ML20011F739

LER 90-002-00:on 891122,value for Distance from Floor to Ctr Line of Level Switch 2-LS-87-21 Transposed in Variable Leg Calculation.Caused by Inattention to Detail.Procedure Revised to Replace Incorrect setpoint.W/900226 Ltr

ML20011F739
Person / Time
Site:	Sequoyah
Issue date:	02/26/1990
From:	Bynum J, Proffitt J TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-002-01, LER-90-2-1, NUDOCS 9003070345
Download: ML20011F739 (5)

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TENNESSEE VALLEY AUTHORITY i

f 6N 38A Lookout Place February 26, 1990 .

U.S. Nuclear Regulatory Commission l ATTN -Document Control Desk l

~ Washington, D.C. 20555 Gentlement f

' TENNESSEE VALLEY AUTHORITY - SEQUOYAH NUCLEAR PLANT UN/T 2 - DOCKET NO.

50-328 - FACIL11T OPERATING LICENSE DPR LICENSEE EVENT REPORT (LER) i 50-328/90002 The enclosed LER provides details cor.cerning an inadequate calculation [

l resulting in the upper head injection system level setpoint being incorrect. "

l This resulted in an operation prohibited by technical specification '

requirements. . This event is being reported in accordance with 10 CFR 50.73,  ;

Paragraph a.2.1.B.  ;

Very truly yours,  !

TENNESSEE VALLEY AUTHORITY ,

f. R. yn , ce President wuclear Power Production L Enclosure 1

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Regional Administration U.S. Nuclear Regulatory Commission l

(, Office of Inspection and Enforcement '

Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 i i

INPO Records Center Institute of Nuclear Power Operations l

1100 circle 75 Parkway Suite 1500 L' Atlanta, Georgia 30339 NRC Resident Inspector Sequoyah Nuclear Plant

-2600 Igou Ferry Road Soddy Daisy, Tennessee 37379

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On November 22. 1989, iiith Unit 2 in Mode 1. TVA issued a CAQR to document an error in upper hcad injection (UHI) scaling calculation. Specifically, the value for the distance from the floor to the ceuter line of Level Switch 2-LS-87-21 was transposed in the calculation of the variable leg. This resulted in establishment of an incorrect sotpoint. The calibration procedure was revised incorporating the incorrect setpointo The calibration procedure was subsequently revised to replace the incorrect setpoint l with a new setpoint established to support a change to the technical specifications l (TSs). TVA reviewed the surveillances performed during the period the procedure etntained the incorrect setpoint values; on July 30, 1988, and November 17, 1988, the cctual as-left values for the setpoint were outside the TS requirements. The CAQR was not initially determined to be reportable because the CAQ Unit failed to obtain a final reportability determination. This error was recognized on January 17, 1990. The root cause of the calculation error is inattention to detail with a contributing cause of cxcessive hours worked. The root cause to the delay in reporting this event is l; inattention to detail by the CAQ processor. The CAQ Unit was counseled concerning their duties in obtaining reportability determinations.

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Ol0 Ol2 0F 0 14 TEXT w nesse apen s severed, use eWomone%AC Fonn asM's10M Description of Event On November 22, 1989, with Unit 2 in Mode 1 (100 percent power, at 2,235 pounds per square inch gauge, and 578 degrees Fahrenheit), TVA issued Condition Adverse to Quality R: port (CAQR) SQQ890622 to document a mathematical error in upper head injection (UHI)

Scaling Calculation B25 881117 807. The error was discovered during a routine Quality Assurance monitoring activity of engineering calculations. The error was in calculation of the setpoint of UHI Level Switch 2-LS-87-21 (EIIS Code BQ) and applied to the Unit 2 switch only. Specifically, the value for the distance from the floor to the center line i cf the switch (47.75 inches) was transposed (45.75 inches) in the calculation of the  !

variable leg. The variable leg is the difference between the setpoint elevation and the  ;

c:nterline of the switch times the specific gravity of the borated water. The reference Icg is the difference between the condensate pot and the centerline of the level transmitters. The setpoint is based on differentini pressure. Thus, the setpoint is the reference leg pressure minus the variable leg pressure. This resulted in j catablishment of an incorrect setpoint. This setpoint could have ultimately resulted in  !

ccrly isolation of the UHI in the event of.an accident. UHI Scaling Calculation B25 881117 807 was prepared to correct previously erroneous setpoint scaling as  ;

identified in LER 50-328/68033. On July 30, 1988, the calibration procedure was '

rcvised, incorporating the incorrect setpoint. On January 26, 1989, the calibration procedure was revised to replace the incorrect setpolut with a new (correct) setroint satablished to support a change to the technical specifications (TSs).

TVA reviewed the performance of Surveillance Instruction (SI) 196. " Periodic Calibration of Upper Head Injection System Instrumentation (18 Months)," from July 30, 1988, through ,

Jcnuary 26, 1989, the period the SI contained the incorrect setpoint value. The procedure required the level switch to be set between 135.8 and 139.8. The setpoint should have been between 137.9 and 141.9 to ensure compliance with TSs. The review rsvealed that on July 30 and November 17, 1988, the actual as-left values for the sotpoint were 137.26 and 137.86, respectively. Therefore, the TS requirements were not met for the surveillance.

CAQR SQQ890622 was issued on November 22, 1989, and the management review committee dotermined that it may be potentially reportable. However, the Condition Adverse to Quality (CAQ) Unit failed to ensure that the final reportability determination was promptly made. This situation was compounded by an error made by the CAQ processor who incorrectly entered the reportability status in the tracking system. The failure to finalize the reportability determination was not recognized until January 17, 1990, when Nuclear Engineering requested feedback on the reportability of the CAQR. At this point,

) the CAQ Unit immediately hand-carried the CAQR to the responsible organization and sxplained the circumstances surrounding the delay. TVA initiated Potential Reportable Occurrence 2-90-009 on January 26, 1990, to document reportability of UHI Level Switch 2-LS-87-21 being outside the TS allowable value.

Csuse of Event The root cause of the calculation error is inattention to detail in transferring a number from one page to the next. A contributing cause to the inattention to detail may h:ve been the number of hours worked in resolving this issue.

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Cause of Event (Continued)

Th3 root cause for the failure to finalize the reportability determination for this  ;

cy:nt was personnel error resulting from lack of attention to detail

'nalysis of Event A

This event is being reported in accordance with 10 CFR 50.73, paragraph a.2.i.B. as an ep; ration prohibited by TSs. .

Th3 UHI system is a subsystem of the emergency core cooling system and provides direct co ling to the reactor core during the blowdown phase of a loss of' coolant accident.

Emergency core cooling from the UHI system is accomplished by injecting a designed volume of borated water into the head of the reactor vessel following a reactor coolant 1 system (EIIS Code AB) depressurization to less than 1250 pounds per square inch. The  ;

-amount of water delivered to the reactor vessel head is controlled by accumulator tank

• 1cvel switch actuation, upon reduction of tank level to within TS setpoint tolerance, which subsequently terminates. injection by closure of flow path isolation valves. Four differential preseure switches connected to the UHI accumulator tank through sense lines initiate closure of the four isolation valves (two in series for each flow path) when th3 differential pressure in the UHI accumulator tank level has reached a pradetermined ,

value. This differential pressure value corresponds to the administrative controlled TS estpoint (87.1 2.0 inches above the UHI accumulator tank vendor working line when corrected for the mass of the cover gas) for accumulator tank 1cvel and delivers to a '

d: signed volume (900-1,180.5 cubic ft.d) of borated water to the reactor vessel head.

TVA used the Westinghouse Electric Corporation methodology (letter dated October 23, 1989, "UHI Evaluation") for determining the volumo of water to be delivered from the UHI  ;

to assess if the incorrect setpoint placed the plant outside the design basis. The volume of water to be delivered is based on the level switch setpoint and the UHI isolation valve closure times. The methodology uses the average of the four level switch settings and the average valve closure time. The average switch setpoint for the surveillances in question were 83.21 inches on July 30 $ 1988, and 87.805 inches in Ncvember 17, 1988. The average valve stroke times used were obtained from the surveillance performed in January 1989 during the Unit 2 Cycle 3 refueling outage. The

.cverage closure time was 3.86 seconds.

The total volume to be injected for given level switch setpoints and volumes injected g 'during valve closure were calculated utilizing information in the Westinghouse cnalysis. TVA determined that Case 2 of the Westinghouse analysis was a good cpproximation of the initial level switch setpoint in which a level setpoint of 88.1 inches was calculated to result in an injected water volume of 800 cubic feet. "

This value was adjusted to reflect the actual setpoints on the dates listed above using the 7.4 cubic foot per inch tank internal volume. Case 1 of the Westinghouse analysis .

~ h:d an average stroke time of 3.9 seconds and this bounded the 3.86-second average for detes in question. The 3.9 second valve closure allowed an additional 257 cubic feet to ba injected. Adding the initial injected volume and the valve closure injected volume together yields the total injected volume of 1,058 cubic feet and 1,055 cubic feet for NRC Form asSA (649:

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sthe two dates in question, both of which are within the safety limits of 900-1,105 cubic fact at the time in question. Westinghouse has reviewed the team's analysis and concurs with the results. Even though the TSs were not met, the design basis safety limits were not exceeded (900-1,105 cubic feet), and the plant remained in a safe analyzed condition. Therefore, this condition did not adversely affect the health and safety of the public.

Corrective Actions ]

The error in the calculation'is considered an isolated case with no corrective action required. SI-196 was revised on January 26, 1989, to replace the incorrect setpoint with a new setpoint established to support a change to the TSs.

-The CAQ Unit has enhanced communications between the CAQ processor and the management review committee representative to ensure that required actions are promptly executed.

In addition, the CAQ Unit was counseled concerning their duties in obtaining reportability determinations. .

Additional Information There have been no. previous reported events of this type.

0738h N?;C Form 386A (tk89)

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