UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, DC 20555-0001

January 27, 2003

NRC INFORMATION NOTICE 2003-03: PART 21 - INADEQUATELY STAKED

CAPSCREW RENDERS RESIDUAL HEAT

REMOVAL PUMP INOPERABLE

Addressees

All holders of operating licenses or construction permits for nuclear power reactors.

Purpose

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

addressees of recently observed inadequately staked capscrews on casing wear rings of

residual heat removal pumps. It is expected that recipients will review the information for

applicability to their facilities and consider actions, as appropriate, to avoid similar problems. 

However, suggestions in this information notice are not NRC requirements; therefore, no

specific action or written response is required.

Description of Circumstances

At Vogtle Electric Generating Plant (VEGP) Unit 2, on October 22, 2002, while the unit was

defueled, residual heat removal (RHR) pump A was started for dynamic fill and vent of the RHR

system. Moments later, the pump tripped. Personnel found that the pump shaft could not be

hand-turned. An investigation determined that a casing wear ring capscrew had come loose

and lodged between the impeller and the back casing wear ring. It was found that the pump

was last operated on October 11, 2002, when the unit was in Mode 6 (refueling). It is believed

that the capscrew came loose and lodged between the impeller and the back casing wear ring

as the pump was being placed into standby status on October 11, 2002. 

The root cause of this event was determined by the licensee to be the failure of the

manufacturer to properly stake the back casing wear ring capscrews. Each capscrew is

torqued and staked as a redundant measure to hold the capscrews in place. Although the back

casing wear rings had been staked, the staking was inadequate to prevent at least one of the

capscrews from backing out of the back casing wear ring after it had lost its torque and become

loose. RHR pump B was inspected and found to have a similar condition. Spare back casing

wear rings in the warehouse were also inspected and found to have inadequately staked

capscrews. Capscrews on the back casing rings of both RHR pumps were properly staked

prior to the pumps being returned to service. 

ML030240029
IN 2003-03

Page 2 of 2

Discussion

The improperly staked capscrews on both RHR pumps represented a condition that could have

prevented fulfilment of a safety function of a system needed to remove residual heat. There is

also the potential for loose parts to result in unpredictable damage to safety related

components for accident mitigation. 

Discussions with pump vendor personnel determined that there are approximately 60 of these

pumps in service in the nuclear industry, most with several years of service, and that this was

the first failure of this type. Additionally, 15 of these pumps, including the 4 pumps in VEGP

Units 1 & 2, had undergone a coupling modification in recent years that replaced the back

casing ring. However, it is not known if the back casing ring defect is limited to only those

casing rings that were procured for the modifications or if the original pump back casing rings

also have this defect. Nonetheless, this was the first failure of this type for any of the 60

pumps.

Vendor: Ingersoll-Rand

Model No: 8X20WDF

Back Casing Ring Part No: 6B

Capscrew No: 118C

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 project manager from the NRC’s Office of Nuclear Reactor

Regulation (NRR). 

/RA/

William D. Beckner, Program Director

Operating Reactor Improvements Program

Division of Regulatory Improvement Programs

Office of Nuclear Reactor Regulation

Technical contacts: D. Billings, NRR G. Bedi, NRR

 301-415-1175 301-415-1393

 E-mail: deb1@nrc.gov E-mail: gsb2@nrc.gov

J. Zeiler, Region 2

706-554-9901

E-mail: jxz@nrc.gov

Attachment: List of Recently Issued NRC Information Notices