NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
November 16, 2000
|NRC INFORMATION NOTICE 2000-17,SUPPLEMENT 1:||CRACK IN WELD AREA OF REACTOR COOLANT SYSTEM HOT LEG
PIPING AT V. C. SUMMER|
All holders of operating licenses for nuclear power reactors except those who have ceased operations and have certified that fuel has been permanently removed from the reactor vessel.
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) supplement to tell addressees more about the crack-like indication found in a weld in the A loop hot leg pipe in the reactor coolant system (RCS) at the V. C. Summer Nuclear Station. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, no specific action or written response is required.
On October 7, 2000, during a containment inspection after entering a refueling outage, the licensee identified a large quantity of boron on the floor and protruding from the air boot around the "A" loop RCS hot leg pipe. The licensee performed a liquid penetrant test (PT) on October 12, 2000, which indicated the existence of a 4-inch long circumferential indication in the first weld between the reactor vessel nozzle and the "A" loop hot leg piping, approximately 3 feet from the reactor vessel. The NRC issued IN 2000-17 on October 18, 2000, to inform addressees of this information.
The licensee subsequently removed all fuel from the reactor vessel to perform more thorough examinations. Ultrasonic examination (UT) and eddy current testing from the inside diameter (ID) of the "A" loop hot leg piping did not confirm a flaw at the location of the circumferential indication found by the initial PT. An additional PT performed on the OD of the pipe on November 12, 2000, confirmed the original 4-inch long circumferential indication, and identified that other smaller circumferential indications were present.
The UT and eddy current testing did identify an indication at a different location. This indication is an axial crack-like indication, is approximately 2.7 inches long, and is located approximately 9 degrees counterclockwise from top dead center (TDC) of the weld. Based on the UT data, the axial crack-like indication begins at the ID and shows evidence of complete through-wall extension. Visual examination from the OD identified a small "weep hole" in the center of the weld at approximately the same circumferential location as the UT and eddy current indications. A PT of this area could not confirm that the axial crack-like indication was present on the OD because of slight leakage from the "weep hole." The UT and eddy current show that the crack-like indication extends from approximately the centerline of the weld toward the reactor nozzle. Final determination of the leakage path is not expected until metallographic examination of the subject weld is completed.
The NRC held a public meeting with the licensee on October 25, 2000 in the Region II offices in Atlanta, GA, to discuss the licensee's activities. A second public meeting will be held at the NRC Headquarters in Rockville, MD, on November 21, 2000, to discuss the licensee's activities to date and proposed actions.
The licensee has assembled a multi disciplinary team, including experts from Westinghouse, the Electric Power Research Institute (EPRI), and other industry experts, to conduct a root cause assessment and develop corrective actions. The NRC is reviewing the licensee efforts. At present, there have been no reports from any other licensee in the United States of similar cracking. Once the failure mechanism is understood, the staff will assess the generic applicability of the event, including the impacts on the in-service inspection (ISI) program and leak-before-break (LBB) analyses.
The NRC staff has received preliminary information that a foreign plant recently found crack indications in a reactor coolant hot leg weld during an in-service inspection. The NRC has also received preliminary information that another foreign plant found a weld crack indication at the interface of the reactor coolant system piping and the residual heat removal system piping. The staff has asked the foreign regulatory bodies for more information about these and has also asked other foreign regulatory bodies to provide information about any similar conditions.
The NRC has developed a Web page to keep the public informed of this event (http://www.nrc.gov/NRC/REACTOR/SUMMER/index.htm). Another supplement to this information notice will be issued when the root cause of the flaw and extent of condition are determined, or when new information becomes available. The NRC will assess the need for further generic action as new information becomes available.
This information notice requires no specific action or written response. If you have any questions about the information in this notice, please call or email one of
the technical contacts listed below or contact the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
|RA/Charles D. Petrone Acting For/
Ledyard B. Marsh, Chief
|Technical contacts:||Eric Benner, NRR
|Billy Crowley, Region II |
|William Koo, NRR
|Attachment:||List of Recently Issued NRC Information Notices|
(ADAMS Accession Number ML003769172)