ML17333A735
| ML17333A735 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 04/09/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17333A734 | List: |
| References | |
| NUDOCS 9701150020 | |
| Download: ML17333A735 (4) | |
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t UNITED STATES NUCLEAR REGULATORY COMMISSiON WASHINGTON, D.C. 20SR~1 SAFETY EVALUATION BY THE OFFIC OF NUCLEAR REACTOR REGULATION R ACTOR VESS L HEAD P NETRA IONS US OF AN ALT NAT V R PAIR T CHNI U
NDIANA M CH GAN POW R COMPANY A
OOK N
R T
N S
N CK T NOS. 50-315 AND 50-3 6
1.0 BACKGROUND
By letter dated March 12,
- 1996, Indiana Michigan Power Company (the licensee) submitted information on its plans to reinspect selected vessel head penetrations (VHPs) at Donald C.
Cook Nuclear Plant (D.C. Cook) during the current outage that began March 23, 1996.
The licensee plans to reinspect VHP 75 from D.C.
Cook Unit 2 because it contained indications that were identified during the 1994 refueling outage.
In addition, VHPs 74, 76, 77, and 78 from Unit 2 will be reinspected to ensure that no new indications are present.
If additional indications are identified, the inspection will be expanded and additional penetrations will be examined.
Any indications that exceed the acceptance criteria proposed by the Nuclear Energy Institute (NEI) and approved by the NRC with comments will be repaired.
- l. 1 SME Code Re uirements There are no requirements in the American Society of Mechanical Engineers (ASME) Code Section XI to inspect the inside diameter of the VHPs.
- Hence, there are no inservice -inspection acceptance standards in Section XI of the ASME Code.
Subparagraph IWA-3100(b) states that if acceptance standards for a particular component are not specified in Section XI, then flaws that exceed the original design specifications given in Section III can be used subject to review by the enforcement authority having jurisdiction at the plant site.
Proposed acceptance criteria are contained in Westinghouse WCAP-14024, "Inspection Plan Guidelines for Industry/Plant Inspection of Reactor Vessel Closure Head Penetration Tubes."
The acceptance criteria were reviewed and accepted with comments by the NRC staff in a letter from W.T. Russell to W. Rasin (NUMARC), "Safety Evaluation for Potential Reactor Vessel Head Adaptor Tube Cracking," November 19, 1993.
The NRC comments have been incorporated into WCAP-14024, Rev. l.
ENCLOSURE 9wosssooao 9so409 PDR ADQCK 050003l5 P
1.2 tin ho se Pl ns f r e ai of A
Westinghouse has developed repair techniques for flaws exceeding the acceptance criteria including one known as the embedded flaw repair method.
D.C.
Cook plans to utilize some of these techniques if flaws exceeding the acceptance criteria are discovered during the reinspection of VHPs.
The NRC staff has found that Westinghouse has submitted acceptable alternatives to the ASIDE Code in WCAP-14519, "RV Closure Head Penetration Tube ID Meld Overlay Repair,"
A Westinghouse Owners Group Program Report (HUHP-5017),
B.M.
Bevilacqua, C.C. Kim, E.S. Diaz, November 1995.
The NRC staff's safety evaluation of this report is contained in a letter to Virginia Electric and Power Company dated February 5, 1996.
The use of this alternative to the Code may be necessary if flaws exceeding the acceptance criteria are found in any of the VHPs.
1.3 D.C.
Cook Pro osed Alternative Meld Re air D.C.
Cook has proposed using the embedded flaw repair method as an alternative to the ASIDE Code requirements if repairs are required to the VHPs.
The flaws will be partially removed using electric discharge machining.
The excavation will be based on the depth of the measured flaw but will be no deeper than
- 0. 125 inch deeps A weld overlay will be performed to restore the tube wall inside diameter (ID) such that the VHP is reinspectable.
This repair may result in an embedded flaw if the flaw is deeper than 0. 125 inch.
After the weld is applied, the weld will be examined using dye penetrant and either eddy-current or UT [ultrasonic testing] to verify an acceptable weld.
D.C.
Cook is proposing to cut a window through the sleeve in sleeved VHPs and to apply a local, axial overlay over the cracked area.
All of the overlays described in MCAP-14519 were circumferentially applied 360'round the VHP.
However, the axial weld repair method has been qualified to Section IX of the Code.
None of the penetrations including the VHP 75 containing indications scheduled for the inspection during the upcoming outage are sleeved.
Three of the four VHPs in *the expansion group are sleeved VHPs.
2.0 VALUATION OF HE P
OPOS D ALTERNAT V MELD R PAIR The staff finds the proposed weld repair to be an acceptable alternative even though the flaw may not be completely removed.
The embedded flaw repair will provide sufficient wall thickness to the VHP such that leakage will not occur through the VHP wall during normal operation.
Code Case N-504-1, Alternative Rules Repair of Class I, 2, and 3 Austenitic Stainless Steel,"
has been approved by the NRC staff for the use of weld overlays over embedded flaws in stainless steel piping.
The proposed weld repair follows the guidelines in Code Case N-504-1 including the excavation of the flaw, the weld overlay, and the post-weld repair nondestructive evaluation.
The embedded flaw repair method has previously been approved for.the Virginia Electric and Power Company North Anna Nuclear Plant.
3.0 ONC US 0 S
The NRC staff concludes that the use of the embedded flaw repair method following the procedures and processes outlined in MCAP-14519 is an acceptable alternative to the ASIDE Code since it either restores the original wall thickness or isolates an embedded flaw from the cracking environment and restores the VHP ID thus providing an acceptable level of quality and safety.
The proposed alternative for the repair of flaws exceeding the acceptance criteria for the D.C.
Cook Power Station, Units 1 and 2 reactor VHPs is therefore authorized as requested pursuant to 10 CFR 50.55a(a)(3)(i).
Principal Contributor:
J. Davis Date:
April 9, 1996
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