ML20029D020

LER 94-007-01:on 931014,high Head Safety Injection Flow Balance Testing Found to Be Below TS Requirement.Caused by Unaccounted for Uncertainties.Cold Leg Safety Injection Leg Throttle Valve adjusted.W/940425 Ltr

ML20029D020
Person / Time
Site:	North Anna
Issue date:	04/25/1994
From:	Kane G VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-007, LER-94-7, NUDOCS 9405030273
Download: ML20029D020 (5)

Text

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10 CFR 50.73 Virginia Electric and Power Company North Anna Power Station P. O. Box 402 Mineral, Virginia 23117 April 25,1994 U. S. Nuclear Regulatory Commission NAPS: MPW Document Control Desk Docket No. 50-339 Washington, D.C. 20555 License No. NPF-7

Dear Sirs:

Pursuant to North Anna Power Station Technical Specifications, Virginia Electric and Power Company hereby submits the following Supplemental Licensee Event Report applicable to North Anna Unit 2.

Report No. 50-339/93-007-01 This Report has been reviewed by the Station Nuclear Safety and Operating Committee and will be forwarded to the Management Safety Review Committee for its review.

Very t uly ours, e ~

G. . ane Station Manager

Enclosure:

cc: U.S. Nuclear Regulatory Commission 101 Marietta Street, N.W.

Suite 2900 Atlanta, Georgia 30323 R. D. McWhorter NRC Senior Resident inspector North Anna Power Station 94o5o3o273 940423

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1 LICENSEE EVENT REPORT (LER) 'E'ICTON C t RE E8T%"O H R R CO MEWS R R BUR

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1 IN#^uTNul"!ATREo"ETTJ"!O /uTs"A"WMME"!!s"d"0M' AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), Office Oh 4 (See reverse for required number of dgts/ characters for each block) MANAGEMENT AND BUDGET WASHINGTON.DC 20603.

FOCILITY NAME (1) DOCKET NUMHEH (2) PAGE(3)

North Anna Unit 2 05000339 1 cF 4 TITLE (4)

HIGH HEAD SAFETY INJECTION FLOW BELOW TECHNICAL SPECIFICATION MINIMUM EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (8)

SEOU AL RE FACILrrY NAMES DOCKET NUMBER (S)

MONTH DAY YEAR YEAR MONTH DAY YEAR l

! 05000 DOCKET NUMBER (S) 14 007 01 04 25 94 10 93 93 05000 C7ERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5:(Check one or more of the followina)(11)

MODE (9) 1 20.405(b) 50.73(a)(2)(iv) 73.71(b) 20.402(b) 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)

POWER Lgvyt 100 20.40s(axi)(ii) 50.36(c)(2) 50.73(a)(2)(vu) OrHER 20.405(ax1)(hi) X 50 m x2xo 50mx2xvmxA) n@a ow a%n 20.405(a)(1)(iv) 50.73(a)(2)(n 50.73(a)(2)(vm)(c) 20.405(a)(1)(v) 50.73(a)(2)(m) 50.73(a)(2)(s)

LICENSEE CONTACT FOR THIS LER (12) l NAME TELEPHONE NUMBER (inctuo Area Code)

Greg Kane, Station Manager (703) 894-2101 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13) couSE SYSTEM COMPONENT MANUFACTURER R RTAB E CAUSE SYSTEM COMPONENT MANUFACTURER Af0 NPR 1

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, SUPPLEMENTAL REPORT EXPECTED (14) i l

YES EXPECTED MONTH DAY YEAR (t yes. cormiete EXPECTED SUBMISSION DATE) x NO S IN ABSTRACT (Limit 101400 spaces, i.e., apprOximately 15 Single-spaced typewritten lines) (16) l On October 14,1993, with Unit 2 in Mode 5 (Cold Shutdown), during High Head Safety injection (HHST) flow balance testing, the "as-found" cold leg branch line flow was found to be below the Technical Specifications (TS) minimum requirement. The sum of the branch line flows, excluding the highest flow rate, is required by T3 4.5.2.h to be greater than or equal to 359 gpm. However, the sum of the two l lowest measured branch flow rates was found at 356 gpm. The cold leg Safety injection throttle valves l

were adjusted so that sum of the two lowest flow rates was equal to 384 gpm.

4 On November 8,1993, concerns were identified about the flow balancing data due to instrument inaccuracies. All three charging pumps were twice declared inoperable, and TS 3.0.3 was entered. At ,

1402 hours0.0162 days <br />0.389 hours <br />0.00232 weeks <br />5.33461e-4 months <br /> on November 9,1993, seat injection flow was decreased to allow two charging pumps to meet

the requirement of the TS, and TS 3.0.3 was exited. This event is reportable pursuant to 10 CFR 50.73 (a)(2)(i)(B) as a condition prohibited by Technical Specifications.

1 The primary suspected cause of the event is previously unaccounted for uncertainties in the Unit 2 HHSI flow balance measurements due tc, adverse system piping geometry's.

No significant safety consequences evolved as a result of this event because a previous analysis has

shown that the existing HHSI branch flows are within the design basis limits. Therefore, the health and

safety of the public were not affected.

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FACluTY NAME (1) DOCKET NUMBER m LER NUMBER (6) PAGE @

yg SEQUENTIAL REVISION North Anna Unit 2 05000 339 2 ' OF 4 93 -

007 -

01 TEXT (p more sp=:e = regned. vee eddeanal NRC Parm 364A s) (17) 1.0 Descriotion of the Event On October 14,1993, with Unit 2 in Mode 5 (Cold Shutdown), during High Head Safety injection (HHSI)

(Ells System Identifier BO) flow balance testing, the "as-found" cold leg branch line flow was found to be below the Technical Specifications (TS) minimum requirement. The sum of the branch line flows, excluding the highest flow rate, is required by TS 4.5.2.h to be greater than or equal to 359 gpm.

However, the sum of the two lowest measured branch flow rates was found at 356 gpm. The cold leg Safety injection throttle valves (Ells Component Identifier INV) were adjusted so that sum of the two lowest flow rates was equal to 384 gpm.  ;

On November 8,1993, concems were identified about the flow balancing data due to instrument inaccuracies. These instruments inaccuracies were a result of the adverse system geometry's. All three charging pumps were declared inoperable at 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br /> because they could not meet the requirements of TS 4.5.2.h and TS 3.0.3 was entered. Based on a preliminary Engineering calculation, the seal l injection flow rates were then adjusted to allow the HHSI flow balance to meet the TS requirement, and two of the charging pumps were declared operable at 1006 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.82783e-4 months <br />. The computer HHSI System model showed that seal injection flow would have to be reduced more than predicted in the preliminary calculation to allow the HHSI flow balance to meet the TS requirements. At 1445 hours0.0167 days <br />0.401 hours <br />0.00239 weeks <br />5.498225e-4 months <br />, all three charging )

, pumps were again declared inoperable, and TS 3.0.3 was entered. NRC discretionary enforcement from l TS 4.5.2.h was requested, and a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> extension to restore two charging pumps to operable status was j received. At 1402 hours0.0162 days <br />0.389 hours <br />0.00232 weeks <br />5.33461e-4 months <br /> on November 9,1993, seal injection flow was further decreased to allow two I charging pumps to meet the requirement of the TS, and TS 3.0.3 was exited. This event is reportable pursuant to 10 CFR 50.73 (a)(2)(i)(B) as a condition prohibited by Technical Specifications.

2.0 Sionificant Safety Conseauences and imolications No significant safety consequences evolved as a result of this event because a previous analysis has l shown that the existing HHSI branch flows are within the design basis limits. Therefore, the health and l Safety of the public were not affected.

3.0 Cause of the Event 1

The Root Cause Evaluation (RCE) for this event has been completed. The primary cause is previously j unaccounted for uncertainties in the Unit 2 HHSi flow balance measurements due to adverse system I piping geometry. The HHSI system piping geometry contributes to a swirl flow to which the ultrasonic flow measurement equipment is extremely sensitive. A lack of understanding concoming the affect swirl flow has on flowmeter accuracy has, in the past, resulted in erroneous data.

The use of new technology (i.e. strap-on ultrasonic flowmeters) was based on an approved vendor's assessment that desired accuracy could be achieved. Available vendor information and vendor training of station personnel were relied upon to ensure proper application of the equipment. The vendor manual

! did not provide complete information conceming limitations of the ultrasonic flowmeters. It has been determined, depending on piping geometry that the flowmeters should be located as much as 100 pipe diameters downstream of any pipe fitting in order to remove the fluid swirl affect. In addition, multiple versus single beam transducer measurement techniques may be required to achieve the desired accuracy, it has also been determined, by in-house testing, that variation in the ultrasonic flowmeter transmit frequency has a large effect on the measured flow rate. The station procedure controlling the use of the flowmeters was generic and did not provide guidance on site specific problems which may be encountered.

NHG t orm 366A (542)

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j rccurY NAME m DOCKET NUMBER G) LER NUMBER (8) PAGE (3)

, North Anna Unit 2 05000 339 3 OF 4 93 -

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01 TEXT tu more space se reemM use edeem NRC Fem 364KW (17) i 3.0 Cause of the Event (continued) l In addition, the current Technical Specification requirements for acceptable HHSI flow balancing are extremely restrictive. After allowing for minor performance differences among individual HHSI pumps, and 1 the reactor coolant pump seal injection flow, there is a very narrow band of allowable flow rates. Achieving i flows with this narrow band requires very accurate flow measurement. Also, the restrictive flow band does not recognize the considerable margin to the safety analysis limits.

1 4.0 Immedinte Corrective Actions l The cold leg Safety injection throttle valves were adjusted so that the sum of the two lowest flow rates was j equal to 384 gpm.

Loctite 290 Threadlocker@ was installed on the valve stem to yoke bushing to prevent valve stem movement.

i l The throttle valves were x-rayed and reviewed with the vendor for defects. It was determined that the i valves were intact.

i The sealinjection flow rates were adjusted to allow the HHSI flow balance to meet the TS requirement.

< NRC enforcement discretion from TS 4.5.2.h was requested and received.

1 5.0 Additional Corrective Actions An emergency TS change consistent with the NRC's enforcement discretion policy has been submitted.

! Further evaluation of the TS will be conducted to determine whether additional enhancements may be j warranted.

1 I 6.0 Actions to Prevent Recurrence

1 i Management has reviewed the recommendations of the completed root cause evaluation and determined I the following actions are necessary to prevent recurrence.

4

] The safety analysis will be evaluated for minimum acceptable emergency core cooling system flow rates to 1 justify a larger band of allowable flow rates.

{ A TS revision to Section 4.5.2.h has been submitted to the NRC to specify flow balance acceptance

, criteria values based on the results of the safety analysis evaluation rather than specific values. This allows 1 for fuel cycle and equipment specific considerations to be accounted for in the balancing test without

! requiring frequent TS changes.

The flow instruments for the cold leg branch lines will be replaced or supplemented with ;nstruments that measure flow more accurately.

6 j N% i Orm 366A @W) i

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FCCR.ITY NAME (1) 00CKEI NJW8E R @ LEA NUWRER(6) PAGE (3)

SEQUEWilAt REVISION YEAR North Anna Unit 2 05000 339 4 OF 4 93 -

007 -

01 TEXT m more space a rapnee. use seasones emc perm suA's) (17)

If continued use of strap-on ultrasonic flowmeters is anticipated for Safety Related apolications, engineering training will be administered for their use.

The station controlling procedure for strap-on ultrasonic flowmeters will be updated to incorporate findings from the RCE with regard to proper use and the limitations of this technology.

An Operating Experience entry will be made to ale,t the industry on the results of the root cause evaluation.

7.0 Similar Eventi LER 50-339/90-008-00 documents the sum of the two lowest branch flows being less than the TS minimum requirement (Unit 2). The cause of this event was instrument uncertainties and improper i methods for measuring flow.

LER 50-339/92-010-00 documents the sum of the two lowest branch flows being below the TS minimum requirement (Unit 2). The cause of this event was valve mispositioning.

LER 50-338/93 009-00 documents the sum of the two lowest branch flow lines being below the TS minimum requirement (Unit 1). The cause of this event was too narrow of a TS allowable flow rate to be consistently met with instrumentation uncertainties.

8.0 AMitbr.pl InformatiQD Unit 1 was at 100% power (Mode 1) and was not directly affected by this event. Corrective actions for Unit 2 will also be performed on Unit 1 as applicable.

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