ML24145A107
| ML24145A107 | |
| Person / Time | |
|---|---|
| Site: | Clinch River, 99902056 |
| Issue date: | 06/20/2024 |
| From: | Hayes M NRC/NRR/DNRL/NLIB |
| To: | Brian Mcdermott Tennessee Valley Authority |
| Fetter, A., NRR/DNRL, 301-415-8556 | |
| References | |
| ERIDS D134 | |
| Download: ML24145A107 (11) | |
Text
June 20, 2024 Mr. Brian McDermott, Director Licensing and Planning New Nuclear Program Tennessee Valley Authority 1101 Market Street LP 1G-C Chattanooga, TN 37402
SUBJECT:
SUMMARY
REPORT FOR THE GEOLOGY, AND GEOTECHNICAL ENGINEERING INFORMATION AUDIT, TENNESSEE VALLEY AUTHORITY, EXEMPTION REQUEST FROM 10 CFR 50.10(c), CLINCH RIVER NUCLEAR SITE
Dear Mr. McDermott:
By letter dated November 30, 2023, Tennessee Valley Authority (TVA) submitted an exemption request to the U.S. Nuclear Regulatory Commission (NRC) to permit early excavation activities at the Clinch River Nuclear Site (CRNS) prior to the issuance of a construction permit (CP) for the BWRX-300 reactor at the site (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23335A100).
As part of the NRC staffs safety review of TVAs exemption request, the Structural, Civil, and Geotechnical Engineering Branch and the External Hazards Branch, Division of Engineering and External Hazards conducted a virtual audit with TVA starting on March 5, 2024, and ending on May 3, 2024. The purpose of this audit was to understand data and information used to support the geological and geotechnical engineering aspects of the exemption request. The audit plan used for this virtual audit is ML24060A069, and the staff also provided a subsequent additional information need request to TVA (ML24075A322). The information provided by TVA in their electronic reading room (eRR) was reviewed by the NRC staff and used to support the staffs development of the safety evaluation for the exemption request.
The audit allowed the staff to better understand the technical details of the proposed excavation process in order to make appropriate safety conclusions concerning TVAs exemption request and consider any implications there might be for the subsequent CP application review. Staff are continuing the review of the exemption request and will present its findings after both the safety and environmental reviews have been completed.
B. McDermott 2
If you have any questions regarding this matter, please contact Mr. Allen Fetter, Senior Project Manager, at (301) 415-8556 or by via email at allen.fetter@nrc.gov.
Sincerely,
/RA/
Michelle W. Hayes, Chief New Reactor Licensing and Infrastructure Branch Division of New and Renewed Licenses Office of Nuclear Reactor Regulation Docket No. 99902056
Enclosures:
- 1. Audit Summary Report
- 2. Table of Audit Information Need Audit Activities, Observations and Resolution/Status of Information Needs cc w/encls.: GovDelivery.com
- via e-mail NRR-106 OFFICE NRR/DNRL/NLIB: PM NRR/DNRL/NLIB: LA NRR/DEX/EXHB NAME AFetter*
SGreen JThompson DATE 05/15/2024 05/24/2024 05/28/2024 OFFICE NRR/DEX/ESEB NRR/DEX/ESEB: BC NRR/DEX/EXHB: BC NAME LCandelarioQuintana ITseng BHayes DATE 05/29/2024 05/28/2024 05/28/2024 OFFICE NRR/DNRL/NLIB: BC NAME GCranston for MHayes DATE 06/20/2024
CLINCH RIVER NUCLEAR SITE, EARLY EXCAVATIONEXEMPTION REQUEST:
GEOLOGY, AND GEOTECHNICAL ENGINEERING AUDIT
SUMMARY
- 1.
Overview On November 30, 2023, Tennessee Valley Authority (TVA) submitted an exemption request to the U.S. Nuclear Regulatory Commission (NRC) to permit early excavation activities at the Clinch River Nuclear Site (CRNS) prior to the issuance of a construction permit (CP) for the BWRX-300 reactor at the site (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23335A100). In preparation for the virtual audit, the NRC staff reviewed the data and information within the early excavation exemption request and identified information needs/audit items that the staff requires to complete its review.
NRC provided audit information needs to TVA in an audit plan (ML24060A069) and via a supplemental information needs request (ML24075A322). TVA posted information in their electronic reading room in response to the NRC information needs and to support the virtual audit. The virtual audit entrance took place on March 5, 2024, and the audit exit briefing was on May 3, 2024. The list of NRC audit team members and TVA staff who participated in the audit are listed below.
Name Affiliation Fetter, Allen NRC Thompson, Jenise NRC Xi, Zuhan NRC Candelario-Quintana, Luissette NRC Cranston, Greg NRC Lassman, Keith NRC Schiele, Raymond J.
TVA Moorrees, Michele TVA This information audit provided the opportunity for members of the NRC staff to discuss the audit items identified during the staffs initial review of the exemption request with TVAs subject matter experts (SMEs), staff and contractors. During the audit, the staff went over the audit items and relevant supporting materials made available by TVA. The audit allowed the staff to better understand the technical details of the proposed excavation process in order to make appropriate safety conclusions concerning TVAs exemption request and consider any implications there might be for the subsequent CP application review.
- 2.
Reference Documents Request for Exemption from 10 CFR 50.10(c) to Allow Excavation at the Clinch River Nuclear Site Prior to Construction Permit Issuance (ML23335A100)
Information Needs (See Audit Plan: ML24060A069 and Supplemental Information Needs: ML24075A322)
2
- 3.
Documents Audited TVAs Conceptual Excavation Plan (CRNS Reading Room available for audit)
Early Site Permit Conditions and Action Items Licensing Requirements and Summary of disposition (CRNS Reading Room available for audit)
- 4.
Audit Results A table outlining how information needs were addressed, and their resolution status is provided in Enclosure 2.
TABLE OF GEOLOGY, AND GEOTECHNICAL ENGINEERING AUDIT INFORMATION NEEDS AUDIT ACTIVITIES, OBSERVATIONS, AND RESOLUTION/STATUS OF INFORMATION NEEDS Information Need/Technical Information Item ID Number (Description)
Question/Request Audit Item/Activity Observations/Status
- 1. Information Need: Permit Conditions Discuss the need to address Clinch River Nuclear Site early site permit (ESP-006 - ML19352D868) permit conditions 2.5-1 (3) and 2.5-2 (4) and if early excavation could impact them, provide a detailed plan outlining how the applicant intends to address each permit condition to ensure compliance with regulatory requirements as part of the exemption request.
TVA SMEs were available to discuss during the virtual audit meeting and supporting documentation associated with the safety analysis portions of TVAs early excavation exemption request was provided in the Clinch River Nuclear Site Reading Room for review.
NRC staff gained understanding about how the applicant intends to address each permit condition in early site permit ESP-006 (ML19352D868) to ensure compliance with the regulatory requirements as part of the exemption request.
For Permit condition #3 the applicant committed to perform a geologic mapping as part of the excavation activities requested on the exemption. The applicant clarified that the geologic mapping will be completed for each lift before the excavation walls are covered by any necessary stabilization activities and the subsequent lift commences. The applicant indicated that the data will be available as it is recovered but that excavation activities are not likely to begin until after the CP application is submitted.
For Permit Condition #4 the proposed foundation elevation for the BWRX-300 reactor building (RB) foundation is located below the required excavation elevation. As part of the exemption and during the excavation, the applicant is committed to remove the material above El.225.9m (741 ft) NAVD 88 in the reactor building area. In addition, the applicant will provide details of its supplemental site
investigation program at the center and perimeter of the RB shaft as part of a future CP or combined operating license (COL) application.
The applicant committed to perform additional investigations in accordance with RG 1.132 at the foundation level, if any significant anomalous issues are discovered while performing the excavation and geologic mapping of the RB shaft. Closed.
- 2. Information Need: CP or COL Action Items Discuss the need to address ESP-006 COL action items 2.5-1 through 2.5-17 as part of the exemption request and acknowledge if the planned excavation support activities described in the exemption request could affect addressing the action items in subsequent CP or COL application. If so, discuss how the applicant intends to address each COL action item.
TVA SMEs were available to discuss during the virtual audit meeting and supporting documentation associated with the safety analysis portions of TVAs early excavation exemption request was provided in the Clinch River Nuclear Site Reading Room for review.
NRC staff gained understanding about how the applicant intends to address each CP or COL action item at a future licensing application. The applicant stated that the activities related to the early excavation exemption request should not affect addressing the CP or COL action items in a future application.
The applicant provided information on preliminary planning efforts for the excavation such as site preparation activities, installation of field instrumentation, methods of excavation, construction of temporary crane pads, temporary dewatering systems, finite element model to assess the impact of dewatering and construction stages on excavation support and foundation, geologic mapping, and stabilization methods. The applicant indicated that the final procedure would specify the stages of excavation and construction of the temporary and permanent excavation support systems. The applicant plans to quantify and incorporate the impacts of rock excavation on the mechanical properties in a numerical simulation for the assessment of the foundations. The applicant will also develop an instrumentation and monitoring program consistent with Chapter 3.4 of the approved LTR NEDO-33914-A to meet regulatory requirements. The applicant plans to monitor lateral and vertical displacement during
excavation and construction, slope movement, heave, changes in pore pressures during excavation and dewatering, and settlement.
The applicant indicated that once developed and finalized the following items can be provided to the NRC upon request: grouting program, final extent of excavation, instrumentation and monitoring program, final backfill and the design of the dewatering and groundwater control.
Closed.
- 3. Technical Information Item:
Supplemental Investigation Additional information on the confirmatory/supplemental borings performed at the site that may address the requirements of Permit Condition 4 as it relates to confirmatory borings at the excavation level and Permit Condition 3 related to geologic mapping of features and structures at the foundation interface TVA SMEs were available to discuss during the virtual audit meeting and supporting documentation associated with the safety analysis portions of TVAs early excavation exemption request was provided in the Clinch River Nuclear Site Reading Room for review.
The applicant provided a brief description about the 2023 supplemental CRN investigation performed. The supplemental investigation included additional drilling and coring of deep borings, borehole geophysical testing and laboratory testing. The applicant indicated that the data is used to characterize subsurface conditions and potential impacts of any anomalies detected in the investigation. The applicant indicated that based on the completed field investigations and confirmatory boreholes around the excavation, no notably different conditions were discovered, and the identification of large voids is highly unlikely.
However, the applicant stated that if during excavation, a large unknown void is identified geological characterization of the void will be performed and the NRC will be notified for inspections per Regulatory Guide 1.132. The applicant would discuss details and results of the supplemental investigation in a future CP or COL application. Closed.
- 4. Technical Information Item:
Excavation and construction sequencing Provide information on excavation and construction sequencing TVA SMEs were available to discuss during the virtual audit meeting and supporting documentation associated with the safety analysis portions of TVAs early excavation exemption request was provided in the Clinch River Nuclear Site Reading Room for review The applicant provided a conceptual excavation plan with activities that it expects to support a safe and efficient excavation for the reactor building. The applicant provided information on preliminary planning efforts for the excavation such as site preparation activities, installation of field instrumentation, methods of excavation, construction of temporary crane pads, temporary dewatering systems, finite element model to assess the impact of dewatering and construction stages on excavation support and foundation, geologic mapping, and stabilization methods. Further, the applicant indicated that the final excavation procedure would specify the stages of excavation and construction of the temporary and permanent excavation support systems. Closed.
- 5. Technical Information Item:
Ground water effects Discussion on groundwater effects during and after excavation and evaluation of the stability of the excavated walls considering the effects of groundwater drawdown (i.e., collapse, rockfall, unexpected changes in ground water conditions)
TVA SMEs were available to discuss during the virtual audit meeting and supporting documentation associated with the safety analysis portions of TVAs early excavation exemption request was provided in the Clinch River Nuclear Site Reading Room for review The applicant indicated that the site-specific data and adjacent historical information from the Clinch River Breeder Reactor Program indicates that minimal groundwater infiltration should be expected. The applicant plans to use temporary dewatering systems during the excavation. In the areas of notable water entry, the applicant plans to seal it via engineered pressure grouting process or localized water collection system.
The applicant will consider the effect of hydrostatic pressure buildup behind the support wall of the vertical shaft excavation during the final design phase. In addition, the applicant indicated that a 3D finite element model will be developed to assess the impact of dewatering and construction stages on the excavation support and foundation of the RB shaft. Closed.
- 6. Technical Information Item:
Retaining Methods The exemption request assumes hard rock conditions for the full extent once the Benbolt formation is encountered. The applicant plans to conduct a vertical excavation and staff needs to understand TVAs contingency plans if the vertical rock surface presents conditions that need retaining methods.
TVA SMEs were available to discuss during the virtual audit meeting and supporting documentation associated with the safety analysis portions of TVAs early excavation exemption request was provided in the Clinch River Nuclear Site Reading Room for review The applicant plans to use a combination of stabilization methods, as needed. (e.g., rock bolts, wire mesh, gravity drains (only if needed to direct water away), and pressurized grout), other stabilization methods will depend on selected excavation method (e.g., compression rings, roller compacted concrete, secant piles, etc.). The applicant indicated that no part of the reactor building walls or foundations will be installed before a CP is approved. Specifically, the applicant confirmed that neither the annulus filled with lean concrete nor the steel plate composite RB walls, as shown in Figure 1 of the exemption request, are considered part of this early excavation exemption request. Furthermore, the applicant stated that the emplacement of the annulus will occur after construction permit issuance and that it will be approximately five feet wide around the shaft, thus separating the RB from excavation and any abandoned ground support stabilization component. Closed
- 7. Technical Information Item:
Effects of initial ground support system considered in the SSI analyses The applicant stated the following on the exemption request: Any effects of the initial ground support system will be considered through seismic soil structure interaction (SSI) sensitivity analyses performed using best estimate properties of surrounding in-situ subgrade materials on an RB finite element model that includes the excavation support structure and the fill material to assess their effect on the BWRX-300 RB seismic response.
Discussion about the initial ground support system and best estimate properties of surrounding in-situ subgrade materials vs. estimates of upper and lower bound properties as part of the SSI sensitivity analysis TVA SMEs were available to discuss during the virtual audit meeting and supporting documentation associated with the safety analysis portions of TVAs early excavation exemption request was provided in the Clinch River Nuclear Site Reading Room for review The applicant indicated that the use of best estimate properties comes from the methodology approved in the LTR, NEDO-33914-A, BWRX-300 Advances Civil Construction and Design Approach. that the applicant expects the methodology to be sufficient but may use additional upper and lower bound estimates within the LTR to incorporate any different excavation conditions that may be encountered.
The staff noted that in the event of the need for additional retaining measures during the excavation and as part of the initial ground support system, the potential effects of the additional retaining measures on the RB structure, especially if exposed to ground water, and the evaluation of the additional retaining measures shall be included as part of the SSI sensitivity analysis. Closed