ML25259A175
| ML25259A175 | |
| Person / Time | |
|---|---|
| Site: | Kemmerer File:TerraPower icon.png |
| Issue date: | 09/15/2025 |
| From: | George Wilson TerraPower |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| Shared Package | |
| ML25259A174 | List: |
| References | |
| TP-LIC-LET-0457 | |
| Download: ML25259A175 (1) | |
Text
15800 Northup Way, Bellevue, WA 98008 www.TerraPower.com P. +1 (425) 324-2888 F. +1 (425) 324-2889 September 15, 2025 TP-LIC-LET-0457 Docket Number 50-613 U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 ATTN: Document Control Desk
Subject:
Submittal of Supplemental Information to Support Kemmerer Unit 1 Construction Permit Application Review
References:
1.
TerraPower, LLC, Submittal of the Construction Permit Application for the Natrium Reactor Plant, Kemmerer Power Station Unit 1, March 28, 2024 (ML24088A059).
This letter transmits information to supplement the construction permit application for Kemmerer Unit 1, provided via Reference 1. Specifically, this letter provides additional design information about sodium pump lube oil and Intermediate Heat Exchanger (IHX) welding. contains proprietary information and as such, it is requested that Enclosure 4 be withheld from public disclosure in accordance with 10 CFR 2.390, Public inspections, exemptions, requests for withholding. An affidavit certifying the basis for the request to withhold Enclosure 3 from public disclosure is included as Enclosure 1. Proprietary materials have been redacted from the report provided in Enclosure 4; redacted information is identified using (( ))(a)(4).
This letter and enclosures make no new or revised regulatory commitments.
Date: September 15, 2025 Page 2 of 2 If you have any questions regarding this submittal, please contact Ian Gifford at igifford@terrapower.com.
Sincerely, George Wilson Senior Vice President, Regulatory Affairs TerraPower, LLC
Enclosures:
- 1. TerraPower, LLC Affidavit and Request for Withholding from Public Disclosure (10 CFR 2.390(a)(4))
- 3. Intermediate Heat Exchanger Tube-to-Tubesheet Welds Design Information
- Non-Proprietary (Public)
- 4. Intermediate Heat Exchanger Tube-to-Tubesheet Welds Design Information
- Proprietary (Non-Public) cc:
Mallecia Sutton, NRC Josh Borromeo, NRC Nathan Howard, DOE
ENCLOSURE 1 TerraPower, LLC Affidavit and Request for Withholding from Public Disclosure (10 CFR 2.390(a)(4))
TerraPower, LLC Affidavit and Request for Withholding from Public Disclosure (10 CFR 2.390(a)(4))
I, George Wilson, hereby state:
- 1. I am the Senior Vice President, Regulatory Affairs and I have been authorized by TerraPower, LLC (TerraPower) to review information sought to be withheld from public disclosure in connection with the development, testing, licensing, and deployment of the Natrium reactor and its associated fuel, structures, systems, and components, and to apply for its withholding from public disclosure on behalf of TerraPower.
- 2. The information sought to be withheld, in its entirety, is contained in Enclosure 4 which accompanies this Affidavit.
- 3. I am making this request for withholding, and executing this Affidavit as required by 10 CFR 2.390(b)(1).
- 4. I have personal knowledge of the criteria and procedures utilized by TerraPower in designating information as a trade secret, privileged, or as confidential commercial or financial information that would be protected from public disclosure under 10 CFR 2.390(a)(4).
- 5. The information contained in Enclosure 4 accompanying this Affidavit contains non-public details of the TerraPower regulatory and developmental strategies intended to support NRC staff review.
- 6. Pursuant to 10 CFR 2.390(b)(4), the following is furnished for consideration by the Commission in determining whether the information in Enclosure 4 should be withheld:
- a. The information has been held in confidence by TerraPower.
- b. The information is of a type customarily held in confidence by TerraPower and not customarily disclosed to the public. TerraPower has a rational basis for determining the types of information that it customarily holds in confidence and, in that connection, utilizes a system to determine when and whether to hold certain types of information in confidence.
The application and substance of that system constitute TerraPower policy and provide the rational basis required.
- c. The information is being transmitted to the Commission in confidence and, under the provisions of 10 CFR 2.390, it is received in confidence by the Commission.
- d. This information is not available in public sources.
- e. TerraPower asserts that public disclosure of this non-public information is likely to cause substantial harm to the competitive position of TerraPower, because it would enhance the ability of competitors to provide similar products and services by reducing their expenditure of resources using similar project methods, equipment, testing approach, contractors, or licensing approaches.
I declare under penalty of perjury that the foregoing is true and correct.
Executed on: September 15, 2025 George Wilson Senior Vice President, Regulatory Affairs TerraPower, LLC
ENCLOSURE 2 PSP and ISP Lube Oil System Design Information Non-Proprietary (Public)
Primary Sodium Pumps and Intermediate Sodium Pumps Lube Oil System Design Information Page 1 of 1 Not Confidential Controlled Document - Verify Current Revision SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All rights reserved.
Multiple barriers exist between primary sodium and each Primary Sodium Pump (PSP) lube oil system.
These barriers include the mechanical shaft seal and the seals for the oil lubricated bearings. The oil lubricated bearings are located above the shaft seal outside of the reactor vessel and outside of the primary coolant boundary. The shaft seal and the oil lubricated bearings are continuously monitored for leakage, such that a leak is detected and mitigated before oil comes into contact with sodium.
The design of leak detection methods has not been finalized. The design will include monitoring of: (1) radioactivity in the head access area (leakage out from the shaft seal); (2) oxygen concentration in the primary cover gas (leakage into the shaft seal); and level of the oil reservoir (leakage out of bearings).
The design of the Intermediate Sodium Pumps lube oil system will utilize the same barriers and features as the PSP lube oil system.
ENCLOSURE 3 Intermediate Heat Exchanger Tube-to-Tubesheet Welds Design Information Non-Proprietary (Public)
Intermediate Heat Exchanger Tube-To-Tubesheet Weld Design Information Page 1 of 5 Not Confidential Controlled Document - Verify Current Revision SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All rights reserved.
The information that follows provides the current approach to design, analyze, and fabricate the Intermediate Heat Exchanger (IHX) tube-to-tubesheet welds for the Kemmerer Unit 1 project. All IHX tube-to-tubesheet welds will meet the fabrication requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC)Section III, Division 1, NB-4350 and will be examined as required by NB-5274. Pressure boundary tube-to-tubesheet welds will satisfy the applicable requirements of Section III, Division 5, HBB-3000 considering the loadings of HBB-3110. This approach is equivalent to the tube-to-tubesheet requirements of NB-3353, as introduced in ASME BPVC Section III, Division 1, 2019 Code Edition.
Tube-to-Tubesheet Welds Code Interpretation Record 24-2742 regarding autogenous welding has been withdrawn. While ASME BPVC Section III, Division 5 does not prohibit autogenous welds, it also does not provide sufficient rules to support their use, meaning a Code Case would be needed supplementally.
The IHX design includes partial penetration tube-to-tubesheet welds as these are not prohibited by the Code and undue analysis or fabrication concerns are not foreseen with using this type of weld at this location. The partial penetration weld is different than a fillet, in that a groove is provided in the tubesheet allowing for enhanced fusion. While hydraulic expansion is performed between the tube and tubesheet for sealing, this is not credited in the joint design. The partial penetration weld is analyzed as a strength weld.
A preliminary sketch of the weld is provided for information in Figure 1.
Intermediate Heat Exchanger Tube-To-Tubesheet Weld Design Information Page 2 of 5 Not Confidential Controlled Document - Verify Current Revision SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All rights reserved.
Figure 1 - Preliminary Partial Penetration Tube-to-Tubesheet Weld Sketch (a)(4)
Intermediate Heat Exchanger Tube-To-Tubesheet Weld Design Information Page 3 of 5 Not Confidential Controlled Document - Verify Current Revision SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All rights reserved.
Tube-to-tubesheet welds are not explicitly addressed in ASME Section III, Division 5. However, HBB-4110(b) requires that the rules of NB-4000 be complied with. The requirements of NB-4350 regarding tube-to-tubesheet welding procedures and qualifications, and the minimum weld throat will be met.
Additionally, HBB-5110(b) requires that the rules of NB-5000 be complied with. The provisions of HBB-5245 for progressive liquid penetrant examination of partial penetration welds will be met, which will also satisfy the requirements of NB-5274. Apart from these instances, HBB-4000 and HBB-5000 do not provide reference to any other requirements pertaining directly to tube-to-tubesheet welds. Therefore, by reference, tube-to-tubesheet welds are permitted by ASME Section III, Division 5, with no explicit exclusions for partial penetration tube-to-tubesheet welds.
HBB-3000 does not have specific rules for tube-to-tubesheet welds.
Given that HBB-3000 does not provide specific requirements for tube-to-tubesheet welds, it is proposed that the partial penetration welds for this high temperature application follow NB-3353, which was introduced in Code Edition 2019. This requirement is specific to tube-to-tubesheet welds and states, All tube-to-tubesheet welds shall meet the fabrication requirements of NB-4350 and shall be examined as required by NB-5274. Pressure boundary tube-to-tubesheet welds shall satisfy the applicable requirements of Section III Appendices, Mandatory Appendix XIII, Article XIII-3000 considering the loadings of NB-3110. In the case of the Natrium1 IHX, since it is a Division 5 component, the rules of HBB-3000 would be followed instead of the Article XIII-3000 requirements. Therefore, the equivalent approach would be All tube-to-tubesheet welds shall meet the fabrication requirements of NB-4350 and shall be examined as required by NB-5274. Pressure boundary tube-to-tubesheet welds shall satisfy the applicable requirements of Section III Division 5, HBB-3000 considering the loadings of HBB-3110.
NB-3353 will be adapted for a high temperature application by applying the following provisions in HBB-3000 to the tube-to-tubesheet weld joints. A summary of the provisions in HBB-3000 that will be applied to tube-to-tubesheet weld joints are as follows:
((
))(a)(4) 1 1 Natrium is a TerraPower & GE Vernova Hitachi Nuclear Energy Technology
Intermediate Heat Exchanger Tube-To-Tubesheet Weld Design Information Page 4 of 5 Not Confidential Controlled Document - Verify Current Revision SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All rights reserved.
((
))(a)(4)
To ensure the weld is appropriately designed and analyzed, ((
))(a)(4) to provide preliminary qualification of the tube-to-tubesheet welds and information for finite element analysis of this region. The welds will be sectioned for examination to characterize ((
))(a)(4) in the finite element model that is used for stress analysis of the tube to tubesheet joints, in accordance with HBB-3353(b).
The proposed analysis and fabrication method would not prohibit the ASME stamping of the vessel and is acceptable with respect to the ASME code rules.
The IHX is designed with ((
))(a)(4). The loads at the tube-to-tubesheet joints are characterized for all design basis thermal transient conditions and evaluated in the stress analysis. The thermal-structural analysis for this region is ongoing, and ((
))(a)(4) to meet the ASME Section III, Division 5 allowable stresses.
For this specific application, the consequence of leakage at a tubesheet weld is part of the IHX leak event family for the assessment of reactivity control, radionuclide retention, heat removal, and dose consequences. ASME event C.2 characterizes the structural loads for an IHX leak. In the event of a leak in a tube, intermediate sodium will leak into the primary sodium. The primary sodium is normally operating at atmospheric pressure, and the intermediate sodium normal operating pressure is around 110 psig.
There is no adverse reaction since fluids on both sides of the pressure boundary are sodium.
The strength of the expansion of the tube into the tubesheet is not credited in the joint design, as it will not be qualified for strength and relax in service. However, if a crevice forms between the tube and tubesheet, the likelihood of degradation is not considered higher relative to other parts of the heat exchanger due to the liquid sodium operating conditions. Operating experience shows that crevice geometries can be of concern in light water reactor applications where boiling may occur at the crevice, thus concentrating chemicals in the crevice region. However, in the Natrium IHX there is more than 600°F margin between the operating temperature of the sodium at the tubesheet and sodiums boiling temperature. Significant chemistry excursions are not expected in the primary sodium, as discussed in PSAR Sections 7.2.3, Sodium Cover Gas, and 7.2.4, Sodium Processing System. If a crevice forms, the volume of the crevice is expected to be very small so only a small amount of sodium would be in contact with the tube.
Intermediate Heat Exchanger Tube-To-Tubesheet Weld Design Information Page 5 of 5 Not Confidential Controlled Document - Verify Current Revision SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All rights reserved.
Creep-fatigue acceptance testing Testing of commercial 304H tube specimens is in-progress. The specimens have prototypic diameter (0.625 inch) and thickness (0.0039 inch), grain size, and align closely with the required production tubing material and chemistry requirements. The testing is being performed to gain understanding and familiarity with HBB-2800, particularly since Note 14 to ASTM E606 identifies that the cycles attainable for tubing compared to solid product forms are expected to be less.
The objectives of the testing are to verify the feasibility of performing HBB-2800 test for thin-wall Type 304H IHX tubing and to assess the margin to the HBB-2800 acceptance criteria (200 cycles without fracture or 20% drop in load range). ((
))(a)(4)
((
))(a)(4)
Following the completion of the commercial tube fatigue acceptance testing, we are performing pre-production qualification of the IHX tubes. This will also include fatigue acceptance testing for each lot to allow for certification of the tubes to ASME Section III Division 5.