United States Nuclear Regulatory Commission - Protecting People and the Environment

Morning Report for March 4, 2004

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Overpower Issues with Ultrasonic Flow Measurement (UFM)


Braidwood 1, Braidwood 2
Dockets: 05000456, 05000457
[1] W-4-LP, [2] W-4-LP
License No:

Exelon Generation Co., LLC
Byron 1, Byron 2
Dockets: 05000454, 05000455
[1] W-4-LP, [2] W-4-LP

MR Number: H-2004-0008
Date: 08/25/2003

Various Sources


A Crossflow ultrasonic flow measurement (UFM) device (manufactured by Advanced Measurement and Analysis Group (AMAG) and marketed by Westinghouse) was installed at Byron and Braidwood in May and April 1999 to measure feedwater flow to the steam generators. The UFMs were implemented June and May 1999, respectively. The UFMs were perceived to be more precise than conventional venturi meters and were not subject to the fouling degradation that can affect venturi meters. The UFMs, as applied at Byron and Braidwood, were installed and used as a calibration tool to correct feedwater venturi flow measurements in order to recover lost megawatts due to venturi inaccuracy issues. The UFMs were not intended to be used as the basis for power uprates and no request was made for the NRC to approve them for that purpose.

In late 2002, the NRC became aware of questions regarding the accuracy of the UFMs at Byron and Braidwood, and possibility of some of the units being in an overpower condition. The licensee reported that there were signal abnormalities from some of the UFMs and, on Byron 1, statistical differences between the measured total feedwater flow and the sum of the flows from the four individual feedwater lines. As a result of additional testing conducted of feedwater flow data derived from the AMAG UFMs by the licensee in 2003, it was concluded that the UFMs were giving non-conservative readings which could lead to the units operating above their licensed power limits. In August 2003, the licensee removed the UFMs from service on Byron, Units 1 and 2 (Event Notification 40117), and Braidwood, Unit 2 (Event Notification 40123). The Braidwood, Unit 1 UFMs were not removed from service at that time because the testing results showed that the UFMs were performing as expected. Later, the UFMs at Braidwood, Unit 1 (Event Notification 40559), were also removed from service.

As listed in Westinghouse Technical Bulletin TB-04-4 and Nuclear Safety Advisory Letter NSAL-03-12, the Crossflow UFM is currently used at 30 power plant units in the USA. Seventeen out these 30 units, including Byron and Braidwood units, used the Crossflow UFM to recover lost power as explained above. The remaining 13 units used Crossflow UFM for Appendix K related measurement uncertainty recapture (MUR) power uprates.

For MUR power uprates, each licensee submitted a license amendment request following guidelines provided in the NRC Regulatory Issue Summary (RIS) 2002-03, "Guidance on the Content of Measurement Uncertainty Recapture Power Uprate Applications" and committed to install the UFM in accordance with the Westinghouse Topical Report CENPD-397-P-A for plant specific installation procedures. The staff generically approved this topical report in March 2000 for Crossflow UFM's design capability to achieve a measurement uncertainty of 0.5% or less, depending upon the plant specific installation. For each MUR related UFM installation, Westinghouse / AMAG performed a plant specific Crossflow measurement uncertainty analysis and the result was used to calculate the unit power measurement uncertainty with the use of Crossflow for measuring feedwater flow to justify the proposed power uprate. The staff reviewed these calculations along with the licensee's application for the proposed power uprate.

For applications of the UFM to recover megawatts lost due to venturi degradation, the staff has not specifically reviewed the installation and use. The Byron/Braidwood overpower issue led to the identification of those power plants that use Crossflow UFMs to recover lost megawatts, as listed in the Westinghouse bulletin and advisory letter. The NRC staff is monitoring Exelon's investigation of the conditions at Byron and Braidwood and is investigating the generic aspects resulting from the recent UFM performance information.

For information regarding power uprates or ADAMS documents please refer to our website at:
http://www.nrc.gov/reactors/operating/licensing/power-uprates.html and

**** Information provided by Westinghouse include:
Technical Bulletin, "CROSSFLOW Ultrasonic Flow Measurement System Signal Issues" - TB-03-6, Date: 09/05/2003 (ADAMS # ML032521438)
Nuclear Safety Advisory Letter, "CROSSFLOW Ultrasonic Flow Measurement System Flow Signal Interference Issues" - NSAL-03-12, Date: 12/05/2003 (ADAMS # ML033421289)
Technical Bulletin, "Information Regarding Recent CROSSFLOW Ultrasonic Flow Measurement System Performance Observations" - TB-04-4, Date: 02/12/2004 (ADAMS # - not available as of release date for this Morning Report)

**** This information from Westinghouse may be obtained at: http://www.rle.westinghouse.com - This site is a free service of Westinghouse Electric Co. but requires specific access through a firewall. Request for access should be made to kleinwd@westinghouse.com

Accession Numbers:

Accession No Accession Date
ML032810527 09/29/2003
ML032810226 09/30/2003


Name Office Abbrev Phone No E-Mail
FOSTER, JACK W NRR (301) 415-3647 JWF@nrc.gov
DICK, GEORGE F NRR (301) 415-3019 GFD@nrc.gov
AHMED, IQBAL NRR (301) 415-3252 IXA@nrc.gov
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