ML20058A762
| ML20058A762 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 10/18/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20058A641 | List: |
| References | |
| GL-88-01, GL-88-1, NUDOCS 9010290153 | |
| Download: ML20058A762 (5) | |
Text
_
pQ Q4 Cp
[k - '
'g NUCLEAR REGULATORY COMMISSION J
UNITED STATES P
j l
WASHING T ON, D, C. 20055 m
l
%,,,,, /,
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION GPU NUCLEAR CORPORATION - INTERGRANULAR STRESS CORROSION CRACKING - INSPECTION AND REPAIRS GPU NUCLEAR CORPORATION OYSTER CREEK NUCLEAR GENERATING STATION DOCKET NO. 50-219
1.0 INTRODUCTION
By letters dated January 20, 23, and 31, 1989, October 30, 1989, and February 21, 1990, GPU Nuclear Corporation (the licensee, GPUN) submitted Intergranular Stress Corrosion Cracking (IGSCC) inspection and repairs report, additional information, and future inspection plans for the Reactor Water Cleanup System (RWCU) during the Oyster Creek Nuclear Generating Station (OCNGS) 13R refueling outage.
The licensee's letters dated October 30, 1989, and February 21, 1990 were in response to NRC letter dated February 16, 1989, requesting the following additional information:
1.
A description of overlay and design report.
2.
A description of inspection personnel, procedures and techniques.
l l
3.
Detailed inspection results of all flawed welds, especially for welds NG-C-9A and NG-D-18.
In light of the inspection results that flaws were found in IHSI 4.
treated welds, please discuss the effectiveness of IHSI in mitigation IGSCC at Oyster Creek.
p
- 5..
The results of failure analysis of a plug removed from weld NG-D-11.
6.
Inspection schedule for Category G_ welds in the reactor cleanup system.
The staff also had some concerns in NRC letter dated February 16, 1989, with
-regard to GPUN's IGSCC inspection program for OCNGS 13R refueling outage as delineated in the licensee's revised GL-88-01 response dated January 31, 1989.'
In addition, the, staff requested that the licensee incorporate the staff's comments-to their GL-88-01 response and resubmit OCNGS's IGSCC inspection program for 13R refueling outage for review by the staff.
2.0 DISCUSSION The licensee's submittals dated January 20, 23, and 31,1989, October 30, 1989, and February 21, 1990, have been reviewed by the staff and have been found to 9010290153 901ois
{DR ADOCK 03000219 PDC l
a be acceptable with the exception of the licensee's inspection plan subsequent to 13R with regard to RWCU welds outboard of the second containment isolation valves.
The licensee reported that a total of 150 welds susceptible to IGSCC l
in various stainless steel piping systems and six structural weld overlays were inspected during'the 12R outage.
Six welds were found to contain IGSCC indi-cations.
Five (two welds in the Recirculation System and three welds in the Isolation Condenser System outside the drywell) required weld repair and one weld in the Recirculation System was analyzed and found to be acceptable for continued operation without repair.
The six inspected overlays contained no indications of IGSCC in the overlays or outer 25% of the original pipe wall.
The following are the licensee's response to the staff's letter dated February 16, 1989:
1.
A description of overlay and design report.
The overlays were designed assuming that a 360 degree through-wall crack existed at each location.
The resultant minimum design thickness provides adequate margin against plastic collapse when evaluated to the requirements of the Code.
The width of the overlays l.
are sufficient to enable ultrasonic examination of the outer 25% of 1
the pipe wall in accordance with the current accepted methods.
The l.
overlays were deposited using the gas tungsten arc method with 308L p
bare wire and only primary stresses were included in the design input.
The measurements to confirm minimum design thickness included the l
first layer that contained an average ferrite number of 7.5 or higher with no single reading less than 5.
l l
2.
A description of inspection personnel, procedures and techniques, l
Ultrasonic testing (UT) was performed by personnel qualified to the NRC/EPRI/8WROG Coordination Plan for Training and Qualification Activities of NDE Personnel.
EPRI qualified personnel performed reviews of all procedures, personnel certifications, and data u
packages.
Both manual and automated UT, or/and in some cases radiographic testing techniques were used to examine stainless steel piping welds.
Manual and automated UT examination procedures were qualified at the EPRI NDE Center and the procedures relied on the 45 degree shear wave examination as the primary detection technique.
The equipment utilized for the automated UT examination was the GE-SMART System; additional examinations were performed with the UTL-KWU L-SAFT (Synthetic Aperture Focusing Technique); and the data acquisition system was the Ultra Image III.
3.
Detailed inspection results of all flawed welds, especially for welds NG-C-9A and NG-0-18.
Six weldments were found to contain indications with UT signals characteristic of IGSCC.
Five of the welds (NG-D-11, NG-D-21, NE-1-66, NE-2-82 and NE-2-100) were repaired with standard weld overlays.
Weld NG-D-18 was analytically determined to be acceptable
as IHSI-treated for continued service without repair and weld NG-C-9A was re evaluated based on the indication size as called in 12R. The results showed that both were acceptable for continued service with-out repair when evaluated to the criteria of the Code and NUREG-0313, Rev.-2.
The evaluation was performed assuming that the weld deposited using the shielded-metal arc process.
The licensee considered the reported crack growth in NG-C-9A was most likely a result of UT accuracy differences.
As IHSI-treated, the licensee does not expect further substantial crack growth to the point where repair action would be required.
The licensee will continue to monitor weld NG-C-9A in future outages.
In addition, weld NZ-3-38 was repaired by weld overlay when it was identified during a start-up sequence walkdown to have a through-wall leak.
CRDR line weld NC-4-6 and a Reactor Head Cooling weld which were not in the scope of GL-88-01 were replaced.
4.
In light of the inspection results that flaws were found in IHSI treated welds, please discuss the effectiveness of IHSI in mitigation IGSCC at Oyster Creek.
The licensee indicated that IHSI treatment of welds was effectively performed.
The likelihood of initiation of IGSCC in uncracked weldments and further growth of shallow, undetected IGSCC has been substantially reduced, if not eliminated.
The extent of IHSI included 4 C-loop safe end welds, 6 Core Spray safe end welds, 19 Core Spray butt welds, 4 Isolation Condenser safe end welds and 9 Isolation Condenser piping end welds.
Four Recirculation safe end welds, 4 Isolation Condenser safe end welds, and 6 Core Spray nozzle safe end welds were inspected I
after IHSI.
Furthermore, 9 of the 19 IHSI'd Core Spray piping welds i
were inpsected during 12R after IHSI and 4 were inspected *in 12R before INSI, and 6 were not inspected during 12R.
Of the 6 welds not inspected during-12R, 3 were inpsected in 11R.
The 9 welds in the Isolation.
Condenser piping inside the drywall were not inspected during 12R af ter IHSI, I was inspected in 12R before IHSI, and 4 were inspected in 11R.
L Three (CNG-D-11, NG-D-18 and NG-D-11) IHSI. threated welds (Category C) were found to contain indications of IGSCC in.this outage.
All three l
_ ere inspected in previous outage (11R) and were reported to contain w
non-IGSCC indications. -The licensee concluded that those cracks found in this outage were most likely present before the performance of ISHI in 11R.
i l
_5.
-The results of failure analysis of a plug removed from weld NG-D-11..
'The GE metallurgical evaluation showed that IGSCC was present, the actual depth was slightly deeper that the UT called depth-(30% vs 27% through--
D wall),.and the licensee concluded that the crack as it currently exists._
was most likely present before decontamination and IHSI performed in 11R.
[
.c
i lC
- o 4
6.
Inspection schedule for Category G welds in the reactor cleanup system.
The licensee proposed to inspect approximately 10% of the RWCU weld population outboard of the containment isolation valves for 13R refueling l-outage.
In addition, the licensee proposes that, if there are no IGSCC indications outside of the second isolation valve during 13R, there would be additional. technical justification for the licensee's original plan dated November 16, 1989.
In the plan dated November 16, 1989, the licensee proposed to perform visual checks during hydro testing of the welds outboard of the second isolation.
The plan to inspect 10% of the subject RWCU welds during 13R is acceptable.
However, the plan to visually inspect (during hydro testing) the subject welds in subsequent refueling outages, if there are no IGSCC indications found in the subject piping during 13R-is unacceptable.
The RWCU has-the most aggressive environment with regard to IGSCC and the licensee should inspect the subject RWCU welds every refueling outage on a sampling bases of at least 10% of the subject RWCU weld population.
The-licensee in responding to other NRC concerns as delineated above will submit a revision to its previous GL-88-01 response.
The new submittal will include a change to the RWCU inspection plan and outline the revised piping replacement plan for the 13R outage.
3.0 CONCLUSION
Based on the review of the licensee's responses dated January 20, 23, and 31, 1989, October 30,11989, and February 21, 1990, the staff concludes that the responses as evaluated are acceptable with the exception of the licensee's inspection plan subsequent to 13R witb regard to RWCU welds outboard of the second containment isolation valves.
The RWCU has the most aggressive environ-ment with regard to IGSCC and the licensee should inspect the subject RWCU welds-every refueling outage including 13R on a sampling bases of at least 10% of the subject RWCU weld population.
Furthermore, based on the review of the information provided by.the licensee, the staff finds the inspection and overlay repairs that.were performed during the 12R ' refuel outage meet the guidelines in GL-88-01.
Because of the timing.
of GL-88-01 issuance, the reduced inspection scope of' Category G welds for 12R refueling outage was accepted.
Therefore, the staff concludes that 0CNGS can be safely operated for one additional fuel cycle in its present configuration with assurance that the integrity of the reactor coolant pressure boundary will
-be maintained.
-Principal Contributors:
T. McLellan and W. Koo Dated: October 18, 1990
(
DISTRIBUTION p" DocketJ,1lef; 3;;r
.NRC & Iocal PDRs Plant '.*ile S. Varga (14E4)
B. Boter (14A2)
S. Norris A. Dro,nerick OGC E. Joroin (MNBB 3302)
ACRS (16)
E. Wenzinger (Region I)
T. McLellan W. Koo