ML20248B891

Safety Evaluation Concluding That IGSCC Insp Scope for Class 1 Piping Meets NRC Requirements & Guidelines of Generic Ltr 84-11

ML20248B891
Person / Time
Site:	Quad Cities
Issue date:	06/06/1989
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20248B883	List: ML20248B879 ML20248B891
References
GL-84-11, NUDOCS 8906090198
Download: ML20248B891 (5)

Text

b, envy t-k, UNITED STATES

~j- g NUCLEAR REGULATORY COMMISSION n  : j. WASHING 10N, D. C. 20555

+

Q.....f ENCLOSURE 1'

i SAFETY EVALUATION.BY.THE.0FFICE.0F NUCLEAR. REACTOR. REGULATION i COMMONWEALTH EDISON.C0tdPANY L QUAD CITIES. UNIT.1 DOCKET.NO. 50-254 1.0~ INTRODUCTION The staff has reviewed the licensee's submittals dated June 1, November 26, December 10,17, and 18,1987 and May 31, 1988 which included descriptions of-inspection results, intergranular stress corrosion cracking (IGSCC) mitigation,

. flaw evaluations, and overlay repairs to support the continued _ operation of Quad Cities Unit 1, in its present configuration for one 18-month fuel cycle.

Ddring the Unit 11987 refuel outage,146 41 ass 1 piping welds susceptible to IGSCC in various austenitic stainless steel piping systems were ultrasonically examined. The results of the inspection showed that f, law indications were

-observed in fourteen welds - with seven in the recirculation system, one in the low pressure coolant' injection (LPCI) system and six in the core spray system..

Of these. newly flawed welds, thirteen were reinforced with weld overlay and one was mitigated with mechanical stress improvement process (MSIP). Twelve previously overlay repaired welds were upgraded to meet the standard design requirements and their surface finishes were improved to facilitate ultrasonic inspection. New flaws were found in a previously unrepaired 28-inch suction

. pipe-to-elbow welo (02BS-59) in the recirculation piping system and the existing flaws were also reported to have grown in sizes. This weld was overlay repaired during this outage. Mechanical stress improvement process was applied to 38 welds in the LPCI and core spray piping systems as a mitigation for IGSCC.

2.0 DISCUSSION 2.1 INSPECTION The licensee reported that there are 232 Class 1 piping welds in Quad Cities, Unit.1 subject to IGSCC inspection. One-hundred forty-six welds were inspected during the 1987 refuel outage. The original sample size of 53 welds was determined in accordance with the guidelines in Generic Letter 84-11, and was expanded to 146 welos after flaws were found in the original and expanded samples.

The staff concludes t' hat the inspection scope for Class 1 piping meets the staff requirements and the guidelines in Generic Letter 84-11 since more than 60% of the IGSCC susceptible welds were inspected during this outage. The staff also concludes that the sample expansion is margin 61 but acceptable because all but j four 28-inch recirculation welds with piping sizes similar to the flawed welds '

were inspected. The staff agrees with the licensee's justification that 890609019e 890606 PDR ADOCK 05000254 o PDC

reexamination of these four 28-inch recirculation welds in this outage would produce little safety benefit because these welds were inspected by qualified examiners during the 1986 outage.

2.2 Ultrasonic. Examination The licensee reported that the IGSCC inspection was performed by Electric Power ResearchInstitute(EPRI)Non-destructiveExamination(NDE)Centerqualified personnel from the General Electric Company (GE). These examiners also passed the latest requalification program. Manual examination was performed on most welds. The fully automated GE " SMART" ultrasonic testing (UT) system was used mainly for examination of overlay repaired welds, welds in high radiation field, and welds with known flaws.

During this outage, flaw indications were found in fourteen welds with seven ~

(four 12-inch, one 22-inch and two 28-inch) in the recirculation system, one (16-inch) in the LPCI system, and six (10-inch) in the core spray system. One flawed (LPCI system) weld was mitigated with MSIP and the other thirteen were reinforced with weld overlay. Almost all the flaws found in the 12-inch recirculation and 6-inch core spray welds were oriented in the axial direction.

Both axial and circumferential flaws were found in the four large diameter welds. The worst axial and circumferential flaws were reported to be 32% and 26% in throughwall depth, and of 1 inch and 4.75 inches in length, respectively.

One unrepaired suction pipe-to-elbow weld (02BS-59) was re-examined during this outage. This weld was found flawed in 1984 and was treated with induction heating stressimprovement(IHSI). The inspection results showed existing flaws have grown in sizes from those reported in 1986 aft'er operation of one fuel cycle. The total flaw length has increased from 7 inches to 24 inches, and the maximum throughwall depth from 24% to 44%. In addition, five new flaws (four circumferential ,

and one axial) were also found in the current examination. This weld was overlay '

repaired during this outage.

An NRC Region III inspector selectively reviewed the ultrasonic examination procedures and data, and held discussions with examiners regarding the non-destructive examinations performed during this refuel outage. The inspector concluded in his report numbered 50-254/87020 dated December 22, 1987, that non-destructive examinations were performed by qualified personnel and no violations of NRC requirements were identified.

2.3 Weld Overlay Repair During this outage, weld overlays were applied to thirteen newly flawed welos and one previously unrepaired weld. In addition, twelve previously overlay repaired welds were upgraded in thickness and improved in the surface finish to facilitate ultrasonic examination. Except for weld 02G-S3, all upgraded overlays meet the requirements of standard overlay. Based on NUREG-0313 Revision 2 , weldments with more than four axial flaws are recommended to be overlay repaired with standard design. Weld 02G-S3 was reported to have eleven axial flaws in 1987 ext.mination. Therefore, this weld should be upgraded to I meet the standard design requirements during the next refuel outage. The i licensee indicated that the existing overlay of weld 02G-S3 could be shown to l

l

l

meet the standard design requirements using the alternate flaw evaluation

l. methodology based on IWB-3642. However, such evaluation was not performed.

Nutech performed the overlay design for the licensee. The designed minimum overlay thickness takes credit for the first overlay layer that passed the delta ferrite examination. For overlays applied to fourteen welds with new flaws,)

14A-S8standard overlay and overlay leakdesign barrierwas applied design wastoapplied three welds (02F-S3, to all others. 02M-54 The staff and finds that the use of overlay leak barrier design for welds 02B-55 and 028-S9 is not conservative because the total length of the circumferential flaws in these welds exceeds 10% of the circumference. NUREG-0313, Revision 2 recommends standard weld overlay design for weldments containing circum-ferential flaw over 10% of the circumference. As a result of the staff's concern, the licensee has committed to upgrade these two welds during the next refueling outage.

Twelve overlay repaired welds in this outage were ultrasonically examined only for bonding adequacy. The licensee indicated that these welds would be surfaced conditioned and ultrasonically examined (overlay and top 25% of the pipe wall) during the next refueling outage. The staff finds that weld 02M-S3 overlay rspaired for a leak barrier in 1984 and installed with a pipe lock has not been properly ultrasonically examined. Therefore, this weld should be surface conditioned and ultrasonically examined in during the ensure the effectiveness of overlay and pipe lock in m,next refueling outage to itigating.IGSCC.

The licensee reported that as-built overlay thickness in each repaired weld meet designed dimensions. The largest overlay shrinkage was reported to be 0.46 inch at weld 02K-S3. Nutech indicated that weld overlay shrinkage induced stresses in the piping system was evaluated using computer program PISTAR, but the results were not presented nor discussed. These results should be presented and discussed when reporting the inspection results during the next refueling outage.

The staff concludes that the weld overlay repairs performed during this outage are acceptable for at least an 18-month fuel cycle.

2.4 Mechanical Stress Improvement. Process O'Donnel and Associates, Inc.(0DAI) performed MSIP for the licensee on 38 welds, which consists of eighteen 16-inch welds in the LPCI system and twenty 10-inch welds in the core spray system. MSIP is a mechanical process that replaces tensile residual stresses on the inside surface of the piping in the vicinity of welds with a zone of compressive residual stresses. MSIP is an acceptable mitigation for IGSCC.

The staff finds that the reported total flaw length of 6.25 inches in the MSIP treated LPCI weld 10BD-S13 (16-inch) exceeds 10% of the circumference. In NUREG 0313, Revision 2, the stress improvement (SI) process including MSIP is considered effective in mitigating IGSCC for welds with no flaws or with only i

minor circumferential flaws, where the maximum depth and length of the flaws do not exceed 30% of throughwall thickness and 10% of the circumference, respectively.

Therefore, weld 10BD-S13 should be inspected every refuel outage in accordance with the IGSCC Category F schedule because the stress improvement credit on inspection is not allowed. After successful completion of four consecutive inspections, this weld may be moved up to Category E for inspection at every other refuel outage.

2.5 Induction. Heating Stress Improvement IGSCC-like flaws were found in eight IHSI treated recirculation piping welds (five 12-inch welds, one 22-inch weld, and two 28-inch welds). The licensee reporteo that a total of 88 welds in the recirculation, shutdown cooling, and residual heat removal piping systems were IHSI treated by Nutech Engineers in 1984. Flaws were found in seven of these welds during this outage. Weld 02BS-59

~(28-inch) was found flawed'in 1984, however, new flaws and growth of existing {

flaws were reported in a re-examination of this weld in this outage. All five 12-inch riser welds contained only axial flaws. The licensee indicated that these axial flaws might have been missed in previous examinations. In the three larger diameter pipe welds, both circumferential and axial flaws were reported.

l The licensee has reviewed both the IHSI heat treatment records and the i construction radiographs of these eight welds. The IHSI records have shown that wcld 028-F1 (22-inch pipe to cross tie valve) was improperly treated due to insufficient heating coil length and weld 02BS-S5 (28-inch pipe to tee joint) might have been marginally treated due to the significant differences in thickness between the tee and the pipe. Construction ra.diographs of the five 12-inch diameter riser welds have shown the characteristics of " wide welds" (i.e. wide rootsandcrowns). The licensee indicated that as-welded residual stresses produced by such welding practices tend to promote axially oriented IGSCC flaws.

. Construction radiographs of the three large diameter welds revealed significant evidence of post weld ID grinding. Most of the reported UT indications appear to fall within the post-weld ground regions.

In view of the cracking reported in 8 IHSI treated welds, the staff recommends i the licensee should increase inspection sampling of those IHSI treated welds during the next refueling outage to ensure IHSI mitigation is effective. Based on the inspection experience learned in this outage, the staff also recommends that higher inspection priority should be given to those welds showing the characteristics of wide root and crown or post-weld ID grinding in their construction radiographs.

2.6 Augmented. Leakage Monitoring program The licensee indicated that the augmented leakage monitoring program for unidentified leakage in accordance with Generic Letter 84-11 will continue to be implemented at the Quad Cities Unit 1 plant. The staff finds that the augmented leakage monitoring program is consistent with the staff position in Generic Letter 88-01 and is acceptable.

3.0 Conclusion Based upon the staff's review of the licensee's submittals, the . staff concludes that the licensee has adequately addressed IGSCC in Class 1 piping with respect to inspections, repairs, and litigations performed during the Quad Cities Unit 1 1987 refuel outage, and that these activities were performed in accordance with the guidelines in Generic letter 84-11. In addition, the staff also concludes that Quad Cities Unit I can be safely operated for another 18-month fuel cycle in the present configuration.

Principal Contributor: William Koo Dated: June 6,1989 O

e E

9

_ . . _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ . _ _ . _ _ _ _ _ _ _ _ _ . _ _ _ - _ _ _ _ _ _ _ _ _ _