ML20115J945
| ML20115J945 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 07/15/1996 |
| From: | Graesser K COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BYRON-96-0202, BYRON-96-202, NUDOCS 9607250160 | |
| Download: ML20115J945 (9) | |
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Commonwealth Edison Company liyron Generating Station 4450 North German Church Road Ilyron. IL 610149794 Tel 815-234-5441 July 15,1996
.LTR:
BYRON-96-0202 FILE:
3.11.0321 Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention:
Document Control Desk
Subject:
Byron Station First Ten Year Interval Inservice Inspection Program Relief Request NR-20 Byron Nuclear Power Station, Units 1 and 2 NRC Docket Numbers: 50: 454 and 455 Pursuant to 10CFR50.55a(6)(ii)(A), Commonwealth Edison Company (Comed) is providing the attached information regarding the ultrasonic examination of reactor vessel welds for Byron Station Units 1 and 2. 10CFR50.55a(g)(6)(ii)(A) requires that licensees submit information to the commission when it is determined they are unable to satisfy the requirements for augmented reactor vessel shell weld examinations. The augmented reactor vessel weld examinations are performed in accordance with ASME Section XI at the Byron Station, Units 1 and 2.
10CFR50.55a(g)(5)(iii) stipulates that when the licensee determines that examinations required by the code or addenda are impractical,information b, +upplied to the commission to support the
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determinations. Therefore, pursuant to 10CFR50.55a(gn5)(iii), this information is being I
provided in the form of a relief request (NR-20).
hDN Relief request NR-20 proposes to revise Byron Nuclear Power Station, Units 1 and 2 inservice inspection requirements for volumetric examination of the following reactor vessel welds:
I circumferential shell and circumferential head. Byron Station has recently completed the Unit I reactor vessel weld volumetric examinations during refuel outage B1R07. Due to physical and geometrical limitations,100% ultrasonic examination of the welds was not possible. The Unit 2 reactor vessel exams are scheduled for B2R07 (Spring 1998). Since the design of the Byron i
Units I and 2 reactor vessels is identical, similar coverage percentages are expected for Unit 2.
I 9607250160 960715 PDR ADOCK 05000454 Q
PDR A Unicom Company
)
Comed respectfully requests that the Nuclear Regulatory Commission (USNRC) review and approve the attached relief request based on the geometric limitations and supporting l
justifications provided.
i Please address any comments or questions regarding this request to Marcia Lesniak, Nuclear Licensing Administrator, at (708) 663-6484.
Sincerely, K. L. Graesser
!~
Site Vice President Byron Station Attachment j
cc:
G. Dick, Byron Project Manager-NRR l
H. Miller, Regional Administrator-Rill
' H. Peterson, Senior Resident inspector-Byron Office ofNuclear Safety-IDNS i
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i BYRON STATION UNITS 1&2 FIRST INTERVAL ISI PROGRAM PLAN-NRC SUBMITTAL RELIEF REQUEST NR-20 (Page 1 of 7)
COMPONENT IDENTIFICATION:
Code Class:
1
Reference:
IWB-2500, Table IWB-2500-1
)
Examination Category: B-A I
Item Numbers:
Bl.11 and Bl.21 i
==
Description:==
Limited Volumetric Examination of Reactor Vessel Circumferential Shell, and Circumferential Head Welds Component Numbers: RPVC-WR16, RPVC-WR29 (Same for both units)
Drawing Numbers:
IRPV-1-ISI (Unit 1) and 2RPV-1-ISI (Unit 2)
CODE REOUIREMENT:
Table IWB-2500-1, Examination Category B-A, Item Numbers Bl.11 and BI 21 require a 100% volumetric I
examination of the Reactor Vessel Circumferential Shell and Circumferential Head wclds as detailed in Figures lWB-2500-1 and IWB-2500-3.
i HISTORY:
Byron Station, during Refuel Outage BIR07, conducted ultrasonic examinations of the Byron Unit 1 Reactor Vessel.
i This was the last refuel outage of the third period of the first Insenice Inspection Interval and occured in April through June 1996. Framatome Technologies Inc. (FTI) was contracted to perform the examinations with their state-of-the-art "URSULA" manipulator and their "ACCUSONEX" UT system. The examinations were performed in j
accordance with the requirements in ASME Section XI, Article IWA-2232, USNRC Regulatory Guide 1.150 and 10CFR50.55 a (g)(6)(ii)(A). The examination scope included 100% of the Reactor Shell welds, Head welds, and Shell to Flange welds (ASME Section XI Table IWB-2500-1, Category B-A), all 8 Reactor Nozzle to Vessel welds and Inner Radius sections (Category B-D), and Reactor Flange threads (Category B-G-1). Byron Station Reactor Vessel (s) do not have any longitudinal shell welds.
l The examinations revealed 4 minor flaws, all within the acceptance criteria of ASME Section XI, Article IWB-3500.
Previously granted relief request NR-1 for Byron Station Units 1 and 2 First Inspection Interval for the Reactor Shell welds was subsequently revoked in 10CFR 50.55 a(g)(6)(ii)(A) with respect to examination coverages. During the performance of the BIR07 examinations, physical obstructions and geometry prevented UT coverage in excess of 90%
of the required volume for the above listed component numbers. Full 100% UT coverage was obtained for the reactor shell welds WR-7, WR-18, and WR-34. The limited amount of examination coverage attained for shcIl welds WR-16 and WR-29 is prmided below in the Basis for Relief.
FTl is contracted to perform the 10 year Reactor Examinations on Byron Unit 2 during the late Fall of 1997 and, as the two Byron reactors are identical, similar coverage percentages are expected.
B ASIS FOR RELIEF:
Pursuant to 10 CFR 50.55a(a)(3)(ii), reliefis requested on the basis that compliance with the specified requirements would result in hardship or unusual difliculty without a compensating increase in the level of quality and safety, 1
l BYRON STATION UNITS I&2 FIRST INTERVAL IST PROGRAM PLAN-NRC SUBMITTAL RELIEF REQUEST NR-20 (Page 2 of 7)
A.
REACTOR VESSEL CIRCUMFERENTIAL SHELL WELDS The examination of the Unit 1 Lower Shell Course-to-Dutclunan weld, RPVC-WR29, is restricted by six (6) core barrel locating lugs welded to the inner surface of the vessel approximately 4 inches above the weld (See Figure 1).
These lugs obstruct the automated UT inspection tool from examining the code required volume of the weld below cach lug (156*). The FTI "URSULA" tool has a 6 degree movement arm and the physical size of the lugs and the
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" yaw" joint of the tool prevented scanning below the lugs back into the weld and surrounding base metal. All utid metal can be examined from both sides where access is available between the lugs (204"). Examinations for perpendicular and parallel reflectors covered areas accounting for 57% of the weld metal and heat affected zone (HAZ). Similarly, 57% of the weld metal can be examined for transverse reficctors from two opposing directions.
The examination of the Unit 2 Lower Shell Course-to-Dutchman weld, RPVC-WR29, is similarly obstructed (see Figure 1). All weld metal can be examined from both sides where access is available between the lugs (204 ).
J Examinations for perpendicular and parallel reflectors can cover areas accounting for 57% of the weld metal and heat affected zone (HAZ). Similarly, 57% of the weld metal can be examined for transverse reflectors from two opposing directions.
B.
REACTOR VESSEL LOWER HEAD CIRCUMFERENTIAL WELDS i
The examination of the Unit 1 Lower Disk-to-Dutchman weld, RPVC-WR16, is restricted by the 58 instrument tubes that penetrate the lower disk and physically obstruct the LTT scarch unit and/or the search unit position desice as shown in Figure 2 and 3. Approximately 19% of the weld length cannot be examined. The weld and the HAZ received essentially 100% coverage for parallel reflectors from the Dutchman side and for transverse reflectors in two opposing directions. Partial coverage is achieved for parallel reficctors from the disk side on the remainder of the l
weld resulting in an aggregate of all scan coverage of approximately 81%.
1 The examination of the Unit 2 Lower Disk-to-Dutchman weld, RPVC-WR16, is similarly restricted, see Figure 2 and
- 3. The weld and the HAZ will receive essentially 100% coverage for parallel reficctors from the Dutchman side and for transverse reflectors in two opposing directions. Partial coverage can be achieved for parallel reflectors from the disk side on the remainder of the weld resulting in an aggregate of all scan coverage of approximately 81%.
C.
REACTOR VESSEL SHELL-TO-FLANGE WELDS l
The examination of the Unit 1 Nozzle Shell Course-to-Flange weld, RPVC-WR7, is located immediately below the tapered portion of the flange which previously prevented 100% examination of the adjacent base metal weld (See Figure 4) based on Presenice Inspection (PSI) results. Coverage percentages indicated were not expected to improve with current examination techniques, however, automated examinations performed in BIR07, Spring 1996, achieved 100% coverage of required examinations. All of the code required weld volume and the adjacent base metal was examined for parallel reflectors.
The examination of the Unit 2 Nozzle Shell Course-to-Flange weld, RPVC-WR7, is similarly obstructed by the vessel flange taper per Figure 4. All of the code required weld volume and the adjacent base metal can be examined for parallel reficctors as shown in Figure 4.
Strict ASME Section 111 quality controls were used when designing, fabricating, and installing these welds. In addition, these welds were volumetrically examined during Presenice Inspections with no irregularities found.
BYRON STATION UNITS 1&2 FIRST INTERVAL ISI PROGRAM PLAN-NRC SUBMITTAL RELIEF REQUEST NR-20 j
(Page 3 of 7)
For welds referenced is Sections A, B, and C above, the probability of a flaw occurring only in one of the areas not being examined is extremely small. Most future indications of significant size will be found by the examination of the weld as it is currently performed.
PROPOSED ALTERNATE EXAMINATION:
The ultrasonic examination of the Byron Unit I reactor vessel was performed to the maximum extent possible. No alternative volumetric examination is proposed to examine the areas not scanned due to obstructions or geometric constraints.
VT-1 inspection was conducted on the weld (s) and HAZ(s) from the inside clad surface utilizing a submersible robot i
during the Byron Unit 1 Refuel Outage BIR07. Additionally, a VT-2 examination during system pressure testing per 1
Category B-P is performed on the Reactor Vessel each refueling outage to verify leaktight integrity of these welds.
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The ultrasonic examination of the Byron Unit 2 reactor vessel will also be performed to the maximum extent possible.
The same obstructions and geometric contraints are expected to limit the examination. The visual examinations will be repeated for the Unit 2 RPV welds.
JUSTIFICATION:
The Code required volumetric examination has been completed to the maximum extent practical using ultrasonic examination techniques for Byron Unit 1. The RPV examinations are conducted using an automated technique from the I.D. of the vessel. Access to allow inspection from the O.D. (shell side) of these welds is restricted due to the structural concrete surrounding the vessel.
Reasonable assurance of the continued insenice structural integrity of the subject welds is achieved without performing a complete Code examination. The weld (s) have received visual examinations (VT-1 and VT-2) to i
visually verify the integrity of the welds.
Compliance with the applicable Code requirements can only be accomplished by redesigning and refabricating the Reactor Vessel (s) and/or building a structure surrounding the vessel (s). Byron Station believes this course of action is a hardship without a compensating increase in the level of quality and safety.
The upcoming Byron Unit 2 Reactor Vessel examination will be performed to the maximum extent practical using the same techniques and examination methods as used for Unit 1.
l PERIOD FOR WHICH RELIEF 1S REOUESTED:
Reliefis requested for the first 10 year inspection interval for Byron Units 1 and 2.
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