ML23255A005

20230913 NRC Public Meeting Slides TVA CRN-1 RB Excavation

ML23255A005
Person / Time
Site:	Clinch River, 99902056
Issue date:	09/13/2023
From:	Allen Fetter Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation
References
Download: ML23255A005 (1)

Text

9/11/2023 1

NRC Public Meeting TVA Clinch River Project CRN-1 Reactor Building Excavation September 13, 2023 Agenda

Introductions

Background Expected Activities/Benefits Exemption Request Schedule Conclusion Questions/Comments 2

Clinch River Nuclear (CRN) Site 1

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2 Background

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• In preparing the CRN-1 site for nuclear construction, TVA intends to excavate for the BWRX-300 Reactor Building in advance of receiving the Construction Permit (CP).

• Per 10 CFR 50.10(a)(2)(v), excavation on its own is not considered to fall into the definition of construction.

• To ensure worker safety during excavation and facilitate construction activities, an initial ground support system is expected to be installed for erosion control prior to and during excavation.

• Initial ground support system serves no function in the completed construction.

• Proposed initial ground support features are infeasible to remove and are planned to be abandoned in place.

• TVA has not yet authorized the deployment of an SMR. Nonetheless, these discussions and efforts regarding excavation activities will enable TVA to move forward in a timely manner, if and when a decision is made to build an SMR.

Initial Ground Support System 4

The following items may be installed as part of the initial ground support system:

secant piles or steel piles through the soil overburden and weathered rock, if

required, rock bolts to secure unstable rock blocks and create a safe and stable excavation, as

required, wire mesh and a thin, non-structural sprayed-gunite lining to stabilize and protect exposed rock walls, horizontal gravity drains to manage groundwater, as required, pressurized grout to seal any notable areas of water entry.

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Benefits of Excavation prior to CP Issuance 5

Reduces risk and improves schedule by completing excavation prior to CP issuance and commencement of construction activities:

Additional subsurface information can be provided to the NRC to consider before the CP is issued.

Allows the extensive geotechnical mapping and surveys to be performed on a more controlled schedule when it is separated from the primary construction schedule.

Identification of any critical features like discontinuities, shear zones, faults, karst features, or potentially unstable blocks will help improve the design of the permanent ground support system prior to construction.

Optimizing the schedule for demonstration of new nuclear plants is imperative to enabling TVA to consider SMRs throughout the TVA Power Service Areas to support TVAs carbon emission reduction aspirations (e.g. net-zero by 2050).

Expected Excavation Activities 6

1. Site preparation activities

2. Installation of field instrumentation

3. Excavation through the soil overburden and weathered rock.

• 1) sloped excavation using conventional earthmoving equipment,

• 2) secant piles or steel piles installed and keyed into the bedrock1.

4. Construction of temporary crane pads.

5. Line drilling around the perimeter of the shaft excavation.

1 If installed will be abandoned in place.

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Expected Excavation Activities 7

6. Excavating through the bedrock will be completed in 8-12 deep lifts.

• 1) Controlled drilling and blasting,

• 2) Expanding chemical grouting, and

• 3) Rock Hammer

7. Temporary de-watering systems, such as pumps and sumps and temporary wells or well points, will be employed during shaft excavation. Areas of notable water entry will be sealed via an engineered pressure grouting process or localized water collection system1.

1 If installed will be abandoned in place.

Expected Excavation Activities 8

8. Geological mapping of the rock walls will be completed during the excavation meeting the requirements of NRC Inspection Manual 88131. The inspection of the shaft walls will be performed as the shaft progresses in lifts.

9. Natural voids or poor quality rock identified during the excavation process or exposed in the walls of lifts will be evaluated and, when required, stabilized. This stabilization may include rock reinforcement (i.e. rock bolts) or treatment with grout1.

1 If installed will be abandoned in place.

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Expected Excavation Activities 9

10.Wire mesh reinforcement, in combination with a non-structural sprayed-gunite lining will be installed on the rock face1. In cases where seepage is noted in the bedrock, horizontal gravity drains1 and/or weep holes will be installed so that the water does not deteriorate the sprayed-gunite lining.

11.The final foundation level at the base of the excavation will be cleaned and mapped in addition to the walls of the final lift. If any anomalous issues are discovered, additional geotechnical investigations will be performed in accordance with RG 1.132.

1 If installed will be abandoned in place.

Exemption Request 10 TVA is considering submitting an exemption request to provide regulatory certainty in moving forward with excavation prior to CP Issuance.

• 10 CFR 50.12 (a)

• 10 CFR 50.12 (b)

It is not expected that an NRC environmental impact statement or environmental assessment will be required for approval of an exemption request as it would meet the criteria of 10 CFR 51.22(c)(25).

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Construction Permit Issuance 11

• As communicated previously, TVA has not yet authorized the deployment of an SMR. Nonetheless, receiving an exemption from 10 CFR 50.10(c) will provide regulatory certainty from NRC moving forward for excavation activities which would enable TVA to move forward in a timely manner, if and when a decision is made to build an SMR.

Q1 Q2 Q3 Q4 Q1 2022 2023 2024 2025 2026 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q2 Q3 Q4 Q4 Q1 Q2 Q3 Q4 Excavation Prepare CPA NRC Review CPA CPA Approval Submit Exemption Request NRC Approval of Exemption Request NRC Acceptance Review Prepare ER NRC Review ER TVA NEPA TVA SEIS Issued Prepare NRC Review Conclusion 12

• The RB excavation is of critical importance to the CRN-1 construction schedule and cannot be conducted without installation of the initial ground support system.

• If excavation for CRN-1 is delayed until issuance of the CP, it is anticipated the demonstration of constructing and licensing an SMR would be delayed over one year, hence delaying the availability of carbon-free electricity generation.

• An exemption request would satisfy the necessary elements of 10 CFR 50.12(a) and 10 CFR 50.12(b), as well as satisfy the requirements for a categorical exclusion in accordance with 10 CFR 51.22(c)(25).

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