UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

September 11, 2002

NRC INFORMATION NOTICE 2002-26: FAILURE OF STEAM DRYER COVER PLATE

AFTER A RECENT POWER UPRATE

Addressees

All holders of operating license or construction permits for nuclear power reactors, except those

that have permanently ceased operations and have certified that fuel has been permanently

removed from the reactor.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert

addressees to a recent failure of a steam dryer cover plate during operations following a power

uprate at a boiling water reactor (BWR). It is expected that the recipients will review the

information for applicability to their facilities and 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.

Description of Circumstances

In March 2002, Quad Cities Unit 2, a BWR, completed a refueling outage. The outage included

a modification to add baffle plates to the steam dryer to reduce the excessive moisture

carryover expected as a result of an extended power uprate from 2511 MWt to 2957 MWt

(17.8% increase). On June 7, 2002, the unit began experiencing fluctuations in steam flow,

reactor pressure and level, and moisture carryover in the main steam lines. After more

fluctuations in June and July, the licensee conducted an engineering evaluation of one of the

fluctuations, and concluded that the steam flow irregularities could be caused by loose parts in

the steam line, and that the loose parts could impair the proper functioning of safety systems.

Initially, the licensee believed that the newly installed baffle plates were the source of the loose

parts. However, after shutting down the unit and removing the reactor pressure vessel head,

the licensee discovered that a dryer cover plate on the outside of the steam dryer had broken

loose. The cover plate separates the steam exit region from the steam dryer and separator

space below. One piece of the dryer cover plate had fallen onto the separator, causing no

apparent damage. Another piece was found in the dryer, and a third piece had lodged in the A

main steam line flow venturi (upstream of the main steam isolation valves). Subsequent

inspections by the licensee discovered that several other pieces had been swept down the A

main steam line downstream of the main steam isolation valves into a turbine stop valve

strainer. Other than minor scratches and gouges to the main steam nozzle and piping, there

was no damage.

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The licensee stated that the preliminary results of scale model testing by General Electric

indicated that the failure of the plate was due to high cycle fatigue. This fatigue was attributed

to excessive vibration caused by the synchronization of the cover plate resonance frequency,

the nozzle chamber standing acoustic wave frequency, and the vortex shedding frequency. 

The first two frequencies depend on the construction and geometry of the dryer. The vortex

shedding frequency depends on the geometry and construction of the dryer and the flow rate of

the steam passing through the dryer area. The licensee concluded that the three frequencies

synchronized in a very narrow band of steam flow at or near the steam flow required to reach

full power under the power uprate.

Discussion

General Electric and the licensee did not foresee this phenomenon. Because of design and

manufacturing differences, General Electric believes that only a few BWRs are susceptible to

this event. Licensees should be aware of similar unanticipated effects from increasing flow,

power, or differential pressure associated with a major modification such as an extended power

uprate.

This information notice requires no specific action or written response. If you have any

questions about the information in this notice, please contact one of the technical contacts

listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

/RA/

William D. Beckner, Program Director

Operating Reactor Improvements Program

Division of Regulatory Improvement Programs

Office of Nuclear Reactor Regulation

Technical Contacts: Karla Stoedter, Region III Robert Caldwell, NRR

(309) 654-2227 (301) 415-1243

E-mail: kkb@nrc.gov E-mail: rkc1@nrc.gov

Carl Lyon, NRR

(301) 415-2296

E-mail: cfl@nrc.gov