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X '.UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555January 30, 1995INACCURATE DATA OBTAINED WITH CLAMP-ONULTRASONIC FLOW MEASUREMENT INSTRUMENTSNRC INFORMATION NOTICE 95-08:AddresseesAll holders of operating licenses or construction permits for nuclear powerreactors.PurDoseThe U.S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to alert addressees to difficulties in accurately measuring flow rateswith clamp-on ultrasonic flow measurement instruments. It is expected thatrecipients will review the information for applicability to their facilitiesand consider actions, as appropriate, to avoid similar problems. However,suggestions contained in this information notice are not NRC requirements;therefore, no specific action or written response is required.DescriDtion of CircumstancesO October 14, 1993, while performing a high head safety injection (HHSI) flowbalance test, the licensee for North Anna Unit 2 determined that the as-foundsafety injection cold leg branch line flow rates did not meet the technicalspecification requirements. The as-found cold leg branch line flow rates hadalso failed to meet the technical specification requirements during theprevious test in April 1992.The North Anna Technical Specifications give limits related to both minimumand maximum safety injection line flow rates. For North Anna, these twotechnical specification limits resulted in an very narrow allowed operatingband, which required the use of highly accurate flow measurement instrumentsfor flow tests.The licensee performed the flow balance using System 990 Uniflow UniversalTransit-Time Flowmeters manufactured by Controlotron of Hauppauge, New York.The Uniflow flowmeter is a clamp-on non-intrusive portable flowmeter that usesmulti-pulse, transit-time ultrasonic technology to measure precisely the flowrate. The flowmeter induces alternate upstream and downstream ultrasonicsignals and measures the difference in transit times. This information isthethen used to determine the axial fluid velocity and the flow rate throughpipe. Inaccuracies associated with the use of these instruments at North Annacombined with the narrow band of allowable flows caused problems whichcontributed to the failure to meet technical specification requirements.P4 RIrp.#sCC's9501240226UtjxW vv-31-150lk (t

v-'IN 95-08January 30, 1995Page 2 of 4DiscussionThe licensee examined the 1993 North Anna Unit 2 flow balance test data andobserved that some of the data indicated that the instrument errorssignificantly exceeded accuracies assumed for the tests. Numerous factors mayaffect the accuracy of this flowmeter including pipe dimensions, fluid floweffects, transducer mounting, and instrument setup and operation. After thetest, the licensee investigated and concluded that the instrument inaccuracymost likely was caused by flow effects associated with the pipingconfiguration. The piping arrangement, which contained several out-of-planebends that forced the flow to change direction numerous times before enteringthe straight section of pipe containing the ultrasonic transducers, may havecaused a stable swirl-type flow profile corkscrewing down the pipe. Thelicensee postulated that the swirl flow added a radial flow error to the testinstruments. The flowmeter was calibrated assuming a primarily axial flowprofile. In subsequent testing at a national laboratory, Controlotronultrasonic flowmeter data varied up to 5% at different orientations around thepipe at a position approximately 15 pipe diameters downstream of a singlebend. The test configuration did not include any out-of-plane bends,indicating that it is also possible for a non-uniform flow profile to exist inthe absence of out-of-plane bends, causing flow measurements with larger thanexpected errors.The licensee noted that the instrument output during the test did not give anyindication of measurement problems. The instruments displayed little noiseand only the expected small-magnitude random flow fluctuations. The lack oferratic instrument readings could easily be interpreted as meaning thereadings were valid (i.e., within the stated accuracy). However, the licenseetested the instrument and determined that it could register a stable readingwhile a significant error was occurring. Therefore, the licensee concludedthat repeatability of the data does not prove that the flow has been measuredaccurately.After the test failure, the licensee found several inconsistencies in the testdata which indicated problems in data accuracy. As an example, when theA HHSI pump replaced the C HHSI pump as the operating pump, without any otherchanges in system resistance, the B cold leg flow rate increased by8.4 percent while the A cold leg flow rate increased by 1.5 percent and theC cold leg flow rate did not change. The licensee concluded that these valuescorresponded to an implausible change in the highest cold leg flow path fromloop A to loop B when the sole change was which injection pump was operating.In addition, the head curve for the A HHSI pump was lower than that for the

I In-'IN 95-08January 30, 1995Page 3 of 4C HHSI pump; thus, the A HHSI pump would be expected to supply flow rates lessthan the C HHSI pump for the same system resistance. However, the ultrasonicinstruments indicated that the A HHSI pump delivered 3.3 percent more flowthan the C HHSI pump. This was contrary to the previously measured pump headcurve data. At the same time, installed plant process instruments indicatedthat the A HHSI pump delivered 3.4 percent less flow than the C HHSI pump, ameasurement consistent with the pump curves.The licensee could not determine with certainty the factors that resulted inthe unanticipated measurement errors in this event. Conditions specific to anapplication can cause deviations from the vendor-supplied instrumentaccuracies. However, during the investigation the licensee developed methodsthat could be used to determine when the ultrasonic flowmeter may not yieldthe assumed accuracy. These methods include comparing ultrasonic flowmeterdata from several locations or different orientations at the same location orby comparing the data from these instruments with data from permanentlyinstalled instruments. Test results can also be compared with expected systembehavior.The NRC staff has approved a request from the licensee of the North Anna plantto modify the technical specification that specifies the acceptance criteriafor the HHSI pump flow rates. The change removes the specific fixed valuesfor the flow from the technical specifications and permits the licensee toestablish allowable values by analysis, providing greater operationalflexibility. The licensee is also planning to (1) install permanent flowinstrumentation that will supply highly accurate data for future flow balancetesting and (2)supply training concerning the accuracy of clamp-on ultrasonicflowmeters to the personnel who use them.Licensees frequently use flow measurements to demonstrate that safety-relatedcomponent performance is adequate to meet the demands indicated by theaccident or transient analyses. Therefore, obtaining accurate flowmeasurements is important to safety. When balancing the flow of HHSIinjection paths, flow rates need to be accurately measured to demonstrate thatthe unit complies with the assumptions in safety analyses and is operated inan analyzed condition. At North Anna the licensee initially failed to detectinaccurate flow data because of a failure to verify the consistency,repeatability and reasonableness of the data from the ultrasonic flowmeasurement instruments. Although technical specification requirements werenot met at North Anna, the licensee later analyzed the issue and concludedthat the HHSI system would have performed its design safety function.

s'-'IN 95-08January 30, 1995Page 4 of 4This information notice requires no specific action or written response. Ifyou have any question about the information in this notice, please contact oneof the technical contacts listed below or the appropriate Office of NuclearReactor Regulation (NRR) project manager.ran K. Grimes, DirectorDivision of Project SupportOffice of Nuclear Reactor RegulationTechnical contacts:Donald R. Taylor, RII(703) 894-5421Larry W. Garner, RII(404) 331-4663Hukam C. Garg, NRR(301) 504-2929Attachment:List of Recently Issued Information Notices

Re-ttachmentIN 95-08January 30, 1995Page I of 1.LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformationNotice No.SubjectDate ofIssuanceIssued to95-07Radiopharmaceutical VialBreakage during Preparation01/27/95All USNRC medical licenseesauthorized to use byproductmaterial for diagnosticprocedures.95-06Potential Blockage ofSafety-Related Strainersby Material Brought InsideContainment01/25/95All holders of OLs or CPsfor nuclear power reactors.95-05Undervoltage ProtectionRelay Settings Out ofTolerance Due to TestEquipment Harmonics01/20/95All holders of ConstructionPermits for nuclear powerreactors.95-04Excessive Cooldown andDepressurization of theReactor Coolant SystemFollowing a Loss ofOffsite Power01/19/95All holders of OLs or CPsfor nuclear power reactors.95-03Loss of Reactor CoolantInventory and PotentialLoss of Emergency Mitigation Functions While ina Shutdown Condition01/18/95All holders of Ols or CPsfor nuclear power reactors.95-02Problems with GeneralElectric CR2940 ContactBlocks in Medium-VoltageCircuit Breakers01/17/95All holders of OLs or CPsfor nuclear power reactors.95-01DOT Safety Advisory:High Pressure AluminumSeamless and AluminumComposite Hoop-WrappedCylinders01/04/95All U.S. Nuclear RegulatoryCommission licensees.OLCP Operating LicenseConstruction Permit

95-08SJanuary 30, 1995Page 4 of 4This information notice requires no specific action or written response. Ifyou have any question about the information in this notice, please contact oneof the technical contacts listed below or the appropriate Office of NuclearReactor Regulation (NRR) project manager.Original signed byBrian K. Grime!Brian K. Grimes, DirectorDivision of Project SupportOffice of Nuclear Reactor RegulationTechnical contacts:Donald R. Taylor, RII(703) 894-5421Larry W. Garner, RII(404) 331-4663Hukam C. Garg, NRR(301) 504-2929Attachment:List of Recently Issued Information NoticesDOCUMENT NAME:95-08.INNOTE: VENDOR COMMENTS RECEIVED, NO SIGNIFICANT CHANGES WERE MADE*DRP:RIIby*RIIby Phoncon*OGCB:DORS*RPB:ADM by FFICE09/07/94*DRP:RI 7/94C/OECB:DOPS09/,W94 /09/22/9409/22/94OFFICENAMEAEChaffee*DATE11 /22/94PhonconOP/Arxies01&1y 95OFFICIAL RECORD COPYTPhoncon

IN 95-XXJanuary XX, 1995Page 3 of 3This information notice requires no specific action or written response. Ifyou have any question about the information in this notice, please contact oneof the technical contacts listed below or the appropriate Office of NuclearReactor Regulation (NRR) project manager.Brian K. Grimes, DirectorDivision of Project SupportOffice of Nuclear Reactor RegulationTechnical contacts:Donald R. Taylor, RII(703) 894-5421Larry W. Garner, RI!(404) 331-4663Hukam C. Garg, NRR(301) 504-2929Attachment:List of Recently Issued Information NoticesDOCUMENT NAME:S:\DOPS SEC\CLAMP-ON.INRmnTE- VENDOR COMMENTS RFCFTVFDOFFICE*RPB:ADMby Emai tNO SIGNIFICANT CHANGES WERE 9/22/94*DRP: RIIby E11/22/9411/OFFICEOFFICE/94OFFICIAL RECORD COPYPhoncon