L-PI-10-061, Supplement to License Amendment Request for Measurement Uncertainty Recapture Power Uprate - Additional Information Regarding Main Steam System Stress Analyses and Electrical Output

Supplement to License Amendment Request for Measurement Uncertainty Recapture Power Uprate - Additional Information Regarding Main Steam System Stress Analyses and Electrical Output

ML101690068
Person / Time
Site:	Prairie Island
Issue date:	06/17/2010
From:	Schimmel M Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-10-061, TAC ME3015, TAC ME3016
Download: ML101690068 (34)

Text

JUN 1 7 2010 L-PI-10-061 I 0 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 License Nos. DPR-42 and DPR-60 Supplement to License Amendment Request for Measurement Uncertainty Recapture -

Power Uprate -Additional Information Recrardina Main Steam Svstem Stress Analvses and Electrical Output (TAC Nos. ME3015 and ME30162

References:

1. Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, "License Amendment Request for Measurement Uncertainty Recapture -

Power Uprate," L-PI-09-133, dated December 28, 2009, ADAMS Accession Number ML093650045.

2. Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, "Supplement to License Amendment Request for Measurement Uncertainty Recapture - Power Uprate - Response to Requests for Additional lnformation (TAC Nos. ME3015 and ME3016)," L-PI-10-036, dated April 19, 2010, ADAMS Accession Number ML101090498.b

3. Letter from T. Beltz (NRC) to M. Schimmel (NSPM), "Prairie Island Nuclear Generating Plant, Units 1 and 2 - Requests for Additional lnformation (RAI) Associated with License Amendment Request Re: Measurement Uncertainty Recapture Power Uprate (TAC Nos.

ME3015 and ME3016)," dated March 17, 2010, ADAMS Accession Number MLI 00740039.

This letter provides additional information in support of a License Amendment Request (LAR) submitted by the Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, in Reference 1. Reference 1 requested an amendment to the Operating License for the Prairie Island Nuclear Generating Plant (PINGP), Units 1 and 2, to increase the licensed thermal power as a result of a measurement uncertainty recapture (MUR) power uprate. In Reference 2, NSPM 1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1121

Document Control Desk Page 2 responded to Requests for Additional Information (RAls) provided by the Nuclear Regulatory Commission (NRC) Staff in Reference 3.

During subsequent discussions with the NRC Staff, questions were raised regarding the impact of the MUR power uprate on the structural integrity of the PINGP Main Steam (MS) system, and also on the electrical output of the PINGP generators and the impacts of increased generation on grid stability. Enclosure 1 addresses questions regarding the Main Steam stress analysis and impacts of the MUR power uprate. Enclosure 2 discusses the electrical output of the PINGP generators and the grid stability studies performed in support of the MUR power uprate. Enclosure 3 provides a Generator Interconnection Study performed by the Midwest Independent System Operator (MISO),

dated May 2006, in support of the MUR power uprate. NSPM submits this supplement in accordance with the provisions of 10 CFR 50.90.

The supplemental information provided in this letter does not impact the conclusions of the Determination of No Significant Hazards Consideration and Environmental Assessment presented in the Reference 1 submittal.

In accordance with 10 CFR 50.91, NSPM is notifying the State of Minnesota of this LAR supplement by transmitting a copy of this letter to the designated State Official.

If there are any questions or if additional information is needed, please contact Sam Chesnutt at 651-267-7546.

Summary of Commitments The information in Enclosure 1 satisfies the commitment made in Reference 2 to submit justification for the Main Steam system stress analysis, including piping, supports, and components by August 27, 2010. The Reference 2 commitment is therefore complete.

This letter contains no new commitments and no revisions to existing commitments.

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

Executed on JUN 1 7 2010 Mark A. Schimmel Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosures (3) cc: Administrator, Region Ill, USNRC Project Manager, PINGP, USNRC Resident Inspector, PINGP, USNRC State of Minnesota

ENCLOSURE 1 Related to a License Amendment Request for a Measurement Uncertaintv Recapture This enclosure provides additional information from the Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, in support of NSPM's License Amendment Request (LAR) for a measurement uncertainty recapture (MUR) power uprate submitted in Reference I.The information in this enclosure addresses the Main Steam (MS) System stress analyses at the Prairie Island Nuclear Generating Plant (PINGP) that were discussed in NSPM's response (Reference

2) to a Request for Additional Information (RAI) provided by the Nuclear Regulatory Commission (NRC) in Reference 3.

During telephone conferences held with members of the NRC Staff on April 26, May 21 and May 24, 2010, the NRC requested additional information supporting that the MUR power uprate would not adversely affect the structural integrity of the MS system.

I. Background In support of the MUR power uprate, NSPM reviewed the analysis of record (AOR) for various plant systems to determine the impact of the uprate on system stress analyses.

This review determined that Main Steam (MS) system design conditions for the MUR power uprate are bounded by the current licensing basis (CLB), but this review also identified certain discrepancies in the MS system piping stress AOR, as stated in Reference I(Enclosure 2,Section IV.l .A.v, page 48). It is important to note that the discrepant conditions discovered in the MS pipe stress analysis are applicable to current operating conditions and were not created by or uniquely associated with the MUR power uprate.

NSPM1sevaluation of the MS pipe stress analysis discrepancies led to the initiation of a revision to the MS pipe stress analysis, as identified in Reference 1 (Enclosure 2,Section IV.l .B.i, page 51). The revised analysis is not yet complete, as described in Reference 2. The following discussion addresses the discrepancies that have been identified in the analysis, the effects of the MUR power uprate, and NSPM1sconclusion that structural integrity of the MS system is maintained both for current operations and for MUR uprate conditions.

2. Discrepant Conditions The discrepancies found in the MS system piping analysis involve errors in the modeling and seismic portions of the stress analysis which are not related to the MUR power uprate. Preliminary calculations have identified several pipe overstress conditions primarily due to inadequate treatment of torsional seismic acceleration and inaccurate modeling of snubbers in the MS safety valve (MSSV) thrust load stress runs.

Page 1 of 5

Enclosure 1 NSPM Response to MS Stress Analysis Questions Resolution of some of these overstress conditions will require physical modifications such as snubber replacement and removal of welded piping auachments, which will require plant shutdown conditions. The re-analysis is still in progress and additional non-conforming conditions may be identified.

Each overstress location identified to date has been identified as a non-conforming condition and entered into the PINGP Corrective Action Program (CAP). Structures, systems, and components (SSCs) such as the MS system piping and supports are evaluated to determine the impact of the overstress condition on the SSC's operability status (e.g., Operable, Inoperable, Operable but Degraded, Operable but Non-conforming). Future non-conforming conditions will be processed in the same manner in accordance with PINGP CAP procedures.

MS system calculated stresses have been evaluated using the Piping Operability Stress Criteria in the PINGP Engineering Manual, and the overstress conditions have been determined Operable but Non-Conforming (OBN). The Piping Operability Stress Criteria requires that total stresses (e.g., due to pressure, dead weight, seismic, and thrust forces) must not exceed 2.0 times the material yield stress at operating temperatures. The stress analyses used to support the OBN evaluations were performed for Hot Zero Power (HZP) system conditions that are bounding for both current operations and for the MUR power uprate conditions at Hot Full Power (HFP),

as shown below.

Parameter Current Post-MUR Operations Power Uprate Design Pressure (HZP) psig 1085 1085 Design Temperature (HZP) OF 600 600 Operating Pressure (HZP, saturated 1005 1005 conditions at 547 OF) psig Operating Temperature (HZP of 547 560 560 plus analytical margin) OF Operating Pressure (HFP) psia 772 (UI) 765 (UI) 719 (U2) 712 (U2)

Operating Temperature (HFP) OF 514.1 (UI) 513.2 (UI) 506.2 (U2) 505.0 (U2)

The OBN process provides relaxed stress acceptance criteria for an interim period and is consistent with NRC Inspection Manual Section 9900, "Operability Determinations and Functionality Assessments for Resolution of Degraded or Nonconforming Conditions Adverse to Quality or Safety."

Based on PINGP's CAP evaluation and Operability Determination process, OBN MS piping conditions are acceptable for continued plant operation on an interim basis.

Analyzed system conditions are bounding for both current operations and MUR uprate Page 2 of 5

b Enclosure 1 NSPM Response to MS Stress Analysis Questions conditions. The PlNGP CAP program requires that corrective actions for non-conforming conditions be completed at the first available opportunity.

3. Effecb of MUR Power Uprate Stress in the MS piping results from deadweight, pressure, thermal, seismic, pipe rupture, and safety relief valve thrust forces in combinations defined by USAR Table 12.2-11, "Load Combinations for Components." The effects of the MUR power uprate on these forces and the applicable AORs include the following:

Thermal and pressure stresses depend on the operating temperature and pressure, respectively, of the piping system. The AOR thermal and pressure stress analysis of the MS system is based on the limiting HZP temperature and pressure, both of which do not change for the MUR power uprate as shown in the table above. For the HFP normal operating conditions as shown above, MS system temperature decreases approximately 1 OF and MS system pressure decreases approximately 7 psia. (Reference I,Enclosure 2, Table IV.1.B.4, page 55). Therefore, thermal and pressure stresses in the AORs bound MUR power uprate conditions.

Deadweight and seismic loads are unrelated to temperature, pressure, or power levels and are not affected by the MUR power uprate. The AOR for deadweight and seismic forces remains bounding.

Pipe rupture loads from steam systems depend upon system pressure and break area. The AOR for the MS system calculates pipe rupture loads based upon the more limiting HZP pressure, which does not change for the MUR power uprate.

Therefore, the MUR power uprate does not affect pipe rupture loads on MS piping and its supports.

MS system flow rates increase approximately 2%, and moisture carryover (MCO) levels increase to approximately 1.4% (Reference 1, Enclosure 2 , IV.l .B.i, page 51). The associated increases in steam flow and density result in higher thrust forces during lifting of the MSSVs. However, the associated CAP operability determination concluded that MS piping stress levels, including MSSV thrust forces at MUR uprate conditions, remain less than the interim Piping Operability Stress Criteria described above, and the associated piping is therefore OBN.

As described previously, the MS piping overstress conditions identified to date have not been created by the MUR uprated power level. Also, since overstress conditions have already been evaluated for conditions that bound MUR uprate conditions, the MUR uprate will not result in any increases in analyzed stress levels. Additional overstress or other non-conforming conditions that may be identified in the future will be processed though the PlNGP CAP program and evaluated against the OBN criteria in the same manner as described above.

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Enclosure 1 NSPM Response to MS Stress Analysis Questions

4. Conclusion The MS piping system at PlNGP has several overstress locations that have been determined Operable but Non-Conforming (OBN) and are acceptable for continued operation on an interim basis. The stress analyses that support the OBN operability determinations have been performed for system WZP conditions that are bounding for both current operations and MUR uprate conditions. The MUR power uprate will not increase analyzed stress levels and the Operability criteria will still be met.

Based on the above, the MUR power uprate is not considered to adversely affect the structural integrity of the system. The current AOR for the MS system piping, along with OBN overstress conditions that are processed through the PINGP CAP program, is bounding for MUR power uprate conditions.

5. Commitments and Actions Previouslv Described In Reference 2, NSPM committed to submit justification for the Main Steam system stress analysis, including piping, supports, and components by August 27, 2010. Also, in Reference 1, although this was not identified as a commitment, NSPM indicated that a revision to the MS stress analysis to ensure that MSSV thrust forces would be acceptable at MUR conditions would be complete prior to uprate (Enclosure 2, page 51).

The information provided above provides justification for the MS stress analysis at MUR uprate conditions based on the current AOR and ongoing efforts to identify, process, and resolve OBN overstress conditions through the PlNGP CAP program. Although the analysis efforts for MS piping, supports, components, and MSSV thrust forces are not yet finalized, the analyses described above and the PlNGP process for ensuring that non-conforming conditions satisfy the operability criteria for MUR conditions, demonstrate the structural integrity of the MS system for MUR uprate conditions.

NSPM therefore considers the commitment identified in Reference 2 and actions described in Reference 1 to be complete.

References

1. Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, "License Amendment Request for Measurement Uncertainty Recapture - Power Uprate," L-PI-09-133, dated December 28,2009, ADAMS Accession Number ML093650045.

2. Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, "Supplement to License Amendment Request for Measurement Uncertainty Recapture - Power Uprate - Response to Requests for Additional Information (TAC Nos. ME3015 and ME3016)," L-PI 036, dated April 19,2010, ADAMS Accession Number MLI 01090498.

Page 4 of 5 NSPM Response to MS Stress Analysis Questions

3. Letter from T, Beltz (NRC) to M. Schimmei (NSPM), "Prairie Island Nuclear Generating Plant, Units 1 and 2 Requests for Additional Information (RBI)

Associated with License Amendment Request Re: Measurement Uncertainty Recapture Power Uprate (TAC Nos. ME3015 and ME30"1)," dated March 17, 2010, ADAMS Accession Numbar ML-I00740039.

Page 5 of 5

ENCLOSURE 2 This enclosure provides additional information from the Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, in support of NSPM's License Amendment Request (LAR) for a measurement uncertainty recapture (MUR) power uprate submitted in Reference 1. The information in this enclosure addresses the effects of the MUR power uprate on electrical output and grid stability of the Prairie Island Nuclear Generating Plant (PINGP). These effects were addressed in NSPM1sresponse (Reference 2) to a Request for Additional Information (RAI) provided by the Nuclear Regulatory Commission (NRC) in Reference 3.

During telephone conferences held with members of the NRC Staff on May 21 and June 1, 2010, the NRC requested clarification of the net and gross generation values for PINGP units, both before and after the MUR power uprate, and of grid stability studies performed to support the uprate. In addition, clarification was requested of the grid analyses that demonstrate sufficient post-trip voltage at PINGP buses after an assumed trip of both units.

1. Effects of MUR power uprate on Electrical Generation The proposed MUR power uprate will increase the licensed thermal power level of each of the two units at the Prairie Island Nuclear Generating Plant (PINGP) from 1650 MWt to 1677 MWt. This represents an increase in electrical generation of approximately 9 MWe per unit.

The corresponding gross and net electrical generation values before and after the MUR power uprate are as follows:

Gross electrical generation:

o Before uprate: 575 MWe (Unit 1 and Unit 2) o After uprate: 584 MWe (Unit 1 and Unit 2); this represents a 9 MWe increase per unit Net electrical generation, which is determined by subtracting station service loads from the gross generation values:

o Before uprate: 551 MWe (Unit I), 545 MWe (Unit 2); note that the differences in Unit 1 and Unit 2 net generation values reflect differences in the sharing of station service loads o After uprate: 560 MWe (Unit I ) , 554 MWe (Unit 2); this represents a 9 MWe increase per unit and reflects the fact that station service loads are not changed by the MUR power uprate Page 1 of 7

Enclosure 2 NSPM Response to Electrical Engineering Questions These generation values represent winter conditions, which typically provide the highest seasonal generation values at PINGP. During winter months, PINGP typically uses cooling water from the Mississippi River. Colder cooling water temperatures produce greater condenser vacuum and more efficient thermal performance, therefore, the plant produces more electrical power for the same reactor thermal power levels. In addition, net generation levels are further increased in winter months because the cooling towers are not operated, resulting in lower station service loads.

1 2. Grid Stabilitv Studies - Generation Levels and Grid Conditions i

i This section discusses the following three grid studies that support the MUR power uprate:

Midwest lndependent System Operator (MISO) Study, March 2006, provided in Reference I,Enclosure 8. This study included steady state and grid stability analyses using a summer case grid model and summer generation values.

MIS0 Study, May 2006, included as Enclosure 3 to this letter. This study included steady state and grid stability analyses using a summer case grid model and higher winter generation values.

IEEE-765 Study, November 2009, provided in Reference I , Enclosure 8. This study included a transient stability analysis and evaluated post-disturbance voltages after a dual-unit trip at PINGP, using summer generation values. This I study was also re-evaluated to consider higher winter generation values.

MIS0 Study - March 2006 The Midwest lndependent System Operator (MISO) evaluated the impact of an MUR power uprate on transmission system performance, in support of the PINGP Large Generator lnterconnection Agreement (GIA). The resulting MIS0 Generation lnterconnection Study, dated March 24, 2006, (hereafter referred to as the March 2006 MIS0 Study) evaluated the addition of 19 MWe to Unit 1 and 19 MWe to Unit 2, for a total of 38 MWe. The additional 19 MWe for each unit includes approximately 9 MWe for the MUR power uprate and approximately 10 MWe to account for unspecified efficiency improvements and equipment changes unrelated to the MUR power uprate.

The March 2006 MIS0 Study was submitted as part of Enclosure 8 in Reference I , and reflects MISO1sdesignations of the uprate projects as G433 (Unit 1) and G434 (Unit 2).

The March 2006 MIS0 Study evaluated the impact of the MUR power uprate project on transmission system performance. System impact studies included steady state and stability analyses based on a grid system model that includes the PINGP generators and station service loads. Steady state analyses included thermal and voltage analyses, which evaluated the effects of a loss of transmission lines or other grid elements. The stability analysis evaluates system stability when subjected to various local and regional disturbances, which included faults and trips.

The following summer generation levels were included in the March 2006 MIS0 Study:

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Enclosure 2 NSPM Response to Electrical Engineering Questions Gross generation after the uprate:

a 569 MWe (Unit I), 565 MWe (Unit 2)

Net generation to the grid after the uprate, determined by subtracting station service loads from the gross generation values:

o 537 MWe (Unit I ) , 532 MWE (Unit 2)

The March 2006 MISO Study evaluated the grid under various system conditions, which represent the most stressed conditions for the analysis being performed.

The March 2006 MIS0 Study steady state analyses determined that the impacts of the MUR power uprate on transmission facility loadings and bus voltages did not result in any new thermal or voltage violations.

The March 2006 MIS0 Study stability analysis evaluated the impact of the proposed MUR power uprate and other unspecified efficiency improvements and equipment changes on system stability. The stability analysis simulated summer off-peak conditions with maximum simultaneous transfer levels across the major interfaces. No stability criteria violations were observed for the simulated disturbances. Results indicate that the interconnection of the proposed MUR power uprate would not a

adversely impact transmission system stability.

j I

MIS0 Study - Mav 2006 In May 2006, MIS0 performed an additional Generation lnterconnection Study analysis based on winter PlNGP generation levels, to more clearly bound the proposed MUR power uprate output levels. This study was performed as a Sensitivity Study for the Generation lnterconnection Study for the MUR power uprate projects, G433 and G434.

The May 2006 MIS0 Sensitivity Study - Generation lnterconnection Study (hereafter referred to as the May 2006 MIS0 Study) is included as Enclosure 3 to this letter.

The enclosed May 2006 MIS0 Study used the same transmission system models used for the March 2006 MIS0 Study, and was also simulated under the most stressed conditions for the analysis being performed. This study included steady state and stability analyses and evaluated the following winter PlNGP generation levels:

Net generation to the grid after the uprate:

o 568 MWe (Unit I), 565 MWe (Unit 2)

Note that these net generation values are comparable to the gross generation values evaluated in the March 2006 report, and these values bound the net generation values for the MUR power uprate.

The steady state analyses in the enclosed May 2006 MIS0 Study determined that the impacts of the MUR power uprate on transmission facility loadings and bus voltages did not result in any new thermal or voltage violations.

Page 3 of 7

Enclosure 2 NSPM Response to Electrical Engineering Questions The stability analysis in the enclosed May 2006 MIS0 Study evaluated the impact of the proposed MUR power uprate and other unspecified efficiency improvements on system stability. The stability analysis simulated summer off-peak conditions with maximum simultaneous transfer levels across the major interfaces, and evaluated winter PINGP generation levels. No stability criteria violations were observed for the simulated disturbances. Results indicate that the interconnection of the proposed projects would not adversely impact transmission system stability.

Xcel Energy and MIS0 subsequently entered into the MIS0 G433lG434 Large GIA, in June 2006. This GIA granted interconnection services to PlNGP Unit Ifor a total of 568 MWe net, and to Unit 2 for a total of 565 MWe net. This is the maximum net output generation allowed under this agreement.

IEEE-765 Studv November 2009 An additional study was performed in 2009 to confirm that the MUR power uprate meets transmission study requirements of IEEE-765, "IEEE Standard for Preferred Power Supply (PPS) for Nuclear Power Generating Stations (NPGS)." This study was a transient stability study that confirmed the strength of the transmission system following disturbances, although it was not required to support the MIS0 GIA. This study also evaluated post-disturbance voltage levels at the PlNGP buses. As stated in Reference 1 (Enclosure 2,Section V.l .D, page 79), the IEEE-765 supplemental analysis demonstrated that following the PlNGP MUR power uprate expansions, the voltages at the PlNGP 161 kV and 345 kV buses were within the PlNGP voltage criteria for all disturbances studied. The 2009 IEEE-765 Study was included in Enclosure 8 to Reference 1.

The IEEE-765 Study evaluated post-disturbance voltage levels at the PlNGP 161 kV and 345 kV buses. The following conditions are evaluated, as specified in IEEE-765:

a. Loss of the nuclear power generating unit (Unit 1, Unit 2, and both units)

b. Loss of the largest or most significant generating unit

c. Loss of the largest or most significant transmission circuit or intertie

d. Loss of the largest or most significant load This study evaluated the following PlNGP summer generation levels:

Net generation to the grid after the uprate:

o 537 MWe (Unit I ) , 532 MWe (Unit 2)

This study verified that there were no stability criteria violations or damping problems for the 38 MWe uprates. This study also included an evaluation of 19 system disturbances, including a trip of both units at PINGP, to determine whether post-event voltages on the PlNGP buses after the system reaches steady state, would meet minimum criteria.

Analyzed PlNGP bus voltages were within the acceptable range for all disturbances evaluated, including a two-unit PlNGP trip, as shown in Table 4-2 of the IEEE-765 Page 4 of 7

Enclosure 2 NSPM Response to Electrical Engineering Questions Study for Fault Codes 'nat' (Unit 1 trip), 'nbt7Uni-L2 trip), and 'nct' (dual unit trip), In addition, the IEEE-765 Study validated the stability results of the March 2006 MIS0 Study.

The November 2009 IEEE-765 Study was re-evaluated for the higher PlNGP winter generation levels as follows:

Net generation to the grid after the uprate:

o 568 MWe (Unit I ) , 565 MWe (Unit 2)

This re-evaluation considered the trips of PINGP Unit 1, Unit 2, and both units in the same manner previously evaluated in the November 2009 IEEE-765 Study, and confirmed the previous results. At the higher PlNGP winter generation levels after the MUR power uprate, post-event voltages at PINGP 161 kV and 345 kV buses were found to satisfy minimum voltage requirements for expected bus alignments.

3. Grid Stability Studies - Response to Disturbances and a Two-Unit Trip The requirement to maintain adequate voltage after a two-unit trip is included in the current licensing basis for PINGP, as discussed in USAR Section 8.2.2, "Offsite Grid Reliability."

I The grid stability analyses included in the MIS0 Studies evaluate grid responses to disturbances local to PlNGP and the most limiting disturbances in the North Dakota, South Dakota, and Twin Cities metro area. Typical MISO-analyzed fault scenarios or disturbances include various ground faults and protective breaker failures that represent generator trips and the loss of transmission lines. The resulting system voltages and oscillations were examined and the MUR power uprate projects were determined to not adversely impact transmission system stability or result in any stability criteria violations.

Voltages at the PlNGP grid interface location are ensured both on a real-time basis by nearly continuous contingency analyses and on a planning basis by use of computer models. The minimum voltages for PlNGP are based on the equipment required to safely shut down the plant after a two-unit trip. These voltages are contained in site calculations for different bus alignments and are included in a site abnormal operating procedure. The minimum voltages to ensure safe shutdown conditions at PlNGP do not change as a result of the MUR power uprate.

Adequate voltage support for post-trip conditions is assured on a real-time basis, as mentioned above, by the Security Analysis computer software. This software continuously looks at the current grid configuration and runs contingency analyses for various grid events, including a dual unit trip at PINGP. The Security Analysis software evaluates grid conditions and calculates parameters such as voltages on the PlNGP 161 kV and 345 kV buses approximately once every 4 to 8 minutes. As long as the resultant voltages are greater than the requirements of station procedures, the analysis assures that adequate voltage would be available to ensure operation of necessary Page 5 of 7

Enclosure 2 NSPM Response to Electrical Engineering Questions shutdown and safety equipment following a Wa-unit trip under the current grid configuration. In the event that minimum required voltages would not be met, an alarm alerts transmission operations personnel to perform corrective actions. If low voltage conditions would still exist, then PlNGP control room personnel are contacted and actions are taken to change either the grid configuration or local plant conditions to ensure that required post-trip voltages can be met.

The current Security Analysis also ensures that post-trip voltages will be adequate at PlNGP buses after the MUR power uprate is implemented, because the MUR power uprate does not change the post-trip voltage requirements used in the Security Analysis. The Security Analysis is part of MIS0 standing operating guidance and NSPM plans to continue this analysis to ensure adequate post-contingent voltages at the PlNGP 161 kV and 345 kV buses, following events that include the trip of both PlNGP units.

In addition to real time studies, grid performance after the MUR power uprate was also evaluated in the November 2009 IEEE-765 study discussed above. As noted previously, the November 2009 IEEE-765 study evaluated a trip of PlNGP Units Iand 2 at post-MUR power uprate conditions, and confirmed that post-trip voltages exceed the minimum voltages established in site procedures, based on the summer generation values considered in that evaluation. These conclusions have also been confirmed for the higher winter generation values, post-MUR power uprate, as identified above.

4. Conclusion In summary, the MIS0 Generation Interconnection Studies performed in March 2006 and in May 2006 both demonstrate that the PlNGP MUR power uprate will not result in additional instabilities in the grid following worst case disturbances or other contingency events. In addition, the Security Analysis computer software real time contingency studies will continue to demonstrate adequate voltage at PlNGP after the MUR power uprate. PlNGP voltage requirements are not changed by the MUR power uprate and grid capabilities for supporting these requirements remain adequate. In addition, the IEEE-765 study performed in 2009 and re-evaluated in 2010 confirm the conclusions of the 2006 MIS0 Studies, and confirm adequate post-trip voltage support after a two-unit trip at PINGP.

Based on the above, the higher generation values associated with the MUR power uprate will not affect grid stability, and post-trip voltages after a trip of both units at PlNGP will continue to exceed minimum voltages for normal bus alignments.

References

1. Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, 'license Amendment Request for Measurement Uncertainty Recapture - Power Uprate," L-PI-09-133, dated December 28,2009, ADAMS Accession Number ML093650045.

Page 6 of 7 NSPM Response to Electrical Engineering Questions

2. Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, "Supplement to 1-icense Amendment Request for MeasuremenWnsertainty Recapture - Power Uprate - Response to Requests for Additional Information (TAG Nos, ME3015 and ME3016)," L-PI-IO-036, dated April 19,2010, ADAMS Accession Number Mt101090498.

3. Letter from T. Beltz (NRC) to M. Schimmel (NSPM), "Prairie Island Nuclear Generating Plant, Units Iand 2 Requests for Additional Information (RAI)

Associated with License Amendment Request Re: Measurement Uncertainty Recapture Power Uprate (TAC Nos. ME3015 and ME3016)," dated March 17, 2010, ADAMS Accession Number MLI00740039.

Page 7 of 7

Enclosure 3 to Letter from Mark A. Schimmel (NSPM) i Document Control Desk (NRC)

I 1 Midwest Independent System Operator (MISO)

"Sensitivity Study - Generation Interconnection Study - Projects #G433 and (3434 38 MW Expansion of Prairie Island Units 1 and 2" dated May 31,2006 19 pages follow

Sensitivity Study Generation Interconnedion Study - Projects # (3433 and (3434 38 MW Expansion of Prairie Island Units 1 and 2 May 3 1,2006 Prepared for:

Midwest I S 0 Prepxed by:

ABB Inc.

940 Main Campus Drive, Suite 300 Raleigh, NC 27606 12 Cornell Road Latham, NY 121 10 ESC Report No. 2005- 1 1 1.25-2.RO3

Author(s): Review4 By: Approved By:

S. Pillutla J. Daniel Executive Summary 1 A generator interconnection evaluation study was recently completed to evaluate the collective impact of generation interconnection requests G433 and G434 on transmission system performance. See reference [I]. Together, these prokcts have requested a combined output of 38 MW (Gross). Project G433 is a 19 MW expansion to Prairie Island #1 and Project G434 is a 19 MW expansion to Prairie Island #2.

In the above study, the MW outputs of the Prairie Island units @re- and post-expansion) were modeled b e d on their Summer maximum ratings. MIS0 recently indicated that the Prairie Island units would have higher ratings in Winter (a total of 6 4 MW higher than the Summer ratings) and requested that a sensitivity study be performed to assess the impact of the proposed interconnections based on the higher pre- and post-project MW outputs.

The scope of the sensitivity study included a limited amount of steady-state and stability analysis to assess the impact of the proposed interconnections on the transmissionsystem. In this study, the p ~ and - post-expansion MW outputs of the Prairie Island units are modeled based on the Winter maximum ratings.

The following is a summary of study results.

Steady-State Analysis:

The interconnection of the proposed projects impacted several transmission facilities and resulted in steady-state criteria violations for system intact and contingency oonditions. These violations are remote from the Prairie Island substation. The transmission outlets out of the Prairie Island substation are not overloaded. Based on the available information, k e remote violations should not limit the ability of the proposed projects to interconnect as Energy Resource.

The violations reported in this study could pdentially limit the ability of the projects to deliver power into the transmission system. MIS0 has indicated that these overloads can not be classified as njection issues and therefore they need not to be mitigated for Energy Resource Interconnection Service.

Stability Analysis :

Stability analysis was perfomed to evaluate the impact of the proposed projects on the system stability. All faults simulated in reference [I ] were tested, No transknt or dynmic instability problems were observed.

Simulation plots for faults agl, ei2, 4b3, 4p3 and pr3 showed poorly damped oscillations in the rotor angles for the following mits, both with and without the proposed projects: Big Falls (4.8 MW unit at bus 60662) and R e d ~ n g(23.2 MW unit at bus 60823). These oscillations are most prominent for faults 4b3,4p3 and pr3 and appear to be confined to the Big Falls and Redwing units ie., the oscillations do not propagate to the bulk power system Prony analysis was used to calculate the oscillation modes ofthe Big Falls and Redwing rotor angles and the corresponding damping ratios for fault "4b3". Results suggest that the damping ratios associated with the rotor angle oscillations at Big Falls and Redwing are in violation of the UAPP Transient Period Damping Criteria even prior to the addition of the proposed projects. Tlxe proposed projects, however, do not adversely impact damping performance and no oscillatory behavior was observed in the Prairie Island rotor angles.

In conclusion, the results of the stability analysis indicate that the interconnection of the proposed projects would not adversely impact transmission systemstability.

The results of this study are based on available data and assumptions made at the time of conducting this study. In particular, it should be noted that the results depend on delivery assumptions ofprior-queued generator interconnections. I f the delivery assumptions of the prior-queued generators change and/or if the prior-queued units drop out of the generator interconnection queue, additional studies may be required to determine possible criteria violations that may limit the ability of the project to inject and/or &liver power into the transmission system. Any additional studies are considered outside of the scope of the system impact studies. The results providkd in this report may not apply if any of the data andor assumptions made in developing the study models change.

LEGAL NOTICE This document, prepared by ABB hc., is an a w m t of work sponsored by Midwest IS0 (MISO). Neither AL3B Inc., nor any person or persons oteting on behalf of either party: (i) makes any warranty or represen&~an,expressed or implied, with respect to the use of any infomation contained in this report, or that the use of my idomGon, apparatus, method, or process disclosed in this report may not privately owned rights, or (ii) assmes any liabilities with respect to the use of or for resulting &om the use of any infomation, apparatus, method, or process disclosed in this document.

iii

Table of Contents 2.1 Base Case Developmext,.,.,,,. .....................................................................................2 2.2 System Intact Analysis ....................................................................................................2 2.3 Contingency Analysis ..............................................................................................3 2.4 Summaryof Results ........................................................................................................7

3. STABILITY ANALYSIS ...................................................................................................8 3.1 Model Development...................................................................................................... 8 3.2 Results of Stability Analysis ...........................................................................................8

4. CONCLUSIONS...............................................................................................................12

5. REFERENCES .................................................................................................................14 APPENDIX A - DATA FILES USED FOR STEADY-STATE ANALYSIS APPENDIX B - STEADY-STATE ANALYSIS RESULTSfSYSTEM INTACT CONDITIONS)

I APPENDIX C - SCREENACCC REPORT FOR STEADY-STATE ANALYSIS

~I APPENDIX D - SIMULATION

SUMMARY

TABLES AND PLOTS FOR SELECTED FAULT SCENARIOS (WITHOUT 6433 AND G434)

APPENDIX E - SIMULATION

SUMMARY

AND PLOTS FOR SELECTED FAULT SCENARIOS (WITH G433 AND G434) 11Ill)ll 1"%1#11

INTRODUCTION A generator interconnection evaluation study was recently completed to evaluate the collective impact of generation intercomection requests W33 and G434 on system performance. See reference 113. Together, these projects have requested a combined output of 38 MW (Gross). Project 6433 is a 1 9 MW expasion to Prairie Island #1 and Project (3434 is a 1 9 MW expansion to Pmirie Island #2.

In the above study, the MW outputs of the Prairie Island units (pre- and post-expansion) were modeled based on their Summer miximum ratings. MISO recently indicated that the Prairie Island units would have higher ratings in Winter (a total of 64 MW higher than the Summer atings) and requested that a sensitivity study be performed to assess the impact of the proposed interconnections based on the higher pre- and post-project MW outputs. For the purposes of this study, the pre- and post-expansion MW outputs of the Prairie Island units were modeled based on the Winter maximum ratings. These values were provided by MISO.

Prairie Island Unit 1:

Net MW Output = 549 MW (pre-project) and 568 MW (post-project)

Prairie Island Unit 2:

Net MW Output = 546 MW (pre-project) and 565 MW (post-project)

The scope of work for the sensitivity study included a limited amount of steady-state and stability analysis to assess the impact of the proposed interconnections on the transmission system.

For steady-state analysis purposes, the same pre- and post-project peak 2007 summer peak load cases that were used in reference [I] were used. The Gross MW outputs of the Prairie Island units were increased by a total of approximately 64 MW in order to obtain the Net MW outputs shown above. System intact and contingency analyses were repeated on these cases using the same criteria described in reference [I]. For contingency analysis purposes, a limited number of single line outages in the vicinity of Prairie Island were tested. Also tested were a small number of multi- terminal contingenck."5ection 2 of this report summarizes the results of the steady-state analysis.

For stability analysis purposes, the same pie- and post-project stability models that were used in reference [I] were used. Again, the Gross MW outputs of the Prairie Island units were adjusted so as to obtain the desired Net MW outputs shown above. All local and regional-contingencies that were tested in reference [I] were repeated. Section 3 of this report summarizes the results of the stability analysis.

2. STEADY-STATE ANALYSIS 2.1 Base Case Development For the purposes of this study, the e pre- and post-project 2007 smmer peak load cases that were used in refwence f l] were used, Gross generation levels at Prairie Island were adjusted to obtain the Net MW outputs listed in Section 1 of this report. As before, generators in the MESO foo@rintbere scaled down in order to account for the increase in generation.

Figures 2.1 and 2.2 show PSSE power flow diagrams of the area in the vicinity of the Prairie Island substation for 2007 summer peak load conditions, both with and without the proposed projects.

System intact and contingency analyses were repeated on these cases using the same criteria described in reference [I]. For contingency analysis purposes, a limited number of single line outages in the vicinity of Prairie Island were tested. Also tested were a small number of multi-terminal contingencies. Appendix A lists the subsystem description, monitored element and the contingency description files used in the power flow analysis.

2.2 System Intact Analysis i

Imact of Proposed Projects on Facility Loadings I

Thermal overloads were observed on several transmission facilities, both with and without the proposed projects (see Appendix B). MAPP DRS ~uidelines*were used to identifl Significantly Affected Facilities (SAF). According to these guidelines, all overloaded facilities that have a TDF (T-sfer Distribution Factor) greater than 2% of the generation addition and an increase in flow of at least 1 MW (without plant vs. with plant) are to be flagged as significantly affected facilities.

Results indicate that the impact of the proposed projects on facility loadings under system intact conditions is negligible. No significant impacts were noted and no new thermal violations were observed.

Impact of Pro~osedProjects on Bus Voltages i Voltage criteria violations were observed at several remote buses, both with and without the proposed projects (see Appendix B). In accordance with MAPP DRS Guidelines, those buses that have a voltage change of more than 0.01 p.u. (without plant vs. with

' MIS0 Footprint was defined as generation in the following areas: Area 356: Ameren, Area 359: Cilco, Area 208:

Cinergy, Area 360: CWLP, and Area 21 1: LGEE, Area 650: Lincoln Electric System, Area 21 8: CONS, A=a 361:

SIPC, Area 202: FEYArea 217: NIPS.

Steady-State Facility & Constrained Path Impact Determination Requirements & Saeening Guidelines for Study Submissions, Prepared by MAPP Design Review Subcommittee (DRS). Oct 28,2003.

plant) are included in the SAF list. The impact of the proposed projects on bus voltages under system intact conditions is negligible, No signgcant impacts were noted and ID new voltage violations were obsewed.

Contingency AnaIysis After establishing the system intact violations, transmission system steady-state performance was compared by performing N- 1 contingency analyses on the sr- peak cases, both with and withaut: the proposed projects. Also tested were a small number of multi-terminal contingencies, See Appendix A. The analyses were conducted using activity ACCC of PSSE.

AC contingency analysis results were post-processed to create SCMENACCC sports to compare the results obtained fiom the pre-project cases vs. those obtained fiom the post-project cases (see Appendix C).

The impact of the proposed projects on facility loadings and bus voltages is s u m m b d below. As before, MAPP DRS Guidelines were used to identify significantly affected facilities.

Imact of Promsed Projects on Facility Loadinns Table 2.1 lists the significantly affected facilities. A comparison of limiting facility loadings in percentage with and without the proposed projects is presented. These tables list only the most limiting contingency (one that causes highest overload) for each overloaded facility. The limiting elements listed in these tables are segregated based on transmission ownership information as available fiom PS'S/E power flow model and inforrnation provided by various transmission owners.

The results of Table 2.1 indicate that the signilicantly affected facilities are remote from the point of interconnection A detailed analysis of the impacts is considered beyond the scope of this study.

Impact of Proposed Projects on Bus Voltages Voltage violations were observed at several remote buses both with and with& the proposed project. No new voltage violations were observed, and the impact of the proposed projects on pre-project voltage vidations is imigniGcant.

El, d l l@

P%l&MB

Figure 3.2: Power Flow Diagram for 2007 Summer Peak Load Conditions (With G433 & GQ34)

Ah i ) l B I""tI1IC 5

Table 2.1: Significantly Affected Facilities for Contingency Conditions (2007 Summer Peak) 2.4 Summary of Resuits The interconnection of the propsed pmjects impacted several transmission f~ilitiesand resulted in steady-slate crikria violations for system intact and contingency conditions.

These violations are xmok &om the Prairie Island substation, The ~ansmissionoutlets out of the Prairie Island substation me not overloaded. Based on the available information, these remote violations should not limit the ability of the proposed projects to interconnect as Energy Resowce.

The violations reported in this study could potentially limit the ability of the projects to deliver power into the &asmission system. MIS0 has indicated that these overloads can not be classified as injection issues and therefore they need not to be mitigated for Energy Resource Interconnection Service.

3. STABILITY A_NALYSIIS 3.1 Model Development For stability analysis purposes, the pre- and post-project stability mdels that were used in reference [1J were used. Again, the Gross MW outputs of the Prairie Island units were adjusted so as to obtain the desired Net MW outputs listed in Section 1 of this report. As before, generators in the MIS0 footprint were scaled down in order to account for the increase in generation. The s e t e v

• prerm was used to adjust the maximum simultaneous hterz'ace levels to the following values: NDEX ( 1950 MW), MHEX

( 2175 MW), and MWSI ( 1480 MW). The case titles for the study cases with and without the proposed intercomections are presented below:

Pre-project Case (Without G433 & (334):

N44-SO07AA.UYVV4V4.SAV;SUMMER;OP LD;SYSTEM INTACT ND=1947,MH=2172,~=1479,OHMH=-197,OHMP=l5O,EWTW=-202,BD=l67 Post-Project Case (With G433 & G434):

S44-SO07AA.UWV4V4.SAV;SUMMER;OP LD;SYSTEM XNTACT ND=1947,MH=2172,MW=1479,OHfrlB=-l97,OHMP=150,EWTW=-202, BD-167 As before, the studies were conducted utilizing the April 2004 MS Windows Version of the NMORWG Stability Package.

3.2 Results of Stability Analysis The fault scenarios considered for stability assessment are the same as those simulated in reference [I]. See Table 3.1. With the exception of faults 4b3, 4p3 and pr3, all other faults listed in this table are standard faults fkom the NMORWG study package. All faults were run for 5 seconds, except for faults pcs, pet, pys, and pyt, which were run to 20 seconds, thus allowing for Prony analyses ofany oscillations that might occur.

Table 3.1 : List of DisfurbancesSimulated for Stabiliv Assessment Table 3.2 summarizes the results. Simulation summary tables and plots for selected fault scenarios for the pre- and post-project cases are praented in Appendices D and E respectively.

No stability criteria violations were observed for the simulated Faults after addition of proposed projects.

Simulation summary tables for fault "agl" showed a transient v&ge violation at bus 67233 "DCGX4 T230". This is the midpoint of a three-winding 345/230/13.8 kV transformer at the Antelope Valley substation. Since the pre- and post-project transient voltages are 0.67 pu, it is concluded that the proposed projects do not adversely impact the voltage at this bus.

Simulation plots for faults agl, ei2, 4b3, 4p3 and pr3 showed poorly damped oscillations in the rotor angles for the following units, both in the pre- and post-project c a w : Big Falls (4.8 MW unit at bus 60662) and Redwing (23.2 MW unit at bus 60823). The oscillations are present even when the faults are run out to 20 seconds and appear to be most prominent for faults 4b3,4p3 and pr3. Also, the oxillations appear to be confined to the Big Falls and Redwing units and do not propagate to the bulk power system. The proposed G433 and G434 projects appear to have no significant impact on these

oscillations, Prony a l y s i s was used to cdeulate t_he oscillation modes of the Big Falls and Redwing rotor angles afl& lfie comspnding b p i n g ratios for fault "4b3". ?he results are s m ~ z e in d Table 3.3. The dmping ratios were compared qainst the MAPP Damping Period ient crite~a3.Per &e W P criteria, the m i ~ m damping ratio for disturbances with fiults is 0.0081633. The Table 3.3 results suggest that the rotor mgle oscillations at Big Falls and Redwing are in violation of the EvZAPP criteria. The proposed projects, however, do not adversely impact d m p b performance and no oscillabq behavior was observed in the Prairie Island rotor angles.

s the stability analysis indicate that the addition of proposed In conclusion, the ~ s u l t of projects would not adversely impact system transmission system stability.

MAPP Members Reliability Criteria and Study Procedures Manual, Prepared by MAPP Planning Standards Development Working Group, November 19,2004 Revision

Table 3.2: Results of Stability Analysis Table 3.3: Comparison of Damping Ratios at Big Fa& and Redtving Without anb With the Proposed G433 & G434 Projects for Fauft "4b3"

4. CONCLUSIONS A generator interconnection evaluation study was recently completed to evaluate the collective impact of generation intercomection requests 0 4 3 3 and G434 on tmsmission system performance. See reference El]. Together, these projects have requested a combined output of 38 MW (Gross), Project a433 is a 19 MW expansion to Prairie Island #1 and Project G434 is a 19 MW expansion to Prairie Island ft;?.

In the above study, the MW outputs of the Prairie Island units &re- and post-expansion) were modeled based on their Summer maximum ratings. MIS0 recently indicated that the Prairie Island units would have higher ratings in Winter (a total of 64 MW higher than the Summer ratings) and requested that a sensitivity study be performed to assess the impact of the proposed interconnections based on the higher pre- and post-project MW outputs.

The scope of the sensitivity study included a limited amount of steady-state and stability analysis to assess the impact of the proposed interconnections on the transmission system. In this study, the pre- and post-expansion MW outputs of the Prairie Island units were modeled based on the Winter maximum ratings.

Based on the technical evaluatioq the following conclusions can be drawn:

Steady-State Analysis :

The interconnection of the proposed projects impacted several transmission facilities and resulted in steady-state criteria violations for system intact and contingency conditions.

These violations are remote from the Prairie Island substation. The transmission outlets out of the Prairie Island substation are not overloaded. Based on the available information, these remote violations should not limit the ability of the proposed projects to interconnect as Energy Resource.

The violations reported in this study could potentially limit the ability of the projects to deliver power into the transmission system. MIS0 has indicated that these overloads can not be classified as injection issues and therefore they need not to be mitigated for Energy Resource Interconnection Service.

Stability Analysis :

Stability analysis was performed to evaluate the impact of the proposed projects on the system stability. All faults simulated in reference [I] were tested. No kansient or dynamic instability problems were observed.

Simulation plots for faults agl, ei2, 4b3, 4p3 and pr3 showed poorly damped oscillations in the rotor angles for the following units, both with ard without the proposed projects:

Big Falls (4.8 MW unit at bus 60662) and Redwing (23.2 MW unit at bus 60823). These oscillations are most prominent for faults 4b3, 4p3 and pr3 and appear to be confined to the Big Falls and Redwing units i.e., the oscillations do not propagate to the bulk power system. Prony analysis was used to calculate the oscillation modes of the Big Falls and

Redwing rotor mgbs md the comspn&mg dmping ratios for fault "4b3". Results suggest that the dmping ratios msociwted with rhe rotor angle oscillations at Big Falls and Redwing are in violation of the MaPP Transient Period Damping Critexia even prior to the addition of the proposed projects. The proposed projec~,however, do not adversely impact h p i w pedomsnce and no oscillatory behavior was observed in the Prairie Island rotor angles.

In conclusion, the results of the stability analysis indicate that the intercomection of the proposed projects would not adversely impact transmission system stability.

I The results ofthis study are based on available data and assumptions made at the time of conducting this stu& In particular, it should be noted that the results depend on delivery assumptions of prior-queued generator interconnections. I f the delivery assumptiom of I the prior-queued generators change andor if the prior-queued units drop out of the generator interconnection queue, additional studies may be required to determine I possible criteria violations that may limit the ability of the project to inject andor deliver power into the transmission system. Any additional studies are considered outsick of the scope of the system impact studies. The results provided in this report may not apply i f any of the data andor assumptions made in developing the study models charrge.

5. REFERENCES

1. -

Generation Inimcomw-tion Shudy ProjecQ # 43433 and G434. 38 MW Expansion of Prairie Islmd UniQ 1 and 2 (Final Report), Prepared by ABB Inc.,

March 24,2006,