ML20034A356
| ML20034A356 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 04/13/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20034A350 | List: |
| References | |
| NUDOCS 9004230112 | |
| Download: ML20034A356 (4) | |
Text
i
/pt Cleg%,,
e a
UNITED STATES i
8" NUCLEAR REGULATORY COMMISSION n
{
- )
WASHING TON. O, C. 20666
\\..../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION i
l RELATING TO INSPECTIONS AND REPAIRS OF 3
INTERGRANULAR STRESS CORROSION CRACKING (IGSCC)
{
BRUNSWICK STEAM ELECTRIC PLANT, UNIT 2 l
CAROLINA p0WER & LIGHT COMPANY (CP&L)
DOCKET NO. 50-324
1.0 INTRODUCTION
The staff has reviewed the licensee's (CP&L) submittals dated June 15 and August 21, 1989, and February 21 and March 16, 1990 and related information regarding the inspection results, IGSCC mitigation, flaw evaluations and overlay repairs perfctmed during the BSEP Unit 2 refuel _ing outage 8 to support the continued operation of the unit in its present configuration for one 18 month fuel cycle.
During the unit refueling outage 8, 139 welds were ultrasonically examined.
Flaw indications were found in two recircula-tion system piping welds (28B10 and 22AM1).
Weld 28810 was repaired with weld overlay of standard design.
The IGSCC crack in weld 22AM1 was evaluated and found suitable for continued operation'without repair.
During this refueling outare, the reactor coolant recirculation system l
l (RCRS) discharge riser piping, safe ends and nozzle butter as well as the j
remaining susceptible portion of the reactor water cleanup (RWCU) system piping in the 4-inch return line were replaced with low carbon austenitic stainless steel materials.
In addition, mechanical stress improvement
?
process (MSIP) was applied to all 36 RCRS replacement welds.
l
- 2. 0 DISCUSSION Inspection The licensee reported that, during this refueling outage,139 welds in IGSCC categories A, C, D, E, and F w. ri ultrasonically inspected.
These welds are located in the recirculati.c' systen, residual heat removal (RHR) system, RWCU system, core spray system and the jet pump instrumentation i
l penetration assemblies.
The original sample consisted of 85 welds.and was I
expanded to 139 welds after flaw indications were found in previously unflawed welds.
All IGSCC Category C welds (48) were inspected because flawed welds were found in the original and expanded samples, The staff l
concludes that the scope of IGSCC inspection and the sample expansion of l
IGSCC Category C welds meet the staff requirements and the guidelines in L
Generic letter 88-01.
l Q
O PNU k
2 Ultrasonic Examination The licensee reported that the IGSCC inspection was perforted by General Electric (GE) personnel qualified at EPRI HDE Center.
These examiners also passed the latest requalification program. The fully autonated GE
" SMART" ultrasonic testing (UT) system was used for examination, where geonetrically feasible.
The automatic system utilizes the Image computer-driven data acquisition system with the ALARA remote scanning dev ice. Manual examinations were perforned where autoratic UT could not be perforted or to supplement the SHART UT examination.
The results of IGSCC inspectinn reported flaw indications in two welds (28810 and 22AM1) in the recirculation piping system.
Weld 2E10 is a 28-inch pipe to punp suction elbow weld in reactor recirmiation loop P.
This weld was reported to have eight axial flaws on the elbow side wie a maximum through wall depth of 20% and a maximum length of 0.55 inch. A weld overlay was applied to this weld to maintain its stmetural int eg rity. Keld 22AMI is a reactor recirculation 22-inch header cross-tie valve-to-pup piece weld.
A circumferential flaw with a through wall depth of 16% and a length of 2.4 inches was reported in the pipe side of this weld.
This weld was not overlay repaired because the crack growth calculation has shown that the flaw will not exceed the ASME Code allowable flaw size at the end of the next 18-nonth fuel cycle.
The NRC Region 11 inspector selectively reviewed the ultrasonic examination pmcedures and data and held discussions with the examiners regarding the non-destructive examinations perforned during this refueling 8 outage.
The inspection report (50-324/90-03), dated January 29 1990,-
concluded that nondestmetive examinations were performed by quallfied personnel and that no violations of NRC requiretents were identified.
Flaw Evaluation Structural Integrity Associates (SIA) perforned crack givwth evaluation for the licensee to justify continued service of weld 22AMI in'its as-flawed condition.
Weld 22AMI contained a small cirmmferential flaw I
with a maxitum through wall depth of 16% and a lenth of 2.4 inches.
SIA computer program pc-G!ACK was used for crack growth calculation.
Applied stresses were ta ken fmm General-Electric Report 23AS485,_" Brunswick Units 1 & 2 Recirculation Pising taalysis" P.evision 0 dated October 1,
'1985, and also included the sounding cases,of System sbrinkage stresses resulting from overlay repairs at other locations. The results of-SIA's evaluation showed that the final flaw size at the end of an 18-month fuel cycle in weld 22AMI will not exceed the ASME Section XI, IWB-3600-a llowable.
The staf f performed an independent-- crac k growth calculation and found its results agreed with those of SIA.
Therefon, the staff concludes that the flawed weld 22AM1 is-accepttble without weld overlay repair for the upcoming 18-month fuel cycle of operation, i
I 1
y
I
' Weld Overlay Repair Weld 28B10 required repair for continued service because this welo contained eight axial flaws.
SI A perforted a standard design of weld overlay repair that ret guidelines provided in Generic Letter 88-01.
The licensee -
reported that the as-built dimensicns of the weld overlay exceed the design minimum cimensions following surface finish inprovement.
The staff concludes that the weld overlay for wcid 28810 15 a cceptab le.
Piping Replacerent General Electric Conpary replaced the renmining portion of the susceptible RWCU siystem piping (4-inch return line from the regenerative heat exchangers to valve 2G31-F042 at the RCIC/Feedwater system tie-in)
. *h low carbon austenitic stainless steel materials.
Pre-service UT u xinations were performed at all replacenent welds.
The RCRS discharge riser piping and the Incor,el 600 safe ends were also replaced with 316NG stainless steel materials.
The new safe ends were designed with no thermal sleeve attachment welds.
The Inconel 182 nozzle bbtter and cladding were replaud with ER309L stainless steel weld materials.
All installed piping and safe ends were electropolished and received pre-oxidation treatnents.
The welding was perforned with controlled heat input to minimize shrinkage stresses and sensitization.
Furthernere, O'Donnell and Associates, Inc. applied mechanical stress inprovenent process (MSIP) at all 36 RCRS replacement welds. UT examinations were performed before and after MS!P treatnent.
The staff concludes that the replaced piping is resistant to IGSCC, and is a ccep table.
Mnimum Wall Thickness for RHR Valve-Nozzle Walls Evaluation The SIA October 26, 1989 report transmitted with CP&L'1etter dated February 21, 1990, indicated tnat mininum wall thickness requirenents were not met at the "A" and "B" RHR valve-nozzle walls in their as built configurations.
In addition, CP&L retained the services of SIA to perform a Safety Evaluation and reconciliation of the as-built and as-required wall thicknesses.
This reconciliation was also provided in the Februa ry 21, 1990 CP&L letter, which showed that anple margin existed in-the valve-nozzle walls. We have reviewed the basis for this reconciliation and have found it acceptable.
3.0 CONCLUSION
Based upon our review of the licensee's submittals, the staff concludes-that the inspections, repairs and mitigations perforned 'during the Brunswick Unit 2 refueling 8 outage were per#orr:ed in accordance with the guidelines in Generic Letter 88-01.
The staff-finds that Brunswick Unit 2 can be safely operated fer the upcoming 18-month fuel cycle in its present configu ration.
Principal Contributor: (illiam H. Koo Dated:
i l
DISTRIBUTION 4
7 HRC PDR Local PDR S. Varga 14-E-4 G. Lainas 14-H-3 E. Adensam 14-B-20 P. Anderson 14-B-20 N. Le 14-B-20 OGC (For inform. Only) 15-B-18 E. Jordan HNBB-3302 ACRS (10)
P-315 BRUNSWICK FILE i
i
__.