ML20086S586

SR-S1-74-03:on 740403,safety Injection Experienced Due to Spurious High Steam Flow Signals in Conjunction W/Low Temp Average or Low Steam Line Pressure Signals.Caused by Fluctuations of Steam Flow Signals Above Setpoint

ML20086S586
Person / Time
Site:	Surry, 05002817
Issue date:	09/10/1984
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
085, 85, SR-S1-74-03, SR-S1-74-3, NUDOCS 8403020455
Download: ML20086S586 (5)

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VanonNr A Er,ECTRIC ann Pownu COMPANY [ .

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September 10, 1974 Yt x Y' a ,. .

N[/;jJJEh Mr.. Norman C. Moseley, Director Serial No. 085 Directorate of Regulatory Operations P0&M/JTB:c1w United States Atomic Energy Commission Region II - Suite 818 Docket Nos. 50-280 230 Peachtree Street, Northwest 50-281 Atlanta, Georgia 30303 License Nos. DPR-32 DPR-37

Dear Mr. Moseley:

The Virginia Electric and Power Company hereby submits forty (40) copies of Special Report No. SR-S1-74-03. This report is being submitted to report the results of our investigation of the effects'which past safety injections have had on each unit. Based on the results of the investigation, it has been concluded that the safety injections which have been experienced here ant adverely ef fected unit integrity or the safety of the station.

Very truly yours,

. . 82db C. M. Stallings Vice President-Power Supply and Production Operations Enclosures 40 copies of SR-SI-74-03 cc: Mr. K. R. Coller, Assistant Director for Operating Reactors s

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O O SPECIAL REPORT SR-SI-74-03 EFFECT OF PAST SAFETY INJECTIONS DOCKET NOS. 50-280 50-281 LICENSE NOS. DPR-32 DPR-37 AUGUST 28, 1974 SURRY POWER STATION VIRGINIA ELECTRIC AND POWER COMPANY I

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1. INTRODUCTION On April 12, 1974, an abnormal occurrence report (AO-SI-73-05) was submitted to the United States Atomic Energy Commission concerning an occurrence on April 3, 1971. This supplement is submitted in response to a commitment made in this report,Section II, page 2, concerning a discussion of the safety injections which have occurred at Surry Power Station.

II. DISCUSSION Since initial operation, the units have experienced numerous safety injections due to spurious "High Steam Flow" signals in conjunction with

" Low T " or " Low Steam Line Pressure" signals. These actuations have occurred at low power levels or shutdown conditions. An investigation of the safety injections on both units was made to determine the cause of the safety injections and the effects they have had on the units.

The cause of the spurious safety injections was found to be flunctuations of the steam flow signals above the setpoint. In order to prevent the continual-recurrence of these spurious signals, it was decided to modify the "High Steam Flow" setpoint curve to allow for these normal differential pressure fluctuations. A change to the Technical Specifications has been requested to accommodate the new setpoints. In addition, during the calibration of steam flow transmitters on Unit No. 1, it was noted that.the transmitters were sensing j a significant dif ferential pressure with no steam flow. It was believed that this differential pressure was caused by a water trap in- the' sensing line.

Inspections revealed a downward slope of the sensing line from the steam line instrument tap through a globe valve to the 90 degree elbow on the transmitter condensate pot. Fundamental globe valve design in combination'with the: sloping line caused steam to condense in the lowest point in the line and form a water j

trap. Disturbances would produce variations in the water and, hence, fluctuations in the pressure differential being sensed. A piping modification was made to provide an upward slope f rom the instrument tap to the condensate pot. Subsequent operation has shown that this modification has reduced the fluctuations of the steam flow signals at low power levels. Thas modification and the change to the "High Steam Flow" setpoint curve should p-event future spurious signals.

The investigation into the effects that the safety injections has had on the units included a review of each safety injection which had occurred, the conditions under which it had occurred, the approximate amount of borated water pumped into the reactor coolant system, and the precicteu effect on the coolant system temperature. The nuclear steam supply system vendor analyzed the data collected on each safety injection to determine if these safety injections had adversely affected unit integrity. The results of the investigation indicate that past safety injections have not aff ected the safety or integrity of the units. Detailed analyses indicate that each unit could sustain 120 design safety injections without adverse affects. Included in these are 20 safety injections with an operational basis earthquake (OBE). It should be noted that the design basis safety injection is more severe than any that have actually occurred on either unit.

III. CONCLUSIONS The spurious safety injections experienced by both units were the result of fluctuations in the "High Steam Flow" signal. A change to the high steam flow setpoint curve in the Technical Specifications has been requested and a piping modification to the steam flow transmitter sensing lines should prevent

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O O recurrence of the spurious signals. The results of our investigation indicate

that these safety injections have not affected the safety or integrity of the units.

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