L-MT-23-052, Subsequent License Renewal Application Supplement 7

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Subsequent License Renewal Application Supplement 7
ML23334A147
Person / Time
Site: Monticello Xcel Energy icon.png
Issue date: 11/30/2023
From: Hafen S
Northern States Power Company, Minnesota, Xcel Energy
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
L-MT-23-052
Download: ML23334A147 (1)
v • d • e


Text

fl Xcel Energy 2807 West County Road 75 Monticello, MN 55362 November 30, 2023 L-MT-23-052 10 CFR 54.17 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket No. 50-263 Renewed Facility Operating License No. DPR-22 Subsequent License Renewal Application Supplement 7

References:

1) Letter from Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy to Document Control Desk, "Monticello Nuclear Generating Plant Docket No. 50-263, Renewal License Number DPR-22 Application for Subsequent Renewal Operating License" dated January 9, 2023, ML23009A353
2) Letter from Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy to Document Control Desk, "Monticello Nuclear Generating Plant Subsequent License Renewal Application Supplement 1" dated April 3, 2023, ML23094A136
3) Letter from Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy to Document Control Desk, "Monticello Nuclear Generating Plant Subsequent License Renewal Application Supplement 2" dated June 26, 2023, ML23177A218
4) Letter from Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy to Document Control Desk, "Monticello Nuclear Generating Plant Subsequent License Renewal Application Supplement 3" dated July 11, 2023, ML23193B026
5) Letter from Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy to Document Control Desk, "Monticello Nuclear Generating Plant Subsequent License Renewal Application Supplement 4 and Responses to Request for Confirmation of Information - Set 1" dated July 18, 2023, ML23199A154
6) Letter from Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy to Document Control Desk, "Monticello Nuclear Generating Plant Subsequent License Renewal Application Supplement 5" dated August 28, 2023, ML23240A695

Document Control Desk L-MT-23-052 Page 2

7) Letter from Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy to Document Control Desk, "Monticello Nuclear Generating Plant Subsequent License Renewal Application Response to Request for Additional Information Set 2 and Supplement 6" dated September 05, 2023, ML23248A474
8) Memorandum from Office of Nuclear Reactor Regulation to Office of Nuclear Reactor Regulation, "U.S. Nuclear Regulatory Commission Summary Of The October 10, 2023, Public Meeting To Discuss Monticello's Condensate Backwash Receiving Tank Fatigue Evaluation" dated November 09, 2023, ML23313A159 Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy hereafter "NSPM", is submitting a supplement to the Subsequent License Renewal Application, listed in Reference 1.

Clarifying information regarding Tables 4.2.3-1 and 4.2.3-2 and an updated reference was provided in Supplement 1, listed in Reference 2. Clarifications to sections of the SLRA discussed in the breakout audits occurring April through June of 2023 were provided in Supplements 2 through 6, listed in References 3 through 8, respectively. Note that Supplement 3 (Reference 4) did not make any changes to the SLRA. Additional clarifications discussed in the breakout audits occurring October through November and the October public meeting of 2023 are being provided in Supplement 7. The supplement is provided in the Enclosures.

In the enclosures, changes are described along with the affected section(s) and page number(s) of the docketed SLRA (Reference 1) where the changes are to apply. For clarity, revisions to the SLRA are provided with deleted text by strikethrough and inserted text by bold red underline . Changes incorporated from previous RAls and supplements are provided by bold, black font and noted in enclosure.

Document Control L-MT Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.

I declare under penalty of perjury that the foregoing is true and correct.

Shawn~

Site Vice Pr sident, Monticello Nuclear Generating Plant Northern States Power Company - Minnesota cc: Administrator, Region 111, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC Minnesota Department of Commerce

Document Control Desk L-MT-23-052 Page 4 Enclosures Index Enclosure Subject No.

01 Supplement to Condensate Backwash Receiving Tank Fatigue Evaluation Core Spray - Summary of Aging Management Evaluation Table 1 Items 02 Updated 03 Loss of Fracture Toughness (Cracking) of RV Supports

Enclosure 01 Supplement to Condensate Backwash Receiving Tank Fatigue Evaluation

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 1 Page 1 of 4 Supplement to Condensate Backwash Receiving Tank Fatigue Evaluation Supplement to Condensate Backwash Receiving Tank Fatigue Evaluation Affected SLRA Sections: 4.6.3 and A.3.6.3 SLRA Page Numbers: 4.6-5 and A-53 Description of Change:

This supplement provides correction to the Condensate Backwash Receiving Tank Fatigue Evaluation.

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 1 Page 2 of 4 Section 4.6.3 on page 4.6-5 is revised as follows:

backwashing of the condensate demineralizers. Backwashed sludge from the condensate demineralizers is collected in the Condensate Backwash Receiving Tank, where it is dewatered and packaged as solid waste for disposal offsite (USAR, Section 9.2.2.1).

Additionally, the internal pressure in the Condensate Backwash Receiving Tank was subsequently increased in support of the EPU. As a result of this pressure increase, a fatigue evaluation was performed to accommodate the increased backwash cycles performed at a greater airburst pressure. This fatigue evaluation projected a conservative value of 160 cycles (i.e., airbursts) per year, which extrapolates to 9,600 cycles over a 60 year operating period (40 years of operation plus 20 years of initial license renewal). Alternating stresses in the system were examined to determine an allowable number of cycles for the tank of 35,000 airbursts under normal and accident conditions. Applying this limit, the usage factor for 60 years of operation was found to be 0.28.

This fatigue evaluation of the Condensate Backwash Receiving Tank meets the six TLAA criteria, as defined by 10 CFR 54.3, and will require analysis as a new TLAA for the subsequent period of operation.

TLAA Evaluation The original calculation assumed 160 cycles per year. Over 80 years of operation, the number of cycles estimated is 12,800. This is conservative as the increased pressure and number of backwash cycles was not implemented until EPU (2008). However, even with this conservatism, fatigue usage for this component is calculated to be 0.37, with significant margin to the limit of 35,000 cycles. The original fatigue evaluation projected a value of 160 cycles (i.e., airbursts) per year, which extrapolates to 9,600 cycles over a 60 year operating period (40 years of operation plus 20 years of initial license renewal). However, this calculation was incorrect because it only considered the airbursts from one condensate demineralizer instead of the five demineralizers at the plant. Additionally, until the modification of the tank and backwash process in 2011 (~41 years of operation), the tank was operated at atmospheric pressure with no significant fatigue cycles. The fatigue calculation was revised to correct these errors and determine the actual fatigue usage that the backwash receiving tank would be expected to see if operated throughout the SPEO.

Each of the five condensate demineralizers is backwashed/precoated with an average frequency of every 26 days (rounded down for conservatism) or 15 backwash cycles per year for a single demineralizer. Using this conservatively approximated frequency results in 75 total backwash cycles per year for the five demineralizers. Each backwash cycle consists of eight airbursts that are used to drive the backwash water used for removing the precoat from the filter elements. A flushing water volume is used to support the air surges to provide a means of localizing element cleaning as well as provide a vehicle for sluicing the spent precoat material from the demineralizers.

Prior to EPU, the tank was operated at atmospheric pressure. Therefore, there were no significant fatigue cycles during the period before 2011. With the

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 1 Page 3 of 4 expected end of plant life being considered as 2050, the tank would be utilized for 39 years from the time when the EPU modification changed the tank and backwash process that resulted in periodic cyclic stresses on the backwash receiving tank. The flushing water volume used during the backwash process changes the available tank volume for the airbursts. Therefore, the 23,400 fatigue cycles (75 backwash cycles per year

  • 8 airbursts per cycle
  • 39 years of operation between the EPU modification and the end of the SPEO) that are estimated to occur in the backwash receiving tank were calculated using the maximum expected water volume in the tank for each airburst (i.e., initial water volume from draining of a demineralizer into the tank plus the water volume added by the flushing water for each air burst). A final conservatism was evaluated by adding an additional year of operation (i.e., 75 more backwash cycles or 600 more fatigue cycles) to the analysis, for a total of 24,000 fatigue cycles. This approach conservatively calculates the stress in the tank from each airburst to provide a bounding fatigue usage for the tank at the end of the SPEO.

In addition to the stresses from the air bursts, load combinations considered for the tank included a consideration of deadweight, pipe reaction, weight of water and temperature (under both normal and accident conditions), and seismic loads among other loads.

The number of OBE cycles evaluated for the torus (1000 cycles) is considered a conservative estimate for the seismic cycles that the backwash receiving tank would be expected to experience. However, for additional conservatism and to simplify the analysis, the seismic cycles were also taken as 24,000.

The worst case accident cycle identified would occur when a valve does not close in the system. For this accident case, 100 instances of this cycling were used to calculate the expected fatigue usage through SPEO.

After analyzing the stresses estimated from the fatigue curve in the ASME Section VIII, 1977 Edition, it was found that the Backwash Receiving Tank is acceptable for an expected end of life in 2050. Including all conservatisms and bounding conditions considered in the evaluation, a cumulative usage through SPEO of 0.58 was calculated; demonstrating reasonable assurance that the backwash receiving tank will perform its intended function through SPEO with considerable margin.

TLAA Disposition: 10 CFR 54.21(c)(1)(ii)

The fatigue parameter calculations are revised and shown to remain acceptable throughout the SPEO based on a revised projection of the cumulative number of each of the cyclic loadings to the end of the SPEO. The resulting fatigue parameter values are verified to remain less than 1.0 for the SPEO. The Condensate Backwash Receiving Tank fatigue evaluation has been projected to the end of the SPEO in accordance with 10 CFR 54.21(c)(1)(ii).

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 1 Page 4 of 4 Section A.3.6.3 on page A-53 is revised as follows:

A.3.6.3 Condensate Backwash Receiving Tank Fatigue Analysis As part of the MNGP EPU program to increase maximum thermal power to 2,004 megawatts thermal (MWt), the largest impact of the Liquid Waste Management System would be the increase in liquid and wet solid waste resulting from more frequent backwashing of the condensate demineralizers. Backwashed sludge from the condensate demineralizers is collected in the Condensate Backwash Receiving Tank, where it is dewatered and packaged as solid waste for disposal offsite.

Additionally, the internal pressure in the Condensate Backwash Receiving Tank was subsequently increased in support of the EPU. As a result of this pressure increase, a fatigue evaluation was performed to accommodate the increased backwash cycles performed at a greater airburst pressure. This fatigue evaluation projected a conservative value of 160 cycles (i.e., airbursts) per year, which extrapolates to 9,600 cycles over a 60 year operating period (40 years of operation plus 20 years of initial license renewal). Alternating stresses in the system were examined to determine an allowable number of cycles for the tank of 35,000 airbursts under normal and accident conditions. Applying this limit, the usage factor for 60 years of operation was found to be 0.28. The original fatigue evaluation projected a value of 160 cycles (i.e., airbursts) per year, which extrapolates to 9,600 cycles over a 60 year operating period (40 years of operation plus 20 years of initial license renewal). However, this calculation was incorrectly based upon there being one condensate demineralizer as opposed to the five that are installed. Each of the five condensate demineralizers is backwashed/precoated every 26 days; yielding 15 backwash cycles per year for a single demineralizer, and 75 total backwash cycles per year. Conservatively assuming a total of 75 backwash cycles per year and 8 airbursts per backwash, there are 600 cycles (i.e.,

airbursts) per year. These cycles were conservatively considered to occur for 40 complete years (from 2011 when the EPU modification was performed through 2050 when the SPEO would end).

After analyzing the stresses estimated from the fatigue curve in the ASME Section VIII, 1977 Edition, it was found that the Backwash Receiving Tank is acceptable for an expected end of life in 2050. Including all conservatisms and bounding conditions considered in the evaluation, a cumulative usage through SPEO of 0.58 was calculated; demonstrating reasonable assurance that the backwash receiving tank will perform its intended function through SPEO.

The original calculation assumed 160 cycles per year. Over 80 years of operation, the number of cycles estimated is 12,800. This is conservative as the increased pressure and number of backwash cycles was not implemented until EPU (2008). However, even with this conservatism, fatigue usage for this component is calculated to be 0.37, with significant margin to the limit of 35,000 cycles.

The Condensate Backwash Receiving Tank fatigue evaluation has been projected to the end of the SPEO in accordance with 10 CFR 54.21(c)(1)(ii).

Enclosure 02 Core Spray - Summary of Aging Management Evaluation Table 1 Items Updated

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 2 Page 1 of 3 Core Spray - Summary of Aging Management Evaluation Table 1 Items Updated Revise Table 1 Items for Four Rows in SLRA Table 3.2.2-1 That has Table 1 Item 3.3.1-007.

Affected SLRA Sections: Table 3.2.2-1 SLRA Page Numbers: 3.2-48, 3.2-49, 3.2-50, and 3.2-51 Description of Change:

SLRA Table 3.2.2-1 Core Spray - Summary of Aging Management Evaluation is revised to replace Table 1 Item 3.3.1-007 with 3.2.1-007. Table 1 Item 3.3.1-007 is not applicable as the line item only applies to PWR plants. Table 1 Item 3.2.1-007 is the correct item that NUREG-2191 Item V.D2.EP-103b corresponds to. Also, for the Core Spray Heat Exchanger Tubes, the Table Item for SRP-SLR item 3.3.1-040 should reference GALL-SLR Chapter VII instead of GALL-SLR Chapter V. This was corrected for that table entry.

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 2 Page 2 of 3 SLRA Table 3.2.2-1 on page 3.2-48 is revised as follows:

Table 3.2.2-1 Core Spray - Summary of Aging Management Evaluation Aging Effect Component Intended Aging Management NUREG-2191 Table 1 Material Environment Requiring Notes Type Function Program Item Item Management Heat Exchanger - Pressure Stainless Raw Water Loss of Material Open-Cycle Cooling V.D2.EP-91 3.3.1- AC (Core Spray Boundary Steel (Internal) Water System VII.C1.A-54 040 Pump Motor Oil (B.2.3.11)

Cooler) Tubes Orifice Pressure Stainless Air - Indoor Cracking One-Time Inspection V.D2.EP-103b 3.3.1- A Boundary Steel Uncontrolled (B.2.3.20) 0073.2.1 (External) -007 Orifice Pressure Stainless Air - Indoor Loss of Material One-Time Inspection V.D2.EP-107a 3.2.1- A Boundary Steel Uncontrolled (B.2.3.20) 004 (External)

Orifice Pressure Stainless Treated Water Loss of Material One-Time Inspection V.D2.EP-73 3.2.1- A Boundary Steel (Internal) (B.2.3.20) 022 Orifice Pressure Stainless Treated Water Loss of Material Water Chemistry V.D2.EP-73 3.2.1- B Boundary Steel (Internal) (B.2.3.2) 022 Orifice Throttle Stainless Air - Indoor Cracking One-Time Inspection V.D2.EP-103b 3.3.1- A Steel Uncontrolled (B.2.3.20) 0073.2.1 (External) -007

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 2 Page 3 of 3 SLRA Table 3.2.2-1 on page 3.2-49 is revised as follows:

Table 3.2.2-1 Core Spray - Summary of Aging Management Evaluation Aging Effect Component Intended Aging Management NUREG-2191 Table 1 Material Environment Requiring Notes Type Function Program Item Item Management Piping, Piping Pressure Stainless Air - Indoor Cracking One-Time Inspection V.D2.EP-103b 3.3.1- A Components Boundary Steel Uncontrolled (B.2.3.20) 0073.2.1 (External) -007 SLRA Table 3.2.2-1 on page 3.2-50 is revised as follows:

Table 3.2.2-1 Core Spray - Summary of Aging Management Evaluation Aging Effect Component Intended Aging Management NUREG-2191 Table 1 Material Environment Requiring Notes Type Function Program Item Item Management Valve Body Pressure Stainless Air - Indoor Cracking One-Time Inspection V.D2.EP-103b 3.3.1- A Boundary Steel Uncontrolled (B.2.3.20) 0073.2.1 (External) -007 SLRA Table 3.2.2-1 on page 3.2-51 is revised as follows:

General Notes A. Consistent with component, material, environment, aging effect, and AMP listed for NUREG2191 line item. AMP is consistent with NUREG2191 AMP description.

B. Consistent with component, material, environment, aging effect, and AMP listed for NUREG2191 line item. AMP has exceptions to NUREG2191 AMP description.

C. Component is different, but consistent with material, environment, aging effect, and AMP listed for NUREG2191 line item. AMP is consistent with NUREG2191 AMP description.

Enclosure 03 Loss of Fracture Toughness (Cracking) of RV Supports

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 3 Page 1 of 4 Loss of Fracture Toughness (Cracking) of RV Supports Cracking is Added in Parenthesis After Loss of Fracture Toughness for the RV Support Components.

Affected SLRA Sections: 3.5.2.1.1, 3.5.2.1.7, Table 3.5.2-1, and Table 3.5.2-7 SLRA Page Numbers: 3.5-3, 3.5-8, 3.5-76, and 3.5-98 Description of Change:

SLRA Table 3.5.2-1 and Table 3.5.2-7 are updated to include Cracking in parenthesis after Loss of Fracture Toughness for the aging effect for the RV steel support assembly components added in Enclosure 01 and 02 of Supplement 5. SLRA Sections 3.5.2.1.1 and 3.5.2.1.7 are updated to include Cracking in parenthesis after Loss of Fracture Toughness.

The information shown in bold black font in the mark-ups represent changes provided in 1 and 02 of Reference 1.

References:

1. L-MT-23-035, Monticello Nuclear Generating Plant, Docket No. 50-263, Renewed Facility Operating License No. DPR-22, Subsequent License Renewal Application Supplement 5, ML23240A695

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 3 Page 2 of 4 SLRA Section 3.5.2.1.1 on page 3.5-3 is revised as follows:

Aging Effects Requiring Management The following aging effects associated with the PCT structure and internal structural components require management:

Cracking Cumulative Fatigue Damage Loss of Bond Loss of Coating or Lining Integrity Loss of Fracture Toughness (Cracking)

Loss of Leak Tightness Loss of Material Loss of Mechanical Function Loss of Mechanical Properties Loss of Preload Loss of Sealing Reduction of Strength

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 3 Page 3 of 4 SLRA Section 3.5.2.1.7 on page 3.5-8 is revised as follows:

Aging Effects Requiring Management The following aging effects associated with the Hangers and Supports structural components require management:

Cracking Crazing Dimensional Change Discoloration Hardening Increase in Porosity and Permeability Loss of Bond Loss of Fracture Toughness (Cracking)

Loss of Material Loss of Mechanical Function Loss of Preload Loss of Strength Reduced Thermal Insulation Resistance Reduction In Concrete Anchor Capacity Reduction or Loss of Isolation Function Scuffing Shrinkage Surface Cracking

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-052 3 Page 4 of 4 SLRA Table 3.5.2-1 on page 3.5-76 is revised as follows:

Table 3.5.2-1: Primary Containment - Summary of Aging Management Evaluation Aging Effect Component Intended Aging Management NUREG-2191 Table 1 Material Environment Requiring Notes Type Function Program Item Item Management Biological Shield Structural Steel Air - iIndoor Loss of Structures None None H, 12 Wall (Columns, Support Uncontrolled Fracture Monitoring (B.2.3.33)

Beams, Liner, Toughness Doors) (Cracking)

SLRA Table 3.5.2-7 on page 3.5-98 is revised as follows:

Table 3.5.2-7: Hangers and Supports Commodity Group- Summary of Aging Management Evaluation Aging Effect Component Intended Aging Management NUREG-2191 Table 1 Material Environment Requiring Notes Type Function Program Item Item Management ASME Class 1 Structural Steel Air - Indoor Loss of ASME Section XI, None None H, 4 Supports Support Uncontrolled Fracture Subsection IWF Toughness (B.2.3.30)

(Cracking)

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