ML20100C991
| ML20100C991 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 01/26/1996 |
| From: | Stetz J CENTERIOR ENERGY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 2352, NUDOCS 9602020064 | |
| Download: ML20100C991 (8) | |
Text
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300 Madison Awonue John P. sosts fotodo, OH 43652-0001 Vice President. Nuclear 419-249 2300 Davls-Besee Docket Number 50-346 License Number NPF 3 Serial Number 2352 January 26, 1996 United States Nuclear Regulatory Commission Document Control Desk Washington, D. C.
20555
Subject:
Request for Relief From Certain ASME Code Requirements for Inservice Inspection for the Davis-Besse Nuclear Power Station Gentlemen:
By letter dated August 14, 1995 (Serial Number 2302), Toledo Edison (TE) submitted three requests for relief from certain requirements of Section XI of the American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code. The requests for relief dealt with examination coverage for surface and volumetric examinations of certain components and were denoted as Relief Requests RR-A10, RR-All and RR-B7.
During the review of these Relief Requests by Idaho National Engineering Laboratories (INEL) for the Nuclear Regulatory Commission (NRC), it was requested that TE provide additional information to support these Relief Requests. This information was discussed between members of the NRC, INEL and TE staffs in a telephone call on December 20, 1995. During the telephone call, the NRC requested that TE submit the information discussed. The attachment to this letter provides the requested information.
Should you have any questions or require further information, please contact Mr. Peter W. Smith, Acting Manager - Regulatory Affairs, at U
(419) 249-2366.
a Very truly yours,
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L. L. Gundrum, NRC Project Manager
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S. Stasek, DB-1 NRC Senior Resident Inspector
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Docket Number 50-346 License Number NPF-3 Serial Number 2352 Attachment Page 1 Toledo Edison (TE) Response to NRC Request for Additional Information on Relief Requests RR-A10, RR-All, and RR-B7 NRC Request:
With regard to Relief Request RR-A10, the Code requires volumetric and surface examinations of Class 1 branch connection welds NPS 4 and larger.
For branch connection welds less than NPS 4, only a surface examination is required. Relief is requested from performing a volumetric examination from the nozzle side of branch connection welds.
The request includes eight welds in 2.5 inch branch connections. Clarify why 2.5 inch branch connections are included in this relief request. Also specify the weld identification number of each weld in the request.
TE Response:
The eight 2.5 inch branch connections welds included in this relief request are four High Pressure Injection (HPI) nozzles and four Reactor Coolant System (RCS) Drain Line nozzles. Toledo Edison recognizes that these nozzles could be classified under Code Item B9.32 and subjected to a surface examination only. Since the nozzle assemblies are 8.75 inches in diameter at their connections to the RCS piping, failure of these welds would result in a significant breach of the RCS. Therefore, TE conservatively classified these welds under Code Item B9.31, NPS 4 or larger, thereby subjecting these welds to both volumetric and surface examinations.
Since TE committed to examine these welds under Code Item B9.31, they are included in this Relief aequest.
The weld identification numbers for each of the ten welds included in this Relief Request are listed below. Note that welds DHA and SNA are NPS 4 or larger.
Decay Heat Nozzle Branch Connection Weld - DHA Surge Line Nozzle Branch Connection Weld - SNA Drain Line Nozzle Branch Connection Welds - DN1, DN2, DN3, DN4 High Pressure Injection Nozzle Branch Connection Welds - IN1, IN2, IN3, IN4 NRC Request:
In Relief Request RR-All, relief is requested from the examination coverage requirements of the Code for eleven Class 1 nozzle-to-vessel velds and eleven inside radius (IR) sections.
Included in the request is the method and
Docket Number 50-346 License Number NPF-3 Serial Number 2352 Attachment Page 2 associated Code interpretations used to determine the percent of coverage for the examination areas.
The examination requirements applicable to these areas are covered in Section V, Article 4 and are summarized as follows:
T-441.3.2.5," Angle Beam Scanning" (in part):
'The examination volume shall be scanned with angle beam search units directed both at right angles to the weld axis and along the weld axis.
Wherever feasible, each examination shall be performed in two directions, i.e., approaching the weld from opposite directions and parallel to the weld from opposite directions. These examinations shall be conducted using two beam angles (nominal of 45 degrees and 60 degrees) from each direction."
T-441.3.2.6," Scanning for Reflectors Oriented Parallel to the Weld" (in part):
"The adjacent 2
base metal in the examination volume must be completely scanned by two angle beams, but need not be completely scanned by both angle beams from both directions (any combination of two angle beams will satisfy the requirement)."
T-441.3.2.7, " Scanning for Reflectors Oriented Transverse to the Weld" (In part):
" Scanning shall be done in two directions 180 degrees to each other to the extent possible. Areas blocked by geometric conditions shall be examined from at least one direction."
Based on these paragraphs, it is the INEL staff's interpretation that all examination areas should be examined in all four directions using two angles to the extent practical.
If this is impractical due to physical obstructions such as component configuration, coverage in one direction with two angle will suffice for axial scans.
Coverage in two directions is required for circumferential scans.
It appears that the licensee has taken the position that scanning with two beam angles in just one circumferential and one axial scan direction is all that is required for adjacent base metal. Applying this logic to calculating examination coverage inflates the reported coverage estimates. A second licensee interpretation is that IR sections are regarded as " adjacent base metal" and one directional scans are considered adequate for meeting the Code requirements for these regions.
From the sketches, it appears that no attempt has been made to interrogate the
Docket Number 50-346 License Number NPF-3 Serial Number 2352 Attachment Page 3 corner region in the circumferential direction to detect corner flaws as depicted in IWB-2500-7. Discuss the techniques used to interrogate the IR region, the associated limitations, and the effort used to maximize coverage of the IR regions.
In addition, confirm that circumferential scans have been performed in two opposing directions and that axial scans have been performed in two directions to the extent practical.
TE Response:
Toledo Edison agrees that the desired scan for the adjacent base material is two angle beams in two directions for both reflectors oriented parallel to the weld and for reflectors oriented transverse to the weld (i.e., four directions using two angles). However, the paragraphs above permit scanning in one direction using two angle beams for both circumferential and axial scans. Therefore, TE interprets the minimum Code requirement for scanning adjacent base material as one direction using two beam angles for each circumferential and axial scan.
It is these minimum requirements on which the Relief Request calculations were made. Minimum requirements for weld metal are two angle beams in two directions for each circumferential and axial direction (9 scans = 4 circumferential + 4 axial + 1 straight beam) and minimum requirements for adjacent base material are two angle beams in one direction for each circumferential and axial direction (5 scans = 2 circumferential + 2 axial + 1 straight beam).
Therefore, TE does not agree that coverage estimates are inflated, as stated by INEL.
Section V, Article 4, paragraph T-441.3.2.1, " General Scanning Requirements," states, in part, "the volume of weld and adjacent base material (volume on either side of the weld seam)...".
This defines adjacent base material as that volume on either side of the weld seam.
Section V, Article 4 provides scanning requirements for the volume of j
weld metal and adjacent base material, but does not provide
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any scanning requirements for the nozzle IR section.
Since the nozzle IR section is not a weld seam, the rules for adjacent base material would apply. As noted above, the minimum scan requirements would be two angle beams in one direction for each of the circumferential and axial scans (i.e., 5 scans) for the nozzle IR secLion volume.
It is these minimum requirements on which the calculations for this Relief Request were made.
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Docket Number 50-346 License Number NPF-3 Serial Number 2352 Attachment Page 4 In all cases, circumferential and axial scans have been performed in two opposing directions to the extent practical.
The IR region is scanned in both axial and circumferential directions as described below.
Axial Scan:
The axial scan is performed using angles of 45 degrees, 60 degrees, and 70 degrees from the vessel surface towards the nozzle until the transducer coupling is lost at the outside radius of the nozzle. The IR region is also scanned axially using angles of 60 degrees and 70 degrees from the nozzle surface to the outside radius of the nozzle until transducer coupling is again lost.
These scans are performed the full 360 degrees around the nozzle and are considered the axial examination.
Circumferential Scan:
A tangential scan in the circumferential direction using 45 degrees, 60 degrees, and 70 degree angles with search unit oscillation (approximately 20 degrees) is per#ormed in two directions the full 360 degrees around the nozzle from the vessel side. Care is taken to ensure the proper skew is maintained by periodically rotating the search unit to direct the sound into the nozzle bore then back to the proper skew angle.
In addition to the tangential scans, the steam generator inlet and outlet nozzles are circumferentially scanned on the nozzle to head bend radius using a contoured 45 degree wedge.
Similar scanning is not practical on the pressurizer nozzles due to the short nozzle bore radius.
Scan Coverage:
The scan coverage for the IR region for the Pressurizer Spray Nozzle is depicted on Relief Request RR-All,, Page 7.
These scans are also typical for the other IR regions addressed in this Relief Request.
The attachment to Relief Request RR-All provides calculations for the scan coverage in the axial and circumferential directions.
Due to the complex geometry of the various nozzle configurations, TE is unable to perform precise calculations of the circumferential coverage without
Docket Number 50-346 License Number EPP-3 0 -
Serial Number 2352 Attachment Page 5 extensive computer modeling. Therefore, TE conservatively did not take credit for circumferential scan coverage in the calculations.
Toledo Edison is confident that a portion of the inside radius region is interrogated in both the axial and circumferential directions. Toledo Edison estimates that approximately 50% to 80% of the IR region is examined to meet Code requirements.
NRC Request:
In Relief Request RR-B7; the welds described appear to be unique (e.g., not defined within any Code Examination Category).
Provide a drawing of the pump showing the nozzles and the location and configuration of the welds.
The subject welds have been classified as pump casing welds but may be more similar in design and loading to nozzle-to-vessel welds or terminal ends to a piping run.
The conservative approach would have been to classify the welds as nozzle-to-vessel welds which may require a volumetric examination depending on thickness and configuration. What is the basis for classifying these components as pump casing welds?
TE Response:
The discussion of this Relief Request suggested that the pump casing welds appear to be unique (i.e., not defined within any Code Category) and may be more similar in design and loading to nozzle-to-vessel welds or terminal ends of a piping run.
Toledo Edison agrees that there is no clear Code Category which defines these welds. Possible options considered were:
Nozzle-to-Vessel Welds:
These welds were not classified as a nozzle-to-vessel welds as they are attached to a pump casing and not a vessel.
Therefore, the nozzle-to-vessel examination requirements would not be applicable to this configuration.
Piping Terminal Ends:
Terminal Ends are defined in IWA-9000 as the extremities of piping runs that connect to structures, components, or pipe anchors, each of which acts as a rigid restraint or provides at least 2 degrees of restraint to piping thermal expansion.
These welds were not classified as terminal ends as the
Docket Number 50-346 License Number NPF-3 io' Serial Number 2352 Attachment Page 6 nozzle is part of the pump (component) and the welds were fabricated under the ASME requirements for the pump casings.
The terminal end is considered to be the pipe-to-nozzle weld.
Pump Casing Welds The welds in question were made by the pump manufacturer.
They were designed, fabricated, and examined in accordance with the ASME requirements for the construction of pumps rather than the rules for vessels or piping.
Therefore, these welds were classified to the closest Code Category (i.e., pump casing welds).
Drawing ISI-SK-052, Sheet 1, which shows the configuration of the pump, is attached. The welds in question are denoted as welds C and I on the drawing. Regardless of the classification of these welds, the examination is limited by the pump's integrally welded support.
During the first ten year Inservice Inspection (ISI) interval at the Davis-Besse Nuclear Power Station, the pump support attachment welds on the suction and discharge nozzles of one pump were exmmined.
In the general vicinity of the pump casing-to-nozzle welds, two welds in the suction piping and two welds in the discharge piping were also examined. During the second ten year ISI interval, the suction side attachment weld, one suction piping weld, and one previously examined discharge piping weld in the general vicinity have been examined to date. No indications which indicate any service related degradation in the structural integrity of the piping or pump were identified.
For future examinations, the examination of the pump casing-to-nozzle welds will be supplemented by the examination of the accessible surfaces of the pump support attachment welds (Examination Category C-C) and the pipe-to-nozzle welds (Examination Category C-F-1) to the extent practical on the suction and discharge on the pumps.
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