L-MT-23-046, Subsequent License Renewal Application Response to Request for Additional Information Round 2 - Set 1

Subsequent License Renewal Application Response to Request for Additional Information Round 2 - Set 1

ML23313A158
Person / Time
Site:	Monticello
Issue date:	11/09/2023
From:	Hafen S Northern States Power Company, Minnesota, Xcel Energy
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-MT-23-046
Download: ML23313A158 (1)

Text

(l Xcel Energy* 2807 West County Road 75 Monticello, MN 55362 November 9, 2023 L-MT-23-046 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 Response to Request for Additional Information Round 2 - Set 1

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) Email from the NRC to Northern States Power Company, A Minnesota corporation (NSPM), d/b/a Xcel Energy, Monticello SLRA - Request for Additional Information - Set 1 dated July 19, 2023, ML23200A350 and ML23200A351

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 Response to Request for Additional Information Set 1 dated August 15, 2023, ML23227A175

4) Email from the NRC to Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy, Monticello SLRA - Request for Additional Information - Set 2 dated August 7, 2023, ML23219A107 and ML23219A108

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 Response to Request for Additional Information Set 2 and Supplement 6 dated September 05, 2023, ML23248A474

6) Email from the NRC to Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy, Monticello SLRA - Request for Additional Information - Set 3 dated August 25, 2023, ML23237A483

Doc um e nt Co ntro l Desk L-MT-23-046 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 3" dated September 22, 2023, ML23265A158 8} Email from the NRC to Northern States Power Company, a Minnesota corporation (NSPM}, d/b/a Xcel Energy, "Monticello SLRA- Request for Additional Information - Round 2 - Set 1" dated October 13, 2023, ML23289A003 Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy hereafter "NSPM", is submitting responses to requests for additional information (RAls) to the Subsequent License Renewal Application, listed in Reference 1.

RAI Sets 1, 2, and 3 were issued by the NRC in References 2, 4, and 6, respectively .

Responses were provided in References 3, 5, and 7, respectively. Additional RAls were issued by the NRC as Round 2 - Set 1 on October 13, 2023 (Reference 8) . The responses to RAI Round 2 - Set 1 are provided in the Enclosures . No SLRA changes have been identified as a result of these responses.

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.

Executed on November- - '\ ~ 2023 .

Shawn Hafe Site Vice President, Monticello Nuclear Generating Plant Northern States Power Company - Minnesota cc : Administrator, Region Ill, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC Minnesota Department of Commerce

Document Control Desk L-MT-23-046 Page 3 Enclosures Index Enclosure Subject No.

01 RAI B.2.3.27-3a 02 RAI B.2.3.17-1a 1

RAI B.2.3.27-3a

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-046 1 Page 1 of 5 RAI B.2.3.27-3a Regulatory Basis 10 CFR 54.21(a)(3) requires an applicant to demonstrate that the effects of aging for structures and components will be adequately managed so that the intended function(s) will be maintained consistent with the current licensing basis for the period of extended operation. One of the findings that the staff must make to issue a renewed license (10 CFR 54.29(a)) is that actions have been identified and have been or will be taken with respect to managing the effects of aging during the period of extended operation on the functionality of structures and components that have been identified to require review under 10 CFR 54.21, such that there is reasonable assurance that the activities authorized by the renewed license will continue to be conducted in accordance with the current licensing basis. In order to complete its review and enable making a finding under 10 CFR 54.29(a), the staff requires additional information in regard to the matters described below.

Background:

As amended by letters dated July 18, 2023 (ML23199A154) and September 22, 2023 (ML23265A158), the SLRA was revised to reflect that uncoated and underground (a) steel piping in the offgas system; and (b) stainless steel piping in the control rod drive (CRD) and radwaste solid and liquid (RAD) systems will be managed for loss of material and cracking (stainless steel only) using the Buried and Underground Piping and Tanks program. In addition, by letter September 22, 2023, a new enhancement and exception were added to the Buried and Underground Piping and Tanks program related to the use of external coatings for underground piping, which stated the following (in part):

• [n]ew and replacement coatings for underground components are to be consistent with Table 1 of [NACE] SP0169-2007 [Control of External Corrosion on Underground or Submerged Metallic Piping Systems] or Section 3.4 of NACE RP0285-2002 [Corrosion Control of Underground Storage Tank Systems by Cathodic Protection]. Existing coatings for underground components at MNGP were installed per site design specifications. Site design specifications did not require coatings on underground components[t]his exception is acceptable because operating experience [OE] demonstrates that the lack of moisture intrusion does not lead to accelerated degradation of the uncoated underground components at MNGP.

The response to RAI B.2.3.27-3 (ML23265A158) states the following (in part):

• [t]he visual examinations of the removed [carbon steel] piping sections showed that both of the CRD pipes experienced severe corrosion of the external surfaces in the regions exposed to the ground water present between the buildings.

• [b]oth CRD pipeswere replaced with uncoated stainless steel piping.

• [a] removable 1/4 stainless steel plate anchored to the wall with stainless steel concrete anchors on the Reactor Building inside wall provides access into the penetration. The Reactor Building wall opening is packed with removable Kaowool [insulation]. The piping is grouted for about 1 foot into the Turbine Building wall. The piping in the Turbine Building is also packed with removable Kaowool.

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-046 1 Page 2 of 5

• [a]ctions have been taken to identify other in scope underground piping that may have been inadvertently omitted from the SLRA.There are 35 penetrations identified where pipe went between the Reactor Building and Turbine Building. All other piping that run through the 1 seismic gap between the Reactor Building and Turbine Building are managed by the External Surfaces Monitoring of Mechanical Components AMP based on the environment and observed condition of the external surfaces of the samples pipingThe expectations of this [program] element [detection of aging effects of the External Surfaces Monitoring of Mechanical Components AMP] are being met with the maintenance notifications to perform periodic inspections described above as part of the evaluation of this issue. [emphasis added]

SLRA Section B.2.3.27, Buried and Underground Piping and Tanks, includes a discussion in the plant-specific OE section about an increasing trend of chloride concentrations in groundwater samples between 2011 and 2015. The SLRA states that the increase in chloride concentration was likely due to salt treatment during the winter months. In addition, as noted in RAI B.2.3.171 (ML23237A483), corrective action document (AR 01223696) states that insulation and grout are possible sources of the chlorides that caused the stress corrosion cracking of the stainless steel standby liquid control tank.

GALL-SLR Report AMP XI.M41, Buried and Underground Piping and Tanks, recommends the following:

• One inspection for underground steel and stainless steel piping in each 10year inspection interval (this number can increase to two inspections for underground steel based on the piping length).

• External coatings for (a) underground steel piping; and (b) stainless steel piping in chloride containing environments.

In addition, GALL-SLR Report AMP XI.M41 states [a]dditional inspections, beyond those in Table XI.M41-2 [Inspection of Buried and Underground Piping and Tanks] may be appropriate if exceptions are taken to program element 2, preventive actions, or in response to plant-specific OE. Also, GALL-SLR Report,Section IX.D, Environments, states that the term underground includes exposure to multiple environments including groundwater and condensation.

Issue:

The justification for the new exception (relating to the lack of external coatings on existing underground piping) does not address the plant-specific OE. Underground piping at the site is exposed to moisture intrusion (i.e., groundwater and condensation) and accelerated corrosion of inscope underground piping has occurred. As noted above, additional inspections, beyond those in GALL-SLR Report Table XI.M41-2, may be appropriate if exceptions are taken to the recommended preventive actions or in response to plant-specific OE. The staff notes that the installation of insulation inside the penetration may tend to aggravate corrosion, if it is exposed to moisture.

Based on (a) plantspecific OE involving severe corrosion of inscope underground piping; (b) absence of external coatings for existing inscope underground steel and stainless steel piping; and (c) potential exposure of the subject piping to elevated levels of chlorides (from either groundwater, grout, or insulation), it is unclear why inspections consistent with GALL-SLR

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-046 1 Page 3 of 5 Report Table XI.M41-2 (i.e., one inspection in each 10year interval) is appropriate for inscope underground steel and stainless steel piping.

Based on the extent of condition discussions in the RAI response, the portions of piping systems that run between the reactor building and turbine building were not inspected as part of the existing External Surfaces Monitoring of Mechanical Components AMP. The response indicates that the expectations of the associated detection of aging effects program element of the AMP are being met with the maintenance notifications to perform periodic inspections described above. It is unclear what maintenance notifications to perform periodic inspections means, and whether the current External Surfaces Monitoring of Mechanical Components AMP includes the inspection activities currently being credited for managing the effects of aging for the pertinent portions of the applicable piping systems. Because the program previously did not include these inspections, it is unclear whether an enhancement to the External Surfaces Monitoring of Mechanical Components AMP is warranted to ensure these credited activities will be performed during the period of extended operation. In addition, because the response cites a portion of the guidance related to inspecting components that are not readily visible whenever they are made accessible, it is not clear what frequency the inspections will be performed.

Request:

1. Based on the issues outlined above (i.e., adverse plantspecific OE, absence of external coatings, potential exposure of piping to elevated levels of chlorides), state the basis for why one inspection in each 10year interval is appropriate for inscope underground steel and stainless steel piping.

2. Provide information whether an enhancement to the External Surfaces Monitoring of Mechanical Components AMP is warranted. Include information related to the frequency of these proposed inspections or the basis for establishing the inspection frequency.

Response to RAI B.2.3.27-3a:

1. The basis for one inspection in each 10-year interval is discussed separately for Off-Gas (Underground Steel) and CRD (Underground Stainless Steel):

Off-Gas (Underground Steel): The Off-Gas Systems in-scope underground steel piping has no record of degradation. There is no MNGP operating experience that identifies moisture intrusion into this one vault with an underground environment. The Table in Section B.2.3.27 on page B-198 of the SLRA as revised in L-MT-23-031 (Reference 2) Enclosure 06b states that the smaller of 2% of the piping length or 2 inspections are required for underground steel piping and Note 1 states underground piping found in the Off-Gas System is included.

The plant-specific OE for the degradation of the steel CRD piping in the seismic gap between the turbine building and reactor building is not applicable because the environment from that OE allowed for periodic wetting of the steel piping by groundwater, which is not the case for the underground piping in the Off-Gas System as stated above. Deficiencies will be documented in accordance with the sites 10 CFR Part 50, Appendix B, Section XVI, Corrective Action Program (CAP) and used to inform changes to the AMP, as necessary.

CRD (Underground Stainless Steel) Piping: MNGP selected the Buried and Underground Piping AMP to manage aging of the CRD piping routed between the turbine building and reactor building in the seismic gap. The configuration of the environment of the CRD piping between the turbine and reactor buildings is unique and is not directly addressed in the

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-046 1 Page 4 of 5 GALL-SLR. The location is susceptible to ground water intrusion and can result in periodic wetting of the piping. Corroded carbon steel piping was replaced with stainless steel piping in the two lowest penetrations between the turbine building and the reactor building. This lowest, below grade reactor to turbine building penetration (for the CRD Piping) was modified to provide access for inspection of the new stainless steel piping. A removable plate allows access for future inspections.

i. The CRD piping is in an underground environment and will be managed by the Buried and Underground Piping and Tanks AMP. The SLRA changes due to recent operating experience are documented in L-MT-23-031 Enclosure 06b (Reference 2) and L-MT 037 Enclosure 01 (Reference 4).

ii. MNGP does have buried, coated stainless steel piping. An inspection of opportunity found stainless steel piping with damaged coating which exposed the piping to groundwater. There was no indication of external corrosion in the stainless steel piping.

iii. Inspection of insulated stainless steel piping at MNGP subject to condensation environment has found no loss of material such as due to pitting and crevice corrosion.

iv. MNGP will inspect the underground stainless steel piping prior to the SPEO and once every 10 years thereafter per Commitment 30 in Table A-3 and Section B.2.3.27 of the SLRA as amended by L-MT-23-025 Enclosure 06a (Reference 1), L-MT-23-031 Enclosure 06b (Reference 2), L-MT-23-036 Enclosure 02 (Reference 3), and L-MT 037 Enclosure 01 (Reference 4).

v. Consistent with the recommendation of GALL SLR, the Buried and Underground Piping and Tanks AMP will confirm that loss of material is not occurring in stainless steel components exposed to an underground environment. Deficiencies will be documented in accordance with the sites 10 CFR Part 50, Appendix B, Section XVI, CAP and used to inform changes to the AMP, as necessary.

vi. The chemical composition of refractory ceramic fiber products such as Kaowool and Cerablanket is 45% alumina, 50 to 55% silica with lesser amounts of ferric oxide, titanium oxide, sodium and potassium oxides and traces of other impurities.

Manufacturers data sheet states Kaowool contains 1 to 2 ppm leachable chlorides. The SDS sheet states this blanket material is not soluble in water. As noted in the plant-specific OE described above for the buried stainless steel piping with damaged coating and absence of corrosion, the groundwater chlorides do not currently require a change in the inspections for the MNGP AMP from what is provided in the GALL-SLR guidance for stainless steel piping.

Consistent with the recommendation of GALL-SLR, the Buried and Underground Piping and Tanks AMP will confirm that loss of material and cracking is not occurring in carbon and stainless steel components exposed to an underground environment. Deficiencies will be documented in accordance with the sites 10 CFR Part 50, Appendix B, Section XVI, CAP.

2. Enhancement for External Surfaces Monitoring of Mechanical Components AMP:

An enhancement to the External Surface Monitoring of Mechanical Components AMP is not warranted for the piping in between the reactor building and turbine building.

The conditions of the piping between the reactor building and the turbine building over the 52+ years of operation do not indicate that other enhancements to the External Surfaces Monitoring of Mechanical Components AMP are needed for SLR and that aging effects

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-046 1 Page 5 of 5 associated with those carbon steel and stainless steel pipes can be managed using the program described in the SLRA. The details of the results of the extent of condition were previously captured in L-MT-23-037 Enclosure 01 (Reference 4). GALL-SLR, Chapter XI.M36 states Surfaces that are not readily visible during plant operations and refueling outages are inspected when they are made accessible and at such intervals that would ensure the components intended functions are maintained.

Inspections are guided by and consistent with the CAP element in GALL-SLR Chapter XI.M37 Element 7. Deficiencies will be documented in accordance with the sites 10 CFR Part 50, Appendix B, Section XVI, CAP.

References:

1. L-MT-23-025, Monticello Nuclear Generating Plant, Docket No. 50-263, Renewed Facility Operating License No. DPR-22, Subsequent License Renewal Application Supplement 2, ML23177A218.

2. L-MT-23-031, Monticello Nuclear Generating Plant, Docket No. 50-263, Renewed Facility Operating License No. DPR-22, Subsequent License Renewal Application Supplement 4 and Responses to Request for Confirmation of Information - Set 1, ML23199A154.

3. L-MT-23-036, Monticello Nuclear Generating Plant, Docket No. 50-263, Renewed Facility Operating License No. DPR-22, Subsequent License Renewal Application Response to Request for Additional Information Set 2 and Supplement 6, ML23248A474.

4. L-MT-23-037, Monticello Nuclear Generating Plant, Docket No. 50-263, Renewed Facility Operating License No. DPR-22, Subsequent License Renewal Application Response to Request for Additional Information Set 3, ML23265A158.

Associated SLRA Revisions:

No SLRA changes have been identified as a result of this response.

2 RAI B.2.3.17-1a

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-046 2 Page 1 of 2 RAI B.2.3.17-1a Regulatory Basis:

Title 10 of the Code of Federal Regulations (10 CFR) 54.21(a)(3) requires an applicant to demonstrate that the effects of aging for structures and components will be adequately managed so that the intended function(s) will be maintained consistent with the current licensing basis for the period of extended operation. One of the findings that the U.S. Nuclear Regulatory Commission (NRC) staff must make to issue a renewed license (10 CFR 54.29(a)) is that actions have been identified and have been or will be taken with respect to managing the effects of aging during the period of extended operation on the functionality of structures and components that have been identified to require review under 10 CFR 54.21. In order to complete its review and enable formulation of a finding under 10 CFR 54.29(a), the staff requests additional information regarding the matters described below.

Background:

The response to request for additional information (RAI) B.2.3.17-1 (refer to letter dated September 22, 2023 (ML23265A158)) revised portions of the subsequent license renewal application (SLRA) to reflect that the Monticello ASME Section XI Inservice Inspection, Subsections IWB, IWC, and IWD (ASME Section XI ISI) program will be used to manage cracking and loss of material for the external portions of the stainless steel standby liquid control tank exposed to uncontrolled indoor air and concrete. The response added new aging management review items (3.2.1-129, 3.3.1-004, 3.3.1-222, and 3.3.1-230) to SLRA Table 3.3.2-17, Standby Liquid Control - Summary of Aging Management Evaluation, with generic note Es indicating a proposal to use a different program than that recommended in NRCs aging management guidance.

The response states:

The ASME Section XI Standby Liquid Control Suction Piping System Leakage Test is performed every two years. The inspection will be part of the ISI AMP for MNGP [Monticello Nuclear Generating Plant], and will provide reasonable assurance that any aging effects for the SLC

[standby liquid control] tank are managed before there is a potential loss of its pressure boundary intended function.

Issue:

The NRC staff notes that prior to the RAI response discussed above, the SLRA had not previously credited the ASME Section XI ISI program for managing the effects of aging for components in the standby liquid control system. In addition, it is unclear what type(s) of ASME Section XI ISI inspection will be performed on the standby liquid control tank, and whether these inspections will also be performed every 2 years. Consequently, unless the ASME Section XI ISI program currently includes the specified activities that are now being credited for managing the effects of aging (loss of material and cracking) for the tank, an enhancement to the ASME Section XI ISI program appears to be warranted.

Monticello Nuclear Generating Plant Docket 50-263 L-MT-23-046 2 Page 2 of 2 Request:

Provide information showing that the activities being credited for managing the effects of aging, as specified in response to RAI B.2.3.17-1, are currently included in the ASME Section XI ISI aging management program or provide information about any enhancement needed to the program to ensure that the associated effects of aging will be adequately managed.

Response to RAI B.2.3.17-1a:

MNGP personnel perform VT-2 examinations on SLC System pressure retaining components in accordance with the ASME Section XI ISI AMP. These exams will detect aging effects that could result in a through wall leak.

The frequency and scope of examinations are sufficient to ensure that the aging effects are detected before the loss of a components intended function(s) and will be adequately age managed during the SPEO. The inspections and their frequency are consistent with ASME code requirements.

The ISI Program Owner ensures compliance with the ISI-PLAN-6-BASIS (6th Interval ISI Plan -

Basis Document) and the ISI-PLAN-6-D (6th Interval ISI Plan - Appendix D, Inspection Plan and Schedule Tables) documents. This ensures performance of the System Leakage Test for the SLC System at least once in each of the 3 periods of the ISI interval. Thus, it will be performed three times in a ten-year period per the ISI Program. This represents a different frequency for the inspection than what was previously stated in the Response to RAI B.2.3.17-1 in Reference 1. However, the frequency of the inspection and its ability to manage aging in the SLC System is in accordance with the ISI AMP.

The Program is implemented by MNGPs ISI Plan and SCPTP (System and Component Pressure Testing Program).

No enhancements to the ISI program are required.

References:

1. L-MT-23-037, Monticello Nuclear Generating Plant, Docket No. 50-263, Renewed Facility Operating License No. DPR-22, Subsequent License Renewal Application Response to Request for Additional Information Set 3, ML23265A158.

Associated SLRA Revisions:

No SLRA changes have been identified as a result of this response.