ML20024D816
| ML20024D816 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 07/29/1983 |
| From: | Reinaldo Rodriguez SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20024D819 | List: |
| References | |
| RJR-83-592, TAC-52047, NUDOCS 8308080250 | |
| Download: ML20024D816 (3) | |
Text
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$SMUD SACRAMENTO MUNICIPAL UTILITY DISTRICT O 6201 S Street, Box 15830, Sacramento, California 95813; (916) 452-3211 RJR 83-592 July 29, 1983 DIRECTOR OF NUCLEAR REACTOR REGULATION ATTENTION JOHN F STOLZ CHIEF OPERATING REACTORS BRANCH 4 US NUCLEAR REGULATORY COMMISSION WASHINGTON DC 20555 DOCKET 50-312 RANCHO SEC0 NUCLEAR GENERATING STATION UNIT N0 1 PROPOSED AMENDMENT N0. 98 - SUPPLEMENT 2 On July 26, 1983, the Sacramento Municipal Utility District requested a Technical Specification change relating to undervoltage relay settings.
Discussions with your staff this week have resulted in some modifications to our proposed change.
Attached to this letter are our proposed revisions and further information relating to our discussions this week.
The timing for installation and testing of this modification was dictated by an overall outage schedule based on workload, manpower availability, and sequence of events.
Extensive testing was performed and attempts were made to set the relays in accordance with existing Technical Specifications. We had no reason to expect an inability to meet the requirements of the existing Technical Specifications; however, we discovered that relay operation, specifi-cally the relay's time delay, was very dependent upon-the initial voltage prior to the degradation. With our expected range of system voltage we could not satisfy the timing requirement on Table 3.7-1 of Amendment No. 46.
As soon as we were aware of this problem an internal request was made for a change to the Technical Specifications. This is documented by a memo dated July 5, 1983. On July 6, 1983 we contacted your staff to determine an acceptable alternate approach.
In addition, we started a broader scope of testing at that time to obtain the data needed to engineer an acceptable solution to the problem.
Discussions occurred on July 14, 18, 21, and 22 with members of your staff and Lawrence Livermore Labs to expose and resolve all concerns regarding our proposed change. What was thought to be an acceptable change was reviewed by all appro-priate parties (Plant Review Committee and Management Safety Review Committee) in-house on July 25 and submitted to you on July 26, 1983.
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f i l Ah ELECTRIC S Y S T E M.S E R VI N G MORE THAN 600,000 IN THE HEART OF CAllFORNiA
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-r JOHN F STOLZ.' July 29, 1983
. Additional discussions' with~ your staff resulted.in this;present revision,.
which supersedes all previous submittals, and was reviewed in-house today for= submittal. As'can be seen, our schedule did not leave time for.the usual-30-dayLnotice or even a 15-day notice to effect-the-Technical Specification change.
. We appreciate your cooperation with our request and will provide any itional information'you may need.
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R. J.~ Rodriguez-
. Executive: Director, Nuc' ar 4
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m RESPONSE.TO NRC QUESTIONS AND REVISED TECHNICAL SPECIFICATIONS The enclosed revised Table 3.7-1 provides four voltage poir.ts as a percentage of setpoint and an operating time for the relay at each point with tolerance.
The table is further clarified by specifying that the time response is based on an initial voltage of 4160 volts for calibrating the relay.
This accurately defines the operating curve for the relay.
The District has reviewed the susceptability of its distribution system to spurious trips due to the operating characteristics of the undervoltage relays
-and concludes that as demonstrated in our over/undervoltage analysis a spurious trip would not occur with the switchyard voltage at nr above 218KV. The District's computer model has shown the acceleration of a condensate pump, the largest motor on a bus common with safety related loads, starting at 3733 volts (214KV switchyard voltage) to be 2 seconds. Additional testing of the relay determined that the operating time range when. dropping from 3809 volts (218KV switchyard voltage) to 3771 volts (216 KV switchyard voltage) is 9.9 to 10.7 seconds. Therefore, the voltage will definitely recover before the relay operates. Also enclosed is a revised paragraph H to the limiting conditions for operation in Amendment 46.
This change further reduces the possibility of spurious trips by limiting pJant operation with the switchyard voltage within the deadband of the relay.
The District's overvoltage protection is discussed in response to Guideline 11 in our response to Nuclear Regulatory Commission Request To Review The Adequacy Of Station Electric Distribution System Voltages (Letter From William Gammill to Power Reactor Licensees Dated August 8, 1979) dated 2/9/81 Revision 2.
This report is an enclosure to the District's 2/17/81 Walbridge to Reid letter.
.As required in Guideline 11 the District analyzed the historical data on maximum voltages in the Rancho Seco; switchyard. This analysis indicated the maximum expected switchyard voltages to be approximately 239Kv.
To provide sufficient margin in the design and to have the upper limit agree with the upper tolerance of the relay the District based its overvoltage analysis on a maximum switchyard voltage of.244KV. A switchyard voltage of 244Kv assuming no load conditions and the existing transformer ratios transforms to 4626 volts on the 4160 volt bus, and 521 volts on the 480 volt bus.
The District reviewed its response and determined that all discussions previously presented are still applicable in view of a relay operating time increase to a maximum of 8 seconds. To further clarify our discussion of MCC control circuits in that response, at 244 Kv the control equipment exceeds its 132 volt maximum operating voltage by 4 volts. This equipment will not operate continuously at
.this voltage (136V); however, it is capable of operating at this level for a period of time far in excess of 8 seconds.
Since our relays are definite time relays the original operating time of 3 seconds was arbitrarily chosen as satisfactory compromise between avoiding spurious trips and providing the required protection.
In view of recent events we are increasing the time delay to avoid spurious trips and are still providing the required protection since the affects of overvoltage operation are long-term.
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