3F0107-06, Response to 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
| ML070320125 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 01/29/2007 |
| From: | Young D Progress Energy Florida |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 3F0107-06, GL-06-002 | |
| Download: ML070320125 (6) | |
Text
Progress Energy Crystal River Nuclear Plant Docket No. 50-302 Operating License No. DPR-72 Ref: 10 CFR 50.54(f)
January 29, 2007 3F0107-06 U.S. Nuclear Regulatory Commission Attn: Document Control Desk 11555 Rockville Pike Rockville, Maryland 20852
Subject:
Crystal River Unit 3 -
Response to 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"
References:
- 1.
Generic Letter 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power," dated February 1, 2006
- 2.
Crystal River Unit 3 Day Response to NRC Generic Letter 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power," dated April 3, 2006
- 3.
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, dated December 5, 2006
Dear Sir:
The Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 2006-02 (Reference 1) to request information concerning plant electric power sources and associated personnel training.
Florida Power Corporation (FPC), doing business as Progress Energy Florida, Inc., provided the response to GL 2006-02 for Crystal River Unit 3 (CR-3) in Reference 2. On December 5, 2006, the NRC issued a Request for Additional Information on this subject in Reference 3 with a requested due date of January 31, 2007. FPC hereby provides the requested information for CR-3.
This letter establishes no new regulatory commitments.
If you have any questions regarding this submittal, please contact Mr. Paul Infanger, Supervisor, Licensing and Regulatory Programs at (352) 563-4796.
Sincerely, Dale E. Young Vice President Crystal River Nuclear Plant DEY/dar
Attachment:
Response to 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" xc:
NRR Project Manager Regional Administrator, Region II Senior Resident Inspector Progress Energy Florida, Inc.
Crystal River Nuclear Plant 15760 W. Powerline Street Crystal River, FL 34428
U.S. Nuclear Regulatory Commission 3F0107-06 Page 2 of 2 STATE OF FLORIDA COUNTY OF CITRUS Dale E. Young states that he is the Vice President, Crystal River Nuclear Plant for Florida Power Corporation, doing business as Progress Energy Florida, Inc.; that he is authorized on the part of said company to sign and file with the Nuclear Regulatory Commission the information attached hereto; and that all such statements made and matters set forth therein are true and correct to the best of his knowledge, information, and belief.
Dale E. Young Vice President Crystal River Nuclear Plant The foregoing document was acknowledged before me this cq day of
,2007, by Dale E. Young.
Signature of Notary Publihc*
EU.ENDEPP0LDER State of Florida MY COMMISSION # DD 408 EXPIRES: July 8,2009
.y,.
W~
d Th.NdwNomi*iI Und f~tto (Print, type, or stamp Commissioned Name of Notary Public)
Personally Known V
Produced
-OR-Identification
PROGRESS ENERGY CRYSTAL RIVER UNIT 3 DOCKET NUMBER 50-302 / LICENSE NUMBER DPR -72 ATTACHMENT Response to 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"
U.S. Nuclear Regulatory Commission Attachment 3F0107-06 Page 1 of 3 Response to NRC Request-for Additional Information Regaarding Resolution o!
Generic Letter 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power" On December 5, 2006, the NRC issued a Request for Additional Information (RAI) to the industry regarding the resolution of Generic Letter (GL) 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power." Enclosure 2 of the RAI contained six follow-up questions to GL 2006-02, and Enclosure 3 identified which of the questions must be answered by each facility. According to Enclosure 3, Crystal River Unit 3 (CR-3) must respond to questions 3 and 5. These responses are provided below.
Question 3:
Verification of RTCA Predicted Post-Trip Voltage 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.
What is the range of accuracy for your GO's contingency analysis program? 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?
What is your standard of acceptance?
Response 3:
Florida Power Corporation (FPC), doing business as Progress Energy Florida, Inc., agrees it is important that the programs used for predicting post-trip voltage be verified to be reasonably accurate and conservative. Grid Operator (GO) methods are in place to manage the process of verifying predictive program results against actual event data that are significant to the nuclear plant. These methods ensure that the predictive programs results are reasonably accurate and conservative. A monitoring / predictive analysis computer program tool operates based on raw data from transducers across the system which is processed through a state estimator to generate a current state snapshot of the system. This output is then processed through a contingency analysis program that generates a new set of results for various scenarios where some of the equipment is out of service. For contingency analyses of CR-3 trips, actual post-trip plant load data are included to ensure accuracy. The reason FPC is confident the post-trip voltages calculated by the GO's contingency analysis program are reasonably accurate and conservative is because the program adds a conservative post-trip voltage drop bias (derived from actual CR-3 trip events) to load flow calculated voltage drops (from the postulated loss of nuclear generation) to arrive at the total predicted voltage drop result.
Unlike many power stations, a transient or trip of the CR-3 generator does not significantly impact the offsite power supply. The output of the CR-3 generator is connected to a 500 KV switchyard.
The source of offsite power for CR-3 is a 230 KV switchyard. These switchyards are electrically separated by approximately thirty-five miles of 230 KV transmission line, approximately thirty-five miles of 500 KV transmission line, and a 230:500 KV transformer located at the Brookridge substation about thirty-five miles away from the plant. The separation between these switchyards and the generating capacity of the three local 230 KV fossil generators at the Crystal River Energy Complex protect the 230 KV switchyard from large voltage perturbations induced by CR-3 tripping off-line (disconnecting from the 500 KV switchyard).
U.S. Nuclear Regulatory Commission Attachment 3F0107-06 Page 2 of 3 CR-3's switchyard configuration is designed to minimize the impact a CR-3 plant trip has on the offsite power source. As such, CR-3 trips have not caused enough of a disturbance to substantiate further scrutiny. However, other events significant to CR-3 have received further analysis. Crystal River Unit 4, a 720 MW coal station, is the largest unit that supplies the 230 KV switchyard.
Predicted results for a trip of Unit 4 and other potential contingencies have compared favorably with actual event data. The range of accuracy for the contingency analysis program has not been quantitatively derived but the results have proven to be conservative.
FPC's standard of acceptance is that an N-1 nuclear plant trip contingency switchyard voltage predicted by the contingency analysis program will be conservative with respect to the actual post-trip switchyard voltage plus a conservative reliability margin specified for the nuclear plant. The contingency analysis program and its use are controlled by North American Electric Reliability Corporation (NERC) Standards.
NERC Standard, TOP-006-1, "Monitoring System Conditions," requires each Balancing Authority and Transmission Operator to use sufficient metering of suitable range, accuracy, and sampling rate (if applicable) to ensure accurate and timely monitoring of operating conditions under both normal and emergency situations. As both a Balancing Authority and Transmission Operator, FPC complies with the metering requirements in this standard to collect the inputs to the state estimation and pre- / post-contingency analysis tools. This further reinforces the accuracy of the results.
A new NERC Standard, NUC-001-1, "Nuclear Plant Interface Coordination," is currently in final stages of development.
Once approved, this standard is expected to address this issue more effectively. Approval is scheduled for early 2007.
U.S. Nuclear Regulatory Commission Attachment 3F0107-06 Page 3 of 3 Question 5:
Seasonal Variation in Grid Stress (Reliability and Loss-of-offsite Power (LOOP) Probability)
Certain regions during certain times of the year (seasonal variations) experience higher grid stress as is indicated in Electric Power Research Institute (EPRI) Report 1011759, Table 4-7, Grid LOOP Adjustment Factor, and NRC NUREG/CR-6890.
Do you adjust the base LOOP frequency in your probabilistic risk assessment (PRA) and Maintenance Rule evaluations for various seasons? If you do not consider seasonal variations in base LOOP frequency in your PRA and Maintenance Rule evaluations, explain why it is acceptable not to do so.
Response 5:
The LOOP initiators used for PRA and Maintenance Rule are not generically adjusted for seasons.
CR-3 schedules major outages to avoid challenges that may be more common during certain months. However, adjustments to LOOP initiators are made on a daily scale based on planned, expected, and actual events. For instance, CR-3 continually monitors weather conditions and has daily phone calls with the Energy Control Center to stay informed of grid conditions. CP-253, "Power Operation Risk Assessment and Management," describes the process used to perform risk assessments of on-line maintenance activities at CR-3 and to manage the risk of these activities. It defines risk level on a color scale based on increasing Incremental Core Damage Probabilities (ICDP). When GREEN, risk level is defined to be acceptable and no mitigative controls are necessary. However, a level of YELLOW indicates significant risk, so additional controls are put in place to manage the increase. When weather or degrading grid conditions warrant, CR-3 will elevate risk level to YELLOW specifically to take advantage of the heightened risk management actions even if the increase in ICPD is not large enough to justify the change in level.
Managing risk on an event basis rather than on a seasonal basis is acceptable because the Maintenance Rule (a)(4) LOOP initiator frequencies are required by procedure to be adjusted (i.e.,
increased) for actual weather conditions and Transmission System Operator-based notifications concerning system load and grid conditions. Escalating the risk level from GREEN to YELLOW when grid or weather conditions warrant it denotes a conservative increase to the LOOP initiator frequency. This explicitly captures the "seasonally biased" effects in the LOOP frequency, but in this scenario, it does so only when conditions justify it. Conversely, the initiator frequency is NOT reduced when good weather or low grid stress prevails. This means Maintenance Rule (a)(4)
LOOP frequencies are overstated (or conservative) in their aggregate impact over the course of a year.
Biasing LOOP risk generically on the season can be problematic. It can result in unnecessary deferrals of switchyard or grid maintenance. A deferral of maintenance simply because it was the wrong season could actually increase risk, since opportunities when weather and grid conditions may have been favorable would be missed. Furthermore, if plant staff is aware of and accounting for weather and grid conditions, a seasonally-biased approach can undermine confidence in the risk assessment program. A reduction in confidence would likely occur because overly-conservative seasonal biases would still be applied to LOOP risk even when actual risk factors are low. This "seasonal" approach can also de-sensitize plant staff such that elevated LOOP risk situations in "off" seasons might not be recognized as carrying higher LOOP risk.
The LOOP initiators used for Probabilistic Safety Assessment (PSA) and Maintenance Rule evaluations are based on plant specific Bayesian updates to applicable industry data that includes plant centered LOOP events and switchyard LOOP events as well as weather and grid related events (whether they be seasonal or not).