ML16131A415
| ML16131A415 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 12/03/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML16131A414 | List: |
| References | |
| NUDOCS 9212110152 | |
| Download: ML16131A415 (5) | |
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0 o0 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SUPPLEMENTAL SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION STATION BLACKOUT RULE (10 CFR 50.63)
DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNITS 1. 2. AND 3 DOCKET NOS. 50-269, 50-270, 50-287
1.0 INTRODUCTION
The NRC staff's Safety Evaluation (SE) pertaining to the Duke Power Company's (the licensee's) response to the Station Blackout (SBO) rule, 10 CFR 50.63, was transmitted to the licensee by letter dated March 10, 1992. The staff's SE found that the licensee's proposed method of coping with an SBO did not conform with the SBO rule, and requested the licensee to submit a revised response addressing the areas of non-conformance. The licensee responded to the staff's SE in a meeting with the NRC staff on June 4, 1992, and a subsequent written response dated July 1, 1992.
2.0 EVALUATION The licensee's responses to the staff's concerns are evaluated below.
2.1 Proposed AC (AAC) Power Source (SE Section 2.2.2)
The licensee proposed the use of the Standby Shutdown Facility (SSF) diesel generator (DG) as a proposed alternate ac (AAC) power source. The staff found it questionable as to whether the SSF would be able to meet an availability/reliability index of approximately 95% required for an AAC source.
SE Recommendation In the SE, the staff recommended that the licensee make modifications to improve the overall reliability of the SSF system to 95% or better, or provide alternative means for coping with an SBO event.
Licensee Response The licensee presented an historical tabulation of the unavailability of the SSF over the 1985 to 1992 period which indicated an availability of 96.175 percent. The licensee described the maintenance program for the SSF facility which would require that unwatering of the Unit 2 condenser cooling water (CCW) intake piping would be kept to a minimum to ensure maximum SSF 9212110152 921203 PDR ADOCK 05000269 P
-2 availability. In addition, maintenance activities will not be planned when either or both Keowee units are unavailable.
The licensee also described the surveillance testing and other testing programs for the SSF DG to ensure that it maintains an acceptable reliability level.
This would require monthly, quarterly, and annual surveillance testing of the DG, and special tests after maintenance and repair activities.
In addition, the licensee has committed to a data trending program to track the reliability and availability of the SSF facility.
Staff Evaluation The staff's review of the licensee's proposed testing and maintenance programs for the SSF facility indicates that there is reasonable assurance that an acceptable level of availability/reliability for the SSF can be maintained.
In addition, the licensee's proposed trending program of the SSF should disclose if the availability/reliability of the SSF is not being maintained at an acceptable level.
Therefore, the staff finds the SSF as a proposed AAC power source to be acceptable.
2.2 Condensate Inventory For Decay Heat Removal (SE Section 2.3.1)
The licensee proposes to use the SSF Auxiliary Service Water (ASW) pump which takes suction from the Unit 2 condenser cooling water piping for condensate makeup during an SBO. This water source is not available while unwatering the Unit 2 condenser cooling water piping. As a result, the staff made the following recommendation in the SE.
SE Recommendation The licensee should ensure that the water from Lake Keowee will be available to the SSF ASW pump at all times or provide an alternate source of water for coping with an SBO event.
Licensee Response The licensee noted that the largest single contributor to SSF unavailability is the unwatering of the Unit 2 CCW intake piping. The licensee proposed programs to maintain this unavailability to an acceptable level as discussed in Section 2.1 above.
Staff Evaluation The staff has accepted the licensee's proposed programs for maintaining the SSF availability (and inherently the CCW intake piping availability) to an acceptable level.
See Section 2.1 above.
-3 2.3 Class 1E Battery Capacity (SE Section 2.3.2)
SE Recommendation The licensee should develop and implement the necessary modifications, such as battery charging from an AAC power source or additional battery capacity, which will maintain the main control rooms functional and manned for the full 4-hour SBO duration.
Licensee Response The licensee proposes to implement load shedding of the non-safety related inverters (IKI, 1KX, 2K1, 2KX, 2KU, 3K1, 3KX, and 3KU) within 30 minutes or less after the loss of ac auxiliary power. The licensee presented a listing of the loads that would be shed and the loads that would remain following the load shedding. The licensee presented battery capacity calculations demonstrating the adequacy of the batteries for the 4-hour coping duration, and recovery therefrom. The battery calculations used a load growth factor of 1.1, an aging factor of 1.25, and a temperature correction factor of 1.11.
Inverter loads were considered as constant power loads; non-inverter loads as static loads.
Staff Evaluation The staff's review of the licensee's load data, assumptions, and battery calculations indicates that with the load shedding proposed, there is reasonable assurance that the Class 1E batteries have sufficient capacity, including margin and correction factors, for the 4-hour coping duration and recovery therefrom.
2.4 Effects of Loss of Ventilation (SE Section 2.3.4)
SE Recommendation The licensee should perform and provide for NRC staff review heat-up calculations for the areas containing SBO equipment associated with instrumentation and control functions (i.e., for the control rooms, switchgear room, inverter room, etc.). If reasonable assurance of equipment operability in these areas cannot be assured, the licensee should implement modifications and procedure changes to assure that the main control rooms are habitable, and that instrumentation and control equipment remains operable during an SBO event and recovery therefrom.
Licensee Response The licensee performed heat-up analyses to determine the effects of loss of ventilation in the control, cable, and electrical equipment rooms during an SBO event. By letter dated July 1, 1992, the licensee provided the details of the analyses for staff review. The initial room temperatures used in the calculations and the calculated peak temperatures in each of these areas were as follows:
-4 Initial Peak Room Temp.(Fo)
Temp.(FO UNIT 1&2 Control Rooms 74 115 Unit 1 Cable Room 74 129 Unit 1 Electrical Equipment Room 86 111 Unit 3 Control Room 74 111 Unit 3 Cable Room 74 113 Unit 3 Electrical Equipment Room 86 111 Control Battery Rooms 74 97 Staff's Evaluation The calculated peak temperatures for the above rooms are well below the temperature limits described in NUMARC 87-00, Section 2.7. Therefore, the staff finds these to be acceptable.
The staff understands the licensee's heat-up calculation methodology to be as follows:
The heat-up calculation uses an iterative method which estimates (assumes) an average temperature of the air over a specified time period (e.g., 95.3'F for the first 30 minutes) and does an energy balance (heat generated = heat transferred to the outside + heat absorbed by the air + heat absorbed by the surrounding walls) to determine what the average air temperature would be over this time interval. If the calculated average air temperature is equal to the assumed value, the energy balance is complete. Otherwise, repeat (iterative) calculations are required until the assumed average air temperature is equal to the calculated value.
The relationship between the calculated average air temperature and the air temperature at the end of the time period assumes the temperature rises in a curved fashion from the initial temperature toward the steady state (ss) value as expressed by the following equation:
dTair/dt = f(Tairss - Ta.,), where Tair is the air temperature at any time.
The licensee's submittal indicates that the steady state value in the above equation is the temperature that the air would rise to in the selected time period if no heat were absorbed by the surrounding walls. However, the licensee's calculations show that a substantial amount of the heat is absorbed by the surrounding walls. This results in a final air temperature consid erably less than that used in the above equation expressing the curvature of the heat rise curve. Projection of the final air temperature from the integrated average air temperature during the time period using an excessive curvature of the heat-up curve would appear to result in a non-conservative final temperature. Therefore, the licensee should address this concern in the documentation that is to be retained by the licensee in support of the SBO rule response.
-5 2.5 EDG Reliability Program (Hydro Units) (SE Section 2.7)
SE Recommendation It is the staff's position that a reliability program for the onsite emergency ac systems (hydro units) should be developed in accordance with the guidance of Regulatory Guide (RG) 1.155, Section 1.2. If the reliability program currently exists, the program should be evaluated and adjusted in accordance with RG 1.155. Confirmation that such a program is in place or will be implemented should be included in the documentation that is to be maintained by the licensee in support of the SBO submittals.
Licensee Response The licensee stated that programs are in place which perform data acquisition and the required testing and maintenance of the hydro units. In order to meet the recommendations of NUMARC 87-00, Appendix D, the licensee has committed to implement a program consisting of further actions to define the Keowee subcomponents and support systems, to track reliability and availability, and take the necessary actions to maintain an acceptable level of availability/
reliability.
Staff Evaluation Staff review of the licensee's proposed Keowee hydro reliability program indicates that it meets the essential elements of RG 1.155, Section 1.2, and is, therefore, acceptable.
3.0
SUMMARY
AND CONCLUSION The licensee responded to the staff's March 10, 1992, SE pertaining to the SBO rule (10 CFR 50.63) in a meeting with the NRC staff on June 4, 1992, and a subsequent written response dated July 1, 1992. The staff has reviewed the licensee's response and finds it to be acceptable except that the licensee should ensure that the heat-up calculations do not result in non-conservative results (Section 2.4).
The licensee has stated that the actions required to perform load stripping, the implementation of administrative controls for room temperatures, and the implementation of the evaluation of the SSF and Keowee reliability/
availability programs will be completed by January 1, 1993.
Date:
December 3, 1992