ML20207C195

Forwards Draft Summary of 861209 Meeting W/Util Re Facility Emergency Electrical Power Sys Design,Per NRR Ofc Ltr 43

ML20207C195
Person / Time
Site:	Fort Saint Vrain
Issue date:	12/22/1986
From:	Heitner K NRC
To:	NRC
References
NUDOCS 8612300072
Download: ML20207C195 (6)

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Docket No. 50-267 MEMORANDUM FOR: Herbert N. Berkow, Director Standardization and Special Projects Directorate Division of PWR Licensing-B THRU: 0. D. T. Lynch, Jr., Section Leader Standardization and Special Projects Directorate Division of PWR Licensing-B FROM: Kenneth L. Heitner, Project Manager Standardization and Special ,

Projects Directorate Division of PWR Licensing-B

SUMMARY

OF MEETING WITH PUBLIC SERVICE COMPANY OF COLORADO '

(PSC) TO DISCUSS FORT ST. VRAIN (FSV) EMERGENCY ELECTRICAL POWER SYSTEM - DECEMBER 9, 1986

Reference:

NRC letter dated November 12,1986 (K. L. Heitner to R. O. Williams, Jr., PSC) on Fort St. Vrain's Emergency Electrical Power System Design.

This meeting was held on December 9, 1986, in order to further discuss Fort St. Vrain's Emergency Electrical Power System. The discussion was based on the staff's recent evaluation of this system, referenced above. Specifically, the meeting agenda involved reviewing the referenced letter, and discussion of alternatives for interim and long-tem solutions to the problems outlined therein.- Attendees at this meeting are listed in Enclosure 1.

At the beginning of the meeting the PSC staff summarized the progress made on changes proposed and agreed to in our previous meeting on this subject on August 14, 1986. These changes included the following:

Removal of common start circuit contacts from relays DEV-86 RT and DEV-86 ET1 between the redundant emergency diesel generators (EDGs):

This change was completed.

Implementation of a temporary modification to the DC power supplies for the degraded grid voltage and undervoltage protection system:

This change was in progress and would be completed by December 19, 1986.

1 PSC also noted that a separate Licensee Event Report would be submitted concerning the exhaust temperature detectors on the emergency diesel engines.

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J Electrical Independence Electrical independence between the control circuits of the two EDGs and their -

respective output circuit breakers was discussed. PSC noted that.they had revised their FSAR commitment (Section 8.1) concerning the EDGs to read as follows:

"The _ onsite electrical system (emergency standby generators) are so designed that they are independent of each other to the extent that no single failure will interfere with the proper operation of the redundant  :

counterpart."

The staff stated that they would review these changes to the FSAR. Discussion continued on the capability of the EDG control system to perform its functions after a single failure. Several single failure sequences were reviewed to understand their impact on both automatic and manual operation rf the EDG control system. PSC concluded that they could demonstrate that no credible single failure could affect the capability to connect manually at least one EDG to its essential bus. Additionally, they would demonstrate that the EDGs could not accidentally be paralleled as a result of a single failure. The staff found this to be consistent with their request in the referenced letter. PSC further stated that they believed that the EDG's would be able to operate automatically if a single failure occurred. The staff roted that automatic operation was desirable, but that manual operation remained acceptable because of the relatively long time required at FSV to begin decay heat removal.

Typically, decay heat removal can begin 1 to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after the reactor is shut down from full power.

j Automatic Throw-Over (ATO) of DC Control Power Supplies for 480 Volt Switchgear i

PSC reviewed the design history of the 480 volt switchgear. The switchgear installed originally was designed with the control power having a manual throw-over capability so it could be powered from either of the redundant DC buses.

In 1983-84, this switchgear was upgraded, and the ATO feature was installed as part of the standard configuration for the new switchgear. PSC noted that ATO consisted of two separate contactors, one in each of the two redundant DC supply circuits to the switchgear. These separate contactors were electrically interlocked. Additionally, the power supply circuit from each DC bus was protected by two independent circuit breakers. PSC believed that multiple failures would be required to result in the loss of both DC buses as a result of a single fault in the switchgear system. ,

i The staff stated that they still remained concerned about the ATO. The staff indicated that there were two acceptable alternatives for the ATO system.

These are:

The ATO could be converted to manual operation by placing the circuit breakers at the switchgear under administrative control. As such, each switchgear cabinet would be manually connected to only one DC bus. In the event of a failure of the source of control power the operators would manually transfer the switchgear to the other DC bus.

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DMFI Alternatively, the ATO feature could be retained if the protective circuit breakers were tested and properly coordinated to assure their performance.

The staff stated that either of these approaches was acceptable as an interim solution to the problems in the existing ATO system. The long-term acceptability of the existing ATO system would be related to how DC power would eventually be supplied to the 480 volt switchgear.

Undervoltage and Degraded Grid Voltage Protection PSC stated that their long-term preference as to provide a third source of DC power from the "C" battery. This would involve adding a DC distribution panel for the "C" battery, and supplying the third set of undervoltage and degraded grid voltage relays from this distribution panel. Thus, a single failure of a DC bus, would not compromise the undervoltage or degraded grid voltage protection system.

Furthermore, PSC stated that they were evaluating if sufficient "C" battery capacity was also available to supply the 480 volt switchgear. In that case, each of the three. sets of switchgear could be powered from 2 different DC buses through the ATO for each switchgear panel. Thus, the operability of at least one DC and one AC bus was assured. The staff stated that this approach was acceptable in principle and should result in an improved emergency electrical power system.

Schedules Schedules for formal submittal of PSC's proposals were discussed. It was agreed between PSC and the staff that, the following actions be taken:

PSC would submit to the staff a basis for accepting the EDG control system. This would be a single failure analysis for the existing, not fully independent, EDG control system that supports the PSC coninitment's as contained in the FSAR.

PSC would also formally propose implementation of a program to address the staff's concerns about the ATO. This interim program would be implemented fully by plant restart, reflecting the discussions above.

PSC also would commit formally to the installation of a third DC bus

as outlined above. The PSC proposal also would contain a schedule for submittal of the detailed design of this system in approximately 6 months; and completion by FSV's fourth refueling with NRC review by early 1988.

All of the above would be submitted for staff review and approval no later than January 10, 1987.

e DMFT PSC also provided comments to the staff concerning the draft Technical Evaluation Report enclosed with the referenced letter. PSC's comments are summarized in a markup of this draft report, which is provided as Enclosure 2.

Kenneth L. Heitner, Project Manager Standardization and Special Projects Directorate Division of PWR Licensing-B Office of Nuclear Reactor Regulation

Enclosures:

As stated cc w, enclosures:

See next page s

a.

Enclosure 1 Meeting - NRC-PSC Emergency Electrical $U ]f*y Power System Ujlp/ dg December 9, 1986 Name Organization Ken Heitner NRC/NRR/DPWRL-B Charles Hinson NRC/NRR/DPWRL-B John Reesy Public Service Company of Colorado Robert Schenderlein Public Service Company of Colorado James Selan Public Service Company of Colordo Jeff Johns Public Service Company of Colorado I. Ahmed NRC J. Calvo NRC/NRR/DPWRL-B H. Berkow NRC/NRR/DPWRL-B

0. Lynch NRC/NRR/DPWRL-B

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