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{{Adams
#REDIRECT [[PLA-6152, Supplemental Information Related to NRC Generic Letter 2006-02, Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power, PLA-6152]]
| number = ML070390133
| issue date = 01/30/2007
| title = Susquehanna - Supplemental Information Related to NRC Generic Letter 2006-02, Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power, PLA-6152
| author name = McKinney B T
| author affiliation = PPL Susquehanna, LLC
| addressee name =
| addressee affiliation = NRC/Document Control Desk, NRC/NRR
| docket = 05000387, 05000388
| license number =
| contact person =
| case reference number = GL-06-002, PLA-6152
| document type = Letter
| page count = 7
}}
 
=Text=
{{#Wiki_filter:Britt T. McKinney Senior Vice President
& Chief Nuclear Officer PPL Susquehanna, LLC 769 Salem Boulevard Berwick, PA 18603 Tel. 570.542.3149 Fax 570.542.1504 btmckinney@pplweb.com I b ppa I
* TM JAN 3 0 2007 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop OP 1-17 Washington, DC 20555-0001 SUSQUEHANNA STEAM ELECTRIC STATION (SSES)SUPPLEMENTAL INFORMATION RELATED TO NRC GENERIC LETTER 2006-02, "GRID RELIABILITY AND THE IMPACT ON PLANT RISK AND THE OPERABILITY OF OFFSITE POWER" PLA-6152 Docket Nos. 50-387 and 50-388 References.
: 1) PPL letter PLA-6031, B. T McKinney (PPL) to USNRC, "Response to NRC Generic Letter 2006-02 Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power, "dated March 28, 2006.2) NRC Request for Additional Information Regarding Resolution of Generic Letter 2006-02, Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power (TAC Nos. MD0947 through MDI050), dated December 5, 2006.The purpose of this letter is to supplement information previously submitted by PPL Susquehanna, LLC (PPL) in response to Generic Letter 2006-02 (Reference 1). The additional information requested by the NRC pertains to Questions 3 and 6 as identified in Enclosure 2 to Reference
: 2. The attachment to this letter provides PPL's response to these questions.
Some of the questions in these RAI's seek information about analyses, procedures, and activities concerning grid reliability of which SSES does not have first-hand knowledge and which are beyond the control of SSES. In providing information responsive to such questions, SSES makes no representation as to the information's accuracy or completeness.
Any questions regarding this request should be directed to Mr. Duane L. Filchner at (610) 774-7819.-A12- 3  Document Control Desk PLA-6152 I declare under penalty of perjury that the foregoing is true and correct.Executed on: J-3D'or')Britt T. McKinney
 
==Attachment:==
 
Supplemental Information cc: NRC Region I Mr. R. V. Guzman, NRC Project Manager Mr. R. Janati, DEP/BRP Mr. C. Welch, NRC Sr. Resident Inspector Attachment to PLA-6152 Supplemental Information PPL Responses to RAI Questions 3 & 6 Attachment to PLA-6152 Page 1 of 4 Supplemental Information PPL Susquehanna, LLC (PPL or SSES) is located in the service territory of the PJM Interconnection, LLC (PJM). The PPL transmission system is operated under the direction of PJM. Generic Letter 2006-02 responses, which identify the "grid operator" (GO), are in reference to PJM, unless otherwise noted. Further, any use of the term "NPP Licensee" refers to the PPL Susquehanna Steam Electric Station (SSES). Some responses contain information that is applicable to PPL or PJM, or both. The applicability is denoted in the response.For access to the text of North American Electric Reliability Council (NERC) or PJM references cited, please go to the following websites: www.nerc.com www.PJM.com NRC Question 3: Verification of RTCA Predicted Post -Trip Voltalle Your response to question 2(g) indicates that you have not verified by procedure the voltages predicted by the online grid analysis tool (software program) with actual real plant trip voltage values. It is important that the programs used for predicting post-trip voltage be verified to be reasonably accurate and conservative.
(3a.) What is the range of accuracy for your GO's contingency analysis program?PJM Response: There is no established numerical range of accuracy for the transmission system operator's (PJM) contingency analysis program. However, state estimation and real time contingency analysis have been used for many years by PJM to aid in evaluating and maintaining transmission system reliability and are proven tools for analyzing transmission system contingencies.
(3b.) Why are you confident that the post-trip voltages calculated by the GO's contingency analysis program (that you are using to determine operability of the offsite power system) are reasonably accurate and conservative?
PPL Response (SSES): We are confident in the post-trip voltages calculated by the GO because of our direct involvement with the GO, the use of well established tools for transmission system analysis, and previously demonstrated performance.
Attachment to PLA-6152 Page 2 of 4 The following explanation is provided by the GO on the use of State Estimation and Real Time Contingency Analysis.PJM Response: Description of State Estimation and Relation to Real Time Contingency Analysis (RTCA)State estimation is an advanced application that is used to ensure that power system analysis that relies on complete power system models can be performed even when incomplete or conflicting data is received from the sensing devices in the field.Basically, the state estimator (SE) compares actual field data to an expected value based on the power system model resident in the application.
If the actual data is unavailable or out of its expected range, the SE will calculate a value and substitute it into the power system model, creating a SE solution, so that other applications can provide reasonable results.The relevance of the SE to the post-contingency voltage calculation discussion is that the SE results are used as the input to the real time contingency analysis (RTCA). The RTCA takes the SE solution and calculates post-contingency flows, voltages and voltage drops for each contingency in the contingency list (in PJM's case, the RTCA analyzes about 4,000 contingencies, approximately every 2 minutes).
However, without a valid SE solution, the RTCA is not possible.On rare occasions, the SE is not able to provide a valid solution due to the magnitude of missing, conflicting, or inaccurate data. Normally, such events are caused by communications or equipment failure in the field. In these cases, PJM is required to notify the Transmission Owners (TOs) that PJM's capability to calculate the necessary nuclear plant post-contingency voltages is temporarily unavailable and that PJM will be deferring to the TOs RTCA results. (Refer to PJM Manual M-0 1 Control Center, Section 2, pg 14.) If both PJM and the TO lose the capability to perform RTCA, the affected nuclear power plants are notified.Advanced applications, like the SE and the RTCA, are critical to executing PJM's tasks as a Reliability Coordinator.
All Reliability Coordinators are required to have such tools to be in compliance with North American Electric Reliability Council (NERC) Standard IRO-002, Reliability Coordination-Facilities.
Requirements addressing the accuracy and capability of field sensors and communications systems that feed the SE are covered in PJM Manual M-0 1, Control Center Requirements, and are necessary to be compliant with NERC Standard TOP-006, Monitoring System Conditions.
Attachment to PLA-6152 Page 3 of 4 Issues related to SE accuracy Input Data Accuracy Continuous and accurate input data is critical to the proper functioning of the SE.An accurate representation of the configuration of the grid components that actually exist in the field is essential.
The data provided by the sensors in the field must be accurately mapped to the correct elements in the SE model.Model Scope and Level of Detail The other key factor to ensuring accurate SE solutions is the scope and level of detail of the model. The model must contain sufficient monitoring capability of its surrounding Reliability Coordinator areas to ensure that potential or actual operating limits are not violated.Steps taken by PJM to assure SE "accuracy" Given the issues stated above, PJM and its members take steps to ensure that the SE runs as accurately as possible, including the following:
Overlapping coverage of PJM and member company state estimators In addition to PJM, the TOs have their own SEs running in parallel with the PJM SE. Although the respective models are different from a scope and level of detail standpoint, these results are generally close. If discrepancies between the two SEs are identified, PJM and the TO work together to correct the problem. During the interim period, the more conservative limit becomes the operational limit.PJM works closely with the TOs and the generation owners to ensure the accuracy of the PJM data model. PJM builds the updated model and verifies its accuracy in a test environment before installing the updated model in the production system.Model updates are performed on a quarterly basis.Review ofpost-contingency parameters prior to switching Prior to switching transmission equipment out of service, the PJM operator is required to calculate the post-switching system parameters in the vicinity of the switching using RTCA. This step is taken to ensure that the switching will not result in a reliability problem. Once the switching has occurred, the operator monitors the post-switching parameters, providing a near real time comparison to the RTCA prediction.
Seldom does that comparison yield an unexpected result, attesting to the accuracy of the SE and RTCA solution.
If a case does yield an unexpected result, it is investigated and corrective actions are taken as appropriate.
Attachment to PLA-6152 Page 4 of 4 (3c.) What is your standard of acceptance?
PPL Response (SSES): PPL's Standard of Acceptance is the same as the NERC Standards of Acceptance.
PPL relies on the GO (PJM) to operate a state estimator and a RTCA program to evaluate the nuclear power plant contingency voltages.
The state estimator and RTCA program are utilized by the GO (PJM) as tools for evaluating and maintaining the reliability of the transmission system. PJM utilizes these tools as a means to satisfy their responsibilities as a NERC Reliability Coordinator as delineated in NERC Standards IRO-002 and TOP-006. The NERC Standards provide the standard of acceptance with which the TSO (PJM) must comply.NRC Question 6: Interface with Transmission System Operator During! Extended Plant Maintenance.
How do you interface with your GO when on-going maintenance at the nuclear power plant, that has been previously coordinated with your GO for a definite time frame, gets extended past that planned time frame?PPL Response (SSES): The on-shift Control Room operations staff and/or the Work Management staff make decisions as required to notify the TO for rescheduling of grid-risk-sensitive maintenance activities based on plant work activities.
Likewise, for maintenance activities at the nuclear power plant that extend beyond the original work schedule, the Control Room operators communicate with the GO through the Generator Power Dispatcher and/or the Transmission Power System Dispatcher as conditions warrant.SSES procedures provide direction to report equipment malfunctions and status changes affecting or potentially affecting station operation to the Generation Power Dispatcher and/or Transmission Power System Dispatcher.
These procedures are followed on a day-to-day basis and have been demonstrated to be effective at controlling risk to generation from a plant and Transmission Operator (TO) perspective.
Following the appropriate procedure and effective communication protocols ensures consistent performance in managing risk and when required, reducing risk by restoring out-of-service equipment and re-scheduling work due to emergent issues as they occur.Plant activities and scheduled transmission outages are coordinated between SSES and the TO to minimize risk before grid risk sensitive maintenance activities are conducted.}}

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