ML20210C663

Safety Evaluation Re Adequacy of Offsite Power Sys.Further Evaluation Cannot Continue Until All Requested Info Received.Surowiec Line Not Acceptable Substitute for Mason Line During Startup or Normal Operations

ML20210C663
Person / Time
Site:	Maine Yankee
Issue date:	04/23/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20210C653	List: ML20210C648 ML20210C663
References
NUDOCS 8705060262
Download: ML20210C663 (2)

Text

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SAFETY EVALUATION BY THE'0FFICE OF NUCLEAR REACTOR REGULATION RELATING TO THE ADEQUACY'0F THE

- 0FFSITE POWER SYSTEM MAINE YANKEE ATOMIC POWER COMPANY (MYAPCO) l MAINE YANKEE ATOMIC POWER STATION'(MYAPS) i DOCKET N0. 50-309 J

1.0 INTRODUCTION AND BACKGROUND

( During a meeting at the MYAPS on August 5, 1986, the staff discussed with i

the licensee the contents of two MYAPCO's submittals concerning-procedures developed to demonstrate the adequacy of the Surowiec 115 kv

line. These procedures-are entitled

1-22-4-1, "Surowiec 115 kv Voltage Test,: and.17-300-1, " Analytical Review of 115 kv System-Parameters." i The staff advised the licensee that these procedures.were just forms

. with spaces.to insert voltages and power recorded at nodes on the Surowiec transmission line, and did not have sufficient supportive description to permit an independent evaluation of how the adequacy of the Surowiec line will be established.

The staff also described the problems that.they had with assessing the

adequacy of the Surowiec line reconductoring,'together.with'the station j transformer tap increases based on the available .information. In addition, questions.were raised by the staff concerning dispatcher .

control of the Surowiec line voltages at the Surowiec substation and the integration of that control with operation of the Maine Yankee Nuclear Power Plant.

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During this meeting, it was brought to the attention of the_ staff that another low offsite power voltage event took place which repeated many of the circumstances of the December, 1982 event. 10n July 18, 1986 the

plant experienced a low voltage condition while trying to start up on the

Surowiec line with the Mason line out of service.

4 2.0 EVALUATION At the staff's request, MYAPC0 committed on August 5, 1986 to provide the following information:

A. A description of the July 1986 low voltage event. '

8. A description of the Surowiec transmission line and its loads and-operation in sufficient detail to permit an independent evaluation -

of the adequacy of the line's capability.

I C. A description of the control of the 115 kv onsite bus voltage by the 1 combined efforts of MYAPS operating staff and the Central Maine

1. Power staff who control the Surowiec substation.

a j- MYAPCO's letter of November 7, 1986 described the December 14, 1982 e

incident, but not the July 18, 1986 low voltage condition. After i

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I subsequent communications between the licensee and the staff in November and December 1986, MYAPCO sent another letter on February 2,1987, with a description of the July 18th event, attached. However, the tolerances on i the voltage and power and the significance of assumed values used in the calculation of the state of the Surowiec transmission line do not support the description of the July 18th event.

The loads that the Bath and Topsham substations supplied on July 18, 1986 i are apparently assumed values used as inputs to preliminary voltage drop l calculations. The MYAPS loads on the Surowiec transmission line (STL) are described as having been derived from the " CMP tape" because the 115 kv bus meters gave inconsistent readings. Based on the 555-9 and SS2-2 UV relays, the Maine Yankee 115 kv bus voltage was between 106 kv and 112 kv on July 18, 1986. Given the number of miscalibrated or malfunctioning transducers described in the February 2 letter, confidence in this range

' is less than desirable because immediately after the July 18th. event.

these relays-were not calibrated. Thus there is a possibility that the actual voltage was even less than 106 kv.

4 An auxiliary power supply voltage study (APSYS) in 1983 found 460 y bus

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voltages as much as 7% below the minima allowed for the safety bus motor l loads. However, it was concluded that the voltage defects were j

acceptable because of conservatisms in the study. Since this study was

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conducted, a 50% increase in the Maine Yankee offsite loads has been reported. It appears that the voltage defects should have also increased. It was calculated in the APSYS that 110 kv would be measured on the Maine Yankee 115 kv bus for cases IA (starting of all safety loads) and 2A (steady state running). However, current preliminary calculations shows 110 kv on the same bus despite 50% increases in the principal offsite loads and a 50% assumed increase in the Maine Yankee onsite loads. These results should be explained and serious

. consideration should be given to perform another APSYS.

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3.0 CONCLUSION

l All of the requested information has not been received, therefore, the staff c~annot conduct any further evaluation, and must maintain the position that the Surowiec line is inadequate to meet the requirements of GDC 17. If MYAPC0 wants to reopen this issue, it should supply the requested infonnation in sufficient detail to demonstrate that the capacity of the Surowiec line is adequate during startup as well as during accident or reactor shutdown conditions. This should include another APSYS in which the model parameters have been verified by voltage and power measurements, with known tolerances, at sufficient points on the Surowiec substation, transmission line and its loads. The licensee

} has recently indicated that an APSYS will be completed in July 1987.

Until such time that this is demonstrated, the Surowiec line cannot be used as an acceptable substitute for the Mason line during startup or normal power operations.

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