ML14184A601
| ML14184A601 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 05/07/1984 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML14184A600 | List: |
| References | |
| NUDOCS 8405210359 | |
| Download: ML14184A601 (6) | |
Text
SAFETY EVALUATION H.B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 DOCKET NO. 50-261 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES INTRODUCTION AND
SUMMARY
Carolina Power and Light Company (CP&L) was requested by NRC letter dated August 8, 1979 to review the electric power system at H.B. Robinson, Unit No. 2. The review was to consist of:
a)
Determining analytically the capacity and capability of the offsite power system and onsite distribution system to automatically start as well as operate all required loads within their required voltage ratings in the event of 1) an anticipated transient, or 2) an accident (such as LOCA) without manual shedding of any electrical loads.
b)
Determining if there are any events or conditions which could result in the simultaneous or, consequential loss of both required circuits from the offsite network to the onsite electric distribution system and thus violating the requirements of GDC 17.
The August 8, 1979 letter included staff guidelines for performing the required voltage analysis and the licensee was further required to perform a test in order to verify the validity of the analytical results.
CP&L responded by letters dated October 5, 1979, July 23, 1980, October 14, 1982, March 23, 1983 and March 9, 1984.
A detailed review and technical evaluation of the submittals was performed by LLL under contract to the NRC, with general supervision by NRC staff. This work is reported by LLL in Technical Evaluation Report (TER),
"Adequacy of Station Electric Distribution System Voltages For The H.B. Robinson Steam 8405210359 840507 PDR ADOCK 05000251 PDR
Electric Plant, Unit 2," dated July, 1983 (attached).
We have reviewed this report and concur in the conclusion that additional information was required to complete the evaluation of the adequacy of the station electric distribution systems to maintain the voltage within the design limits of the required Class 1E equipment for worst case station electric load and grid voltage.
On March 7, 1984, CP&L provided the necessary information to complete our evaluation. We have reviewed the same and find them acceptable.
EVALUATION CRITERIA The criteria used by LLL in this technical evalution of the analysis includes GDC 13 ("Instrumentation and Control"), GDC 17 ("Electric Power Systems") of Appendix A to 10 CFR 50; IEEE Standard 308-1974 ("Class 1E Power Systems for Nuclear Power Generating Stations"), ANSI 'C84.1-1977 ("Voltage Ratings for Electric Power Systems and Equipment - 60 Hz"), and the staff positions and guidelines in NRC letter to CP&L dated August 8, 1979.
ANALYSIS AND TEST FEATURES Initially CP&L analyzed the adequacy of the plant's onsite distribution based on the postulated extremes of grid voltage range from 0.95 pu to 1.06 pu.
The initial results of the analysis showed that in most cases the worst case terminal voltages were within the equipment design ratings. However, the cases where the voltage was marginal were reanalyzed by using an actual grid voltage schedule (0.97 -1.01 pu) as maintained by the system control center. The following is a list of the major assumptions used for the analysis:
(1) Design brake horsepower (BHP) was used for the large and medium sized motors (approximately TO% greater than the recorded running load).
The data is taken from the FSAR and manufacturer speed-torque curves.
(2) Nameplate horsepower, Pfrun = 0.88, Pf
= 0.20, eff 0.92 and LRA/FLA - 6.5 was used where actual data was not available.
(3) Motor cable feeder size and length used from breaker coordination study.
(4) Transformer nameplate data with assumed X/R ratios.
The assumed ratios were based on NEMA and ANSI standards and actual compiled Westinghouse transformer data.
(5) MCC starter data from manufacturer.
(6) Safety injection loads per FSAR.
(7) Power factor used at BHP extrapolated from typical motor characteristic curves.
The worst case Class 1E equipment terminal voltages occur under the following conditions:
(1) The maximum steady-state voltage occurs when the offsite grid is at its maximum expected voltage of 1.06 pu of the 115 Kv nominal with the plant in a cold shutdown mode. All buses are lightly loaded.
(2) The minimum steady-state voltage shows when the plant is operating at 100% and a LOCA occurs. All electrical loads required to support this mode being supplied power from the startup transformer via the 115 Kv system while the 115 Kv system maintains a minimum operating voltage of 0.97 pu.
This is to show realistic system voltage profiles based on the voltage schedules maintained by the system control center.
(3) The minimum transient voltage occurs when the plant is operating at 100% power and a unit trip occurs. The offsite 115 Kv system is at 0.95 pu and a reactor coolant pump is being started.
The analysis submitted demonstrated that the offsite source (voltage schedule of 0.97 pu to 1.01 pu) and the onsite distribution system has the capacity and capability to start and operate the Class IE equipment within their voltage design rating under worst case conditions. However as for the extremes of the grid voltages (0.95 pu to 1.06 pu) assumed in the analysis, this was shown to be marginal equipment voltages. To ensure the above grid voltage shedule is maintained the licensee has committed to install undervoltage and overvoltage monitors on the offsite 115 Kv system so that appropriate corrective action can be taken upon receiving an alarm.
CP&L verified their analytical results by performing tests., The power source for the test was the startup transformer loaded to a minimum of 40% and the unit at 50% reactor power. The verification test results indicated a maximum percentage error for steady state conditions of + 1.1% and - 2.69% for transient conditions at the 480-Volt class IE buses. A negative percentage error indicates that the measured values were higher than the calculated values.
Nevertheless these percentage errors are within the accuracy requirement outlined in the staff position and are acceptable.
CONCLUSIONS We have reviewed the LLL Technical Evaluation Report and concur in the findings that:
(1) CP&L has provided verified voltage analysis to demonstrate that Class 1E equipment voltage will remain within acceptable operating limits for the worst case conditions analyzed.
(2) The test used to verify the analysis was valid and showed the analysis to be acceptable.
(3) 'Spurious tripping from e offsite sources will not occ under worst case conditions. Spurious tripping is prevented during the starting of the reactor coolant pump by manually bypassing/reinstating the degraded grid protection scheme.
(4) For the maintained voltage schedule of 1.01 pu, the Class 1E equipment's maximum grid voltage design limit will not be exceeded under maximum grid voltage (minimum plant load) conditions.
(5) No event or condition will result in the simultaneous or consequential loss of both required circuits to the onsite distribution system (compliance with GDC 17).
However, there will be a time delay of 16 to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> if a loss of the immediate access offsite power supply occurs. During this contin gency, the plant safety related equipment will be supplied by the emergency diesels. There are two such diesels,'in addition, a third diesel dedicated to shutdown has been provided.
The following information was required to be submitted by the licensee:
(1) The setpoints for the overvoltage and undervoltage monitors on the 115 Kv system and the corrective actions to be taken upon receiving an alarm.
(2) Update the plants FSAR and incorporate limiting conditions for operation in the Technical Specifications on the use of backfeeding through the main/unit auxiliary transformer to the Class 1E buses.
It should also include any administrative controls.
(3) Include in the design modification for the bypassing/reinstatement of the degraded grid protection scheme during RCP starting, a failure-to reinstate alarm or provide for automatic bypassing/reinstatement.
(4)
Results of the in-plant tests for verifying the acceleration times of the starting loads used in the voltage profile analyses.
By letter dated March 9, 1984 the licensee resolved the above items:
(1)
CP&L has provided the setpoints for the 115 kv system over and undervoltage alarms.
(2) CP&L has also stated that technical specification change request regarding use of the backfeed through the main and unit auxiliary transformers will be forthcoming.
(3) As for our concern for a failure-to-reinstate the degraded grid protection scheme following bypass during RCP starting, the licensee committed to install an indicator in the control room.
(4) Finally, in-house tests were performed to confirm the estimated acceleration times used for the pumps in the analyses. The test results confirm the study assumptions.
We, therefore, find the H. B. Robinson Unit No. 2 design to be acceptable with respect to the adequacy of station electrical distribution system voltages.