ML20049J616
| ML20049J616 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 03/09/1982 |
| From: | Prevatte R Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20049J614 | List: |
| References | |
| NUDOCS 8203180497 | |
| Download: ML20049J616 (4) | |
Text
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION i
CONCERNING ADEQUACY OF STATION ELECTRICAL DISTRIBUTION SYSTEM VOLTAGES FOR ARKANSAS NUCLEAR ONE, UNIT NO. 1 DOCKET NO. 50-313 INTRODUCTION AND
SUMMARY
Arkansas Power and Light Company (AP&L) was requested by NRC letter dated August 8,1979 to review the electric power system at Arkansas Nuclear One Unit 1.
The review was to consist of:
a)
Dett: mining analytically the capacity and capability of the offsite power systen 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 electric loads.
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b)
Detemining if there are any events or conditions which could result in th'e simultaneous or, consequential loss of both required circuits l
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 perfoming the required voltage analysis and the licensee was further required to perform a test in i
order to verify the validity of the analytical results. AP&L responded by letters dated August 23, 1978, October 25,1978, March 13.1979, May 21,1979, 1 79, October 19, 1981 and October 30, 1981. A 8203180497 E203by"-+ '
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r detailed review and technical evaluation of the submittals was performed by Lawrence Livermore Laboratory (LLL) under contract to the NRC, with i
general supervision by NRC staff. This work is reported by LLL in Technical Evaluation Report (TER).
" Adequacy of Station Electrical Distribution System Voltages, Arkansas Nuclear One, Unit 1," dated 16 Decenber 1981 (attached). We have reviewed this report and concur in the conclusions that the offsite power system and the onsite distribution system are capable of providing acceptable voltages for worst case station electric load and grid voltages.
EVALUATION CRITERIA The criteria used by LLC in this technical evaluation of the analysis includes GDC 5 (" Sharing of Structures, Systems, and Components"),
GDC 13 (" Instrumentation and Contro19 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 'AP&L dated l
August 8, 1979.
l 1
ANALYSIS ann TEST FEATURES AP&L analyzed each offsite power source to the onsite distribution system under l
maximum and minimum load conditions with the offsite power sources 'at maximum and minimum anticipated voltage,1.05 and 1.0 per unit on the 500 kv and I
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161,KY systems.
An analysis was also performed with both units (1 and 2) transferring their station load to the alternate source, start-up transformer 2.
Th'e analysis included the t '*.sient effects on the Class 1E equipment from starting a large Class 1E and non-Class 1E load.
It has been established that the 4160 volt and 480 volt emergency loads will operate within allowable voltage limits when supplied from the offsite power system. AP&L in a telephone call between G. Vissing, LPM, NRC and L. Young, Licensing AP&L, has committed to perform tests to verify the voltage analysis resu,1ts. These tests are to be completed during the refueling outage currently scheduled for Spring 1983.
The licensee will confirm this camnitment in a formal letter. AP&L has not outlined the scope of these tests.
As a minimum NRC requires the following criteria be met:
1.
Loading the station distribution buses, including all Class 1E buses down to the 120/208 volt level, to at least 30%;
2.
Recording the existing grid and Class 1E bus voltages and bus loading down to the 120/208 volt level at steady state conditions and during starting of both a large Class 1E and non-Class 1E motor (not concurrently).
NOTE: To minimize the number of instrumented locations-(recorders) during the motor starting transient tests,,the. bus voltages and loading need only be recorded on that string of buses which previously showed the lowest analyzed voltages.
Using the analytical techniques and assumptions of the previous voltage 3.
analyses, and the measured existing grid voltage and bus loading conditions recorded during conduct of test, calculate a new set of voltages for all Class 1E buses do'n to the 120/208 volt level.
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- 4.
- Compare the analytically derived voltage values against the t.est results.
5.
With good correlation between the analytical and the test results the test verification requirenents will be met.
In general the test results should not be more than 3% lower than the analytical results; however the difference between the two when subtracted from the voltage levels deter-mined in the original analysis should never be less than the Class lE equipment rated voltages.
DESIGN CHANGES As a result of the voltage analysis AP&L proposed the following design changes:
1.
During the automatic fast transfer from the Unit Auxiliary Transfomer to Start-Up Transfomer 1, all auxiliary loads except the Class 1E loads are transferred in bulk with subsequent load sequencing of the Class 1E loads.
2.
During the automatic fast transfer from the Unit Auxiliary Transfomer to Start-up Transfomer 2 (Start-up Transfomer 1 not available), selected non-Class 1E loads (two reactor coolant pumps, three circulating water i
pumps, two condensate pumps, and two chiller ptznps) are load shed before the transfer to reduce loading.
3.
Install interlocks to prevent the simultaneous automatic transfer of Unit 1 and Unit 2 loads to Start-Up Transfomer 2.
4.
Renove the automatic slow transfer from the Unit Auxiliary Transfomer to Start-Up Transfomer 1 to prevent simultaneous starting of all station
' auxiliary loads.
4
. 5 Install manual blocking circuitry to prevent operation of the second-level undervoltage relays during the starting of a reactor coolant pum. p or a condensate pump.
6.
Install second level undervoltage relays on each 480 volt Class IE bus.
7 Replacement of all undersized control transfomers.
The above modifications were previously reviewed by the NRC, found acceptable in a Safety Evaluation Report dated December 17, 1979 and subsequently implemented.
CONCLUSIONS We have reviewed the LLL Technical Evaluation Report and concur in the findings that:
1.
Upon completion as a result of implementation of the proposed modifications, acceptable voltages will be provided to all Class lE equipment during the postulated worst case conditions.
2.
Spurious separation from the offsite power systs will not occur during the start of a reactor coolant pump or condensate pump.
3.
The modifications will ensure that the electric power system for ANO-1 is in conformance with GDC 17.
4.
The requirments of GDC 5 for multi-unit stations was met by installing the interlock to prevent simultaneous automatic transfer of both unit station loads to Start-Up Transfomer 2.
5.
Verification tests for the voltage analysis should be completed as scheduled.
i l
Dated: fiarch 9, 1982 The following NRC personnel have contributed to this Safety Evaluation Report:
Richard Prevatte.