Note to readers: The following analysis of the Monticello Nuclear Generating Plant extended power uprate amendment comes directly from the beta version of Everstar's Gordian Research platform and was edited only for web formatting and to remove internal Gordian links. It was generated in about two minutes using this prompt: "for the monticello epu, produce a detailed summary of this application and all RAIs, RAI responses, and supplements. produce a table of the RAIs including the branch asking them and create a graphical timeline of the correspondence." For more insights, see related posts on uprates or contact hello@everstar.ai to get on the waiting list for an account.

Monticello Extended Power Uprate: Comprehensive Regulatory Review and Timeline

Executive Summary

The Monticello Nuclear Generating Plant (MNGP) Extended Power Uprate (EPU) application represents a significant licensing action that underwent extensive regulatory review. Initially submitted in March 2008, the application was withdrawn and resubmitted in November 2008, requesting an increase in maximum authorized power from 1775 MWt to 2004 MWt (approximately 13% increase). The review process spanned approximately five years, involving multiple technical branches of the Nuclear Regulatory Commission (NRC), numerous Requests for Additional Information (RAIs), and several major supplements. This comprehensive analysis examines the application's history, technical content, regulatory interactions, and ultimate approval in December 2013 as Amendment No. 176 to the Renewed Facility Operating License. [0] [1]

Technical Analysis

Application History and Evolution

The EPU application underwent significant evolution throughout its review process. The initial application was submitted on March 31, 2008, by Nuclear Management Company, LLC (NMC), requesting to increase power from 1775 MWt to 1870 MWt (approximately 5% increase). During the acceptance review phase (May-June 2008), the NRC requested substantial additional information, leading to six supplemental information packages. Despite these supplements, the NRC staff determined on June 20, 2008, that the application lacked sufficient information in several technical areas, prompting NMC to withdraw it with plans to resubmit. [2] [3] [4] [5]

The application was resubmitted on November 5, 2008, by Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy. This revised application requested a more substantial increase in power from 1775 MWt to 2004 MWt (approximately 13% increase). The resubmitted application incorporated lessons learned from the acceptance review of the initial application and provided more comprehensive technical information. [0] [6]

Key Technical Modifications and Analyses

The EPU involved numerous plant modifications and technical analyses to support operation at the higher power level. A central component was the installation of a Replacement Steam Dryer (RSD), which required extensive acoustic and structural analyses to ensure its integrity under EPU conditions. The steam dryer analyses were particularly complex, involving multiple rounds of RAIs between 2012 and 2013. [3] [7] [6] [7]

Other significant technical aspects included modifications to the Automatic Depressurization System (ADS) bypass timer setpoint, analyses of grid stability through the Midwest Independent Transmission System Operator (MISO), and comprehensive evaluations of plant systems to ensure they could accommodate the higher power level. The EPU also required reanalysis of design basis accidents, evaluation of component integrity under increased loads, and assessment of flow-induced vibration effects. [8] [9] [10]

The implementation strategy evolved over time. Initially planned for a two-phase implementation in 2009 and 2011, the EPU was ultimately scheduled for implementation following the 2013 outage. This timeline shift was documented in communications with MISO, which had approved the full power increase in a signed Interconnection Agreement executed on October 6, 2009. [10]

Regulatory Review Process

The regulatory review process was extensive, involving multiple technical branches of the NRC. Following acceptance of the resubmitted application, the NRC issued numerous RAIs from December 2008 through May 2013. These RAIs addressed a wide range of technical areas, including probabilistic risk assessment, environmental impacts, materials engineering, reactor systems, electrical systems, mechanical and civil engineering, and balance of plant systems. [11] [12] [13] [14] [15]

The most intensive period of RAI issuance occurred in March 2009, when multiple technical branches issued RAIs nearly simultaneously. Another significant period of regulatory interaction occurred between October 2012 and March 2013, focusing primarily on the replacement steam dryer analyses. The final RAIs were issued in March and May 2013, addressing remaining reactor systems and mechanical engineering questions. [16] [17] [18] [19]

Throughout the review process, NSPM provided several major supplements to the application, including a Replacement Steam Dryer Supplement (June 2010), Updates to Docketed Information (December 2010), Update on EPU Commitments (August 2011), and a Supplement to Revise Technical Specification Setpoint for the ADS Bypass Timer (October 2012). Final supplements in 2013 addressed gap analysis updates and completion of EPU commitments. [6] [3] [9] [12]

Regulatory Considerations

NRC Technical Branch Reviews

The EPU application underwent comprehensive technical review by multiple NRC branches, each focusing on specific aspects of the proposed power uprate:

Reactor Systems Branch (SRXB): Reviewed core performance, thermal-hydraulic design, and safety analyses. This branch issued RAIs in February 2009 and March 2013, focusing on reactor systems performance under EPU conditions. [20] [19]

Mechanical and Civil Engineering Branch (EMCB): Evaluated structural integrity of components and piping. Their review was particularly intensive, with RAIs issued in March 2009 and May 2013, addressing mechanical aspects of the EPU. [15] [19]

Electrical Engineering Review Branch (EEEB): Assessed electrical power systems and grid stability, issuing RAIs in March 2009 that focused on the ability of electrical systems to support the increased power output. [18]

Balance of Plant Review Branch (SBPB): Reviewed secondary plant systems, with RAIs issued in March 2009 addressing the performance of balance of plant systems under EPU conditions. [10]

Probabilistic Risk Assessment Branch (APLA): Evaluated risk impacts of the EPU, issuing RAIs in December 2008 and April 2009 that focused on the risk implications of operating at the higher power level. [20] [21]

Environmental Branch: Assessed environmental impacts, with RAIs issued in December 2008 addressing the environmental consequences of the power uprate. [15]

Steam Generator Tube Integrity & Chemical Engineering Branch: Reviewed materials and chemistry issues, issuing RAIs in February 2009 that addressed materials performance under EPU conditions. [22]

Reactor Inspection Branch: Evaluated inspection-related concerns, with RAIs issued in March 2009 focusing on inspection requirements for the uprated plant. [17]

The diversity of technical branches involved in the review reflects the comprehensive nature of the regulatory assessment required for an EPU. [8]

Commitments and License Conditions

Throughout the EPU review process, NSPM made various commitments to address NRC concerns and ensure safe operation at the higher power level. These commitments included performing analyses of the Condensate and Feedwater system performance, implementing modifications to pipe supports, and making Appendix R modifications to vent and purge valves. [6] [14]

In September 2013, NSPM provided a final update on the status of EPU commitments, proposed license conditions, and a revised power ascension test plan. This submittal represented the culmination of the regulatory process, addressing all remaining items needed for NRC approval of the EPU. [9]

The NRC's final safety evaluation, issued with Amendment No. 176 in December 2013, included specific license conditions related to the EPU implementation, particularly regarding the replacement steam dryer monitoring and verification. The safety evaluation documented the NRC's comprehensive review of all aspects of the EPU, including the resolution of all RAIs and the acceptability of NSPM's commitments. [1]

Uncertainties and Limitations

Technical Challenges and Resolutions

Several significant technical challenges emerged during the EPU review process. The most complex issue was the replacement steam dryer analysis, which required extensive acoustic and structural evaluations to ensure its integrity under EPU conditions. This analysis was the subject of multiple rounds of RAIs between 2012 and 2013, reflecting the technical complexity and safety significance of this component. [3] [7] [6] [7]

Another significant technical issue was the use of containment accident pressure for net positive suction head (NPSH) calculations. This topic has been the subject of ongoing regulatory attention and required detailed analysis to ensure adequate NPSH for safety-related pumps under EPU conditions. [12]

Grid stability was also a key concern, requiring coordination with MISO to ensure the electrical grid could handle the increased output. The initial EPU implementation timeline was adjusted, with the Commercial Operation Date extended from May 2011 to August 2013, requiring notification to MISO but not triggering a restudy requirement under the Midwest ISO electric tariff. [10]

Regulatory Process Challenges

The regulatory process itself presented challenges, as evidenced by the withdrawal and resubmission of the application. The initial application was deemed insufficient in several technical areas, highlighting the comprehensive nature of the information required for NRC review of an EPU. The resubmitted application incorporated lessons learned from this experience, providing more detailed technical information. [2] [20]

The extended timeline of the review process, spanning approximately five years from initial application to final approval, reflects both the technical complexity of the EPU and the thoroughness of the NRC review. This extended timeline required NSPM to adjust its implementation plans and manage the regulatory process through multiple supplements and RAI responses. [9] [12]

Recommendations and Next Steps

Table of RAIs by NRC Branch

The following table summarizes the major RAI issuances by NRC technical branch:

Graphical Timeline of Key Correspondence

Lessons Learned and Future Applications

The Monticello EPU application process offers valuable lessons for future power uprate applications. The initial rejection during acceptance review highlights the importance of providing comprehensive technical information from the outset. The extensive RAI process, particularly regarding the replacement steam dryer, demonstrates the level of technical detail required for complex modifications associated with power uprates. [2] [3] [7]

The evolution of the implementation timeline, from a two-phase approach to a single implementation following the 2013 outage, illustrates the need for flexibility in planning and coordination with grid operators. The multiple supplements to the application reflect the dynamic nature of the regulatory process and the need to address emerging issues throughout the review. [9] [10]

For future EPU applications, early engagement with all relevant NRC technical branches, comprehensive technical analyses, and detailed implementation planning would help streamline the regulatory process. The Monticello experience demonstrates that replacement of major components, such as the steam dryer, requires particularly rigorous analysis and may become the critical path for regulatory approval. [3] [7] [6] [7]

The final approval of the Monticello EPU in December 2013, authorizing an increase in maximum power level from 1775 MWt to 2004 MWt, represents the successful culmination of a thorough regulatory process that ensured the plant could operate safely at the higher power level. [1]

[1] Monticello Nuclear Generating Plant - Extended Power Uprate Final Safety Evaluation (non-proprietary) Redacted.: ML13343A006

[2] Monticello Nuclear Generating Plant - Issuance of Amendment No. 176 to Renewed Facility Operating License Regarding Extended Power Uprate (TAC No. MD9990).: ML13316B298

[3] Monticello Extended Power Uprate: Withdrawal of Proposed License Amendment.: ML081770562

[4] Monticello, Enclosures 1 & 2 to L-MT-12-114 - Responses to the Gap Analysis and Marked Up Page Changes to EPU Documentation Based on the Gap Analysis Results, Part 1 of 3.: ML13039A200

[5] Monticello - Extended Power Uprate (EPU): Completion of EPU Commitments, Proposed License Conditions and Revised Power Ascension Test Plan.: ML13275A063

[6] Monticello, Responses to Requests for Additional Information on Extended Power Uprate: Replacement Steam Dryer (TAC MD9990).: ML13071A615

[7] Monticello Extended Power Uprate: Replacement Steam Dryer - Responses to Requests for Additional Information for Acoustic/Structural Analyses Set #3.: ML13078A390

[8] Monticello - Extended Power Uprate: Response to NRC Balance of Plant Review Branch SBPB Request for Additional Information (RAI) dated March 23, 2009.: ML091670410

[9] Monticello Extended Power Uprate: Response to NRC Reactor Inspection Branch Request for Additional Information (RAI) dated March 20, 2009 (TAC No. MD9990).: ML091671787

[10] Monticello, Extended Power Uprate: Response to NRC Electrical Engineering Review Branch (EEEB) Request for Additional Information (RAI) dated March 28, 2009.: ML091470559

[11] Response to NRC Environmental Branch Requests for Additional Information (RAIs) dated December 18, 2008 (TAC No. MD9990).: ML090300303

[12] Monticello, Extended Power Uprate (USNRC TAC MD8398); Acceptance Review Supplemental Information.: ML081490639

[13] Monticello Extended Power Uprate: Response to NRC Probabilistic Risk Assessment (PRA) Licensing Branch Request for Additional Information (RAI) Dated April 29, 2009 (TAC No. MD9990).: ML091520133

[14] Monticello, Extended Power Uprate: Acceptance Review Supplemental Information Package 3.: ML081550504

[15] Monticello - Response to NRC Probabilistic Risk Assessment (PRA) Branch Requests for Additional Information (RAIs) dated December 5, 2008.: ML090360545

[16] Monticello Nuclear Generating Plant - Uprate (EPU): Update on EPU Commitments.: ML11249A045

[17] Monticello Extended Power Uprate: Response to NRC Mechanical and Civil Engineering Review Branch (EMCB) Requests for Additional Information (RAIs) Dated March 28, 2009.: ML092390332

[18] Monticello - Extended Power Uprate, Acceptance Review Supplemental Information Package 6.: ML081640435

[19] Monticello Extended Power Uprate: Supplement to Revise Technical Specification Setpoint for the Automatic Depressurization System Bypass Timer (TAC MD9990).: ML12307A036

[20] Monticello Extended Power Uprate: Response to NRC Requests for Additional Information and Supplemental Information (TAC MD9990).: ML081490639

[21] Monticello, Extended Power Uprate: Response to NRC Reactor Systems Branch and Nuclear Performance & Code Review Branch Request for Additional Information (RAI) Dated February 23, 2009.: ML091130636

[22] Monticello Nuclear Generating Plant - Response to NRC Steam Generator Tube Integrity & Chemical Engineering Branch Request for Additional Information (RAI) dated February 11, 2009.: ML090560464

Photo courtesy of NRC.