ML20238A680

Safety Evaluation Re Insps & Repairs of Igscc.Plant Can Be Safely Operated for Another 18-month Fuel Cycle in Present Configuration

ML20238A680
Person / Time
Site:	Hatch
Issue date:	09/04/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20238A670	List: ML20238A668 ML20238A680
References
TAC-64777, NUDOCS 8709090385
Download: ML20238A680 (3)

Text

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1 ATTACHMENT 1

_ SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO INSPECTIONS AND REPAIRS OF IG5CC HATCH UNIT 1 GEORGIA POWER COMPANY DOCKtl NO : 50-321  ;

INTRODUCTION During the current Hatch unit i refueling outage, a total of 103 welds susceptible to intergranular stress corrosion cracking (IGSCC) were ultra-sonically inspected. The inspected samples included 25 overlay repaired welds and 9 unrepaired piping welds. The results of the inspection showed that flaw ir,dications system (RWCU).

were observed in 3 welds in the reactor water cleanup piping overlays. New flaws All those cracked RWCU welds were reinforced with weld  !

were also reported in the overlays of two repaired welds and three unrepaired welds in the recirculation piping system. The reported new flaws in those five previously flawed welds were relatively minor, and no additional repair was required. The licensee indicated that a mini-test of hydrogenwaterchemistry(HWC)atHatchunitIwillcontinuetobeperfcrmed -

during the upcoming cycle, and that a permanent HWC program will be determined

, after an evaluation of the mini-test results and industry wide experience.

DISCUSSION The staff has reviewed the licensee's submittals including the inspection results, flaw evaluations and overlay designs to support the continued operation of Hatch unit I for one 18-month fuel cycle in its present configurations. The details of the review follow:

, Scope of Inspection:

The licensee's initial inspection sample of 95 welds was patterned after the draft of NUREG 0313. Revision 2 as issued for public comment. The total IGSCC susceptible welds in Hatch unit I were reported to be 153 welds. The inspection sample was expanded from the initial 95 welds to 103 welds because crack-like indications were found in three core spray welds (Category C) in the initial sample. The scope of the sample expansion was limited to 6-inch RWCU welds in Category C and did not include the large diameter (12-28 inch) piping welds. All large diameter piping welds in Category C were treated with I inductionheatingstressimprovement(IHSI)andwereinspecteddurjeglast outage. Over 50% of those welds were re-exaa;ined in this outage. Although the cracking in the flawed RWCU welds is relatively minor, the 11eensee has committed to inspect the remaining Category C welds not inspected in this i outage and all lower Category welds at the next refueling outage. We conclude i that the scope of the current inspection performed in this outage is l acceptable.

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Ultrasonic Examination:

The licensee reported that the IGSCC inspection of the welds and weld overlays was performed by EPRI NDE Center qualified personnel from Southern Company ,

Services (SCC). The procedures used in the examination were based on the l techniques and methodology demonstrated at EPRI NDE Center. Both axial and  !

circumferential flaws were found in the flawed RWCU welds. Those flaws were l reported to be relatively short, and the total flaw length in each of those flawed welds is not longer than 0.7 inch. The deepest flaws in axial and l i

'circumferential orientation were 66% and 55% of the through wall thickness, respectively. New flaws and recharacterization of previous flaws were ,

l reported in the overlays of two reparfed welds and three unrepaired welds in the recirculation system. The licensee indicated that the new and recharacterized flaws found in this outage resulted from the use of more sensitive inspection procedures, and was not due to crack growth or initiation of new cracks. The inspection procedures used in this outage was reported to be improved scanning in the from 10% to 25%, following) aspects:-(1)

(2 broadened increase screen range of slower and (3) minimum overlay in scanning speed. The improvamed procedures are believed to provide better detection capability for small indications.

NRC Region !! inspectors have selectively reviewed the ultrasonic examination. {

procedures and data, and held discussion with the examiners regarding the l

. non-destructive examinations performed during this outage. NRC Region II j concluded in their reports (50-321, '"i4/87-10, dated July 9,1987 and 50-321,366/87-12, dated July 15,1987) that nondestructive examinations were performed by qualified personnel and that no violations of NRC requirements were identified.

Flaw Evaluation:

Structural Integrity Associates (SIA) performed the flaw evaluations for the licensee. The results of their evaluation indicate that the three cracked RWCU  !

welds require only minor repair to prevent leakage, because the reported '

indications are all very short. No repair is required on five previously flawedwelds;threeunrepairedrecirculationwelds(1831-IRC-28A-2,(1831-1R 1831-1RC-288-8 and 1831-1RC-288-10) and two overlay repaired welds )

q and1E11-1RHR-248-R-12). An additional minor flaw was found in welds 28A-2 and 288-8, and two flaws in weld 288-10 were recharacterized. Those welds were treated with INSI during the previous outage. Other than weld 28B-10, the total flaw length in each weld was less than 10% of the pipe circumference.

$1A's evaluation has shown that, even if credit for IHSI is not considered, the final flaw size at the end of an 18-month fuel cycle is well within.the allowables of the ASME Code Section XI IWB 3640. The flaws absorved in the two repaired overlays were not connected to the pipe inside di surface.

Those flaws were determined to be fabrication defects in the over meterials(

such as lack of fusion in the first overlay layer). SIA's evaluation has shown that the observed flaws in the overlays are acceptable without repair ,

because it meets the criteria in ASME Code Section XI. IWB-3500 for sub-surface  :

plannar flaws. SIA's evaluation has also shown that, even if the flawed l

overlay layers are not considered, the remaining as-built overlay thickness of  ;

the two repaired welds still meets the required minimum thickness for standard  !

overlays. '

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e: Weld Overlay Design:

Limited' service overlay (two overlay' layers) design was used for the three flawed RWCU welds. Because the reported flaws in those welds are short, structural reinforcement is not required. The main purpose of the limited service overlay design is to provide a leak barrier for the flawed weld. It also has the advantage of minimizing personnel radiation exposure and inducing less shrinkage stress as a result of the repair. The licensee also indicated that the overlay repaired RWCU welds might be. upgraded or replaced during the next refueling outage. We conclude that the repaired RWCU welds are acceptable for continued service for another 18-month fuel cycle.

CONCLUSION Based on our review of the licensee's submittals, we conclude that the Hatch unit 1 plant can be safely operated for another 18-month fuel cycle in the present configuration.

Principal Contributor: W. Koo l

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