ML20127L768
| ML20127L768 | |
| Person / Time | |
|---|---|
| Issue date: | 12/02/1992 |
| From: | Strosnider J Office of Nuclear Reactor Regulation |
| To: | Richardson J Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9301270307 | |
| Download: ML20127L768 (5) | |
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WASHINGTON, D.C. 20565 DEC 0 21992 MEMORANDUM FOR:
James E.
Richardson, Director Division of Engineering FROM:
Jack R.
Strosnider, Chief Materials and Chemical Engineering Branch Division of Engineering
SUBJECT:
SUMMARY
OF MEETING WITH NUMARC AND PWR OWNERS GROUPS CONCERNING PRIMARY WATER STRESS CORROSION CRACKING (PWSCC) OF CONTROL ROD DRIVE (CRD) PENETRATIONS AT REACTOR VESSEL HEAD On November 20, 1992, the staff met with members of NUMARC and PWR owners groups for an update of the status and the progress to-date of the PWR owners group's Inconel 600 program regarding the safety evaluaton and the inspection of control rod drive (CRD) penetrations at reactor vessel head.
NUMARC coordinated the owners group's presentation in thin meeting.
A list of meeting attendees is attached.
During this meeting the Westinghouse owners group (WOG) presented the results of a safety evaluation to justify continued operation of Westinghouse PWR plants with the potential for CRD penetration cracking.
The WOG presented safety evaluation is considered preliminary and the WOG is continuing studies to resolve possible conservatisms in the analyses, particularly with regard to postulated crack growth rates.
The WOG performed a bounding safety evaluation by considering the outer-most CRD vessel head penetrations in a 4-loop PWR plant.
The 4-loop plant was selected since the residual stresses resulting from the weld off-set are larger than for the other Westinghouse plants.
The safety evaluation covers four areas; stress analysis, crack propagation, leakage assessment and wastage assessment.
For stress analysis a 3-D finite element model was used to perform an elastic-plastic analysis.
The stress analysis results were that the tensile stresses are highly localized and that the ratio of axial stresses to hoop stresses would not support development of circumferential cracks.
The crack growth law used to predict crack growth was based on that developed by Peter Scott of Framatone.
The laboratory test data and field experience were used to establish the temperature effect on crack growth for Inconel 600 since the crack growth rate is highly temperature dependent in a pure water environment.
The results of the crack growth calculations were: (1) the crack growth above the weld would be very slow due to a decrease in stresses, (2) the crack i
orientation would continue to be axial or pessibly skewed hk i
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James E. Richardson 2
at about 30' and 40' for more centrally located penetrations.
The critical flaw size was estimated to be about 20 inches.
The leak rate for a one inch through wall crack above the attachment weld was calculated to be about 0.074 gpm, using a two-phase flow formulation.
The results of leak rate calculations showed that a through wall crack about 2 to 3 inches long would exceed the technical specification limit of 1 gpm for unidentified leakage.
The wastage effect on the structural integrity of the reactor vessel head was evaluated based on Combustion Engineering (CE) test results.
The CE tests were performed on mock-ups of pressurizer heater sleeve penetrations.
The tests measured the boric acid corrosion effect on the pressurizer shell material resulting from a leaking heater sleeve penetration.
The reported wastage rate was about 1.07 in' per year for the low alloy carbon steel shell material.
Based on this wastage rate, WOG's evaluation was that the reactor vessel head could withstand continuous leakage for 6 years before its thinning would result in violation of the ASME Code stress allowables.
In summary, WOG's cafety evaluation concluded the following:
(1) Axial cracking in the reator vessel CRD penetrations is not an immediate safety issue.
(2) Based on stress analysis, circumferential cracking is not likely to occur.
(3) Axial cracking is not expected to reach the critical flaw size without the detection of the leakage.
(4) Based on the wastage assessment, the reactor vessel head, even if degraded by leakage could operate for up to 6 years without repair.
The WOG response to the following four issues raised by NRC staff during the August 18, 1992 meeting were:
(1) Effect of grinding sono grinding was performed after welding on penetrations that the functional gage would not pass through.
Based on the Calvert Cliff experiences regarding the reaming effect on the stress corrosion cracking of pressurizer thermal sleeve penetrations, the effect of cold work applied after welding on crack propagation is not expected to be large.
The results of microhardness measurements also show that the grinding influence is limited to only 10 mils of the ID surface material.
l
James E. Richardson 3
l (2)
Flaw acceptance criteria since the calculated critical flaw size is very large, the WOG stated that the lea" age is expected to be detected long j
before the flaw reaches critical. size.
However, leakage of the primary-pressure boundary was not acceptable to the WOG,-
therefore, a proposed acceptable flaw criteria should_be established to prevent leaks.
The WOG goal was to_ avoid leakage for a period of 2 years to allow time'for planning-for repair.
The proposed flaw acceptance criteria is preliminary because an industry wide consensus needs to be developed.
(3)
NDE techniques The EPRI is coordinating the effortlof developing acceptable NDE techniques for inspecting _the CRD penetrations.
Because of the' limited access of the CRD penetrations, special NDE techniques are required to perform the_ required inspection.
WOG stated that time is required to evaluate the currently available NDE techniques regarding their capabilities and-accuracies in flaw detection and sizing.
(4)
Update of radiation exposure information The WOG provided additional exposure data pertaining to the inspection and repair performed at Ringhals 3.
The total exposure associated with the penetration inspection and repair were reported to be about 3,7 manrem and 0.7 manrem, respectively.
The low exposures for inspection resulted from the use of automated inspection equipment.
The staff stated with more overseas PWR plants finding cracked CRD penetrations, it is necssary to perform inspection at U.
S.
plants to reduce uncertainty,as to whether_or not-the U. S.
plants are cracked.
The staff acknowledged the benefit of 1
implementing a well thought out inspection plan using-demonstrated.NDE techniques to minimize exposure.
However, the-staff also indicated that it should not take too long to develop such a plan considering the current state of inspection and repair methods and_the rapid progress being made in this area.
NUMARC indicated that the effort in developing acceptable NDE
- techniques and proper tooling would be the critical-path-for-starting inspection of domestic plants._ Westinghouse _and EPRI's best estimates was that it would take about-one year to complete all the activities associated with this effort.
Based on this schedule, inspection could begin in early 1994.
NUMARC also
a James E. Richardson 4
identified approximate completion dates for the following activities:
(1) Final WOG safety evaluation - early 1993 (2) Developinent of crack growth confirmatory data and industry wide flaw acceptance criteria - November, 1993 (3) Development of remedial actions such as peening and nickel plating - preliminary results by fall, 1993 NUMARC agreed to submit a docketed WOG safety evaluation report for NRC staff review by January 4, 1993.
NUMARC will meet with NRC staff again in February 1993 to report the progress of the on-going activities and the status of owners groups' Inconel 600 program pertaining to-the cracking of CRD penetrations.
The staff requested NUMARC to provide a more detailed action plan, identifying the issues and strategy for inspection and repair as well as milestones and completion dates during the next meeting.
WYY Jack R.
Strosnider, Chief Materials and Chemical Engineering Branch Division of Engineering 4
Enclosure:
1.
A List of Meeting Attendees cc:
Partlow F. Miraglia T.
Murley W.
T.
Russell J.
B.
D.
Liaw C. Hinson C.
Serpan W.
Rosin /NUMARC S.
Burns /WOG J.
Taylor /B&WOG J. Hutchinson/CEOG 4
A.
Marion/NUMARC DISTRIBUTION Central Files EMCB RF DET RF WKoo RHermann JStrcnr der NRC & Local PDRs ru Dg,@pB DE:{ jM -
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WHK6d' RHermenn JRStrosnider 11/df/92 11/Jc /92 11/g /92 OFFICIAL RECORD COPY DOCUMENT NAME: G:\\koo\\numarc.whk
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> t ENCLOSURE 1 ATTENDANCE LIST
^
NOVEMBER 20, 1992 MEETING WITH NUMARC AND PWR OWNERS GROUPS CONCERNING PWSCC OF-INCONEL 600 l
NAME POSITION / AFFILIATION TELEPHONE NO.
William H.
Koo Senior Materials Engineer, (301)504-2706 NRC/NRR/DE/EMCB Robert Hermann Section Chief, NRC/NRR/EMCB (301)504-2768 1
Jim Richardson Director, Div. of Engg., NRR (301)504-2722 Don Wright BG&E/CEOG.lloy 600 (410)787-5518 Working Group Chairman R.
Scott Boggs FPL/CEOG Materials & Chemistry (407)694-4207 SC Chairman John J. Hutchinson FPL/CEOG STRG Committee (407)694-4211 Tom Spry CECO /WOG Inconel 600 (708)515-7268 Task Team Chairman Sid Burns SNC/ Chairman, WOG MTL SC (205)868-5061 Alex Marion NUMARC (202)872-1280 Morris Schreim NUMARC (202)872-1280 Steve Hunt Dominion Engineering (703)790-5544 Ken Yoon B&W Nuclear Technologies (804)385-3280 i
Jim Taylor B&W Nuclear Technologies (804)385-2817 Al Curtis Aptech Engineering Services (615)499-3777 4
l T.
D.
Walt Gen. Manager, Tech. Functions (503)556-5670 Warren Bamford Westinghouse Energy Systems (412)374-6515 l
Michael G.
Ball Westinghouse Energy Systems (412)374-6519 Pete Leonbrum ABB-CE (203)285-4737 Krish Rajan ABB-CE (203)752-2835 Mike Melton Arizona Public Service Co.
(602)340-4623 Brian Lippond MPR Associates, DC (703)519-0200 Hank Sepp Westinghouse (412)374-5282 l
Kevin Gravey Serch Licensing /Bechtel (301)417-3299 Lynn connor STS (301)652-2506 i
Gary Sherwood WOPCO (414)755-2321 Phil Hildebrandt Dominion Engg., Inc.
(703)790-5514 C.
P Lashkari PSE&G-(609)339-2754 Greg Calhoun-W Nuclear Services division (412)374-4244 Bruce Bevilacqua Engineer, Westinghouse (412)374-6345 Frank Ammiran EPRI NDE Center (704)S47-6100 Phil Richardson CEOG, Project /ABB (203)285-5643 4
John Galembush Westinghouse (412)374-5036 Mike Schoppman Florida Power & Light (301)652-2500 Gutti Rao' Westinghouse (412)374-6233-Hal Gustin' Structural Integrity Associates (408)978-8200 Alex Autcavage AG&E (716)771-2246 David Mishiewicz FPC (813)866-4414 David Whitaker Duke Power (704)382-7246 David Boyle Westinghouse (412)374-6690 Anothony Robinson BWNS (804)385-3290 4
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