ML022490219
| ML022490219 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 09/17/2002 |
| From: | Wang A NRC/NRR/DLPM/LPD4 |
| To: | |
| Wang A, NRR/DLPM, 415-1445 | |
| References | |
| TAC MB4961 | |
| Download: ML022490219 (5) | |
Text
September 17, 2002 LICENSEE:
Omaha Public Power District (OPPD)
FACILITY:
Fort Calhoun Station, Unit 1
SUBJECT:
STEAM GENERATOR INSPECTION PHONE CALL
SUMMARY
On May 9 and May 17, 2002, the NRC staff participated in conference calls with Omaha Public Power District staff regarding the steam generator (SG) tube inspection activities at the Fort Calhoun Station (FCS).
The OPPD staff requested a call on May 9, 2002, to discuss an issue that the NRC staff had recently identified at another pressurized water reactor (PWR). The purpose of the call was to determine if this issue was applicable to FCS. The issue dealt with the question as to the appropriate extent of inspection with specialized probes (e.g., rotating pancake coil (RPC) probe) in the hot leg tubesheet when circumferential flaws were identified well below the expansion transition region. The NRC staffs position is if circumferential cracks are found in the upper 5-inch zone at the top-of-tubesheet (TTS), this is a clear indication for the potential for similar cracks to be present deeper within the thickness of the tubesheet. Therefore, if circumferential cracks are found in the upper 5-inch zone at the TTS, the staff interprets the technical specifications (TS) and 10 CFR Part 50, Appendix B, Criterion IX, to require the expansion of the inspections deep into the tubesheet where such cracks may potentially exist with probes capable of detecting such cracks.
The OPPD staff indicated that the typical RPC inspection scope in that region at FCS extended from five inches below to five inches above the hot leg TTS. OPPD stated that circumferential cracking had not been identified in this region at FCS. The NRC staff agreed that it is not unreasonable for OPPD to assume, at this time, a low potential for circumferential cracks deeper in the tubesheet, given the absence of such cracks in the upper portion of the tubesheet. Thus, the staff concluded that such inspections are not required at this time.
The NRC staff participated in a second conference call with OPPD staff on May 17, 2002, to discuss the ongoing SG inspection activities. The issues discussed included those listed in the enclosure to the letter requesting this conference call, which was sent to OPPD on May 13, 2002 (ADAMS Accession No. ML021290192). The licensee provided written material that is enclosed to this summary, in support of this call.
At the time of the call, the bobbin coil inspections were almost complete and RPC inspections were ongoing. Details of the licensees initial inspection scope and expansion criteria are described in the licensees written materials. Clarification of two of these topics were discussed during the conference call.
1.
The largest dents, up to 100 volts, are in the population of dents at vertical support strap
- 1. However, other dent locations (e.g., at eggcrates) also contain some large dents.
The dent reporting threshold is 3 volts. 2.
There are approximately 150 freespan dings per steam generator. The licensee used the eddy current low frequency screening analysis technique developed at another PWR that recently identified cracking in freespan dings.
OPPD stated that axial outside diameter stress corrosion cracking (ODSCC), axial primary water stress corrosion cracking (PWSCC) and circumferential ODSCC had been identified at FCS during the current outage.
OPPD stated that axial ODSCC located at the hot leg sludge pile, tube support structures (eggcrates and drilled support plates) and freespan locations is the primary defect mechanism at FCS. OPPD provided additional details on these indications as follows:
NUMBER OF AXIAL ODSCC INDICATIONS TABLE 1 SG A*
SG B*
Hot Leg Sludge Pile 8
6 Tube Support Structures 16 19 Freespan 7
4 These numbers vary slightly from those provided in the written material.
The eddy current analysis is ongoing and it is a fluid situation.
The axial indications in the hot leg sludge pile were located within one inch of the top-of-tubesheet.
The most significant indication identified was located in SG B at the 4th hot leg support. This location contained a small dent. This indication exceeded the in-situ pressure test screening criteria and will be in-situ pressure tested.
Circumferential ODSCC has also been identified during the current outage. Two indications are located at hot leg drilled support plates. Three indications are located at the hot leg expansion transition, which is the first time circumferential ODSCC has been identified at this location at FCS. None of these indications exceeded the in-situ pressure test screening criteria.
One axial PWSCC indication was identified in SG B at the 2nd hot leg eggcrate. This is the first time axial PWSCC has been identified at FCS. OPPD re-analyzed previously analyzed eddy current data from dented tube support intersections to ensure that all indications were properly identified and recorded. One hundred percent of the dents at the 1st and 2nd hot leg supports were scheduled for RPC testing, which was an expansion beyond the initial inspection scope.
The NRC staff did not identify any issues requiring followup, but requested that OPPD contact the NRC if the remaining inspections identified any significant degradation, a degradation mode or location other than that discussed during the conference call, or a failure of an in-situ pressure test.
/RA/
Alan B. Wang, Project Manager, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-285
Enclosure:
E-mail with Information on Steam Generators cc w/encl: See next page The NRC staff did not identify any issues requiring followup, but requested that OPPD contact the NRC if the remaining inspections identified any significant degradation, a degradation mode or location other than that discussed during the conference call, or a failure of an in-situ pressure test.
/RA/
Alan B. Wang, Project Manager, Section 2 Project Directorate IV Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-285
Enclosure:
E-mail with Information on Steam Generators cc w/encl: See next page DISTRIBUTION:
PUBLIC PDIV-2 Reading RidsNrrDlpm (JZwolinski/TMarsh)
RidsNrrDlpmLpdiv (WRuland)
RidsNrrPMAWang RidsNrrLAEPeyton RidsOgcRp RidsAcrsAcnwMailCenter RidsRegionIVMailCenter (CJohnson)
DMcCain SMorris, EDO JHannon ACCESSION NO.: ML022490219 NRC-001 OFFICE PDIV-2/PM PDIV-2/LA PDIV-2/SC NAME AWang EPeyton SDembek DATE 9/13/02 9/11/02 9/16/02 DOCUMENT NAME: C:\\ORPCheckout\\FileNET\\ML022490219.wpd OFFICIAL RECORD COPY
Ft. Calhoun Station, Unit 1 cc:
Winston & Strawn ATTN: James R. Curtiss, Esq.
1400 L Street, N.W.
Washington, DC 20005-3502 Chairman Washington County Board of Supervisors P.O. Box 466 Blair, NE 68008 Mr. John Kramer, Resident Inspector U.S. Nuclear Regulatory Commission Post Office Box 310 Fort Calhoun, NE 68023 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 Ms. Sue Semerera, Section Administrator Nebraska Health and Human Services Systems Division of Public Health Assurance Consumer Services Section 301 Cententiall Mall, South P. O. Box 95007 Lincoln, Nebraska 68509-5007 Mr. David J. Bannister Manager - Fort Calhoun Station Omaha Public Power District Fort Calhoun Station FC-1-1 Plant Post Office Box 550 Fort Calhoun, NE 68023-0550 Mr. John B. Herman Manager - Nuclear Licensing Omaha Public Power District Fort Calhoun Station FC-2-4 Adm.
Post Office Box 550 Fort Calhoun, NE 68023-0550 Mr. Richard P. Clemens Division Manager - Nuclear Assessments Omaha Public Power District Fort Calhoun Station P.O. Box 550 Fort Calhoun, Nebraska 68023-0550 Mr. Daniel K. McGhee Bureau of Radiological Health Iowa Department of Public Health 401 SW 7th Street Suite D Des Moines, IA 50309 Mr. R. T. Ridenoure Division Manager - Nuclear Operations Omaha Public Power District Fort Calhoun Station FC-2-4 Adm.
Post Office Box 550 Fort Calhoun, Nebraska 68023-0550