ML060730047
| ML060730047 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 03/13/2006 |
| From: | Harden P Nuclear Management Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML060730047 (14) | |
Text
Palisades Nuclear Plant Operated by Nuclear Management Company, LLC March 13,2006 Technical Specification 5.6.8 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Palisades Nuclear Plant Docket 50-255 License No. DPR-20 Res~onse to Request for Additional Information (RAI) on Steam Generator Tube lntearitv Assessment from the 2004 Refueling Outaae By letter dated October 4, 2005, Nuclear Management Company, LLC provided the Palisades Nuclear Plant (PNP) Steam Generator Tube Integrity Assessment Report for the 2004 refueling outage. By letter dated January 12,2006, the Nuclear Regulatory Commission (NRC) issued a RAI on the subject report. provides the RAl responses for the PNP.
Summaw of Commitments This letter contains no new commitments and no revisions to existing commitments.
Paul A. Harden Site Vice President, Palisades Nuclear Plant Nuclear Management Company, LLC Enciosures (3)
Administrator, Region Ill, USNRC Project Manager, Palisades, USNRC Resident Inspector, Palisades, USN RC 27780 Blue Star Memorial Highway Covert, Michigan 49043-9530 Telephone: 269.764.2000
ENCLOSURE 1 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION PALISADES NUCLEAR PLANT Nuclear Regulatory Commission (NRC) Request
- 1. In a conference call with the NRC staff on August 3 1, 2004, Nuclear Management Company (IVMC) indicated that rotating-pmbe inspections were to be performed on the square bend region of tubes surrounding tube R99C 140 in E-50B. Please discuss the results of these inspections.
Nuclear Management Company, LLC (NMC) Response 1 NMC discovered that the October 4, 2005 report is missing indications. Only 751 of 856 of the reported indications in Steam Generator E-50A and 681 of 899 of the reported indications in Steam Generator E-50B were provided to the NRC. This condition was entered into the NMC corrective action program, The missing indications for each SG are provided as Enclosure 2 and Enclosure 3.
During the 1999 refueling outage, in Steam Generator E-50B, one tube, R99 C140, had a 67% wear indication. This indication was evaluated and satisfied the structural integrity performance criterion for PNP steam generator tubing.
Rotating-probe inspections were performed on the square bend region of the tubes surrounding tube R99 C140 using a +Pointm exam. This was performed to ensure that no tube to tube contact was occurring with additional operation. 100% bobbin inspection was also performed on all active tubes in this steam generator in the 2004 refueling outage. In addition, all four adjacent tubes to tube R99 C140 were +PointTM tested from the top eggcrate support (05H) through vertical strap VSI, which included the entire square bend region on the hot leg side. Only one wear indication measuring 13% was reported from bobbin on an adjacent tube at the diagonal bar hot side (DBH). This was confirmed as wear with +Pointm testing.
NRC Request 3n page three of NMC's October 4, 2005, report, NMC indicated that it
'dentified possible looseparts indications during the inspection. Please jjscuss whether a foreign object search and retrieval (FQSAR) was 3erformed on each steam generator (SG), and whether the loose parts were
=moved. If the parts were not removed, or the locations were not visually
'nspected, please discuss the results of any evaluations performed to ensure
'hese parts (or suspected parts) would not result in a toss-of-tube-in fegrity for
'he period between inspections.
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NMC Response FOSAR operations were performed in each steam generator. Two objects that potentially could have impacted steam generator tube integrity were successfully removed from the steam generators. The remaining objects identified were either sufficiently small or of a non damaging nature (i.e., sludge collars, small sludge rocks, etc) such that tube wear is not expected. No tube wear was reported at the top of tubesheet for the 2004 refueling outage. All possible loose-part (PLP) locations identified and immediately surrounding tubes were
+Pointm tested. NO degradation was reported.
NRC Request Table 1 of NMC's October 4, 2005, report indicates that various signals were reported as distorted suppott indications, non-quantifiable indications and DNI.
Please clarify what indications are classified as DIVI.
NMC Response A DN1 is a dent or ding with an indication. All DNI indications from bobbin are
+PointTM tested. Table I below shows the indications classified as DMI.
NRC Request For the single axial indications, please supply the following information:
Discuss the Iocation of the flaw relative to the support structure (i-e., at support or in free span).
Discuss whether there were any dentddings at these locations. If so, provide the denuding voltage.
Discuss the severify of the #a ws, and whether they initiated from the inside or outside diameter, Discuss whether these indications were found with a bobbin or a +PointTM mil.
NMC Response
- 4.
- a.
See additional details in the Location column of Table 1 below.
- b.
See additional details in the Bobbin column of Table I below.
- c.
See additional details in the +PointTM column of Table 1 below.
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All six indications were initially identified with the bobbin probe as DNI, DSI or NQI. All six indications were subsequently +Pointm coil tested and characterized as SAI.
Table 1 Table 2 Three Letter NDE Codes 1 Three Letter 1 NDETerm I
SIG E-SOA E-50A E-50A E-50A E-50A E-50B Bobbin Flaw Type Voltage DinglDent Voltage NQI 0.47 No Ding DNI 0.44 volt 1.58 volt Ding DSI 1.07 volts No Ding MQI 0.20 volt No Ding NQI 0.17 volt No Ding DNI 0.67 volt
- 2. f 2 volt Din g I
DNI I Dent or Ding With Indication
+Pointm Flaw Type Voltage Mechanism SAI 0.28 volt ODSCC SAI 0.36 volt ODSCC SAI 0.43 volt ODSCC SAI 0.23 volt ODSCC SAI 0.19 volt ODSCC SAI 0.59 volt ODSCC Row I
55 78 115 80 78 Code DSI 1 NQl I I Non Quantifiable Indication Distorted Support Indication I
PLP 1 Possible Loose Part Col 28 79 110 149 SAI I Single Axial Indication Location 04H +22.66" Freespan DBH+8.97" Freespan in square bend 07C-0.8 1 "
Eggcrate Support TSH+15.54j1 Freespan 06H+1.98" Freespan VS5+16.27" Freespan in s g uare bend WAR 1 Wear I
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NRC Request A number of indications wem reported in SGs A and B. Please summake the mechanisms responsible for these indications (e-g., wear at vertical straps, wear at tube eggcrate supports, efc.). Please provide your eggcrate support thickness (i. e., axial extent), and discuss how your eddy-current measuremen fs are referenced. For example, does "2H + 0.85" indicate that the indication is 0.85-inch from the middle of the second hot-leg suppod? In addition, please discuss whether any of the indications near the eggcrate supports am in the h e span.
NMC Response The mechanisms responsible for these indications were attributable to wear damage at vertical straps, diagonal bars and tube eggcrate supports.
The eggcrate support thickness (axial dimension) is 2.00 inches; the individual straps comprising the eggcrate structure are 0.090 inch thick. The tube bundle is supporled by stainless steel eggcrate lattice type supporls comprised of horizontal eggcrate supports, vertical straps and diagonal bars.
Standard eddy current practice defines the center of a structure as 0.00 inch elevation. Therefore, an elevation report of 2H +0.85 represents an elevation 0.85 inch above the center of the structure.
The free span indication locations are shown in Table 1 above.
NRG Request Please discuss the case of the single volumetric indications identified in R21C62 and R2 7C 120 in SG E-50A. In addition, phase discuss the severity of these indications.
NMC Response There were two indications of wear (WAR) which were reported from the > 5.0 voIt dingldent +Pointm rotating coil program. These two tubes, R21 C62 and R27 C120 in SG E-50A, were reported to contain indications of WAR at the VS4 location, coincident with a dent signal. The +PointTM signals were suggestive of low-level structure wear, and were not overlapping with the dent signal. Due to the indicated shallow depth of the structure wear signal and influence of the dent, the bobbin coil did not identify the potential wear signal. A qualified wear depth sizing procedure does not exist for justification of continued operation, therefore these tubes were reported as single volumetric indication (SVI) and conservatively repaired by plugging.
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The two plugged WAR indications were sized using the +PointTM using both the tapered wear scars on the ASME standard and using an EPRl volumetric standard containing flaws that were much shorter than the actual wear in the tubes to determine a conservative estimate of the wear depth. Using both types of wear depth measurements from +PointTM, the depths measured between 12%
and 23%.
NRC Request Please confirm that all inspected tubes had adequate tube integrity at the time of NMC's last inspection.
NMC Response During the Palisades' Refueling Outage 17 (2004) steam generator tube inspection, no indications exceeding the structural integrity limits for either axial or circumferential degradation or wear (i.e., burst integrity > 3 times normal operating primary to secondary pressure differential across SG tubes) were detected. Therefore, no tubes were identified to contain eddy current indications that could potentially challenge the Reg. Guide 1.121 tube integrity recommendations. Based on the obsenred degradation and corresponding wear growth rates for Operational Cycle 17, the Palisades SGs are expected to satisfy the NEI 97-06 structural and leakage performance criteria at Operational Cycle 18.
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Enclosur~ 2 Additional Steam Generator E-50A Indications Page I of 3
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Page 3 of 3 Additional Steam Generator E-50B Indications Page 1 of 5
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