ML16141A985
| ML16141A985 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 12/22/1995 |
| From: | Wiens L NRC (Affiliation Not Assigned) |
| To: | Hampton J DUKE POWER CO. |
| References | |
| TAC-M93550, NUDOCS 9512280164 | |
| Download: ML16141A985 (10) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 December 22, 1995 Mr. J. W. Hampton Vice President, Oconee Site Duke Power Company P.O. Box 1439 Seneca, SC 29679
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION RELATING TO OCONEE ELECTRICAL SYSTEM ISSUES (TAC NO. M93550)
Dear Mr. Hampton:
On December 13, 1995, the U.S. Nuclear Regulatory Commission (NRC) staff met with you and representatives from your staff to discuss issues related to the emergency electrical system at the Oconee Nuclear Station and the results of the Keowee reliability analysis. At that meeting, the discussions focused on the information provided in your letter dated December 12, 1995, that responded to the NRC staff's request for additional information transmitted to you on November 8, 1995. Based on the December 12, 1995, letter and these discussions, the NRC staff has the need for some of your responses to be further clarified or expanded. In addition, the staff has also determined from its overall review of the electrical system issues that supplemental information is necessary for us to complete our review of these issues. The specific details of the staff's request for this additional information is provided within the questions listed in the enclosure to this letter. Your response to these questions is requested by January 31, 1995.
Due to the scope of the information needed and the time constraints for the response, the NRC staff has attempted to identify those questions that Duke Power Company should place higher priority when allocating resources. These are questions Al, Al, BI thru B8, and C6. Based on the information currently available, the remaining questions are of lesser priority, but will provide information for the staff to more completely develop its conclusions.
This requirement affects nine or fewer respondents and, therefore, it is not subject to the Office of Management and Budget review under P.L.96-511.
9512280164 951222 PDR ADOCK 05000269 P
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J. W. Hampton
-2 December 22, 1995 If you have questions regarding this matter, contact me at (301) 415-1495.
Sincerely, Original signed by:
L. A. Wiens, Senior Project Manager Project Directorate 11-2 Division of Reactor Projects-I/II Office of Nuclear Reactor Regulation Docket Nos. 50-269, 50-270 and 50-287
Enclosure:
As stated cc w/encl:
See next page DISTRIBUTION:
Docket File G. Lainas OGC, 0-15 B18 PUBLIC J. Calvo ACRS, TWF PDII-2 R/F M. Virgilio E. Merschoff, RII S. Varga E. Butcher R. Crlenjak, RII J. Zwolinski J. Rosenthal Document Name:
G:\\OCONEE\\0C93550.RAI To receive a copy of this document, indicate in the box: "C" = Copy without attachment/enclosure "E" = Copy with attachment/enclosure "N"
= No copy OFFICE LA:PD22:DRPE E
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NAME
.ILBerry P-(b iPiLano L4i-LWiens.
DATE 12/ o? /95 12/ 1_/95 12 n
/95 OFFICIAL RECORD COPY (7,~Q
J. W. Hampton 2 -
December 22, 1995 If you have questions regarding this matter, contact me at (301) 415-1495.
Sincerely, L. A. Wiens, Senior Project Manager Project Directorate 11-2 Division of Reactor Projects-I/II Office of Nuclear Reactor Regulation Docket Nos. 50-269, 50-270 and 50-287
Enclosure:
As stated cc w/encl:
See next page
Mr. J. W. Hampton Duke Power Company Oconee Nuclear Station cc:
Mr. Paul R. Newton Mr. Ed Burchfield Duke Power Company, PB05E Compliance 422 South Church Street Duke Power Company Charlotte, North Carolina 28242-0001 Oconee Nuclear Site P. 0. Box 1439 J. Michael McGarry, III, Esquire Seneca, South Carolina 29679 Winston and Strawn 1400 L Street, NW.
Ms. Karen E. Long Washington, DC 20005 Assistant Attorney General North Carolina Department ~of Mr. Robert B. Borsum Justice B&W Nuclear Technologies P. 0. Box 629 Suite 525 Raleigh, North Carolina 21602 1700 Rockville Pike Rockville, Maryland 20852-1631 Mr. G. A. Copp Licensing -
ECO50 Manager, LIS Duke Power Company NUS Corporation 526 South Church Street 2650 McCormick Drive, 3rd Floor Charlotte, North Carolina 28242-0001 Clearwater, Florida 34619-1035 Dayne H. Brown, Director Senior Resident Inspector Division of Radiation Protection U. S. Nuclear Regulatory Commission North Carolina Department of Route 2, Box 610 Environment, Health and Seneca, South Carolina 29678 Natural Resources P. 0. Box 27681 Regional Administrator, Region II Raleigh, North Carolina 27611-7681 U. S. Nuclear Regulatory Commission 101 Marietta Street, NW. Suite 2900 Atlanta, Georgia 30323 Max Batavia, Chief Bureau of Radiological Health South Carolina Department of Health and Environmental Control 2600 Bull Street Columbia, South Carolina 29201 County Supervisor of Oconee County Walhalla, South Carolina 29621
REQUEST FOR ADDITIONAL INFORMATION OCONEE EMERGENCY ELECTRICAL SYSTEM A.
OUESTIONS REGARDING TESTING Al Provide the specific acceptance criteria (voltage, frequency, time, etc.) for each test identified in the Duke Power Company (Duke) letter.
of November 17, 1995. Discuss how that criteria relates back to the required design basis operation of the equipment being tested and assures its proper performance during the design basis scenario.
A2 Provide a functional description of the emergency power switching logic (EPSL) and discuss how the EPSL testing described in the November 1, 1995, letter verifies each of those functions. Also, describe how the features in the logic that may not be exercised during a normal performance test (like redundant or protective features) are tested.
Provide a copy of the EPSL test procedures.
A3 Are there additional tests, surveillances, or calibrations, separate from those identified in the November 17, 1995, letter, used to support operability of required equipment? If so, identify them.
A4 Identify the frequency of the periodic tests identified in the November 17, 1995, letter.
A5 What failures have been discovered as the result of performing.the tests described in the November 17, 1995, letter?
A6 How is proper loading and voltage regulator and governor response verified during periodic testing of the Keowee units for the LOCA/LOOP scenario from the standby condition? Based on the information in the November 17, 1995, letter, it is not apparent whether any periodic test has replaced the "J" test that would load a Keowee unit at 11 seconds while the unit is still accelerating. The tests that were identified only load the units while operating at nominal frequency and voltage.
A7 Provide the results of the recent modified "J" tests. Discuss how the test results support the 11 second loading scenario. Also, provide information to supplement your response in the November 17, 1995, letter to provide details regarding each instance that this test is referenced as providing data necessary to answer the staff's question (for example, in response to question 4).
A8 Test 8, as referenced in the November 17, 1995, letter, shows that a Lee combustion turbine-generator (CTG) is tested by loading it to the approximate accident loads of an Oconee unit by using non-essential Oconee loads. Test 3 shows that an idling Keowee unit is loaded using actual auxiliary loads of a shutdown Oconee unit. If our assumption that the total load used in Test 3 (approximately 2 MVA) is substantially less than the load used in Test 8 is correct, why isn't
-2 the more substantial loading (approximating accident loads) used in Test 8 also used in Test 3? The NRC staff also understands that Test 9 (Lee CTG to the grid verification test) will replace Test 8 in a proposed change to Oconee Technical Specifications. How will the Lee CTG transmission path to Oconee, and the Lee CTG voltage and frequency response, be verified if Test 8 is eliminated?
A9 Identify any periodic or one-time-only electrical tests that have been performed on the standby shutdown facility (SSF) and the test acceptance criteria. Identify any electrical surveillances or calibrations used to support operability of required electrical equipment.
B.
QUESTIONS REGARDING 11-SECOND LOADING OF KEOWEE UNIT UNDERGROUND PATH BI How has the CYME analysis, which assumes nominal voltage and frequency, been used to judge the adequacy of the 11-second loading criteria for a Keowee unit underground path which actually begins loading at about 60 percent of nominal voltage and frequency? Since the explanation in the November 17, 1995, letter is very general and qualitative, provide any quantitative insights or assumptions to explain the extrapolation of the CYME results as verification of the 11-second loading case at 60 percent voltage and frequency.
B2 What assumptions were used for motor starting and operating characteristics under constant V/Hz conditions? Has information been solicited from.the vendors of those motors regarding performance and reliability under reduced voltage and frequency? If so, provide the vendor conclusions. A constant V/Hz will only be maintained at the Keowee generator terminals. Voltage drops from the generator to the terminals of Oconee equipment will result in proportionately lower voltages than frequency at the terminals of the equipment. Have these voltages been calculated and the results on equipment operation been analyzed? The voltage drops will not all necessarily be proportional to the nominal voltage and frequency case because the paths from the Keowee generator to the Oconee equipment terminals will have different reactance to resistance (X/R) ratios for the nominal case than for the 60 percent case. Since smaller cables typically have smaller X/R ratios than larger cables, they should have proportionately larger voltage drops than the larger cables during the 60 percent case than during the nominal case.
B3 Were the effects of potential extended locked-rotor conditions on motors analyzed due to the proportionately lower voltages at 60 percent frequency than at nominal frequency? Were the effects on motor-operated valves (MOVs) and their motor contactors analyzed as well as on constant duty motors? Are the thermal overloads on MOVs bypassed at Oconee?
Describe the treatment of thermal overloads at Oconee such as the criteria and method for bypassing or how their settings are determined.
-3 B4 Have the effects of reduced frequency and voltage at the 11-second loading point been analyzed for electrical equipment other than motors connected to the Oconee ac busses? Has information regarding performance and reliability under these conditions been solicited from the equipment vendors? If so, what were the results or conclusions?
B5 In a Duke letter dated February 22, 1995, Duke responded to NRC staff questions on an Oconee Technical Specification revision and provided a timeline for the LOCA/LOOP scenario from Keowee standby start following plant modification no. NSM-ON-52966. On that timeline, does T-0 represent the time that the LOOP signal comes in from the loss of voltage or degraded voltage relays after their respective timers have timed out, or does it represent the time at which a loss of offsite power actually occurs? What are the setpoints of the loss of voltage and degraded voltage relays that sense lost or degraded voltage, and what are their time delays? What is the location point on the system where the voltage is being sensed? Provide the same information for the voltage relays that provide breaker closure permissives?
B6 The timelines for the LOCA/LOOP scenario appear to indicate that the Keowee load rejection scenario is the most limiting from the time perspective. If this is the case, it appears that the loading of the underground path for the standby start scenario could be delayed until the Keowee unit is at nominal frequency and voltage and still meet accident time requirements assuming failure of the underground path.
Therefore, is it necessary to load the underground unit at 11 seconds?
87 One of the potential problems that could occur for the loading at 11 seconds is that all equipment may not physically start at 11 seconds but may rather start in a somewhat random fashion according to-the voltage and frequency recovery at their terminals. If there are interlocks with other equipment, either direct or through process controls (like pressure or flow permissives), this might result in tripping or locking out of equipment. One mechanism for creating a lockout could be the actuation of circuit breaker anti-pump circuits.
Have these possibilities and effects been considered?
B8 For the loss of power to the main feeder buses (MFB) following a plant trip (non-LOCA) such as caused by a failure of the startup transformer or a failure to transfer to it, will the Keowee unit underground path reenergize the buses at 60 percent of nominal frequency and voltage or at nominal voltage and frequency? Does the Keowee unit start prior to or following the 20-second MFB delay? What is the magnitude of the MFB load if the loss of MFB scenario occurs and what are the loads that are powered?
-4 C.
QUESTIONS REGARDING THE KEOWEE VOLTAGE REGULATOR AND GOVERNOR Cl Provide a description of the differences between normal operation and emergency operation of the Keowee voltage regulator and governor.
Include the differences for start, acceleration, generator breaker closure, steady-state operation, load application and load reject.
C2 Table C.1-1 in the Keowee Probablistic Risk Assessment (PRA) identifies an event on September 20, 1992, concerning the base adjust and voltage adjust portions of the Keowee voltage regulator. It states that the cause was dirty base adjust contacts, which was corrected by running the base adjuster back and forth a couple of times and spraying the base adjuster with solvent. The staff feels that this problem is similar to one identified by it in question 7 of the NRC November 2, 1995, letter to Duke. This appears to be a credible failure that could result in a low voltage output from Keowee in a range that would result in degraded voltages on Oconee equipment. Provide your comments or conclusion in this regard.
C3 In the November 17, 1995 response to the staff's question 6, it is indicated that the minimum excitation limiter (MEL) of the voltage regulator responded to the failure of the volts/hertz limiter card by maintaining field excitation at the minimum excitation limit. What is the corresponding generator output voltage at the setpoint of the minimum excitation limit when Keowee is supplying Oconee loads?
C4 Is the volts/hertz limiter functional during all Keowee operating modes?
In several places where potential governor failures that could result in a low frequency were discussed in the November 17, 1995, letter, it was stated that these failures would also result in a low voltage output from Keowee. Is this due to the action of the volts/hertz limiter?
C5 In the November 17, 1995, response to staff question 10, it was stated that alarms indicating low governor oil pressure, indicative of possible low frequencies, are provided in the Keowee control room. What is the frequency output of the Keowee machines that would correspond to the low governor oil pressure setpoint?
C6 The Keowee PRA identified a number of Keowee voltage regulator and governor failures that could result in out-of-tolerance voltages and frequencies being applied to redundant Oconee electrical equipment.
These failures, among others, are titled:
(a) Keowee Unit 1 Base Adjust is Set Incorrectly, (b)
KHU-1 Voltage Adjust Failure Drives Generator Output Too High/Low, (c)
Keowee Unit 1 Governor Fails to Position Wickett Gates With Unit Running, and (d)
Keowee Unit 1 Governor Fails to Position Wickett Gates During a Hot Start. Although many of these failures would likely drive the output frequency and voltage to a level that would either separate the Keowee unit from the Oconee loads or alarm the condition so that operators could separate the loads, some failures could result in a voltage or frequency that neither initiates
-5 an alarm or trip. For example, in the November 17, 1995, response to staff question 10, it appears that a low voltage (above approximately 47 percent) or low frequency on the underground path would not cause an alarm or trip. While the design and modifications made to the Keowee governors, voltage regulators, and generator breaker control have addressed a number of the more likely failure modes and occurrences, it is not clear to the NRC staff that the probability of occurrence of an out-of-tolerance voltage or frequency is sufficiently low relative to the potentially negative effects on multiple and redundant Oconee electrical equipment. Figures 7.2-1, 7.2-3, and 7.2-4 in the Keowee PRA indicate that voltage regulator and governor failures are of relatively, high importance for Keowee reliability and unavailability. However, the Oconee PRA does not examine the more negative effects of these failures should out-of-tolerance voltages and frequency be applied to Oconee electrical equipment (equipment tripping, fuse blowing, or other possible damage). The Oconee PRA assumes only that the Keowee power supply is lost. Provide the Duke opinion with appropriate basis on each of the above NRC staff observations.
D.
GENERAL QUESTIONS 01 Identify the procedures available to operators covering emergency operation of Keowee, the Standby Shutdown Facility, the Oconee Switchyard, and the Lee CTGs. Describe, in general terms, the operations addressed by each procedure. How often are operators trained and tested on these procedures?
D2 What alarms exist at the Oconee and Keowee sites to alert operators to the fact that a battery charger has been lost? Are there any battery chargers at Oconee or Keowee (e.g., the battery chargers in the Oconee 230 kV switchyard or at the SSF) that, if lost, would not cause an alarm in a manned control room? What procedures exist to direct or guide operator actions needed to restore each of the battery chargers that cause an alarm when lost? In particular, are there procedures in place to direct or guide operators to start the SSF diesel generator if the normal power source to the SSF battery chargers is lost? Are there any batteries at Oconee or Keowee that could discharge without operator knowledge as a result of a lost battery charger? If a system is equipped with a standby battery charger (e.g., the 230 kV switchyard has a standby battery charger), will the loss of the standby battery charger initiate an alarm if this device is operating in place of the primary charger?
In order to evaluate the timeliness of operator actions needed to restore a lost battery charger, the staff must understand the sizing criteria for battery selection and the battery's current load profile (or the maximum time for which the battery is expected to be capable of supplying its loads). In this regard, provide the sizing criteria used
-6 to select the two 230 kV switchyard batteries, the two SSF batteries and the two Keowee batteries, and the expected load profile for each battery. Provide sufficient information to verify that these batteries can be expected to perform adequately for the required duration after their respective battery chargers have been lost. Based on this information, provide your conclusions regarding the adequacy of operator actions needed to restore a lost battery charger within the required coping duration.
03 Summarize the methodology for implementation of the Maintenance Rule at the Lee Station.