ML20238F655
| ML20238F655 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 08/28/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20238F647 | List: |
| References | |
| NUDOCS 9809040175 | |
| Download: ML20238F655 (11) | |
Text
. .
e nts p k UNITED STATES g j 2
NUCLEAR REGULATORY COMMISSION g WASHINGTON, D.C. 20se6-0001 k . . . . . ,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE FIRST 10-YEAR INTERVAL INSERVICE INSPECTION PROGRAM COMMONWEALTH EDISON COMPANY BYRON STATION. UNIT 1 DOCKET NO. STN 50-454
1.0 INTRODUCTION
The Technical Specifications (TS) for Byron Station, Unit 1, state that the inservice inspection of the American Society of Mechanical Engineers (ASME) Code Class 1,2, and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code (Code) and applicable addenda as required by 10 CFR 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(6)(g)(i).10 CFR 50.55a(s)(3) states that attematives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed attematives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1,2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the pre-service examination requirements, set forth in the ASME Code,Section XI, " Rules for Inservice inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The applicable edition of Section XI of the ASME Code for the Byron Station, Unit 1, first 10-year inservice inspection (ISI) interval is the 1983 Edition through Summer 1983 Addenda.
Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission in support of that determination and a request made for relief from the ASME Code requirement. After evaluation of the determination, pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose alternative requirements that are determined to be authorized by law, will not endanger life, property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed.
ENCLOSURE 9809040175 980828 PDR ADOCK 05000454 G PDR
l 2-l The augmented reactor pressure vessel (RPV) examination requirements of 10 CFR
- j. 50.55a(g)(6)(ii)(A), require that a licensee must volumetrically examine essentially 100 percent l - (i.e., >90 percent) of each of the item 81.10 shell welds. As an altomative to the regulations, the l- licensee proposed that the limited examinations that were performed be considered as L acceptable to satisfy the augmented reactor vessel examination requirement.
By letter dated July 15,1996, the licensee submitted an altomative to 10 CFR $0.55a(g)(6)(iii)(A) augmented RPV examination and a request for relief for Byron Station, Units 1 and 2. The licensee provided additional information in its letter dated October 7,1997. In the licensee's
, letter dated October 7,1997, it revised Requests for Relief NR-20, Revision 1, and NR-25,
' Revision 0, for Unit 1, and deleted all references to Unit 2. Relief requests for limited examinations for Unit 2 will be submitted upon completion of the Unit 2 augmented RPV examinations, which were scheduled for the Spring of 1998.
2.0 EVALUATION The staff, with technical assistance from its contractor, the Idaho National Engineering and l Environmental Laboratory (INEEL), has evaluated the information provided by the licensee in
! support of its altemative to 10 CFR 50.55a(g)(6)(iii)(A) augmented RPV examination and request for relief pursuant to 10 CFR 50.55s(g)(6)(i) for Byron Station, Unit 1. Based on the results of the
- review, the staff adopts the contractor's conclusions and recommendations presented in the Technical Letter Report (TLR) attached.
Reauest for Relief NR-20. Revision 1 in accordance with 10 CFR 50.55a(g)(6)(ii)(A), all licensees must implement once, as par 1 of the inservice inspection interval in effect on September 8,1992, an augmented volumetric examination of the RPV welds specified in item B1.10 of Examination Category B-A of the 1989 Edition of the ASME Code,Section XI. Examination Category B-A, items 21.11 and B1.12 require volumetric examination of essentially 100 percent of the RPV circumferential and longitudinal shell welds, as defined by Figures lWB 25001 and -2, respectively. Essentially
- 100 percent, as definsd by 10 CFR 50.55a(g)(6)(ii)(A)(2), is greater than 90 percent of the examination volume of each weld.
Pursuant to 10 CFR 50.55a(g)(6)(ii)(A)(5), the licensee has proposed an attemative to the o
coverage requirements of the augmented RPV examinatico required by the regulations. The l essentially 100 percent coverage requirement could not be met for Wolet RPVC-WR29.
Essentially 100 percent of all other Examination Category B-A, item B1.10 welds have been examined. The licensee stated: '
l-l The ultrasonic examination of the reactor vessel was performed to the maximum extent
- possible. No attemative volumetric examination is proposed to examine the areas not scanned due to obstNetions or geometric constraints.
VT-1 inspa@n wn conducted on the wmd eini HAZ [ heat-artected zone) from the inside clad surface utilizing a submersible robot during the Byron Unit 1 Refuel Outage B1R07.
Additionally, a VT-2 examination during system pressure testing per Category B-P is performed on the RPV each refueling outage to verify leaktight integrity of these welds.
Additionally, leakage during operation would be detected by operating shiftly surveillance of the RPV incore tunnel sump run data,
- i. At Byron, Unit 1, the augmented coverage requirements can not be met for shell Wold 1- RPVC-WR29 due to physical restrictions that limit scan coverage. Adjacent core barrel locating lugs which are welded to the RPV intamal surface limit coverage to 57. percent of the weld metal and HAZ. To achieve complete coverage for the subject welds, design modifications would be j required to increase access from the inside surface (10).
The licensee has examined more than half of the subject weld and has examined greater that 90 percent of all other RPV shell welds. Furthermore, the licensee performed a remote VT-1 visual examination of the interior cladded surface of the weld and HAZ using a submersible robot. Based on the cumulative volumetric examination coverage obtained, in combination with the remote visual examination, the staff concludes that any significant pattoms of degradation, if present, would have been detected and that the examinations performed provide an acceptable level of quality and safety. ' Therefore, the licensee's proposed altemative is authorized pursuant
. to 10 CFR 50.55a(g)(6)(ii)(A)(5) and 10 CFR 50.55a(a)(3)(i) for the first 10-year interval.
Reauest for Relief NR-25. Revision 0
' ASME Code,Section XI, Examination Category B-A, item B1.11 requires 100 percent volumetric examination, as defined by Figure IWB-2500-1, for RPV circumferential shell welds. Pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from examining RPV circumferential shell -
Weld RPVC-WR29 to the extent required by the Code.
The Code requires 100 percent examination of RPV lower shell course-to-dutchman Weld RPVC WR29. However, access to this weld is obstructed by six core barrel locating lugs which are adjacent to the weld. These locating lugs limit the volumetric examination and make the Code coverage requirements impractical to meet for Weld RPVC-WR29. To meet the Code requirements, the RPV would require design modifications to allow access for complete 'i examination. imposition of this requirement would create a considerable burden on the licensew.
. The licensee examined 57 percent of the Code required volume for the subject weld, along with i complete volumetric examination of the remaining RPV shell welds. In addition, a VT-1 visual examination was performed on the welds and HAZ(s) using a submersible robot. The combination of these examinations would have detected any existing pattems of degradation and provide reasonable assurance of the continued structuralintegrity for the RPV Based on the
- impracticality of meeting the Code requirements, and the reasonable assurance of the structural integrity provided by the examinations that were performed, the staff concluded that relief is
. granted pursuant to 10 CFR 50,55a(g)(6)(i) for the first 10-year interval. l
3.0 CONCLUSION
l i
. The staff has reviewed the licensee's submittals and concludes that for Request for Relief NR-20, Revision 1, the licensee's augmented inspection provides added assurance of structural integrity of the reactor vessel. Therefore, the licensee's proposed altemative to the regulations is authorized pursuant to 10 CFR 50.55a(g)(6)(ii)(A)(5) and 10 CFR 50.55a(a)(3)(l) for the first 10 year interval. .
i 3
i L-
4 For Request for Relief NR-25, Revision 0, the staff concluded that the Code coverage requirements are impractical for the subject weld. Therefore, relief is granted pursuant to 10 CFR 50.55a(g)(6)(i) for the first 10-year interval.
The Commission will evaluate determinations that Code requirements are impractical. The Commission may grant such relief and may impose attemative requirements as it determines is authorized by law giving due consideration to the burden upon the licensee if the requirements were imposed on the facility.
Attachment:
Technical Letter Report Principal Contributor: T. McLellan Dated: August 28, 1998 l
l l
\
puru g t UNITED STATES s" j t
NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20066 4 01 TECHNICAL LETTER REPORT ON THE FIRST 10-YEAR INTERVAL INSERVICE INSPECTION REQUESTS FOR RELIEF NR-20 REV.1 AND NR-25. REV. O FOR COMMONWEALTH EDISON COMPANY BYRON NUCLEAR POWER STATION. UNIT 1 DOCKET NUMBER: 50-454
1.0 INTRODUCTION
By letter dated July 15,1996, the licensee, Commonwealth Edison Company, submitted NR-20 for the first 10-year inservice inspection (ISI) interval for Byron Nuclear Power Station, Units 1 and 2. NR-20 addressed limited examinations of the reactor pressure vessel (RPV) welds. The Nuclear Regulatory Commission (NRC) requested additional information by letter dated June 30, 1997. As a result of the NRC request for additionalinformation (RAl), the licensee submitted, by letter dated October 7,1997, Requests for Relief NR-20, Revision 1 and NR-25, Revision 0 for Unit 1, and eliminated all references to Unit 2. Relief requests forlimited examinations on Unit 2 will be submitted upon completion of the Unit 2 augmented RPV examinations, which are scheduled for the spring of 1998. The Idaho National Engineering and Environmental Laboratory (INEEL) staff has evaluated the information provided by the licensee in support of these requests for reliefin the following section.
2.0 EVALUATION The Code of record for the Byron Nuclear Power Station, Unit 1 first 10-year inservice inspection intervalis the 1983 Edition through Summer 1983 Addenda of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. The information provided by the licensee in support of the requests for relief has been evaluated and the bases for disposition are documented below.
A. Recuest for Relief NR-20. Revision 1. Examination Cateaory B-A. Item B1.11. Auomented Reactor Pressure Vessel (RPV) Examination per 10 CFR 50.55afo)(6)(ii)
Reaulatorv Requirement: In accordance with 10 CFR 50.55a(g)(6)(ii)(A), all licensees must implement once, as part of the inservice inspection intervai in effect on September 8,1992, an augmented volumetric examination of the RPV welds specified in item B1.10 of Examination Category B-A of the 1989 Edition of the ASME Code,Section XI. Examination C3tegory B-A, items B1.11 and B1.12 require volumetric examination of essentially 100% of the RPV circumferential and longitudinal shell welds, as defined by Figures lWB-2500-1 and -2, respectively. Essentially 100%, as defined by 10 CFR 50.55a(g)(6)(ii)(A)(2), is greater than 90% of the examination volume of each weld.
l Licensee's Proposed Attemative: Pursuant to 10 CFR 50.55a(g)(6)(ii)(A)(5), the licensee has proposed an attemative to the coverage requirements of the augmented RPV examination required by the regulations. The essentially 100% coverage requirement ATTACHMENT i
2-could not be met for Wold RPVC-WR29. Essentially 100% of all other Examination Category B-A, item B1.10 welds have been examined. The licensee stated:
The ultrasonic examination of the reactor vessel was performed to the maximum extent possible. No attemative volumetric examination is proposed to examine the areas not scanned due to obstructions or geometric constraints.
VT-1 inspection was conducted on the weld and HAZ from the inside clad surface utilizing a submersible robot during the Byron Unit 1 Refuel Outage B1R07.
Additionally, a VT-2 examination during system pressure testing per Category B-P is
- performed on the RPV each refueling outage to verify leaktight integrity of these welds. Additionally, leakage during operation would be detected by operating shiftily surveillance of the RPV incore tunnel sump run data."
Licensee's Basis for Reauestina Relief (as stated):
Pursuant to 10 CFR 50.55a(g)(6)(ii)(A)(5), relief is requested from the augmented requirement to examine ' essentially 100%' of the examination volume of the RPV circumferential shell weld, RPVC-WR29, on the basis that the attemative to the examination requirements provides an acceptable level of quality and safety.
Augmented examination of the subject RPV shell weld was conducted on Byron Unit i during the B1R07 refuel outage (fall 1996). During this exam, physical obstructions and geometry prever,ted (UT) coverage in excess of 90% of the required volume. The examination of the Unit 1 Lower Shell Course-to-Dutchman weld, RPVC-WR2g, is restricted by six core barrel locating lugs welded to the inner surface of the vessel approximately four inches above the weld. These lugs obstruct the automated UT inspection tool from examining the Code required volume of the weld below each lug (156*). The FTl 'URSULA' tool has a six degree movement arm. The physical size of the lugs and the ' yaw' joint of the tool prevents scanning below the lugs back into the weld and surrounding base metal. All weld metal can be examined from both sides where access is available between the lugs (204*).
Examination 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 reflectors from two opposing directions.
Examinations of the welds from the OD of the vessells not practicable due to the structural concrete surrounding the vessel. The annulus between the vessel and the structural concrete does not allow for even remote ultrasonic techniques to be employed. To achieve 100% ultrasonic examination coverage of this weld vrould i
require redesign and prefabrication of the RPV to eliminate the core barrel lower lugs.
I For weld RPVC-WR29, the probability of a flaw occurring 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.
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 and automated technique from the ID of the r
3-vessel. Access to allow inspection from the CD (shell side) of these welds is restricted due to the rioncrete structure surrounding the vessel.
Reasonable assurance of the continued inservice structuralintegrity of the subject wolds is achieved without performing a complete Code examination. The weld received visual examinations (VT-1 and VT-2) to visually verify the integrity of the wold.
Compliance with the applicable Code requirements can only be accomplished by redesigning and prefabricating the Reactor Vessel and/or building structure surrounding the vessel. Byron Station believes this course of action is a hardship without a compensating increase in the level of quality and safety and that the altemative provides an acceptable level of quality and safety.
History:
During Refuel Outage B1R07, Byron Station conducted ultrasonic examinations (UT) of the Byron Unit 1 RPV. This was the last refuel outage of the third period of the ,
First inservice inspection Interval and occurred in April through June 1996.
Framatome Technologies Inc. (FTI) was contracted to perform the examinations with their state-of-the-are 'URSULA' manipulator and their 'ACCUSONEX' UT system.
The examinations were performed in accordance with the requirements in ASME Section XI, Article IWA-2232, US NRC Regulatory Guide 1.150 and 10 CFR 50.55a(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 eight Reactor Nonle-to-Vessel welds and inner Radius sections (Category B-D), and Reactor Flange threads (Category B-G-1).
Byron Station RPVs do not have any longitudinal shell welds.
The B1R07 examinations revealed two minor recordable indications in item B1.10 RPV circumferential shell weld WR-29,1 minor recordable indications in item B1.10 RPV shell weld WR-34, and one minor recordable indication in item B5.010 RPV noule to safe end weld RPVS-H. All indications are within the acceptance criteria of ASME Section XI, Article IWB-3500.
During the performance of the B1R07 examinations, physical obstructions and geometry prevented UT coverage in excess of 90% of the required volume for component RPVC WR29. Full 100% UT coverage was obtained for the item B1.10 RPV shell welds WR-18 and WR-34. Full 100% UT coverage was obtained for the item B1.30 RPV shell to flange welds WR-7. Additionally, limited amount of examination coverage was attained for item B1.20 RPV head weld WR 16. The
. examination limitation for WR-16 is addressed in Byron Station Unit 1 First :
Inspection Interval Relief Request NR-1 that was previously approved by the NRC in an SER dated August 1991 (EGG-MS-9117). The portion of NR-1 that addressed the examination limitations of weld WR-16 was not affected by 50.55a(g)(6)(ii)(A).
Strict ASME Section lli quality controls were used when designing, fabricating, and installing these welds. In addition, these welds were volumetrically examined during Preservice inspection ultrasonic examination of the Byron Unit 1 RPV was conducted during the fall of 1981 and did not reveal any recordable indications for f
L I
i
f the Category B-A RPV shell welds. Preservice Examination ultrasonic limitations were addressed in the Byron Units 1 and 2 inservice inspection Program First inspection Interval Relief Request NR-1. Portions of previously granted relief request NR-1 for Byron Station Units 1 and 2 First inspection interval for the Reactor Shell welds specified in Code item B1.10, were revoked in 10 CFR 50.55a(g)(6)(ii)(A) with respect to examination coverages."
Evaluation:
I To comply with the augmented reactor vessel examination requirements of 10 CFR 50.55a(g)(6)(ii)(A), licensees must volumetrically examine essentially 100% of each of the item B1.10 shell welds. In accordance with the regulations, essentially 100% is defined as greater than 90% of the examination volume of each weld.
At Byron Unit 1, the augmented coverage requirements cannot be met for shell Weld RPVC-WR2g due to physical restrictions that limit scan coverage. Adjacent core barrel locating lugs which are welded to the RPV intomal surface limit coverage to 57% of the weld metal and heat affected zone.- To achieve complete coverage for the subject welds, design modifications would be required to increase access from the inside surface (ID).
, As a result of the augmented volumetric examination rule, licensees must make a reasonable. offott to maximize examination coverage of their reactor vessels, in cases where examination coverage from the ID is inadequate, examination from the outside l surface (OD) using manual inspection techniques is a potential option. However, at Byron Unit 1, the concrete building structure prevents access for equipment and personnel from ,
the OD. Therefore, it is concluded that the licensee cannot enhance coverage by I examining from the OD.
The licensee has examined more than half of the subject weld and has examined greater that 90% of all other RPV shell welds. Furthermore, the licensee performed a remote VT-1 visual examination of the interior cladded surface of the weld and HAZ using a submersible !
robot. Based on the cumulative volumetric examination coverage obtained, in combination ;
with the remote visual examination, the INEEL staff concludes that any significant patterns !
of degradation, if present, would have been detected and that the examinations performed j provide an acceptable level of quality and safety. Therefore, it is recommended that the ;
licensee's proposed attemative be authorized pursuant to 10 CFR 50.55a(g)(6)(ii)(A).
! B. Reauest for Relief NR-25. Revision 0. Examination Cateoorv B-A. Item B1.11. Reactor l
Pressure Vessel (RPV) Circumferential Shell Weld RPVC-WR2g Code Requirement: Examination Category B-A, item B1.11 requires 100% volumetric, as .
defined by Figure IWB-2500-1, for RPV circumferential shell welds. !
Licensee's Code Relief Reauest: Pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from examining RPV circumferential shell Weld RPVC-WR2g to the extent required by the Code. l l
1 l
_ __ _____-___ _ L
5-Licensee's Basis for Reauestina Relief (as stated):
Pursuant to 10 CFR 50.55a(g)(5)(iii), relief is requested from the ASME Code item B1.11 requirement to examine ' essentially 100%' of the examination volume of the RPV circumferential shell weld, RPVC-WR29, on the basis that conformance with the Code requirements is impractical.
Augmented examination of the subject RPV shell weld was conducted on Byron Unit 1 during the B1R07 refuel outage (fall 1996). During this exam, physical obstructions and geometry prevented UT coverage in excess of 90% of the required volume. The examination of the Unit i Lower Shell Course-to-Dutchman weld, RPVC-WR29, is restricted by six core barrel locating lugs wolded to the inner surface of the vessel approximately four inches above the weld. These lugs obstruct the automated UT inspection tool from examining the Code required volume of the weld below each lug (156'). The FTI'URSULA' tool has a six degree movement arm. The physical size of the lugs and the ' yaw' joint of the tool prevents scanning below the lugs back into the weld and surrounding base metal. All weld metal can be examined from both sides where access is available between the lugs (204').
Examination 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 reflectors from two opposing directions.
Examinations of the welds from the OD of the vesselis not practicable due to the structural concrete surrounding the vessel. Removal of the obstruction (structural concrete) would require extensive structural modifications and the man-hour / exposure expenditures are impractical. The annulus between the vessel and the structural concrete does not allow for even remote ultrasonic techniques to be employed. The development of sophisticated tooling to examine the weld from the OD would result in only marginal increases in the examination coverages. To !
achieve 100% ultrasonic examination coverage from the ID of this weld would i require redesign and prefabrication of the RPV to eliminate the core barrellower lugs and reposition the weld relative to the lugs.
For weld RPVC-WR29, the probability of a flaw occurring 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. i Justification:
The Code required volumetric examination has been completed to the maximum L extent practical using ultrasonic examination techniques for Byron Unit 1. The RPV i i
examinations are conducted using and automated technique from the ID of the l vessel. Access to allow inspection from the OD (shell side) of these welds is restricted due to the concrete structure surrounding the vessel. j Reasonable assurance of the continued inservice structuralintegrity of the subject wolds is achieved without performing a complete Code examination. The weld received visual examinations (VT-1 and VT-2) to visually verify the integrity of the weld.
e i
i 6-Compliance with the applicable Code requirements can only be a.::complished by redesigning and prefabricating the Reactor Vessel and/or building structure surrounding the vessel. Byron Station believes this course of action is a hardship without a compensating increase in the level of quality and safety and that the altemative provides an acceptable level of qualit/ and safety.
1 During the performance of the B1R07 examinations, physical obstructions and geometry prevented UT coverage in excess of 90% of the required volume for component number RPVC-WR29. Full 100% UT coverage was obtained for the item B1.11 RPV shell welds WR-18 and WR-34. Full 100% UT coverage was obtained for the item B1.30 RPV shell to flange welds WR-7. Additionally, limited amount of examination coverage was attained for item B1.21 RPV head weld WR-i 16. The examination limitation for RPVC-WR16 is addressed in Byron Station Unit 1 l First inspection interval Relief Request NR-1 that was granted in an SER dated August 1991 (EGG-MS-9117).
Strict ASME Section til quality controls were used when designing, fabricating, and installing these welds. In addition, these welds were volumetrically examined during Preservice Inspection ultrasonic examination of the Byron Unit 1 RPV was conducted during the fall of 1981 and did not reveal any recordable indications for the Category B-A RPV shell welds. Preservice Examination ultrasonic limitations were addressed in the Byron Units 1 and 2 Inservice Inspection Program First inspection Interval Relief Request NR-1. Portions of previously granted relief request NR 1 for Byron Station Units 1 and 2 First ;nspection Interval for the Reactor Shell welds specified in Code item B1.10, were revoked in 10 CFR 50.55a(g)(6)(ii)(A) with respect to examination coverages."
Licensee's Prop'osed Altemative (as stated):
The ultrasonic examination of the reactor vessel was performed to the maximum extent possible. No altemative volumetric examination is proposed to examine the areas not scanned due to obstructions or geometric constraints.
VT-1 inspection was conducted on the weld and HAZ from the inside clad surface utilizing a submersible robot during the Byron Unit 1 Refuel Outage B1R07.
Additionally, a VT-2 examination during system pressure testing per Category B-P is performed on the Reactor Vessel each refueling outage to verify leaktight integrity of those welds. Additionally, leakage during operation would be detected by operating shift surveillance of the RPV incore tunnel sump run data."
Evaluation:
(
The Code requires 100% examination of RPV lower shell course-to-dutchman Wold RPVC-WR29. However, access to this weld is obstructed by six core barrel locating lugs which are adjacent to the weld. These locating lugs limit the volumetric examination and make the Code coverage requirements impractical to meet for Wald RPVC-WR29. To meet the Code requirements, the RPV would require design modifications to allow access for complete examination.' imposition of this requirement would create a considerable '
burden on the licensee.
.. . c,
.7 The licensee examined 57% of the Code-required volume for the subject weld, along with complete volumetric examination of the remaining RPV shell welds. In addition, a VT-1 visual examination was performed on the welds and HAZ(s) using a submersible robot.
The combination of these examinations would have detected any existing pattoms of degradation and provide reasonable assurance of the continued structuralintegrity for the RPV. Based on the impracticality of meeting the Code requirements, and the reasonable assurance of the structural integrity provided by the examinations that were performed, it is concluded that relief should be granted pursuant to 10 CFR 50.55a(g)(6)(i) for the first 10-year interval.
3.0 CONCLUSION
The INEEL staff has reviewed the licensee's submittals and concludes that for Request for Relief NR-20, Revision 1, the licensee's proposed altamative provides an acceptable level of quality and safety. Therefore, it is recommended that the licensee's proposed attemative to the regulations be authorized pursuant to 10 CFR 50.55a(g)(6)(ii).
For Request for Relief NR-25, Revision 0, it is concluded that the Code coverage requirements are impractical for the subject weld. Therefore, it is recommended that relief be granted pursuant to 10 CFR 50.55a(g)(6)(i).
I
(
,