S. NRC for termination of the groundwater monitoring program at Zion. By letter dated November 5, 2019 (ML19303C215), the NRC staff determined that the proposed termination of the Zion groundwater monitoring program was acceptable.
Subsequently, ZS identified a commitment in Zion TSD 17-004, that groundwater sampling
would continue until license termination and a reference to that commitment in the NRCs safety evaluation approving the LTP (ML18164A222). By letter dated May 19, 2020 (ML20139A115) the NRC confirmed acceptance of the groundwater monitoring performed as of that date as satisfying the commitment for groundwater monitoring until license termination.
In its request for PSR, Rev 3 (ML21102A397), ZS states that:
In May of 2006, tritium (H-3) was positively detected in one well at a maximum observed concentration of 586 pCi/L. Also, in May of 2006, Sr-90 was positively detected in a well up-gradient from the groundwater flow direction and that should not have been impacted by ZNPS activities. As the observed Sr-90 concentrations were barely above the MDC of the analysis, and the results within the range of uncertainty, the results were classified as false positive.
From 2006 until 2020, ZSRP has monitored eleven (11) wells on a quarterly basis in accordance with the Zion Radiological Groundwater Protection Program (RGPP). All samples were analyzed for tritium, gamma radionuclides, gross-alpha and beta (suspended and dissolved), hard-to-detects, and Sr-90. Gamma-radionuclides and HTD radionuclides (including Fe-55, Ni-63 and Sr-90) were not positively detected in any groundwater monitoring sample taken from any of the eleven (11) wells since May of 2006. In addition, from 2006 until the 1st quarter of 2018 and from the 1st quarter of 2019 until the present, tritium was not positively detected at a concentration greater than the MDC of 200 pCi/L. However, during the 1st and 3rd quarter of 2018 into the 1st quarter of 2019, samples taken from well MW-ZN-08S indicated positive tritium at concentrations exceeding the MDC of the analysis. The positive tritium results ranged from 200 to 416 pCi/L. It was postulated that the source of the tritium was slightly contaminated concrete that was placed on the ground in the vicinity of the well prior to loadout and disposal as waste. There are no other indications of positively detected plant-derived radionuclides being detected in any well sample since.
ZS then stated that it would conservatively use the maximum observed positively detected tritium concentration of 586 pCi/L as representative of any potential residual tritium radioactivity in groundwater. As no other radionuclides were positively detected in groundwater since the units were placed into SAFSTOR in 1988, only tritium will be included for the assessment of compliance dose. The tritium concentration of 586 pCi/L was multiplied by the Basement Fill Model (BFM) Groundwater Exposure Factor for tritium of 4.43E-05 mrem/y per pCi/L to determine a dose of 0.026 mrem/year.
6.2 NRC Evaluation of Groundwater Dose The NRC staff reviewed the information provided for the groundwater dose in the PSR Request as well as the data tables in the 2016 through 2019 Annual RGPP Reports for Zion Units 1 and
- 2. As noted above, the NRC staff previously approved the cessation of the groundwater monitoring program in 2019 and found that the information collected as of May 19, 2020 was
adequate. While the NRC staffs review found that ZS slightly misstated the range of tritium found in 2018 (the maximum was 507 pCi/L instead of 416 pCi/L) this does not impact the conservative groundwater dose assumptions that ZS made in its demonstration of compliance and was likely due to a simple human error as both values were present in the 2018 data tables.
The NRC confirmed that no other plant associated radionuclide being monitored for was detected in the monitoring wells during the 2016 through 2019 period (naturally occurring K-40 was occasionally detected and gross beta results consistently trended at less than 20 pCi/L).
Thus, the NRC staff find that ZS use of the 2006 maximum tritium value of 586 pCi/L appears appropriately conservative for demonstrating compliance. While NRC staff do not believe reporting of groundwater data should be limited to stating the lower limit of detection when decommissioning (e.g., MARSSIM guidance for soil analyses reporting is to provide the result, error, and MDC), the NRC staff did not find any indication that other plant related radionuclides may be present at concentrations below the detection limit.
The NRC staff verified the calculation of 0.026 mrem/yr dose using a 586 pCi/L concentration and 4.43E-5 exposure factor as provided in Table 6-1 above.
7 FINAL DOSE SUMMATION AND ANALYSIS As described above, per 10 CFR 20.1402, Radiological criteria for unrestricted use, a site will be considered acceptable for unrestricted use if the residual radioactivity that is distinguishable from background radiation results in a TEDE to an AMCG that does not exceed 25 mrem (0.25 mSv) per year and are ALARA. To demonstrate that the Zion site meets these criteria, ZS provided a summary of its estimate of the dose from residual radioactivity remaining on the site from all media in an Attachment to ZS-2020-0011, Revision 3 (). The NRC staff also performed an independent evaluation of the total dose. The NRC staff reviewed the total dose provided by ZS as well as independent NRC calculations of an elevated area identified by ORISE (as described above in Section 3.4.2) and the potential dose from DRPs (as described above in Section 3.7).
7.1 Summary of Final Dose Provided by Licensee ZS provided a summary of its estimate of the dose from residual radioactivity remaining on the site in an Attachment to ZS-2020-0011, Revision 3 (ML21103A229 Pkg). Dose summation for compliance was conducted as discussed in Chapter 6, Compliance with the Radiological Criteria for License Termination, of the Zion LTP, Revision 2, as approved in the associated NRC safety evaluation dated September 28, 2018, after FSS was completed in all 128 SUs using the below equation.
= ( BASEMENT + +
+ ) x 25 mrem/yr The results of the final compliance dose were calculated by ZS using the Maximum SOF dose for the four source terms at the site. ZS dose summation, as provided in its PSR request, is
replicated in Table 7-1 below. The bases for these values and the NRCs evaluations of these values are described above. As can be seen in this table, the total dose calculated by ZS is 18.75 mrem/yr, which is less than the 25 mrem/yr criteria in 10 CFR 20.1402.
Table 7-1, Zion Final Compliance Dose Summation (Based on Information in ZS-2020-0011, Rev 3*)
Dose Source SU Base Case SOF (mrem/yr)
Max BcSOFBASEMENT Unit No. 1 Containment 0.444* 11.1 Max BcSOFSOIL 12106K 0.078 1.95 Max BcSOFBURIED Primary Water Supply Header 0.227 5.68 PIPE Max SOFEGW(elevated Groundwater 0.001 0.026 groundwater TOTAL 0.75 18.75
- ZS reported an SOF value of 0.443 in ZS-2020-0011, Rev 3, but as noted in Section 4.3.9 of this SER, there appeared to be a transcription error and the correct value reported in the Unit 1 Containment basement release record is an SOF of 0.444, which corresponds to a dose of 11.1 mrem/yr.
7.2 Potential Particle Dose As stated previously in the SER, there are no known DRPs remaining at the site after extensive effort to identify and collect all DRPs so the anticipated dose from DRP exposure is zero.
However, the NRC staff recognize the possibility of human error or other extenuating circumstances creating a low probability of encountering a DRP. As such, the NRC staff elected to treat the possibility of encountering a DRP as a less likely but plausible condition to risk inform the decision for site release. As discussed in Attachment A to the PSR SER (ML23286A304 Pkg), the hypothesized dose resulting from exposure to any DRP collected during the 2023 surveys was assessed as being less than 10 mrem TEDE. Less than twenty mrem was estimated as the possible dose should a DRP not have been detected during the surveys because the estimated sensitivity of the scanning techniques employed ranged to almost twice the activity in any identified and collected DRPs. In addition, the possible SDE and LDE hypothesized from exposures to a DRP were less than 2 rem which is significantly less than any deterministic effects threshold or the occupational limit for SDE (50 rem). Therefore, NRC staff concluded that it is very unlikely that an exposure to a DRP would occur at the site after license termination and, if exposure to a DRP did occur, the resulting exposure would be less than the public dose limit in 10 CFR 20.1302, Compliance with dose limits for individual members of the public (i.e., less than 100 mrem/yr TEDE).
7.3 NRC Evaluation of Final Dose The NRC staff reviewed ZS calculation of total dose and concluded that it was acceptable because they used the methodology that was previously approved in the LTP. As described in more detail earlier in this SER, the NRC staff also confirmed that the values that ZS assumed for the Max BcSOFBASEMENT, Max BcSOFSOIL, Max BcSOFBURIED PIPE, and Max SOFEGW were
developed appropriately4 (see sections above for more details on the NRCs evaluation of these values). As noted above, the compliance dose summation corresponds to 18.75 mrem/yr, which is less than the unrestricted release criteria of 25 mrem/yr. For these reasons, the NRC staff concludes that the total dose calculated by ZS for this PSR request are acceptable and are consistent with the release criteria in 10 CFR 20.1402, Radiological Criteria for Unrestricted Uses.
The NRC staff did note one discrepancy, previously discussed in Section 3.4.2 of this SER, which had to be considered because the 2023 confirmatory survey reported an apparent elevation/hot spot (residual radioactivity in soil exceeding the DCGLs) near the conjunction of open land SUs 12112, 10224C, and 10223 that was unassessed by ZS. Due to the timing of the confirmatory report (it was drafted in October 2023 and issued in November 2023), there was little opportunity for ZS to investigate and remediate or bound the area of concern. Therefore, NRC staff evaluated the sample results and considered the size of the impacted area to be between 3 m2 and 10 m2 because there was no areal bounding of the impacted area and ORISE surface scanning indicated increased measurements over an approximately 5 m2 area.
The NRC staff acknowledge that these area estimates are likely very conservative. Using the sites area factors, the NRC staff estimated the incremental dose from the hot spot to be between 4.1 mrem/yr and 8.4 mrem/yr which, when added to the dose estimated for soil in each SU near the hot spot, the SUs would have doses ranging from 4.2 mrem/yr to 8.8 mrem/yr. This addition of dose from the hot spot would make SU 12112 have the highest estimated soil dose out of all the site soil SU which, if considered in the compliance dose determination, could cause the site to fail its demonstration of compliance (per the ZS LTP methodology of determining the all-pathway dose for the Zion site) when using the upper range dose estimate. However, NRC staff recognize that the ZS compliance dose demonstration is very conservative in that it takes the highest dose from each of the media under consideration without regard to where they are located on the site and it is not plausible one individual could be exposed to the highest dose components of each media. Further the unit of compliance is a SU and all SUs must pass the unrestricted release dose criterion at a site. Another way of explaining that is that the SUs are designated as such because they are generally considered as being a locality where an AMCG would be present for an extended period resulting in a hypothetical dose as determined by the scenario used for DCGL development. The NRC staff therefore considered all of the impacted media in each of the three SUs near the hot spot and found that the actual dose from all media applicable in just these SUs, and considering the range of incremental dose from the hot spot, would range from 5.0 mrem/yr to 14.9 mrem/yr. Therefore, staff concluded that there is reasonable assurance that the 25 mrem/yr dose criterion would be met even though the hot spot found through the confirmatory survey in 2023 was not considered in ZS demonstration of compliance determination.
Also, as described in Section 7.2, there are no known DRPs remaining at the site after extensive effort by ORISE and ZS to identify and collect DRPs so the anticipated dose from 4 Note that there was a minor transcription error for the reported Max BcSOFBASEMENT value that does not affect the NRCs overall conclusions (see Section 7.1)
DRP exposure is zero. However, to risk inform the NRCs review, the NRC staff assessed the hypothetical dose from a DRP if any were to remain (see Attachment A of the PSR SER (ML23286A304 Pkg)) and concludes that the potential dose from any DRPs remaining on-site should be less than the public dose limits and wouldnt cause deterministic effects.
Chapter 4 of the LTP describes the ALARA considerations and evaluations that were performed by ZS. For structures, the remedial actions that would contribute to ALARA included: Scabbling and Shaving; Needle Guns; Chipping; Sponge and Abrasive Blasting; Pressure Washing; Washing and Wiping; High-Pressure Water Blasting; Grit Blasting; and Removal of Activated/Contaminated Concrete. For soil, an ALARA analysis was conducted to determine the residual radioactivity concentrations that would be considered ALARA. The ZS analysis determined that remediating soil and disposing of it as waste at a licensed facility to meet the DCGLs is ALARA consistent with the example evaluations done in NUREG-1757, Vol 2, Rev 2, Appendix N. ALARA analyses were also conducted to determine what residual radioactivity concentrations in structures would be considered ALARA. ZS evaluated concrete scabbling or shaving remediation activities and concluded that further remediation of concrete beyond that required to demonstrate compliance with the 25 mrem/yr dose criterion is not justified. The NRC staff evaluated the analyses in its SER (ML18164A222) and noted that The licensee provided its ALARA analysis process in LTP Section 4.4. The licensees formulas for calculating the remediation levels conform to the guidance provided in Appendix N of NUREG-1757, Vol 2, Rev 2. The NRC staff determined that the licensee has met the requirements of 10 CFR 50.82(a)(9)(ii)(C) requiring the LTP to include [p]lans for site remediation by providing a detailed discussion of its radiological remediation site plans for the remaining decommissioning activities. While no evaluations were performed for remediation of buried piping or penetrations, the NRC staff concludes that the remedial actions performed, as previously mentioned, provide reasonable assurance that that the remediation resulted in residual radioactivity that is ALARA.
The FSSRs and release records demonstrate that soil and structures meet the applicable DCGLs consistent with the ALARA analyses. In addition to the preceding, the NRC staff note that extensive delays and costs have been incurred due to the presence of DRPs at the site, the cleanup of which demonstrated ALARA in practice due to significant costs incurred compared to the number of DRPs removed from the site and their potential dose impact. The scanning surveys conducted after the 2021 Confirmatory Survey used techniques that the NRC staff consider adequate for identifying both hot spots of activity and DRPs. The areas of the site most likely to have been impacted by DRPs were fully scanned, including consideration of subsurface soil, using appropriate techniques and demonstrate compliance with both 10 CFR 20.1501(a).
8 CONCLUSIONS The requirements at 10 CFR 50.82(a)(11) establish the criteria to be used by the NRC for terminating the license of a power reactor facility that has an approved LTP. These criteria include: (1) dismantlement has been performed in accordance with the approved LTP, and (2) the final radiation survey and associated documentation demonstrate that the facility and site have met the criteria for decommissioning in 10 CFR Part 20, Subpart E, Radiological Criteria for License Termination and Subpart F Surveys and Monitoring.
The NRCs previous review of ZS LTP determined that the proposed DCGLs would ensure that the release criteria in 10 CFR Part 20, Subpart E, Radiological Criteria for License Termination and the requirements in 10 CFR Part 20, Subpart F Surveys and Monitoring were met. While the LTP did not address DRPs, the NRC staff believe DRPs have been adequately addressed because of the surveys conducted and removal of all DRPs encountered over the past couple of years. The NRC has concluded that all decommissioning and dismantlement activities have been completed in the SUs to be released from the Zion Facility Operating licenses, and the release of the subject SUs supports the process of license termination by demonstrating that the requested portion of the site can be released from the Part 50 licenses.
The FSS results provide reasonable assurance that the residual radioactivity in each of the SUs meets the criteria established in the Zion LTP and in 10 CFR 20.1402. The NRCs review of the Zion FSSR and supporting information provided in the responses to RAIs determined that the final survey reports, as amended, were consistent, and demonstrated compliance, with the Zion LTP. The compliance dose calculated for the site was equal to 18.75 mrem/yr, which is within the criteria established in 10 CFR 20.1402. Therefore, the FSS results demonstrate that the survey areas to be released meet the radiological criteria for unrestricted release. The NRC staff determined that the maximum calculated dose for any SU (considering all media in a SU) was less than 15 mrem/yr, which is less than the NRC unrestricted release criteria of 25 mrem/yr and is therefore acceptable. While all identified DRPs have been removed from the site, the NRC staff consider it very unlikely a DRP was missed and would be encountered by the public.
The NRC staff estimated that the exposure to DRPs would result in a potential dose that is less than the public dose limit (100 mrem/yr TEDE) and would not cause deterministic effects which is consistent with guidance regarding a less likely but plausible scenario. For the reasons stated in this section of the SER, the NRC staff conclude that the reported FSSs were adequate and demonstrate compliance with 10 CFR 20.1402.
The NRC also concludes that a Level 2 consultation with the EPA is not required based on the as-left soil radioactivity concentrations. The NRC staffs review of ZS submittal requesting the release of 128 SUs from the Facility Operating Licenses for the Zion site, multiple NRC inspections and confirmatory measurements substantiated that ZS decommissioning and FSS programs adequately assessed the radiological conditions at the site.
Principal Contributors:
Karen Pinkston Louis Caponi Greg Chapman Date: November 8, 2023
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Table of Abbreviations AMCG Average Member of the Critical Group ADAMS Agencywide Document Access and Management System ALARA As low as reasonably achievable ARERR Annual Radioactive Effluent Release Report BIL Basement Investigations Levels CAB Controlled Area Boundary CCDD Clean construction and demolition debris CEDE Committed Effective Dose Equivalent CEG Constellation Energy Generation, LLC DCGL Derived Concentration Guideline Level DFSAR Decommissioning Final Safety Analysis Report DQO Data Quality Objectives DRP Discrete Radioactive Particles EDE Effective Dose Equivalent EGC Exelon Generation Company EPA ENVIRONMENTAL PROTECTION AGENCY FHB Fuel Handling Building FSAR Final Safety Analysis Report FSS Final Status Survey FSSR FSS reports GElS Generic Environmental Impact Statement GI Gastrointestinal GTCC Greater Than Class HSA Historical Site Assessment HTD Hard-to-detect IC Insignificant Radionuclide Contribution ICRP International Commission on Radiological Protection ISFSI Independent Spent Fuel Storage Installation LAR License amendment request LDE Localized dose equivalent LLBP Less Likely but Plausible ISOCS In-Situ Object Counting System LTP License Termination Plan MARSSIM Multi-Agency Radiation Survey and Site Investigation Manual MDA Minimum detectable activity MDC Minimum Detectable Concentrations MDCR Minimum Detectable Count Rate ML Main Library MOU Memorandum of Understanding NRC Nuclear Regulatory Commission NCV Non-Cited Violation OCB Oil circuit breakers ODCM Off-site Dose Calculation Manual ORAU Oak Ridge Associated Universities ORISE Oak Ridge Institute for Science and Education OpDCGL Operational Derived Concentration Guideline Level OpSOF Operational Sum of Fractions QAPP Quality Assurance Project Plan PSR Partial site release
RGPP Radiological Groundwater Protection Program RA Radiological assessments RAI Requests for Additional Information REMP Radiological Environmental Monitoring Program RFTA Request for Technical Assistance ROC Radionuclide of Concern SOF Sum of fractions SPF Spent Fuel SDE Shallow dose equivalent exposure SER Safety evaluation report SFP Spent fuel pool SU Survey units TB Turbine Building TEDE Total effective dose equivalent TLD Thermoluminescent dosimeter TS Technical Specifications UCL Upper Confidence Level URS Unconditional Release Survey VCC Vertical Concrete Cask WWTF Waste Water Treatment Facility ZNPS Zion Nuclear Power Station ZS ZionSolutions, LLC ZSRP Zion Station Restoration Project