RIS 2007-24, NRC Staff Position on Use of the Westinghouse Crossflow Ultrasonic Flow Meter for Power Uprate or Power Recovery
| ML063450261 | |
| Person / Time | |
|---|---|
| Issue date: | 09/27/2007 |
| From: | Case M J NRC/NRR/ADRA/DPR |
| To: | |
| References | |
| FOIA/PA-2008-0046, OMB 3150-0011 RIS-07-024 | |
| Download: ML063450261 (6) | |
OMB Control No.: 3150-0011 UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555-0001September 27, 2007NRC REGULATORY ISSUE SUMMARY 2007-24NRC STAFF POSITION ON USE OF THE WESTINGHOUSECROSSFLOW ULTRASONIC FLOW METER FOR POWER UPRATE ORPOWER RECOVERY
ADDRESSEES
All holders of operating licenses for nuclear power reactors, except those who havepermanently ceased operations and have certified that fuel has been permanently removedfrom the reactor vessel.
INTENT
The U.S. Nuclear Regulatory Commission (NRC) is issuing this regulatory issue summary (RIS)to inform addressees that NRC has written a letter to Westinghouse Electric Corporation (WEC)suspending NRC's approval of WEC's topical report on the CROSSFLOW ultrasonic flow meter(UFM) for new and future use until the staff's concerns are resolved. This RIS does not transmitany new requirements and does not require any specific action or written response. However,the information provided in the letter to WEC, including the Safety Evaluation attached to theletter, may have applicability to current users of the CROSSFLOW UFM.
BACKGROUND INFORMATION
Licensees use UFMs to provide better accuracy than the venturis that have typically been usedfor measuring feedwater flow rate in nuclear power plants. Feedwater flow rate is an importantinput parameter in establishing the plant's operating power level. The operating power limit isdefined in the plant's operating license.UFMs are used (a) to compensate for fouling in venturis that could lead to operation at less thanthe licensed thermal power limit and (b) in conjunction with measurement uncertainty recapture(MUR) power uprate license amendments to operate at higher power levels. The formerapplication, generally known as power recovery, is implemented under Title 10 of the Code ofFederal Regulations (10 CFR) Section 50.59 and does not require NRC staff review. The latterapplication, referred to as a MUR power uprate, requires a license amendment request (LAR)
under 10 CFR 50.90 since the licensed thermal power will increase. 1Caldon is now a part of the Measurement Systems Division of Cameron InternationalCorporation ("Cameron"). The name "Caldon" continues to be used in describing their UFMs.Since 2002 there have been a number of instances, at some plants that have implementedUFMs under 10 CFR 50.59, where use of UFM instrumentation has led to operation up to a fewpercent above the licensed power level. This occurs when UFM instrumentation does notprovide the improved or decreased flow rate uncertainty that is claimed by the vendor. However, the staff's experience with reviewing postulated loss-of-coolant accident (LOCA) andnon-LOCA events at these higher power levels, is that the consequences of these events areonly slightly affected by the small variations in power level that could result from the increase infeedwater flow rate uncertainty. The small effect on the consequences and, therefore, lowsafety significance are due to the margins between the results of the analyses and theacceptance criteria, and conservatisms assumed in the licensing basis accident and transientanalyses. Nevertheless, to preclude recurrence, the NRC staff conducted a genericre-evaluation of the thermal-hydraulic and fluid dynamic aspects of UFMs.Two vendors, Caldon
1 and WEC, currently supply UFMs to nuclear power plants for improvingfeedwater flow rate measurement accuracy. In a letter dated July 5, 2006 (AgencywideDocuments Access and Management System (ADAMS) Accession No. ML061700222), theNRC staff informed Caldon that it completed its re-evaluation of the Caldon UFM. The staffconcluded that the performance of the Caldon Check and CheckPlus UFMs are consistent withthe Caldon Topical Reports ER-80P, Revision 0, and ER-157P, Revision 5, previously approvedby NRC, subject to satisfying a confirmatory item related to transducer replacement that wasexpected to introduce a very small uncertainty that would not significantly change claimed totaluncertainty, and that there was a sound thermal-hydraulic and fluid dynamic basis for using theCaldon UFMs.However, in a letter dated September 26, 2007 (ADAMS Accession No. ML071650263) theNRC staff informed WEC that it completed its re-evaluation of the CROSSFLOW UFM, asdescribed in WEC's Topical Report CENPD-397-P, Revision-01-P, "Improved FlowMeasurement Accuracy Using Crossflow Ultrasonic Flow Measurement Technology," and asdescribed in NRC's approval of the topical report. The staff has concluded, based oninformation received subsequent to the staff's initial approval of the topical report, that itsapproval of that report should be suspended. Accordingly, the staff is suspending its March 20,2000 (ADAMS Accession No. ML003694197), approval of CENPD-397-P, Revision-01-P, fornew and future use until the staff's concerns are resolved. The basis for the action is in thestaff's Safety Evaluation attached to its letter to WEC.RegulationsNuclear power plants are licensed to operate up to a specified reactor core thermal power limit. 10 CFR Part 50, Appendix K, requires licensees to assume that the reactor has been operatingcontinuously at a power level at least 1.02 times the licensed power level when performingLOCA and emergency core cooling system performance analyses. This requirement is includedto ensure that instrumentation uncertainties are adequately accounted for in the analyses. Appendix K to 10 CFR Part 50 allows licensees to assume a power level less than 1.02 timesthe licensed power level, but not less than the licensed power level, provided the licensee has demonstrated that the proposed value adequately accounts for instrumentation uncertainties.As an example, in a MUR power uprate license amendment application, a licensee maypropose to use a power measurement uncertainty of 0.5 percent. To achieve this level ofaccuracy, the licensee proposes to use a UFM for measuring main feedwater flow rate toprovide a more accurate measurement of feedwater flow rate than (a) the feedwater flow ratemeasurement accuracy assumed during the development of the original 10 CFR Part 50,Appendix K requirements and (b) the current method of feedwater flow rate measurement usedto calculate reactor thermal output. In this example, the licensee substantiates that the UFM willmeasure feedwater mass flow rate consistent with a total power measurement uncertainty of 0.5 percent. On this basis, a licensee will then propose to reduce the power measurementuncertainty to 0.5 percent. The improved power measurement uncertainty would obviate theneed for the 2 percent power margin originally required by Appendix K to 10 CFR Part 50,thereby allowing an increase in the licensed reactor thermal power limit by 1.5 percent.For those licensees who use UFMs for power recovery, an increase in the licensed reactorthermal power limit is not requested and the 2 percent power margin required by Appendix K to10 CFR Part 50 is maintained. However, with the use of an NRC-approved UFM, a licenseemay adjust the feedwater flow rate measurement reading obtained from a venturi to account forthe fouling of the venturi that may occur during operation. Since UFMs are not subject to foulinglike a venturi, the licensee can take advantage of an NRC-approved UFM's increased accuracyto develop a correction factor that can be applied to the venturi to determine feedwater flowrate, allowing the licensee to operate the reactor closer to its licensed limit. This is allowed by10 CFR 50.59(c)(2)(viii) since the change would not result in a departure from a method ofevaluation described in a licensee's Final Safety Analysis Report (FSAR) used in establishingthe design bases or in the safety analyses. Specifically, 10 CFR 50.59(a)(2)(ii) indicates thatchanging from a method described in the FSAR to another method that has been approved bythe NRC for the intended application is not a departure from a method of evaluation describedin the FSAR.
SUMMARY OF THE ISSUE
The NRC staff has suspended its approval of WEC's topical report on the CROSSFLOW UFMfor new and future use until the staff's concerns are resolved. Accordingly, the staff will notapprove any LARs for MUR power uprates using the CROSSFLOW UFM that rely on NRC'sprevious approval of WEC's topical report without additional justification that is acceptable to thestaff. The staff will inform individual licensees that have submitted LARs for MUR poweruprates using the CROSSFLOW UFM of the status of their submittals given that NRC'sapproval of WEC's topical report has been suspended. Additionally, licensees should no longerconsider the topical report "approved by NRC for the intended application" under 10 CFR50.59(a)(2)(ii) in future 10 CFR 50.59 evaluations of changes to support power recovery.The staff has provided its reasons for suspending approval of the WEC topical report for newand future use, until the staff's concerns are resolved, in NRC's letter to WEC datedSeptember 26, 2007. The specific weaknesses are summarized as follows:1.The assumption that laboratory calibration results are transferrable to an in-plantconfiguration without additional in-plant calibration, without a complete uncertainty evaluation, and without traceability to a nat ional standard. Alternatively, if in-plantcalibration is used to eliminate this assumption, the weaknesses of in-plant calibrationwithout a complete uncertainty evaluation and without traceability to a national standardmay remain.2.The treatment of the impact of acoustic noise on CROSSFLOW and the ability to detectand remove the effects, including determination of residual uncertainty.3.The lack of periodic in-plant calibration using an instrument traceable to a nationalstandard and lack of assurance that CROSSFLOW operation remains within the claimeduncertainty.4.The lack of specific restrictions over a range of flows and plant configurations that definewhere the CROSSFLOW calibration can be considered valid.5.Inadequate description of the installation and use of CROSSFLOW consistent with theactual calibration and commissioning practices.Regarding licensees of plants that rely on the topical report for a MUR power uprate or powerrecovery, the NRC is not requesting a written response from these licensees due primarily tothe small effect on the consequences of postulated licensing basis accident and transientanalyses, and low safety significance of the issue. However, it is expected that licensees willreview this new information for applicability to their fac ilities and consider actions, asappropriate, to assure that their plants operate in accordance with their licensing bases. Licensees that currently rely on the topical report are expected to ensure that CROSSFLOWcontinues to function consistent with all requirements and the plant's licensing bases (e.g.,10 CFR 50.46, Appendix K to 10 CFR Part 50, and the plant's licensed maximum rated thermalpower). Additionally, the NRC staff expects licensees to address and, if necessary, correctidentified deficiencies at their plants and comply with applicable reporting requirements.
BACKFIT DISCUSSION
This RIS informs addresses that the NRC staff has written a letter to WEC suspending itsapproval of WEC's topical report on the CROSSFLOW UFM for new and future use until thestaff's concerns are resolved. This RIS requires no action or written response and, therefore, isnot a backfit under 10 CFR 50.109. Consequently, the NRC staff did not perform a backfitanalysis.
FEDERAL REGISTER NOTIFICATION
A notice of opportunity for public comment on this RIS was not published in the FederalRegister because it is informational.
CONGRESSIONAL REVIEW ACT
The NRC has determined that this RIS is not a rule as designated by the Congressional ReviewAct (5 U.S.C. §§801-808) and, therefore, is not subject to the Act.
PAPERWORK REDUCTION ACT STATEMENT
This RIS does not contain information collection requirements that are subject to therequirements of the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.).
CONTACT
Please direct any questions about this matter to the technical contact listed below./RA/Michael J. Case, DirectorDivision of Policy and RulemakingOffice of Nuclear Reactor Regulation
Technical Contact:
Warren C. Lyon, NRR 301-415-2897 Email: wcl@nrc.govNote: NRC generic communications may be found on the NRC public Web site,http://www.nrc.gov, under Electronic Reading Room/Document Collections.
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