ML24094A214
| ML24094A214 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 04/19/2024 |
| From: | Marlayna Vaaler Doell Reactor Decommissioning Branch |
| To: | Dostal J Oyster Creek Environmental Protection |
| References | |
| Download: ML24094A214 (1) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 Jeffrey P. Dostal, Site Vice President Oyster Creek Nuclear Generating Station 741 Route 9 South Forked River, NJ 08731
SUBJECT:
OYSTER CREEK NUCLEAR GENERATING STATION - PREAPPLICATION READINESS ASSESSMENT OF THE HOLTEC DECOMMISSIONING INTERNATIONAL LICENSE TERMINATION PLAN
Dear Jeff Dostal:
On April 4, 2024, members of the U.S. Nuclear Regulatory Commission (NRC) staff completed a preapplication readiness assessment (hereinafter readiness assessment) of the draft License Termination Plan (LTP) application for the Oyster Creek Nuclear Generating Station (OCNGS). The readiness assessment, as requested by Holtec Decommissioning International, LLC (HDI) (Agencywide Documents Access and Management System (ADAMS)
Accession Nos. ML24033A327 and ML24081A288), was limited to the draft LTP content associated with the design and planning for the final status survey of the OCNGS site and the approach for addressing compliance with the radiological criteria for license termination.
HDI requested the readiness assessment in order for the NRC staff to: (1) identify information gaps between the draft LTP and the technical content required for the final application submitted to the NRC staff, as set forth in Title 10 of the Code of Federal Regulations (10 CFR)
Section 50.82, Termination of license, (2) identify technical or regulatory issues that may complicate the acceptance or technical reviews of the application, and (3) become familiar with the LTP, particularly in areas where HDI is proposing new concepts or novel decommissioning approaches. The NRC staffs readiness assessment plan used to conduct the review of the OCNGS LTP can be found in ADAMS under Accession No. ML24085A790.
The NRC staff conducted the readiness assessment from April 1-4, 2024, via HDIs secure SharePoint portal in accordance with NRC Office Instruction LIC-116, Preapplication Readiness Assessment (ML20104B698). The readiness assessment is not part of the NRCs official acceptance review process. The staff performed the readiness assessment to understand the level of detail of the OCNGS LTP draft application and to identify any major issues or information gaps between the draft application and the technical content required to be included in the final application submitted to the NRC. Therefore, the observations from the readiness assessment do not predetermine whether the application will be docketed.
In general, the NRC staff found that HDIs draft OCNGS LTP structure is in alignment with 10 CFR 50.82 and the guidance contained in NUREG-1700, Standard Review Plan for Evaluating Nuclear Power Reactor License Termination Plans, Revision 2 (ML18116A124) and NRC Regulatory Guide 1.179, Standard Format and Content of License Termination Plans for Nuclear Power Reactors, Revision 2 (ML19128A067). However, there are certain areas where additional information will need to be provided during the formal NRC review of the OGNGS April 18, 2024
J. Dostal LTP. The enclosure to this letter provides further details and specific NRC staff observations on the draft OCNGS LTP application.
HDI should consider the entirety of the NRC staff observations provided during the preapplication interactions on the OCNGS LTP to support development of a high quality application. Please consider the observations from the readiness assessment while finalizing your application and, if necessary, reevaluate the application submission date based on your evaluation of the time needed to address the readiness assessment observations.
The NRC staff remains committed to working with HDI in ongoing and future preapplication engagement activities. HDI is encouraged to engage the NRC staff if additional clarity is needed on any of the NRC staffs observations. Based on the nature of the readiness assessment, additional items may be identified during the acceptance review of the anticipated LTP application that were not identified during the readiness assessment.
In accordance with 10 CFR 2.390 a copy of this letter will be available electronically for public inspection in the NRC Public Document Room or from the Publicly Available Records component of NRCs ADAMS. ADAMS is accessible from the NRC Website at http://www.nrc.gov/reading-rm/adams.html.
If you have any questions concerning this matter, please contact me at (301) 415-3178 or via e-mail at Marlayna.Doell@nrc.gov.
Sincerely, Marlayna V. Doell, Project Manager Reactor Decommissioning Branch Division of Decommissioning, Uranium Recovery and Waste Programs Office of Nuclear Material Safety and Safeguards Docket Nos.: 50-219 and 72-15 License No.: DPR-16
Enclosure:
Readiness Assessment Observations cc w/attachment: Oyster Creek ListServ Signed by Doell, Marlayna on 04/18/24
Enclosure OYSTER CREEK NUCLEAR GENERATING STATION PREAPPLICATION READINESS ASSESSMENT OBSERVATIONS FOR THE DRAFT LICENSE TERMINATION PLAN Docket No. 50-219 READINESS ASSESSMENT OBSERVATIONS The readiness assessment of the Oyster Creek Nuclear Generating Station (OCNGS) license termination plan (LTP) draft application focused on the major areas identified from past LTP applications to be challenging technical and regulatory areas. Specific areas where the Nuclear Regulatory Commission (NRC) staff is providing feedback to Holtec Decommissioning International (HDI) include:
overall final status survey design and related activities deselection of certain radionuclides of concern from the initial suite based on risk use of surrogate ratios for certain hard to detect radionuclides volumetric residual radioactivity considerations subsurface soil characterization and continuing characterization plans the approach used to survey and assess dose from discrete radioactive particles and elevated measurement areas the approach and criteria used to survey and assess dose from subsurface residual radioactivity (e.g., subsurface soil excavations, reactor basement substructures, and materials planned for reuse) support for elimination of groundwater dependent exposure pathways development of derived concentration guideline levels (DCGLs), including compliance and alternative exposure scenarios The NRC staffs observations on the design and planning for the final status survey of the OCNGS site, which are discussed in Chapter 5 of the draft OCNGS LTP, are captured in tabular format in the first section of this report.
The following abbreviations are used to categorize each observation:
HP are the health physics observations related primarily to the design and planning for the final status survey for the OCNGS site.
COM are the observations related to the approach for addressing compliance with the radiological criteria for license termination.
GW are the hydrogeologic observations related to groundwater and surface water considerations for the site.
The NRC staffs observations on the licensees approach for addressing compliance with the radiological criteria for license termination, which are discussed in Chapter 6 of the draft OCNGS LTP, are listed in the second section of this report. These comments are provided to assist the licensee in preparing for future interactions on the portions of the dose compliance model (less likely but plausible scenario considerations) that were not yet submitted to the NRC.
OBSERVATIONS ON THE DESIGN AND PLANNING FOR THE FINAL STATUS SURVEY Item No.
Chapter 5, Final Status Survey Design and Planning HP-1 Table 5-2, OCNGS Site-Specific Radionuclides of Concern 5-5 Table 5-2 notes the major radionuclides in bold. Describe what is meant by major radionuclides. The LTP should explain how site characterization data was used to verify dose significant and insignificant radionuclides of concern (ROCs).
HP-2 Section 5.2.1, Data Quality Objective (DQO) 5-7 Section 5.2.1 lists the seven steps of the DQO process without any further elaboration. The LTP should discuss in detail the data quality objective process and each of its elements (i.e., state the problem, identify the decision, identify the inputs to the decision, define the study boundaries, develop a decision rule, specify limits on decision errors, and optimize the design for obtaining data).
HP-3 Section 5.2.2, Classification of Survey Units; Section 5.2.2.3, Changes to Classification 5-7, 5-8 The LTP should explain the additional actions to be taken if changes to survey unit classification are less restrictive than originally stated.
HP-4 Section 5.2.4, Sample Size Determination 5-9 The LTP should clarify what value is used for the upper bound of the gray region (UBGR).
HP-5 Section 5.2.6, Background Reference Area; Section 5.2.7.2, Multiple Radionuclide Evaluations 5-12, 5-13 Chapter 5 indicates that there will be some consideration of background radiation. The LTP should elaborate on the types of background subtraction used (i.e., ambient, media-specific, or no background), when each is applied, and how media-specific backgrounds are derived.
Item No.
Chapter 5, Final Status Survey Design and Planning HP-6 Section 5.2.7.3, Deselection of Insignificant Radionuclides 5-13 The staff notes that the adequacy of the analysis of insignificant contributor analysis is pending a review of OCNGS Technical Basis Document (TBD) No. 24-01-12-2888, Revision 0, Dose Contribution from Insignificant Radionuclides in the Oyster Creek Site-Specific Suite of Radionuclides.
HP-7 Section 5.2.7.3, Deselection of Insignificant Radionuclides 5-13 The section indicates that no hard to detect (HTD) radionuclides were identified in samples above the minimum detectable concentration (MDC), except for Sr-90. However, the major radionuclides listed in Table 5-2 include C-14 and H-3. The LTP should clarify which radionuclides will be considered during routine measurements and sampling.
HP-8 Section 5.2.7.3, Deselection of Insignificant Radionuclides 5-13 The LTP should explain (1) the derivation of the radionuclide fractions used as input to insignificant contributor determinations, (2) the process for considering radionuclide results with values less than the MDC and negative values in the determination of radionuclide fractions, and (3) plans for verification of insignificant contributors throughout decommissioning.
HP-9 Section 5.2.7.4, Surrogate Ratio DCGLs 5-14 The section discusses the calculations of surrogate DCGLs, the process for when surrogate ratios may be applied, a generic statement on how surrogate ratios will be determined, and how surrogate ratios will be verified with individual samples. The LTP should include more detailed information on the development of surrogate ratios, including the basis for the ratios and the assumed values (e.g., maximum, 95% percentile), and whether these vary by media. The LTP should also address verification of surrogate ratios throughout decommissioning.
Item No.
Chapter 5, Final Status Survey Design and Planning HP-10 Section 5.2.7.4, Surrogate Ratio DCGLs 5-14 The LTP should explain the origin of Equation 5-4 for determining the surrogate DCGL and all the variables in the equation.
HP-11 Section 5.2.7.5, Gross Activity DCGLs 5-16 The LTP should explain how the radionuclide fractions were determined for use in the gross activity DCGL equation. Discuss the criteria for re-evaluating the gross activity DCGL when new radionuclide distributions are determined and how this revised DCGL will be applied to previously evaluated areas.
HP-12 Section 5.3, Survey Measurement Methods; Section 5.3.3, Alternative Survey Plan; 5.3.4.6, Exterior Surfaces of Building Foundations; Section 5.4.2, Advanced Technologies; Section 5.5.3.6, Remediation and Reclassification 5-17, 5-20, 5-23, 5-25, 5-37 In Section 5.4.2, the licensee commits to development of a TBD for ISOCS, bulk monitors, and well logging. Additional discussions are provided in other sections of the LTP. The LTP should clarify the advanced survey techniques currently planned for use at OCNGS.
The licensee should also include a discussion of the contents of the proposed TBD in the LTP. For example, description of equipment, intended uses, calibration methods, operational checks, sensitivity, quality control requirements, etc., as applicable.
HP-13 Section 5.3.2.7, Volumetric Soil Samples 5-19 The LTP should explain the criteria for performing subsurface soil contamination investigations and how this will be conducted. The LTP indicates subsurface samples will be taken at a depth exceeding 15 centimeters up to a depth of 1 meter. The LTP should discuss the justification for limiting the maximum depth of planned subsurface soil sampling and investigation to one meter.
HP-14 Section 5.3.4.1, Pavement-Covered Areas and Shallow Concrete Slabs 5-20 The LTP should discuss any volumetric sampling to be conducted for pavement-covered areas and shallow concrete slabs.
Additionally, clarify whether the pavement-covered areas and soil underneath are considered the same or separate survey units.
Item No.
Chapter 5, Final Status Survey Design and Planning HP-15 5.3.4.3, Embedded Piping and Buried Piping 5-21 The LTP should clarify when building surface DCGLs and embedded piping DCGLs will be applied to embedded piping.
Discuss the technical justification for using building surface DCGLs as a conservative approach for subsurface applications.
HP-16 5.3.4.7, Survey Considerations for Suspect Discrete Radioactive Particle Areas 5-23 The LTP should describe the process for NRC notification of discrete radioactive particle (DRP) events occurring during the final status survey activities. For example, is the plan to document these occurrences in a Condition Report? The licensee may consider including material from Section 5.5.3.4, Discrete Particle Identification, in this section to partially address the question of data captured and actions taken upon identification of DRPs.
HP-17 Table 5-7, Typical FSS Instrument 5-25 In the third row of Table 5-7, the detector type is listed as a gas-flow proportional counter. The detector model is listed as a Ludlum 43-68/43-93. The Ludlum 43-93 is a scintillation detector.
Modify the table to reflect the correct detector model.
HP-18 Table 5-8, Typical FSS Detection Sensitivities 5-25 There are several red X's in the table for count time, static MDC, and scan MDC. Include these values in the version of the table included with the final LTP to facilitate verification of calculations and comparison to the LTP MDC commitments. Additionally, a scan MDC has not been provided for the Model 44-10 detector. The note references an efficiency table for photon emitting radionuclides, which is not directly relatable to the DCGL.
HP-19 Section 5.4.5.7, Pipe Survey Instrumentation 5-31 The instrument sensitivity for piping instruments should be included in Table 5-8. The LTP should discuss the approach to calibrating instruments used for survey of buried or embedded piping.
Item No.
Chapter 5, Final Status Survey Design and Planning HP-20 Section 5.4.5, Minimum Detectable Concentration 5-26 thru 5-31 The staff notes that a final determination of instrument efficiencies and MDC adequacy is dependent on the review of the TBD Instrument Efficiency Determination for Use in Minimum Detectable Concentration Calculations in Support of the Final Status Surveys at OCNGS. Specifically, more detailed information is needed on the radionuclide fractions used to determine weighted efficiencies and on the inclusion of the source to detector distance effects in calculation of the total efficiency.
HP-21 Section 5.5.1.3, Isolation and Control Measures 5-32 thru 5-33 The LTP should explain the processes planned to prevent spread of residual radioactivity to the environment (e.g., dust suppression, containment with negative ventilation, methods for control of contamination at the source) during demolition and dismantlement.
Discuss conditions that may result in repeating the FSS following recontamination of a post-FSS survey unit.
HP-22 Section 5.5.1.3, Isolation and Control Measures 5-32 thru 5-33 The LTP should describe the plans for survey of haul paths to be used during dismantlement and waste removal activities.
HP-23 Section 5.5.3.2, Investigation Levels Table 5-12 The LTP should elaborate on what statistical parameter will be used for the Class 1 direct investigation level and how that parameter will be determined.
HP-24 Table 5-13, Soil Area Factors; Table 5-14, Building Surface Area Factors 5-36 Np-237 and Pu-240 are included as radionuclides of concern in Table 5-2 of the LTP. However, Table 5-13 does not contain a value for Np-237 and Table 5-14 does not contain values for Np-237 and Pu-240. The LTP should explain the exclusion of these radionuclides from the area factor tables.
Item No.
Chapter 5, Final Status Survey Design and Planning HP-25 Section 5.5.3.5, Remaining Underground Structures 5-37 The licensee commits to submitting a TBD for DCGLs and dose assessment for remaining underground structures prior to implementation. However, Chapter 6 of the draft LTP includes a discussion of below-grade concrete structure DCGLs. The LTP should clarify whether these are the DCGLs intended for use for remaining underground structures, or if additional underground structure DCGLs will be developed in a future TBD.
HP-26 Section 5.6.1, Data Verification and Validation 5-39 Under the review criteria for data acceptability, there is a mention of special methods for data collection. The draft LTP goes on to state these special methods are described in Section 5.6.1 of the LTP or will be the subject of an NRC notice of opportunity for review.
The LTP should clarify what is meant by special methods. A description of these methods should be included in the final LTP or a supplemental document for review by NRC staff.
HP-27 Section 5.6.5, Determination of Compliance 5-42 The LTP should include a discussion of the approach to demonstrating compliance with the dose criterion (10 CFR 20.1402) for an individual who could potentially be exposed to multiple contaminated media (e.g., surface soil, subsurface soil, pavement-covered areas and shallow concrete slabs, embedded and buried piping, buried structures, groundwater, backfill materials) and radionuclides. Additionally, explain the approach for incorporating dose contributions from insignificant radionuclides.
Item No.
Chapter 5, Final Status Survey Design and Planning HP-28 Section 5.6.7, Data Management 5-43 The LTP should include a discussion of the quality control (QC) surveys and samples to be performed to verify the validity of the FSS results. These QC surveys may include replicate measurements, field blanks and spiked samples, split samples, third-party analysis, and sample recounts. Describe the criteria for QC investigations and follow-up actions to QC failures.
HP-29 Section 5.7.2, Final Status Survey Report 5-44 Section 5.7.2 lists those items to be included in the final status survey report. In addition to the items listed, the licensee should include a summary of the DCGLs used, the parameters used to determine the number of samples (e.g., width of the gray region, estimated variance or standard deviation, decision errors) and a justification for their selection, the statistical test and associated parameters (e.g., decision errors, critical values), and a statement of whether the survey unit demonstrated compliance with the release criteria (see NUREG-1757, Section 4.5).
HP-30 Generic The LTP should clarify whether concrete will be used as backfill. If used, describe the methodology for survey and sampling.
HP-31 Generic The LTP should include a discussion of the approach used for situations where the actual MDC is greater than or equal to the required MDC for small areas of elevated activity. The discussion should include methods for calculation of the area bounded by samples, new area factors, adjusted number of statistical samples (nemc), and any adjustments made to sample spacing.
HP-32 Generic For the vendor laboratory, the final LTP should describe the analysis type, technique, method, and MDCs by media.
Item No.
Chapter 5, Final Status Survey Design and Planning COM-1 Table 5-3, DCGLs by Radionuclide and Medium Type 5-6 The staff notes that if using a single soil DCGL which includes subsurface soil, the DCGLs should consider the actual depth and thickness of residual radioactivity expected to remain at the time of license termination, which could vary across the site. The benefit of development of separate surface and subsurface soil DCGLs is dependent on the level of credit needed to demonstrate compliance (e.g., if a single bounding set of DCGLs is acceptable for use, the use of single DCGL could simplify the compliance demonstration).
Nonetheless, sensitivity analysis on depth and thicknesses of residual radioactivity should be performed to inform survey design (i.e., to inform the need for depth discrete measurements of surface and subsurface layers for comparison against DCGLs to ensure that elevated residual radioactivity concentrations are not diluted in a larger thickness of clean soil if either surface or deeper subsurface soil concentrations are found to be most important to dose).
COM-2 Table 5-4, Suggested Survey Unit Sizes 5-9 Because the size of subsurface excavations and/or subsurface survey units may be different compared to surface units and the licensee appears to be relying on a single set of DCGLs for soil, additional information is needed on the survey strategy for different surface and subsurface survey units to demonstrate compliance (e.g., survey unit sizes, number of samples, depth of samples, and survey methods). See guidance contained in DUWP-ISG-02, Draft Interim Staff Guidance: Radiological Survey and Dose Modeling of the Subsurface To Support License Termination (ML23177A008),
to help inform acceptable methods for subsurface surveys.
Item No.
Chapter 5, Final Status Survey Design and Planning COM-3 Section 5.2.4.3, Relative Shift 5-11 The draft LTP states that the default value of the lower bound of the gray region (LBGR) is set initially at 0.5 times the DCGL. However, the staff notes that MARSSIM guidance recommends use of a conservative estimate of the mean concentration in the survey unit to ensure sufficient power to reject the null hypothesis.
Only if no or limited data are available to design the survey should these type of assumptions be used to design the survey, which will put the licensee at risk of failing a Scenario A test if the LBGR or variability in the survey unit is underestimated.
COM-4 Section 5.2.4.4, Wilcoxon Rank Sum Test Sample Size 5-11 This section indicates the licensee is considering background radiation for some radionuclides. The LTP should clarify which radionuclides are assumed to be in background and the selection of background reference areas. If subsurface residual radioactivity is present, the licensee should explain how the surface and subsurface soil reference areas will be delineated.
COM-5 Section 5.2.6, Background Reference Area 5-13 The LTP discusses the use of the Kruskal-Wallis test to determine that there are no significant differences in the mean background concentrations among potential reference areas. However, the staff notes that the Kruskal-Wallis test is only used if the licensee plans to apply Scenario B (indistinguishable from background) to demonstrate compliance If using Scenario B to show radionuclides are indistinguishable from background residual radioactivity levels, this should be clear from the survey plan.
Item No.
Chapter 5, Final Status Survey Design and Planning COM-6 Section 5.2.7.3, Deselection of Insignificant Radionuclides 5-14 The staff notes that in making the determination that a radionuclide or pathway is insignificant, uncertainty in parameters and exposure pathways should be considered. For example, if radionuclides present at the site could have a significant dose if certain plausible exposure pathways are considered, then the licensee should consider retaining the radionuclide for detailed analysis.
Furthermore, the licensee should ensure that parameters are conservatively selected in determining the dose contributions of the radionuclide and pathway.
COM-7 Section 5.2.7.3, Deselection of Insignificant Radionuclides 5-14 The LTP states that site characterization data have shown that the HTD nuclides in the suite are consistently below or slightly above the MDC in laboratory results, which supports classifying them as insignificant radionuclides. The staff notes that this would have to be shown to be the case based on dose modeling (or review of the MDCs against the DCGLs showing they are a small fraction less than 10 percent of the DCGL).
GW-1 Section 5.3.5, Groundwater 5-23 In regard to groundwater, the licensee should consider:
(1) Stating the period planned for groundwater monitoring data collection to be used for dose calculations.
(2) Clarifying the purpose of the statement that groundwater monitoring will continue until it becomes necessary to close the wells to prevent potential contamination pathways. NRC staff guidance indicates that monitoring should continue until the last soil Item No.
Chapter 5, Final Status Survey Design and Planning disturbance after decommissioning to capture possible releases caused by demolition activities.
(3) The plan indicates that measurements from the groundwater monitoring program will be used for dose calculations. Explain how the current monitoring network reflects likely maximum concentrations in the groundwater considering likely source areas (including any possible releases during decommissioning activities) described in Chapter 2 of the LTP and considering the conceptual site model for flow and transport.
(4) The licensee states that concentrations of available well water will remain below derived concentrations from the U.S.
Environmental Protection Agencys (EPAs) minimum concentration levels (MCLs) for beta and photon emitters. The final LTP should confirm that the sum of the fractions for the ensemble of radionuclides will be used for confirmation of this statement.
(5) To ensure that existing groundwater contamination is a small fraction of the dose release criteria, Section 5.3.5 indicates that the concentrations of well water will remain below the derived concentrations for EPA beta/photon MCL. The final LTP should reconcile the current radionuclide measurements of the groundwater protection program with the suite of radionuclides in LTP Table 5-2.
Alternatively, the final LTP could provide a basis for reducing the suite of radionuclides (Table 5-2) to a subset of radionuclides appropriate for groundwater. The staff notes that the OCNGS groundwater protection program includes tritium, Sr-90, Sr-89, gross alpha, and gross gamma; thus, the reconciliation may include the specific measurement method and trigger levels for additional measurements/methods.
OBSERVATIONS ON THE APPROACH FOR ADDRESSING COMPLIANCE WITH THE RADIOLOGICAL CRITERIA FOR LICENSE TERMINATION Summary List of Comments on Chapter 6 of the Draft OCNGS LTP 1.
Chapter 6 provides insufficient information to support elimination of a residential scenario as a compliance scenario(s). Additional information is needed to show that residential land use in the next 100 years is not reasonably foreseeable. Supporting references may contain additional information that is not currently available in the report.
Statements are made that sufficient land is available for residential development; however, no supporting data is presented in the LTP and land use data in the area surrounding the site show a significant portion of the area is developed for residential land use. The demand for additional residential development and the land available for development in the area are unclear. This type of information is needed to support elimination of a resident scenario as a compliance scenario.
Likewise, statements are made that the soil is not conducive to agricultural purposes; however, soil data surrounding the site also show the potential for local gardening or farming in the area. Additional information is needed to rule out the potential residential gardening on the site as a reasonably foreseeable exposure scenario.
2.
Chapter 6 provides insufficient information to support elimination of the groundwater pathway. Arguments related to physical limitations (e.g., yield),
groundwater quality (e.g., unavailability of potable water supply source due to high salinity), and/or administrative controls on groundwater use at the site typically provide stronger support for elimination of the groundwater pathway.
Information on groundwater well use in the surrounding community should also be provided to support elimination of the groundwater pathway. Additionally, while groundwater may not be used for drinking water, other groundwater dependent pathways may need to be considered (e.g., use of groundwater for irrigation).
Additionally, the State of New Jersey should provide input on whether it agrees with OCNGSs elimination of the groundwater pathway when calculating clean-up levels for unrestricted release of the site.
3.
Chapter 6 of the LTP cites RESRAD documentation for parameter support in multiple instances without additional support. As stated in NUREG-1757, Volume 2, Revision 2, Appendix I, the RESRAD deterministic defaults are not acceptable for use without further justification. Instead, a graded approach should be used with more support provided for parameters important to dose.
While the RESRAD default parameter distributions can be used for parameter assignment to perform probabilistic sensitivity analysis, as documented in sources such as NUREG/CR-7267, NUREG-1757, Volume 2, Revision 2, guidance indicates that for risk-significant parameters such as distribution coefficients or Kds that additional support may be needed (i.e., that the 25th or the 75th percentile values from the parameter distributions may not be demonstrably conservative). A good understanding of the factors influencing any risk-significant Kds identified in probabilistic sensitivity analysis is needed along with a review of the literature supporting the site-specific values to ensure that a deterministic value is conservatively selected.
For example, even if site-specific soil types are used to define the parameter distributions, other factors such as geochemical conditions (e.g., pH, Eh, presence of complexing agents or competing ions) may be important to selection of the Kd for a particular site as evidenced by the fact that Kds for a particular radionuclide can vary orders of magnitude for the same soil type. In some cases, the pedigree of the data used to define the parameter distributions may be poor and some minimal level of effort is needed by the licensee to justify the selection of risk-significant parameters in their dose modeling calculations to derive DCGLs.
4.
Chapter 6 of the LTP should evaluate all parameters important to dose in developing DCGLs for above-ground building structures (e.g., a sensitivity analysis on room size appears warranted). Additionally, justification should be provided for elimination of the renovation scenario if renovation of the remaining buildings following license termination may be reasonably foreseeable.
5.
No basis is provided for the assumption that only the thickness of the basement substructures located above the water table will be assumed to be excavated in the excavation scenario used to derive DCGLs for basement substructures expected to remain at the time of license termination. If industrial use of the site following license termination is expected, arguments should be presented on reasonable excavation depths associated with construction of substructures to support planned new industry development.
Because the groundwater pathway is eliminated in the compliance scenario, the excavation scenario drives the dose for basement substructures. Sensitivity analysis on excavation volume or infinite source arguments may be made to support the assumed depth of excavation assumption in developing the DCGLs.
Acute exposure to construction workers digging up reactor basement substructures should also be addressed to ensure that chronic exposure to the industrial worker following redistribution of residual radioactivity on the surface is a bounding exposure scenario for the radionuclides considered. Qualitative arguments may be acceptable for elimination of certain exposure scenarios from detailed analysis.
6.
Use of RESRAD-ONSITE to estimate the dose from instantaneous release of residual radioactivity to groundwater should be further justified commensurate with the risk-significance of groundwater related pathways. As discussed in DUWP-ISG-02, use of RESRAD-ONSITE to develop DCGLs for substructures can lead to an underestimate of dose due to excessive groundwater well dilution.
For example, the assumption that the reactor basement substructures are not a barrier to natural groundwater flow requires additional support as it may lead to an underestimate of dose. Additionally, the source and source to well geometries in the RESRAD-ONSITE conceptual model are constrained leading to assignment of source and other parameters that are not consistent with the actual distribution of residual radioactivity in the subsurface and the potential conditions expected at the site at the time of license termination, which can also lead to an underestimate of groundwater concentrations and dose.
Conservative assumptions regarding the amount of dilution can also be made to allow use of RESRAD-ONSITE as described in DUWP-ISG-02. The risk-significance of this comment and the amount of credit needed for groundwater dilution will be based on the exposure scenarios and groundwater dependent pathways that are considered or eliminated during DCGL development.
7.
Well drilling and excavation scenarios that can bring residual radioactivity at depth to the surface are considered in the development of DCGLs for basement substructures, but could need additional support. Assumptions are made regarding the distribution of residual radioactivity at the surface (e.g., area and thickness of residual radioactivity distributed on the surface) that may be important to dose and would benefit additional support. A sensitivity analysis could be conducted to support the parameter values selected to ensure that the doses are not underestimated for the set of radionuclides of concern studied.
8.
The RESRAD simulations appear to overlap the contaminated zone (CZ) with the unsaturated zone (UZ) layer. If the CZ straddles to the water table, there is no UZ (UZ thickness is 0 meters).
9.
Justification should be provided regarding the lack of consideration of excavation of buried and embedded piping in the DCGL calculations.
- 10. EPA documentation may not be acceptable for use in estimating dose from existing residual radioactivity in groundwater. For example, MCLs are based on outdated internal dosimetry (ICRP 2) and may not be acceptable for use without further justification. Chapter 4 in DUWP-ISG-02 provides information on calculation of pathway dose conversion factors using RESRAD-ONSITE as well as various methods to estimate dose from existing groundwater contamination.
Editorial Comments 1.
Page 5 bullet 4 states that soil conditions and land use trends make it clear that the use of the site for agricultural purpose is unlikely. This text likely should read that future agricultural use of the site is a less likely but plausible scenario unless you are differentiating between residential farming versus gardening, with residential gardening being evaluated as less likely but plausible in the current Chapter 6.
2.
Chapter 6 text repeatedly refers to parameters are being sensitive. The results are sensitive to changes in parametersthe parameters themselves are not sensitive.
Another way to communicate the risk-significance of the parameters is to state that the parameters are important to dose or that they are risk-significant parameters.
3.
Section 6.8.1.1 (page 46), the second sentence in the section appears to be incomplete.
REFERENCES 1.
Regulatory Guide 1.179, Standard Format and Content of License Termination Plans for Nuclear Power Reactors, Revision 2 (ML19128A067).
2.
NUREG-1700, Standard Review Plan for Evaluating Nuclear Power Reactor License Termination Plans, Revision 2 (ML18116A124).
3.
NUREG-1757, Volume 2, Consolidated Decommissioning Guidance: Characterization, Survey, and Determination of Radiological Criteria - Final Report, Revision 2 (ML22194A859).
4.
NUREG-1575, Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM), Revision 1 (ML003761445 and ML003761454).
5.
DUWP-ISG-02, Draft Interim Staff Guidance: Radiological Survey and Dose Modeling of the Subsurface To Support License Termination (ML23177A008).
ML24094A214; Ltr ML24094A214 OFFICE NMSS/DUWP/RDB NMSS/DUWP/RDB NMSS/DUWP/RDB NAME MDoell SAnderson MDoell DATE Apr 9, 2024 Apr 18, 2024 Apr 18, 2024