ML20195J640
| ML20195J640 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 06/14/1999 |
| From: | Pulsifer R NRC (Affiliation Not Assigned) |
| To: | Kingsley O COMMONWEALTH EDISON CO. |
| References | |
| TAC-MA5367, NUDOCS 9906210064 | |
| Download: ML20195J640 (4) | |
Text
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4 UNITED STATES s
j NUCLEAR REGULATORY COMMISSION t
WASHINGTON D.C. 30806 0001
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June 14, 1999 Mr. Oliver D. Kingsley, President Nuclear GeneraOn Group Commonwealth edison Company Executive Towers West lil 1400 Opus Place, Suite 500
' Downers Grove, IL 60515
SUBJECT:
REVIEW OF REMEDIATION PLAN FOR QUAD CITIES, UNIT 1 IGSCC SUSCEPTlBLE WELDS (TAC NO. M/ 5367)
Dear Mr. Kingsley:
In a letter 6ted March 31,1999, (. cmmonwealth Edison Company (Comed or the licensee) transmitted to NRC a remediation plan for the welds that are susceptible to Intergranular Stress Corrosion Cracking (IGSCC) at Quad Cities Nuclear Power Station, Unit 1. Due to the detection of flaws in a number of 28-inch pipe welds treated by an induction heating stress improvement (lHSI) process during the last two refueling outages (Q1R14 and Q1R15), the licensee's remediation plan is focused on lHSI treated welds that have received a less than optimal stress improvement treatment or have exhibited inconsistent ultrasonic testing (UT) results and welds that have not been given a stress improved treatment. In summary, the licensee proposed to perform the following mitigation of the susceptible welds: (1) perform mechanical stress improvement process (MSIP) on two welds that had a marginal IHSI treatment, (2) perform automated UT on 14 IHSI treated welds that have an inconsistent UT
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history, (3) perform MSIP on seven Category D welds (non-resistant), (4) perform weld overlay repair on three Category F welds (cracked welds), and (5) apply noble metal chemistry (NMC)
'/o injection process to reduce the susceptibility of some components to IGSCC. The licensee had stated that the proposed NMC mitigation will be performed during the upcoming refueling outage (Q1R16), however, the licensee has subsequently performed and completed the NMC injection during planned outage Q1P02 on April 12,1999.
,g The staff has reviewed the licensee's remediation plan and has determined that the proposed remediation plan willincrease the IGSCC resistance of those affected welds. However, the staff has some concems regarding the proposed remedy plan. The staff renests that the licensee address the concems as discussed below and propose a plan to implement corrective Cfhl0$
actions.
(1)
In a letter dated January 26,1999, the licensee transmitted to the NRC the results of the root cause analysis of flaws in lHSI treated recirculation system piping welds. The results of the review for the effectiveness of IHSI treatment were shown in Table 4.2.4.2 of the referenced letter. The review results showed that the majority of the welds either received a limited treatment or ineffective treatment. As one of the corrective actions I
resulting from the root cause analysis, the licensee changed the IGSCC inspection schedule of 16 lHSI treated 28-inch pipe welds from Category C to Category D because these welds were considered to not have received an effective IHSI treatment The P
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9 inspection schedule for Category C welds is 100 percent every 10 years, and for Category D welds, it is all welds every two refueling cycles. However, the staff notes that in the proposed remediation plan (letter dated March 31,1999),15 of those 16 welds are now determined to have received an effective lHS1 treatment. As a result 12 of the 15 welds will retum to Category C and the remaining three welds will retum to Category C after receiving a satisfactory inspection during the upcoming outage (Q1R16). One of the 16 welds was determined to have a marginal IHSI treatment and will be mitigated with MSIP treatment. The licensee stated that the initial assessment results as presented in the January 26,1999, letter were based on limited data and resulted in an under-estimation of the IHSI effectiveness. Therefore, after performing a detailed assessment of the IHSI application parameters, the licensee concluded that for most welds, the IHSI treatment was effective. However, the licensee did not provide any detailed discussion regarding the differences in the data bases used in the two assessments of the effectiveness of lHSI treatment. Therefore, the staff requests that the licensee document the acceptance criteria and provide a detailed account of the assessment process and results on a weld-specific basis. Furthermore, the licensee i
should revise the January 29,1999, letter by updating the reported results of the IHSI treatment and discussing the reasons for the discrepancies of the two assessments of the effectiveness of lHSI treatment.
(2)
The staff does not agree with the licensee's proposal of not implementing any corrective action on weld 02AS-F8, since the licensee has not provided edequate justification for its proposed action. Weld 02AS-F8 is a weld connecting recirculation suction pipe to 1-0202-4A valve. As discussed below, the staff has concem regarding the IGSCC resistance of this weld. Therefore, the staff recommends that the inspection schedule of the subject weld 6hould be increased to that of Category D to ensure maintaining the structural integrity of the weld. The staff's recommendation is based on the following considerations.
(a)
The 1-0202 4A valve cast body is reported to have a low ferrite content. The test results showed that six places tested have ferrite number (FN) less than five and one place with FN between 5 to 10. In accordance with Generic Letter 88 01, cast austenitic stainless steel with FN less than 7.5 is considered to be not resistant to sensitization and IGSCC. The staff notes that the licensee's proposal depends, in part, on the industry experience that there have beon no reported IGSCC failure in cast austenitic stainless steel in this country.
However, the past industry experience can not be counted on to preclude the potential of IGSCC at a casting with low ferrite content, especially at the heat affected zone (HAZ) adjacent to a weld and at an area where weld repair had been performed.
(b)'
in Table 4.2.4.2 of the licensee's letter dated January 26,1999, the IHSI effectiveness of the pipe to valve weld 02AS-F8 was Ced as ineffective. The licensee did not discuss the reasons in its remediation plan that this is no longer a concem.
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O. Kingsley (c)
The staff notes that two lHSI treated welds,02AS-S6 and 02AS-F9, adjacent to weld 02AS-F8, were overlay repaired. Weld 02AS-S6 is on the pipe side of weld
- 02AS-F8 and was overlay repaired in 1996. The information regarding the effectiveness of lHSI treatment on this weld was not available. Weld 02AS-F9 is located down stream of the 1-202-4A valve and was overlay repaired during the last refueling outage in 1998. The staff notes that the effectiveness of lHSI treatment on weld 02AS-F9 was rated as ineffective in the referenced Table 4.2.4.2. Considering the cracking of the two adjacent welds and the lack of ferrite content in the adjoining valve body, there is a high likelihood that weld 02AS-F8 is susceptible to IGSCC similar to its adjacent welds.
(d)
The licensee's proposal depends, in part, on the contention that the casting failure at the Oskarsham plant in Sweden was unique because the subject casting is made of a different alloy (Cast 347) and the root cause of the failure is still under investigation. However, the staff understands that, in addition to lacking of ferrite content, the material chemistry of the subject casting is outside the specification and does not meet the required stabilizing elements over carbon content ratio. This would further increase its susceptibility to IGSCC and could cause the subject casting to behave similarly to that of non-stabilized stainless steel. Based on the above discussion, the staff believes that it is prudent to increase the inspection schedule of the subject weld to ensure maintaining the structuralintegrity of the weld.
Sincerely, Original Signed By Robert M. Pulsifer, Project Manager, Section 2 Project Directorate 111 Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-254 cc: See next page.
Distribution:
Docket File PUBLIC PDill r/f W. Bateman ACRS, T2E26
'OGC M. Ring, Rlli DOCUMENT NAME: G:\\PDill-2\\ quad \\MA5367ltr.wpd To receive's copy of this document,Indicefe'in e o px: "C" = Copy without encio ryk *E" = Copy with enclosures "N" - No copy OFFICE PM:LPDill 8MMill O. SC:1,Polll/-
1 NAME RPULSIFElpk)" dMDCftE AWENQLDLg -
DATE 06/ // /99 06/ (A b9 06NU /99 OFFICIAllRE ORD COPY k
i O. Kingsley Quad Cities Nuclear Power Station.
Commonwealth Edison Company Units 1 and 2 Commonwealth Edison Company Vice Prasident-Law and
. Quad Cities Station Manager Regulatory Affairs i
22710 206th Avenue North MidAmerican Energy Company Cordova, Illinois 61242 9740 One River Center Place j
106 E. Second Street U.S. Nuclear Regulatory Commission.
P.O. Box 4350 i
Quad Cities Resident inspectors Office Davenport, Iowa 52808 22712 206th Avenue N.
i Cordova, Illinois 61242 Mr. David Helwig i
Senior Vice President Chairman Commonwealth Edison Company Rock Island County Board Executive Towers West lli of Supervisors 1400 Opus Place, Suite 900 1504 3rd Avenue Downers Grovo, Illinois 60515 Rock Island County Office Bldg.
RockIsland, Illinois 61201 Mr. Gene H. Stanley PWR Vice President lilinois Department of Nuclear Safety Commonwealth Edison Company Office of Nuclear Facility Safety Exe:utive Towers West lll 1035 Outer Park Drive 1400 Opus Place, Suite 900 Springfield, Illinois 62704 Downers Grove, Illinois 60515 Regional Administrator Mr. Christopher Crane U.S. NRC, Region lli BWR Vice President 801 Warrenville Road Commonwealth Edison Company Lisle, Illinois 60532-4351 Executive Towers West 111 1400 Opus Place, Suite 900 William D. Leach Downers Grove, Illinois 60515 Manager-Nuclear MidAmerican Energy Company Commonwealth Edison Company
- 907 Walnut Street Site Vice President - Quad Cities P.O. Box 657 22710 206th Avenue North Des Moines, Iowa 50303 Cordova, Illinois 61242-9740 Mr. R. M. Krich..
Commonwealth Edison Company Vice Fresident - Regulatory Services Reg.' Affairs Manager-Quad Cities Commonwealth Edison Company 22710 206th Avenue N.
Executive Towers West lli Cordova, Illinois 61242-9740 1400 Opus Place, Suite 500 Downers Grove,lilinois 60515 Ms. Pamela B. Stroebel Senior Vice President and General Counsel Document Control Desk-Licensing Commonwealth Edison Company Commonwealth Edison Company P.O. Box 767 1400 Opus Place, Suite 400 Chicago, Illinois 60690-0767 Downers Grove, Illinois 60515 m