ML17228B100
| ML17228B100 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 04/12/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17228B099 | List: |
| References | |
| NUDOCS 9504170178 | |
| Download: ML17228B100 (7) | |
Text
ENCLOSURE 1
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THE REQUEST FOR AUTHORIZATION OF ALTERNATIVE EXAMINATION FOR REACTOR VESSEL WELDS FOR FLORIDA POWER AND LIGHT COMPANY ST.
LUCIE NUCLEAR PLANT, UNIT 2 DOCKET NUMBER: 50-389
1.0 INTRODUCTION
In a letter dated October 12, 1994, the licensee, Florida Power and Light Company (FPL), proposed an alternative examination to the requirements of 10 CFR 50.55a(g)(6)(ii)(A), Augmented Examination of Reactor Vessel.
This section requires licensees to implement a one-time examination of "essentially 100N" of the reactor pressure vessel shell welds as specified in Item Bl.10, Examination Category B-A, "Pressure Retaining Welds in Reactor Vessel," in Table IWB-2500-1 of the 1989 Edition of the ASME Section XI.
10 CFR 50.55a(g)(6)(ii)(A)(2) defines "essentially 100%%uo" examination as more than 90K of the examination volume of each weld.
The schedule for implementation of the augmented inspection is dependent upon the start date of the 10-year inservice inspection (ISI) interval that was in effect on September 8,
1992.
2.0 EVALUATION AND CONCLUSIONS The staff, with technical assistance from the Idaho National Engineering Laboratory (INEL), has evaluated the information provided by the licensee in support of its alternative to the examination requirements of 10 CFR 50.55a(g)(6)(ii)(A).
Based on the information submitted, the staff adopts the contractor's conclusions and recommendations presented in the attached Technical Letter Report.
The alternatives contained in FPL's submittal are authorized pursuant to 10 CFR 50.55a(g)(6)(ii)(A)(5) as they provide an acceptable level of quality and safety.
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ENCLOSURE 2
TECHNICAL LETTER REPORT ON THE REQUEST FOR AUTHORIZATION OF ALTERNATIVE TO THE AUGMENTED REACTOR PRESSURE VESSEL EXAMINATION FOR FLORIDA POWER AND LIGHT COMPANY ST.
LUCIE NUCLEAR PLANT, UNIT 2 DOCKET NUMBER'0-389
1.0 INTRODUCTION
As the result of a September 8,
1992, revision to the regulations, licensees of operating commercial nuclear power reactors must implement a one-time augmented examination of all reactor pressure vessel (RPV) shell welds.
In accordance with the regulations, licensees must perform volumetric examinations of "essentially 100X" of RPV shell welds as specified in the 1989 Edition of ASHE Section XI.
By letter dated October 12, 1994, the licensee, Florida Power and Light Company, submitted a "Request for Authorization of an Alternative Examination" to the augmented RPV examination specified in 10 CFR 50.55a(g)(6)(ii)(A).
The Idaho National Engineering Labor atory (INEL) staff has evaluated the information provided by the licensee in support of this request in the following section.
2.0 EVALUATION The information provided by the licensee in support of the alternative to the augmented RPV examination has been evaluated and is documented below.
The augmented RPV examination was performed during a 1989 refueling outage of the first 10-year inservice inspection (ISI) interval which ended August 8, 1993.
The Code of record for the St. Lucie, Unit 2, first 10-year interval is the 1980 Edition through Minter 1980 Addenda of ASHE Section XI.
Au mented Examination of Examination Cate or B-A Item 81. 10 Reactor Pressure Vessel RPV Shell Welds Re ulator Re uirement:
10 CFR 50.55a(g)(6)(ii)(A)(2) requires that all licensees augment their RPV examination by implementing once, as part of their ISI program in effect on September 8,
1992, the examination requirements for RPV shell welds specified in Item Bl. 10 of Examination Category B-A, "Pressure Retaining Welds in Reactor Vessel," in Table IWB-2500-1 of subsection IWB of the 1989 Code.
As specified by the
Code, this augmented examination must include volumetric examination of "essentially 100%"
of the length of each RPV shell weld classified under Item Bl. 10.
Licensees with fewer than 40 months remaining in the ISI interval in effect on September 8,
- 1992, may defer the augmented examination to the first period of the subsequent interval under the conditions listed in 10 CFR 50.55a(g)(6)(ii)(A)(3).
~li <<i:
0 iii i i,iiii,iiii ii-i ii effect at St, Lucie, Unit 2.
As allowed by the regulations, the licensee is using the first interval RPV examinations to satisfy the augmented examination requirements.
However, the coverage requirements for the augmented RPV shell weld examination, as specified by 10 CFR 50.55a(g)(6)(ii)(A), cannot be completely satisfied at St. Lucie, Unit 2.
Therefore, the licensee has requested that the limited RPV examinations performed during the first 10-year ISI interval be considered an acceptable alternative to the regulatory requirements.
The coverage and limitation for each of the Item Bl, 10, Examination Category B-A shell welds is listed in the table below.
- ,-:;::Wel'd:::'::Ho:.-::".-:";
201-141 101-171 106-121 101-124A 101-124B 101-124C
','.Examiiiati on':;:Area'.,';::;.:':,::::::::::::::.':::;::".::.:::: ':
Lower head-to-shell circ. weld Lower shell-to-intermediate shell circ. weld Upper shell-to-intermediate shell circ. weld Intermediate shell ion
. weld Intermediate shell ion
. weld Intermediate shell long, weld 93X 88%
100X 100X 100%
87%
Core barrel anti-rotation lu s RPV material specimen tubes None None None RPV material specimen tubes
'or the purpose of the augmented examination, essentially 100X is more than 90X of the examination volume of each weld,'s defined in 10 CFR 50.55a(g)(6)(ii)(A)(2).
Au mented RPV Examination Covera e
Wel d:.'Ho. ';-
101-122A 101-122B 101-122C 101-142A Examination Area Upper shell long.
weld Upper shell long.
weld Upper shell long.
weld Lower shell long. weld Covera e
92X 94%
100X Limitati on--
Adjacent outlet nozzle integral extension Adjacent inlet nozzle inner blend Adjacent inlet nozzle inner blend None 101-142 B Lower shell long. weld 100X None 101-142C Lower shell long.
Meld 93X RPV material specimen tubes Licensee's Discussion of Au mented Examination (as stated):
"The change in the regulation has little or no effect on the St.
Lucie Power Plant, Unit 2, First 10-Year Inservice Inspection Interval scheduled examinations, as FPL performs essentially 100X examination of all reactor pressure vessel weld lengths, to the extent practical each inservice inspection interval.
"The last mechanized (automated) examination act.ivity was performed during the 1989 refueling outage, which was part of the first inservice inspection interval in effect on September 8,
- 1992, when the rule change became effective.
"Because FPL inservice examinations were extended to include essentially 100X of all reactor pressure vessel welds the augmented reactor vessel examination requirements of the rule change which became effective on September 8,
- 1992, meet the examination requirements for reactor vessel shell welds specified in Examination Item Bl. 10 of Examination Category B-A, "Pressure Retaining Welds in Reactor Vessel," in Table IWB-2500-1 of Subsection IWB of the 1989 Edition of Section XI, Division 1, of the ASME Boiler and Pressure Vessel
- Code, and subject to the conditions specified in 10 CFR 50.55a(g)(6)(ii)(A)(3) and (4).
"During the 1989 refueling outage, of the St.
Lucie Nuclear Power Plant, Unit 2, First Inservice Inspection Interval, Southwest Research Institute (SwRI) using their Enhanced Data Acquisition System performed the Reactor Pressure Vessel mechanized (automated) ultrasonic examinations.
These examinations covered essentially 100X of all Reactor Pressure Vessel shell circumferential and longitudinal welds, to the extent practical within the design, geometry and materials of construction.
"All of the RPV welds were examined for 100X of accessible weld lengths.
The flow skirt, core barrel lugs, and material specimen tubes limited
full length scanning access to some welds.
The outlet nozzle integral extensions and flange-to-shell weld joint configuration limited full c'overage of some weld volumes by all ultrasonic examinations techniques.
"A full vee path calibration of the 45'hear wave scan was used to compensate for, limitations encountered in the near surface and those due to geometric shadowing.
A 50/70'i-modal ultrasonic examination was used for examination of the inner 24 percent t [thickness].
"These examinations were conducted to satisfy the requirements of the 1980 Edition through the Winter 1980 Addenda of Section XI.
In addition to the 80W80 Code requirements, the mechanized examination activity was extended to include all Reactor Pressure Vessel accessible weld lengths.
"Because of the limited access between the vessel and bioshield wall, conducting the examinations from the external surface for the purpose of investigating the small amount of weld volume missed during the mechanized inside surface examinations would require the destruction of the insulation during the removal
- process, excessive
- manhours, manrem, and substantial costs without providing any substantial increase in the quality and safety of the unit."
Licensee's Pro osed Alternative Examination (as stated):
"It is the intent of FPL to use the First Inservice Inspection Interval examinations to satisfy the augmented examination requirements of the rule change."
"The extent of examination volume achieved ultrasonically and the alternate scans performed (see Examination Coverage Table) coupled with the system pressure tests provide assurance of an acceptable level of quality and safety.
As an alternative FPL performed the following:
I) "Periodic System Pressure test per Category B-P, Table IWB-2500-1.
2)
"Conduct essentially 100X Mechanized (automated)
Ultrasonic Examinations to the extent practical on all reactor pressure'vessel welds from the inside surface.
- 3) "50/70'i-modal ultrasonic examination of the inner 25 percent t.
4)
"Conduct a full vee 45'hear wave examination to the extent practical to compensate for recorded limitations.
5)
"Employ, as they become available additional examinations, inspections and/or techniques that would provide a substantial increase in the examination of areas currently missed under current examination techniques."
Evaluation:
The regulations require an augmented volumetric examination of the RPV shell welds in accordance with the 1989 Edition of ASHE Section XI for each operating reactor.
To satisfy the augmented examination requirements, licensees must perform the required volumetric
j
~'xamination on essentially 100N
(>90/o) of each of the Item B1.10 shell colds.
Licensees that make a determination that they are unable to completely satisfy the requirements specified by the regulations must submit information to the Commission to support that determination and shall propose an alternative to the examination requirements that would provide an acceptable level of quality and safety.
This proposed alternative may be used when authorized by the Director of the Office of NRR.
The rule change was prompted by certain concerns regarding the integrity of aging vessels and the relatively low examination cover ages, particularly for BWR vessels.
To provide increased assurance of the integrity of operating
The licensee, Florida Power and Light, has determined that the augmented l
RPV examination requirements cannot be completely satisfied as specified in 10 CFR 50.55a(g)(6)(ii)(A) at St. Lucie, Unit 2, and has submitted information to support that determination.
In addition, the licensee proposed an alternative to the augmented examination requirements and has requested authorization of that alternative.
It is evident from the licensee's submittal that the volumetric examinations were performed to the extent practical from the ID surface using mechanized inspection equipment.
In an attempt to maximize
- coverage, the licensee supplemented the examinations with a full vee
- path, 45 shear wave examination to compensate for limitations encountered in the near surface and for geometric interference.
This effort resulted in coverage in excess of 90/o for all but two welds, which were limited to 87X and 88X of the required volume.
Complete coverage was achieved for five of the remaining ten welds.
The INEL staff believes that the examination coverage attained was sufficient to detect any existing patterns of degradation.
Examination from the external surface of the vessel is not feasible because of limited access between the vessel and the bioshield and the significant burden associated with destruction,
- removal, redesign and reinstallation of the insulation surrounding the vessel.
Assuming access
p 4'
~
~
could be attained, the increase in examination coverage would be
'esignificant compared with the percentage already examined.
Therefore, the INEL staff concludes that imposing additional examinations from the external surface would result in a significant burden without a substantial increase in quality and safety.
Based on review of the information submitted by the licensee, it is concluded that the licensee has maximized examination coverage to the extent feasible.
The extent of volumetric examinations achieved utilizing alternative scanning methods provides adequate assurance of the RPV's structural integrity.
Therefore, it is recommended that the licensee's proposed alternative be accepted.
3.0 CONCLUSION
The INEL staff has reviewed the licensee's submittal and concludes that the licensee has maximized examination coverage to the extent feasible and that there is no reasonable way to increase examination coverage.
The extent of volumetric examinations achieved was sufficient to detect patterns of degradation that may have been present.
Therefore, it is recommended that the licensee's proposed alternative be accepted.
I