ML041350122
| ML041350122 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 05/13/2004 |
| From: | Hartz L Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 04-272 | |
| Download: ML041350122 (9) | |
Text
VIRGINIA ELECTRIC A N D POWER COMPANY RICHMOND, VIRGINIA 23261 May 13, 2004 U.S. Nuclear Regulatory Commission Serial No.04-272 Attention: Document Control Desk NLOS/GDM R1 Washington, D.C. 20555 Docket No. 50-281 License No. DPR-37 VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNIT 2 ASME SECTION XI FOURTH INSERVICE INSPECTION (ISI) INTERVAL UPDATE RISK INFORMED INSERVICE INSPECTION (RI-ISI) PROGRAM Previously, Virginia Electric and Power Company (Dominion) submitted for your approval an ASME Section XI Class 1 RI-IS1 program for Surry Unit 2. This program was approved for the third IS1 interval in an NRC letter dated January 26, 2001.
Pursuant to 10 CFR 50.55a(a)(3)(i), Dominion requests that the Surry Unit 2 RI-IS1 program be approved for the ASME Section XI fourth IS1 interval. The ASME Section XI code of reference for the fourth interval is the 1998 Edition through the 2000 Addenda.
Consistent with the Westinghouse Owners Group (WOG) RI-IS1 methodology documented in WCAP-14572, Rev. 1-NP-A, new information has been incorporated into our RI-IS1 analysis as part of the living program. The new information was limited to changes to the Probabilistic Risk Assessment (PRA) model and deterministic information supplied to the expert panel since the last evaluation. Failure probability information for Surry Unit 2 remained unchanged during that time involved. (Note: Surry Unit 2 does not include Alloy-600 within the piping welds of the RI-IS1 program.)
The changes to the PRA model required re-perForming the risk evaluation; however, no previously identified low safety significant (LSS) segments were reclassified as high safety significant (HSS).One segment previously identified as HSS was reanalyzed as moderate safety significant (Risk Reduction Worth (RRW) <1.005 and >1.001) numerically, but was retained as HSS by the expert panel.
The expert panel concurred with the existing classifications, except for segments ECC-008, 009, 010, 01 1, 012, and 013. These segments are the ASME Class 1 portion of the safety injection system. The expert panel originally classified these segments as high safety significant (HSS) even though numerically they were low safety significant (LSS). The basis for this decision was a subjective concern about the possibility of the single check valve boundary failing (i.e., stuck-open) between the segments in question and the connecting HSS segments. However, as part of the review of the updated results, the expert panel noted that new testing confirming check valve closure was now required when the check valves in question were flowed. Because of the new testing requirement for the check valves, the expert panel voted unanimously to return the classification of these segments to LSS in agreement with the numerical results. The expert panel did retain the six volumetric examinations associated with these segments
SN 04-272 Docket No. 50-281 Page 2 o f 3 to maintain the original selection number. As such, the number and location of the volumetric examinations between the intervals remains the same for Surry Unit 2. The new LSS classification for the segments above eliminates six visual VT-2 exams previously required for the RI-IS1 program; however, Code pressure testing is still being performed.
The change-in-risk analysis was also re-performed in accordance with WCAP-14572 to compare the original Section XI program with the revised fourth interval RI-IS1 program.
One segment was identified as needing to be added to maintain overall risk neutrality.
This resulted in the requirement that one additional visual VT-2 exam be performed.
The attached Table 1 provides more detailed information regarding the RI-IS1 program and changes between the intervals.
Additionally, Relief Request R-1 was approved per 10 CFR50.55a(a)(3)(ii) in the third IS1 interval by the letter referenced above. (Note: The branch connection addition was approved by letter dated September 23, 2003). This relief request represented a deviation from the WOG methodology with regard to inspection of socket welds and their branch connections. The relief request is again being requested pursuant to 10 CFR 50.55a(a)(3)(ii) for the fourth IS1 interval and is attached as Relief Request R-1.
The changes in the RI-IS1 program for Surry Unit 2 between the third and fourth IS1 intervals are considered minor. We do not believe that a detailed NRC review of the RI-IS1 program is necessary, since the evaluation of the third IS1 interval program would still be applicable to the fourth IS1 interval as supporting acceptable levels of quality and safety.
If you have any questions or require additional information, please contact Mr. Gary D. Miller at (804) 273-2771.
Very truly yours, Leslie N. Hartz W Vice President-Nuclear Engineering Attachments Commitments made by this letter: None
SN 04-272 Docket No. 50-281 Page 3 o f 3 cc: U.S. Nuclear Regulatory Commission Region I1 Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23 T85 Atlanta, GA 30303-3415 Mr. S. R. Monarque U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 8H12 Rockville, MD 20852 Mr. G. J. McCoy NRC Senior Resident Inspector Surry Power Station Mr. R. A. Smith Authorized Nuclear Inspector Surry Power Station
Serial No.04-272 Docket 50-281 Attachment 1 TABLE 1 STRUCTURAL ELEMENT SELECTION RESULTS AND COMPARISON TO ASME SECTION XI 1989 EDITION REQUIREMENTS ASME Section XI Fourth IS1 Interval Update Risk Informed lnservice Inspection (RI-ISI) Proaram SURRY POWER STATION UNIT 2 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)
Serial No.04-272 Docket 50-281 Attachment 1 Table - 1 STRUCTURAL ELEMENT SELECTION RESULTS AND COMPARISON TO ASME SECTION XI 1989 ED1 ON REQUlREh iNTS System Number of Degradation Class ASME Weld Count' Previous 3rd Interval RI-IS1 4'h Interval RI-I3 High Safety Mechanism(s) Code ASME XI Significant Category
-=xamination Segments
[No. of HSS
-- /ohmetric &
Butt Sockel Surface or SES \lumber o SES \lumber oi in surface Only Matrix Exam Matrix Exam Augmented Region locations Region Locations Program /
Total No. of Segments in Augmented Program) -
ACC 0 TF Class 1 B-J 34 0 10 0 0 CH TF. VF Class 1 B-J
-83 182 70 la 6a la 6" ECC TF, Class 1 B-J 70 157 45 1a,l b 7b+ 18' 1a,l b,3 lb+12'+
Stratification 6d RC 35(3/3) TF, VF, Class 1 B-F 18 0 18 la, lb, 2 6' 1a,l b,2 6' Striping/ B-J 246 285 166 12a+1b+ 12" + 2b +
Stratification, 26' 26' SCC -
~
RH 0 TF Class 1 B-J 19 0 4 0 0 Class 1 B-F 18 0 18 6' 6' B-J 452 624 295 18a+ 8b + 18" + 3b+
TOTAL 48 (3/3) -- 44' 38' + 6d Total 470 624 313 18a + 8b + 18" + 3b+
- 50' 44' + 6d
Serial No.04-272 Docket 50-281 Attachment 1 Notes:
- 1)Section XI nonexempt welds only (> 1 inch) a) VT-2 examination of segment due to failure mechanism postulated as vibration fatigue.
b) Scheduled VT-2 examination of segment socket welds.
c) HSS scheduled volumetric examinations.
d) LSS scheduled volumetric examinations.
ACC - Safety injection piping associated with the accumulators CH -Chemical and Volume Control piping ECC - High pressure and low pressure safety injection common header piping RC - Reactor coolant piping RH - Residual Heat Removal piping TF - Thermal Fatigue (normal heat-up and cool-down, with and without snubber malfunctions)
VF - Vibratory Fatigue SCC - Stress Corrosion Cracking
Serial No.04-272 Docket 50-281 Attachment 2 Relief Reauest R-I ASME Section XI Fourth IS1 Interval Update Risk Informed lnservice Inspection Proqram SURRY POWER STATION UNIT 2 VIRGINIA ELECTRIC AND POWER COMPANY (DOMIN10N)
Serial No.04-272 Docket 50-281 Attachment 2 Relief Request R-1 Surry Unit 2 I. Identification of Components ASME Class 1 socket weld connections and their branch connections, nominal pipe size 2 inches (NPS 2) and smaller, identified as being high safety significant (HSS).
II. Impractical Reauirements Surry Unit 2 has previously received NRC approval to use an alternative Class 1 RI-IS1 program per WCAP-14572, Rev. 1-NP-A, (WCAP) in lieu of ASME Section XI requirements for piping (Categories B-F and B-J). WCAP-14572, Rev. 1-NP-A, Table 4.1 -1, requires examination of HSS components based upon the postulated failure mechanism for the element of piping being examined. This requirement does not consider the geometric limitations imposed by socket welds and their branch connections, NPS 2 and smaller, when volumetric examinations are specified. As such, the current WCAP examination requirement is considered impractical.
Ill. Basis for Relief Pursuant to WCAP-14572, Rev. 1-NP-A, certain socket weld connections and their branch connections, NPS 2 and smaller, have been identified as HSS and require volumetric examination for their postulated failure mechanism. Currently only 3 piping segments have been identified for Surry Unit 2. These volumetric examinations are associated with a postulated thermal fatigue damage mechanism, which is selected as the default mechanism for HSS segments when there is no assumed active mechanism or other postulated mechanism occurring.
Performing a volumetric examination on a socket weld connection or the branch connection, NPS 2 and smaller, provides little or no benefit, due to limitations imposed by the joint configuration and the smaller pipe size. The socket welds are partial penetration welds and the branch connections may be partial or full penetration welds. These weld designs and pipe sizes under current Category B-J requirements would only require a surface examination.
The only thermal fatigue that could credibly affect the subject piping would be the low cycle fatigue previously considered in the design. Low cycle fatigue has a very low probability of causing cracking. Furthermore, even if cracking were to occur, it would most likely originate on the inside diameter of the pipe. In addition, the Class 1 RI-IS1 program did not identify any locations susceptible to external chloride stress corrosion cracking. The Class 1 piping is not located in areas that are subject to an aggressive environment that would promote external chloride stress corrosion cracking (i-e., there are very low levels of chloride (if any) and moisture is not typically present on the pipe). No other externally driven
Serial No.04-272 Docket 50-281 Attachment 2 damage mechanism can reasonably be postulated for this piping. Cosequently, a surface exam would be of negligible benefit.
The ASME Code Committee has recognized the problem this relief request is addressing and has substituted the VT-2 examination method for all damage mechanisms on socket weld connections selected as HSS. ASME Code Case N-577-1 has been issued and provides the requested substitution in Note 12 of Table 1 of the Code Case. Incorporation of the branch connection, NPS 2 and smaller, into the Code Case is now under consideration by the committee for similar size and joint configuration limitation reasons.
The industry is evaluating volumetric examination methods for socket welded connections for certain damage mechanisms. Dominion is following this effort and will address these developments as part of the WCAP-14572 living program process, if applicable.
Performing volumetric examinations on socket weld connections or their branch connections, NPS 2 and smaller, would result in unusual difficulty without providing any meaningful results or compensating increase in the level of quality and safety. Therefore, relief is requested per 10 CFR 50.55a(a)(3)(ii).
Substituting a VT-2 examination as an alternative on a refueling outage frequency for these locations ensures reasonable assurance of component integrity.
IV. Proposed Alternative A VT-2 exam will be performed on the subject socket weld connections and their branch connections, NPS 2 and smaller, on a refueling outage frequency while the component is pressurized.
The VT-2 examination and pressure test required by Relief Request R-1 will conform to the requirements of ASME Section XI IWA-2000 & 5000 of the 1998 Edition through 2000 Addenda. Additionally, NRC approved Code Case N-498-1 (or later revision as approved by the NRC) may be applied for the end of interval testing.
The following pressure test hold times will apply:
0 Insulated components - 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> minimum at test pressure 0 Non-insulated components - 10 minutes minimum at test pressure A similar relief request was recently approved for Surry Unit 1 (3rdIS1 Interval) in an NRC letter to Virginia Electric and Power Company dated September 23, 2003. This precedent is directly applicable to Surry Unit 2.