ML20246J553

Safety Evaluation Concluding That Plant Can Be Safely Operated for Another 18-month Fuel Cycle in Configuration Following Reload 5,per Improvements,Insps & Repairs to Plant IGSCC

ML20246J553
Person / Time
Site:	Brunswick
Issue date:	05/09/1989
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20246J545	List: ML20246J541 ML20246J553
References
GL-84-11, IEIN-84-41, NUDOCS 8905170109
Download: ML20246J553 (3)

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j NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 l

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO INSPECTIONS AND REPAIRS OF IGSCC CAROLINA POWER & LIGHT COMPANY, et al.

BRUNSWICK STEAM ELECTRIC PLANT, UNIT 1 DOCKET NO.: 50-325 INTRODUCTION The staff has reviewed the licensee's submittals dated May 19 and May 22, 1987 including the inspection results, flaw evaluation, and overlay design to i support the continued operation of ilrunswick Steam Electric Plant, Unit 1, (Brunswick Unit 1) in this configuration for the 18-month fuel cycle following Reload 5.

During the Brunswick Unit I refuel 5 outage, all Class 1 piping welds susceptible to integranular stress corrosion cracking (IGSCC) were ultrasonically inspected.

In addition, 6 Inconel 182 buttered nozzle welds and 10 recirculation inlet safe-end thermal sleeve attachment welds were also ultrasonically examined. The results of the inspection showed that flaw indications were cbserved in a recircu-lation manifold weld (B32-AM3), and that the flaw size in a previously unrepaired in the recirculation piping system remained unchanged.

weld The newly (28-inch, B-32-A8)(B32-AM3) cracked weld was reinforced with weld overlay.

Weld overlay was also applied to three 4-inch bypass line welds as a mitigation to IGSCC.

All 32 previously everlay-repaired welds were upgraded including improving the overlay surface condition to facilitate ultrasonic inspectien.

lne licensee indicated that special surveillance measures for coolant leakege have been implemented at the Brunswick Unit 1 plant. These surveillance measures are consistent with the guidelines provided in Attachment I to Generic Letter 84-11 and will provide assurance for early detection of cocacnt leakage.

Di3CUSSION Inspection and Piping Replacement The licensee reported that 108 Class 1 piping welds in Brunswick Unit 1 are susceptible to IGSCC, and that all those welds were inspected during the refuel 5 outage. The inspected welds include 32 previously overlay-repaired welds and one unrepaired weld. Except for seven welds, all IGSCC susceptible welds were either overlay-repaired or mitigated by induction heating stress improvement (IHSI). Ten recirculation inlet safe-end thermal sleeve attachment welds were also inspected. In addition, six Inconel 182 buttered welds including two 12-inch recirculation inlet nozzles, two 28-inch recirculation suction nozzles and two 10-inch core spray nozzles were also inspected in accordance with IE Notice 84-41.

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Only two welds (4-inch in diameter) in the reactor water clean-up (RWCU) Class I piping system are susceptible to IGSCC. These two welds and associated piping were replaced with nuclear grade materials during this outage. The nuclear grade stainless is an acceptable replacemer.t materfcl because of its good resistance te IGSCC.

We conclude that the scope of the inspection perfonned and piping replaced during this outage is acceptable.

Ultrasonic Examination -

The licensee reported that the IGSCC inspection of the welds and weld overlays was performed by EPRI NDE Center qualified personnel from General Electric Company (GE). The fully automated GE " SMART" ultrasonic testing (UT) system was used for examination wherE geometrically feasible. Manual examinations were performed where automatic UT could not be performed. The sizing of IGSCC indications was performed using 2 to 5 MHz. refracted longitudinal transducers. The sizing methods used included Satellite Pulse Observation.

Technique (SPOT), Pulse Arris al Time Technique (PATT), ID and OD creeping wave technique, and tip diffractio i techniques, as applicable.

The circumferential flaw found in weld B32_AM3 was reported to have a maximum depth of 30% of pipe wall thick'ess and a length of 3.7 inches. This indication was reported in a previous inspe -tion as a low amplitude root indication. Prior to the examination of unrepaired welds, each weld crown was contoured smooth to enhance the acoustic coupling of the UT transducer to the pipe. For overlay repaired welds, the overlay surfaces were finished to EPRI recommended requirements to facilitate UT examination. For the examination of thermal sleeve attachment welds and and Inconel butter welds, calibration ies performed on as-build mock-up blocks.

NRC Region II inspectors have selectively reviewed the ultrasonic examination procedures and data, and held discussions with the examiners regarding the non-destructive examinations performed during this outage. NRC Region II concluded in their re dated March 18, 1987, and 50-325/87-08, dated April 15, 1987)thatports (50-325/87-04, nondestructive examinations were performed by qualified personnel and that no violations of NRC requirements were identified.

Flaw Evaluation Nutech performed the flaw evaluation for the licensee. Fracture mechanics evaluation using the Nutech Nutcrack computer program was performed for previously unrepaired weld 832-A8. The flaw size in weld 832-A8 was reported to have a maximum depth of 20% of pipe wall thickness and a length of two inches. A sustained stress of 10,043 psi, including deed weight, internal pressure, thermal expansion and weld overlay shrinkage stresses, was used in the crack growth calculation. Nutech's evaluation also employed the post-IHSI residual stress distribution. The results of their evaluation ir.dicate that the flaw in weld 832-A8 will not propagate. Laminar flaw indications with undetectable width were observed in five repaired overlays.

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a 9 3-These indications were confined in the overlays and were not connected to the pipe inside diameter surface. Nutech's evaluation showed that the observed flaws in the overlays are acceptable without repair in accordance with the criteria in ASME' Code Section XI IWB-3500 for subsurface plannar flaws.

The staff concludes that the flaw evaluations are acceptable.

Weld Overlay Design A standard overlay in accordance with the draft of NUREG 0313. Revision 2, was used for the flawed B32-AM3 weld and three 4-inch bypass branch connection welds, which were not flawed. Thirty-two weld overlays repaired in previous i

outages were upgraded during this outage. Of these 32 welds, 29 welds were upgraded in overlay thickness and length in addition to overlay surface finish, and three welds were improved only in surface finish. Except for weld 832-A15 which contained only one short (0.5 inch) axial crack, all previously repaired welds were upgraded to meet the requirements for standard overlay design during this outage. The designed overlay thickness did not include the first overlay layer that passed the penetrant and ferrite tests.

The staff concludes that all overlay repaired welds (36) are acceptable for cor.tinued service for another 18-month fuel cycle.

Special Surveillance Measures The licensee indicated that special surveillance measures for coolant leakage have been implemented at Brunswick Unit 1. The staff has reviewed the measures, and they are consistent with the guidelines provided in Attachment I to Generic Letter M-11, will provide assurance for early detection of coolant leakage, and are acceptable.

pCLUSION Based on our review of the licensee's submittals, as discussed above, we have concluded that the Brunswick Unit 1 plant can be safely operated for another 10-month fuel cycle in the configuration following Reload 5.

Prinicpal Contributed: W. Koo

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