ML20211P893
| ML20211P893 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 10/14/1997 |
| From: | Dennig R NRC (Affiliation Not Assigned) |
| To: | Gambhir S OMAHA PUBLIC POWER DISTRICT |
| References | |
| NUDOCS 9710220024 | |
| Download: ML20211P893 (7) | |
Text
_ _ _
October 14, 1997
- Mr. S. K. Cambhir Division Manager = Engineering and Operations Support Omaha Public Power District Fort Calhoun Station FC 2-4 Adm.
Post Office Box 399 Hwy. 75 North of Fort Calhoun Fort Calhoun, Nebraska 68023-0399
SUBJECT:
REQUEST FOR A TECHNICAL REVIEW OF A DRAFT INFORMATION NOTICE REGARDING EXTRACTION STEAM PIPE RUPTURE AT THE FORT CALHOUN STATION Dear Mr. Gambhir.
The U.S. Nuclear Regulatory Commission is planning to issue an information notice (IN) discussing a potential generic problem related to the rupture in the extraction steam piping on April 21,1997, at the Fort Calhoun Station. We ask that you review the enclosed draft of that IN to enst:re the technical information regarding the event is accurate. Your cooperation in this matter is appraciated. Please retum any comrnents you may have as soon as possible. A copy of this request and your response will be placed in the Public Document Room for review by the public. Your response should be malled to:
U.S. Nuclear Regulatory Commission ATTN: Thomas Greene Mall STOP: 011E4 Washington, D.C. 20555-0001 Please address any questions you may have on this matter to Thomas Greene of my staff.
Mr. Greene can be reached at 301415-1175. If no comments are received by the close of business on October 22,1997, we will assume the technical information in the notice is correct.
Sincerely.
Original signed by Robert L. Dennig, Chief Events Assessment and Generic Communications Section Events Assessment, Generic Communications,
,.1 c2d and SpecialInspections Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation Docket No. 50-285 rmn ; - - - _y incicsure: Draft Information Notice cc w/ encl: See next page DISTRIBUTION:
Docket Files PUBLIC PD42 Rdg/ File PECB R/F JWRoe SARichards RLDennig TAGreene RWharton DOCUMENT NAME: G:\\ TAG \\LETCHKWK.FTC To receive a copy of tNo document indice'e in ihe bor C= Copy wAo attachmenUenclosure E= Copy wth attachmenUenclosure N = No copy OFFICE PECB
- EM:PD42 SC:PEchb C:PECB b
NAME TGreene S arton RDenni SRichards YV DATE 10/?/97 10A0 /97 10b97 10//(/97 OFFICIAL RECORD COPY 9710220024 971014 11 l
l l!Il l! l lIll l l!ll ll ll t
PDR ADOCK 05000285 I
I i
G PDR
- * * '
- c *
- c,
- Mr. S. K. Gambhir Odober M,1997 Division Manager. Engineering and Operations Support Omaha Publ.c Power District Fort Calhoun Station FC 2-4 Adm.
Post Ofnee Box 399 Hwy. 75 North of Fort Calhoun Fort Calhoun, Nebraska 68023-0399
SUBJECT:
REQUEST FOR A TECHNICAL REVIEW OF A DRAFT INFORMATION NOTICE REGARDING EXTRACTION STEAM PIPE RUPTURE AT THE FORT CALHOUN STATION Dear Mr. Gambhlr.
The U.S. Nuclear Regulatory Commission is planning to issue an information notice (lN) discussing a potential geno 61c problem related to the rupture in the extraction steam piping on April 21,1997, at the Fort Calhoun Station. We ask that you review the enclosed draft of that IN to ensure the technical information regarding the event is accurate. Your cooperation in this matter is appreciated. Pleas.
returre any comments you rur, have as soon as possible. A copy of this request and your response will be placed in the Public Document Room for review by the public. Your response should be mailed to:
U.S. Nuclear Regulatory Commission ATTN: Thomas Greene Mall STOP: 0-11E4 Washington D.C. 20555-0001 Please address any questions you may have on this matter to Thomas Greene of my staff.
Mr. Greene can be reached at 301-4151175. If no comments are received by the close of business on October 22,1997, we will assume the technical information in the notice is correct.
Sincerely, Original signed by Robert L. Dennig, Chief Events Assessment and Generic Communications Section Events Assessment, Generic Communications, and Special Inspet.tions Branch -
Division of Reactor Program Management Office of Nuclear Reactor Regulation Docket No. 50 285
Enclosure:
Draft Information Notice cc w/enci: See next page DISTRIBUTION:
Docket Files PUBLIC PD42 Rdg/ File PECB R/F JWRoe CARichards RLDennig -
TAGreene RWharton DOCUMENT NAME: G:\\ TAG \\LETCHKWK.FTC To r.ce a copy of th document. indicate in the box c copy wie attachment / enclosure E= Copy wth attachment! enclosure N = No copy OFFICE PECB
,P_M PD42 SC:PECb C:PECB b
NAME TGreene " (29 hharton RDenbg SR. chards M'
DATE 10/?/97 10 # /97-10/b97 10/T/97 OFFICIAL RECORD COPY
O Hr. S. K. Gambhir 2-CC:
Winston & Strawn ATTN: Perry D. Robinson. Esq.
1400 L Street, N.W.
Washington. DC 20005-3502 Mr. Jack Jensen. Chairman Washington County Board of Supervisors Blair. Nebraska 68008 Mr. Wayne Walker Resident inspector U.S. Nuclear Regulatory Connission Post Office Box 309 Fort Calhoun. Nebraska 68023 Regional Administrator. Region IV U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive. Suite 1000 Arlington. Texas 76011 Ms. Cheryl Rodgers. LLRW Prog am Manager Environmental Protection Section Nebraska Department of Health 301 Centennial Hall. South P.O. Box 95007 Lincoln. Nebraska 68509 5007 Mr. James W. Chase Manager Fort Calhoun Station Post Office Box 399 Fort Calhoun. Nebraska 68023 Mr. James W. Tills Manager - Nuclear Licensing Omaha Public Power District fort Calhoun Station FC 2-4 *Am.
Post Office Box 399 Hwy. 75 - North of Fort Calhoun Fort Calhoun. Nebraska 68023 0399 I
i l
f*
e ~ :
,,e
{ h $i. 'i "d
l UNITED STATES NUCLEAR REGULATORY COMMISSION l
OFFICE OF NUCLEAR REACTOR REGULATION V!ASHINGTON, D C. 20555-0001 October xx,1997 NRC INFORMATION f('>Ti% E/-XX. :4UPTURE lN EXTRACTION STEAM PIPING AS A RESULT OF FLOW-ACCE' ERATED CORROSION Addressees All holders of operating licenses for nuclear power reactors except those who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor v;stel Purpose The U S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addresseJs to potential genene problems related to the occurrence end prediction of flow-accelerated corrosion (FAC) in extraction steam systems. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropnate, to avoid similar problems. Hoveever, suggestions contained in this information notice are not NRC requirements; therefore, no spxific action or wntten response is lequired.
Desenotion c' Circumstances On Apnl 21,1997, a catassophic rupture of a large radius (sweep) elbow occurred in the fourth stage extraction steam piping at the Fort Calhoun Station, a nuclear power plant. The rupture occurred in a carbon steel piping system that was being monitored by the licensee's erosion / corrosion control program. The component containing the break was being monitored via a FAC degradation predictive methodology rather than through non-destrur.tive examination techniques Discussion On Apnl 21,1997, Omcha Public rower Distnct's Fort Calhoun Station, while operating at 100-perceat power, expenenced an approximate 0.56 m (6 ft') rupture of a 30.5-centreter 2
(12-inch)-diameter sweeo el' cr/ in the fourth-stage extraction steam piping. The operator, o
upon hearing steam noise and observing steam nsing from the turbina deck, believed that a steam line had broken and manually scrammed the reactor. As a precautien, emergency boration was initiated The main turbine tripped automatically as a iesult of the reactor inp The turbine trip had the effect of isolating the rupture Plant systems and related parameters responded as expected during the event.
The steam-line rupture damaged a non safety related electricalload center in the vicinity of the pipe break Additionally, collateral damage was expenenced in ceveral cable trays ana pipe hangers, and insulation containing asbestos was blown throughout the turbine building Certain portions of the fire protection systern actuated in response to fusible knks in the Up EK. ; P
- .G. Q~f r ri
9 IN 97 XX October XX,1997 Page 2 of 4 sprinkler heads melting because of high temperature. Because there were no personnelin the immediate vicinity of the rupture, no one was injured. The fourth stage extraction steam system emanates from the outlet of the high-pressure turbine and preheats the feecWater heaters. The design operating conditions in the piping are 2068 kilopascal gauge (300 psig) 4 and 218'C (425'F), with a steam quality of approximately 92 percent. The piping is fabncated of A 106B carbon steel and has a nominal wall thickness of 0.953 centimeter (0.375 inch). The Scensee's preliminary root cause assessment attributed the failure to FAC in the extraction steam piping. Initialindications of degradation in the extraction stearn line at the Fort Calhoun facility were first discovoreri in 1985, when the furthest upstream (short-radius) elbow was replaced because of a pinhole leak. At that time, the next upstream (sweep) elbow was also replaced as a result of observed degradation.
The failed piping was modeled in the licensee's erosion / corrosion program, but the actual wall thickness had never been measured by nondestructive examination techniques. Rather, the licensee had relied on a predictive methodology (CHECWORKS) to predict the condition d
i of the sweep elbows in the extraction steam systems. The CHECWORKS methodology had predicted a lower wear rate for the sweep elbows relative to other potential wear locations I
within the fourth-stage extraction steam system.
As a result of the rupture, the licensee inspected all other sweep elbows that had not been previously inspected. The licensee determined that the measured wall thickness (0.112 centimeter (0.044 inch)) of the furthest downstream sweep elbow in the fourth stage extraction piping was also significantly below minimum wall thickness (0.272 centimeter (0.107 inch)) specified by code requirements and had to be replaced. Additionally, another sweep cibow in the fourth stage extraction piping was also replaced because thu wear (measured wall thickness of 0.394 centimeter (0.155 inch)) was considered excessive, even though it was not below the minimum al;owable thickness The sweep elbows in the second-stage extraction steam system were found to have acceptable wall-thickness readings.
Following the event, it was discovered that the CHECWORKS predictions (as modeled by the licensee) for the fourth-stage extraction steam system were not consistent with the actual observed wear rates as measured following the event In particular, the components whose relative wear rates were predicted to be the highest for th's specific application (i.e., short-radius elbows and tees) did not exhibit signi'icant actual measured wear. Conversely, the larger radius elbows (which had been predicted to exhibit a lower relative wear rate) were shown to be weanng at rates higher than predicted for this specific application. It appears that the licensee did not fully recognize the implications of these anomalies immediately.
Subsequent investigations by the licensee determined that the lower than-expected wear rate for at least one location may have been caused by the licensee's providing incorrect wear data for one short-radius elbow. The wear was underpredicted because the licensee failed to consider that the elbow had been replaced in 1985. When inspection data were recorded in 1987, it we assuraed that the wear on this elbow represented 14 years of service rather than the actual 2 years of service. The use of the incorrect value for wear had the effect of biasing the "line correction factors" in the CHECWORKS model. Thus, a lower than-actual relative wear rate would have been predicted for all components in the system.
l IN 97 XX October XX,1997 Q
Page 3 of 4 This event revealed the importance of incorporating accurate plant specific data from nondestructive examination programs for use in predictive methodologies. Additionally, insights were gained about the importance of thoroughly investigating unanticipated or anomalous results when using predictive modeling approaches.
Related Genene Communications in NRC Bulletin 87-01, " Thinning of Pipe Walls in Nuclear Power Plants," July 9,1987, the staff asked licensees and applicants to inform the NRC about their programs for monitonng the wall thickness of carbon steel piping (Accession 8707020018).
In NRC Generic Letter 89 ^9, " Erosion / Corrosion Irduced Pipe Wall Thinning," May 2,1989, the staff asked licensees and applicants to implement long-term erosion / corrosion monitoring programs (Accession 8905040276).
Additionally, the following NRC information notices (ins) provide information about similar events related to FAC:
IN 82 22, " Failures in Turbine Exhaust Lines," July 9,1982 (Accession 8204210392).
IN 86106, "Feedwater Line Break " December 16,1986 (Accession 8612160250)
IN 87 36, "Significant Unexpected Erosion of Feedwater Lines," August 4,1987 (Accession 8707290264).
IN 8817, " Summary of Responses to NRC Bulletin 87-01, ' Thinning of Pipe Walls in Nuclear Power Plants,'" Apnl 22,1988 (Accession 8804180039).
IN 89 53, " Rupture of Extraction Steam Line on High Pressure Turbine," June 13.1989 (Accession 8906070273).
IN 91 18. "High Energy Pipe Failures Caused by Wall Thinning," March 12,1991 (Accession 9103060153).
IN 91 18. Supplement 1. "High Energy Pipe Failures Caused by Wall Thinning, December 18,1991 (Accession 9112120218).
IN 93-21 " Summary of NRC Staff Observations Compiled Dunng Engineenng Audits or Inspections of Licensee Erosion / Corrosion Programs," March 25,1993 (Accession 9303190051).
IN 9511. " Failure of Condensate Piping Because of Erosion / Corrosion at a Flow-Straightening Device " February 24,1995 (Accession 9502210050).
DRAFI
IN 97 XX October XX,1997 Page 4 of 4 This information notice requires no specific action or written response. However, recipients are reminded that they are required to consider industry-wide operating expenence (including NRC information notices) where practical, when se';ing goals and performing penodic evaluations under Section 50.65, " Requirement for monitonng the effectiveness of maintenance at nuclear power plants," to Part 50 of Title 10 of the Code of Federal Reaulations. If you have any questions about the information in this notice, please contact the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
Jack W. Roe, Acting Director D. vision of Reactor Program Management Office of Nuclear Reactor Regulation Technical contact: J. Shackelford, RIV 817-860 8144 DRAR E-mail jls2@nre gov Attachment-List of Recently Issued NRC Information Notices