ML19347F186
| ML19347F186 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 04/30/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19347F179 | List: |
| References | |
| NUDOCS 8105150428 | |
| Download: ML19347F186 (6) | |
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ENCLOSURE i SAFETY EVALUATION ORESDEN - UNIT NO. 1 DOCKET NO. 50-10 ACEQUACY OF STATION ELECTRIC OISTRIBUTION SYSTEM VOLTAGES INTRODUCTICN AND
SUMMARY
Comonwealth Edison Company (Ceco) was requested by NRC letter dated August 8, 1979 to review the electric power system at Dresden Unit 1.
The review was to consist of:
(a) Detemining analytically the capacity and capability of the offsite power system and the onsite distribution system to automatically start as wek1 as operate all required safety 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 electM c loads.
(b) Detemining 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 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 order to verify the validity of the analytical results. CECO responded by letters dated February 1,1980, June ll,1980 and June 30, 1980. A detailed j
review acd technical evaluation of the submittal was performed by EG&G under l
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. contract to NRC, and with general supervision by NRC staff. This work was reported in EG&G's Technical Evaluation Report (TER), " Adequacy of Station Electric Distribution System Voltages, Dresden Station - Unit 1" dated March,1981 (attached). We have reviewed this report and concur in the conclusion that the analyses provided by Ceco show that the offsite power system and onsite distribution system are capable of providing acceptable voltages at the tenninals of the Class 1E equipment for worst case station electric load and grid voltages; however they have not provided a test verification of the analyses.
EVALUATICN CRITERIA The criteria used by EG&G in this technical evaluation of the analysis includes $2C 5 (" Sharing of Stractures, Systems, and Components") GOC 13
(" Instrumentation and Control"), and 3DC 17 (" Electric Power Systems") of Appendix A to 10 CFR 50; IEEE Standard 308-1974 (" Class 1E hwe: Systems for Nuclear Power Senarating Stations"); ANSI C34.1-1977 (" Voltage Ratings for Electric Power Systems and Equipment-6CH2)"; and the staff positions and guidelines in the NRC letter to CECO dated August 8,1979.
ANALYSIS AND TEST FEATURES The analysis was perfonned using the reserve auxiliary transformer (transfonner #12) with maximum and minimum switchyard (grid) voltages of 142 kv and 133 kv, and using transformer #13 with maximum and minimum switchyard voltages of 36.3 kv and 34.8 kv. The maximum load voltages occur with either transformer #12 or #13 supplying power concurrent with maximum grid voltage, and the minimum load voltages occur with transformer #12 supplying power concurrent with minimum grid voltage.
It has been established that emergency 4 kv loa:is would opera,te within allowable
. limits for the worst case conditions noted above. The analysis indicated the maximum no-load 480 volt emergen y bus voltage would be slightly in excess of equipment rated voltages, but this is considered to be of no concern since the voltages would drop to within rated values when loads are connected.
There is also a possibility that during the minimum expected transient voltage condition 480 volt motor contactors may not be capable of being picked up, but this is acceptable since such a transient is of a moment.ary nature and no contactor dropout or spurious shedding of any loads will result.
A test verification has not been submitted to show that the analyses of the Dresden 1 s'tation distribution system are an accurate representation of the actual voltages. Ceco previously perfonned verification tests on Zion Station Units 1 and 2 and Quad Cities Station Unit 2 and subsequently indicated these tests should suffice as verification of the analyses done for their other remaining stations as well, since the same computer program was used for each, and infonnation entered into this program for each station such as transformer taps, transformer impedances, etc., were verified in the field to be the correct values. These tests are not considered to be adequate verification of the Dresden Unit 1 analysis however, due to the substantial differences between the j
Dresden Unit 1 station distribution system and the distribution systems of the other stations. A separate test verificaticn of the Dresden Unit I analysis is therefore required.
It should be performed in accordance with the following guidelines:
a) loading the station distribution buses, includilig all Class 1E buses down to the 120/208 y level, to at least 30%;
1 l b) 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 the 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 matcr starting transient tests, the bus voltages and loading need only be recorded on that string of buses which previously showed the lowest analyzed voltages.
c) using the analytical techniques and assumptions of the previous voltage analyses, and the measured existing grid voltage and bus loading conditions recorded during conduct of the test', calculate a new set of voltages for all the Class lE buses down to the 120/208 volt level; d) compare the analytically derived voltage values against the test results.
With good correlation between the analytical results and the test results, the test verification requirement will be met. That is, the validity of the mathematical model used in perfennance of the analyses will have been established; therefore, the validity of the results of the analyses is also established.
In general the test results should not be more than 3% lower than the analytical results; however, the difference
I between the two when subtracted from the voltage levels determined in the original analyses should never be less than the Class lE equipment rated vol tages.
CONCLUSIONS We have reviewed the EG&G Technical Evaluation Report and concur in the findings that:
(1) Ceco has provided voltage analyses to demonstrate that the Class lE equipment terminal voltages remain within acceptable operating limits for the postulated worst case conditions.
(2) Ceco should perform a test on Dresden Unit 1 to verify the accuracy of their analyses.
(3) CECO's reaffirmation of compliance with GDC 17 requirements is acceptable.
(4) Upon the review and approval of the degraded grid voltage protection modifications proposed by Ceco and currently being reviewed by EG&G, there will be acceptable assurance that spurious tripping of offsite power to Class lE equipment will not take place upon starting a large non-Class lE load.
o
6-We therefore find the Dresden Unit 1 design to be acceptable with respect to the adequacy of station electric distribution system voltages subject to the satisfactory ccmpletion of the verification testing required above. We shall address the verification testing in a supplement to this report.
1 Attached:
Report No. EGG-EA-5325 Date: April 30,1981 e
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