ML19341A431
| ML19341A431 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/31/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19341A430 | List: |
| References | |
| NUDOCS 8101230504 | |
| Download: ML19341A431 (16) | |
Text
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UNITED STATES g
I NUCLEAR REGULATORY COMMISSION g
WASHINGTON, D. C. 20555 J_.,..... )n E SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REG"LATION SUPP: ~ING AMENDMENT NO. 54 TO PROVISIONAL OPERATING LICENSE NO. DPR-19 AND AMENDMENT NO. 47 TO FACILITY OPERATING LICENSC N0. DPR-25 DOCKET NOS. 50-237 AND 50-249
1.0 INTRODUCTION
By application dated. July 31, 1978, and supplements thereto dated September 11, 1978, January 12, 1979, and June 26, 1979, Commonwealth Edison Company (the licensee) requested changes to the Technical Specifications appended to Facility Operating License No. DPR-19 for the Dresden Nuclear Power Station Unit No. 2 and DPR-25 for Unit No. 3.
The proposed changes would replace the existing inservice inspection program in Section 4.6.F with a program that meets the requirements of 10 CFR 50.55a(g). This inservice inspection program is applicable to the 40-month period that commenced on November 1, 1978. The pump and valve testing portion of the licensee's proposed program will be addressed in a separate action when that portion of the review is complete.
The proposed inservice inspection program includes request for relief from certain ASME Code requirements pursuant to 10 CFR Part 50.55a(g)(6)(i).
Evaluation of those requirements which the licensee has determined to be impractical for implementation at the facility and for which the licensee has requested relief are discussed below.
2.0 EVALUATION The NRC staff has reviewed and evaluated the Inservice Inspection Program (excluding testing of pumps and valves) for the Dresden Nuclear Power Station Unit Nos. 2 and 3, and finds it in compliance with Paragraph (g) of 10 CFR 50.55a, " Inservice Inspection Requirements". Pursuant to 10 CFR Part 50.55a(g)(6)(i), relief may be granted from specific requirements stated-in the ASME Boiler and Pressure Vessel Code,Section XI, 1974 Edition including Addenda through Surmier 1975, which we have concluded to be impractical for the facilities because of component or system design, geometry, or materials of construction.
In some cases, relief may be granted only after performing the alternative inspection requirements which the staff deems necessary.
Such relief and alternative requirements are autho-
'rized by law and will not endanger lifa or property or the cc:mion defense and security and are otherwise in the public interest giving due consideration to the burden upon the licer)see that c.ould result if the requirements were imposed on the facility.
In some cases, relief should not be granted because of the factors stated in the evaluation of the specific request.
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e I.
Relief Request Evaluations A.
Reactor Vessel Core Region Weld Examination (Relief Request C-1), Examina-tion Category 8-A, Item B1.1.
Code Requirement:
Volumetric examination of the longitudinal and circumferential welds in the core beltline region.
Examination shall cover at least 10% of the length of each longitudinal weld and 5% of the length of each circumferential weld, with the minimum length of the weld examined to be one wall thickness.
Examinations may be performed at or near the end of the inspection interval.
Code Deviation Request:
Request relief from volumetric examination of welds.
Reason for Request
There is one circumferential vessel weld and portions of six longitudinal relds in the core beltline region. Accessibility for inspection of these welds was not provided for in the plant design.
Inspection from outside the vessel is precluded due to the vessel insulation and the close proximity of the biological shield wall.
This mirror-type insulation on the vessel wall is made up of interlocking panels making removal difficult. The annular dimension between the shield wall and the insulation is only four inches which is not sufficient to allow direct access to personnel.
Inspection of these welds from inside the vessel is hampered by the vessel internal design.
The core shroud, jet pumps, and other brackets are not designed to be removed. At this time, no inspection method is available and these welds require relief from the code requirements.
Staff Evaluation:
Imposition of the exact Code requirements would subject the licensee to extreme hardships in necessitating removal of portions of the concrete biological shield and the permanently installed insulation to perform the required examina-tion of the welds listed from the vessel outside surface.
Limitations of design of the vessel insulation and biological shield wall make these inspections impractical.
The reactor vessel is presently monitored for radiation damage in the beltline region.
This vessel surveillance program is in compliance with ASTM E185-66, and has been evaluated with respect to the requirements of ASTM E185-73. We have determined that the surveillance program meets the essential requirements of ASTM E185-73 and, therefore, will provide sufficient data to monitor radiation damage to the vessel beltline materials.throughout the vessel's service life.
In addition, the vessel was designed and fabricated in accordance with the rules of Sec' tion III of the ASME Boiler.and Pressure Vessel Code.
We have evaluated the vessel's fracture toughness properties and find that they meet 2
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i the principal requirements set forth in 10 CFR Part 50, Appendix G.
Utilizing the results of the surveillance program to monitor material damage from neutron irradiation and the guidelines in Regulatory Guide 1.99 to establish operating limitations will ensure that the reactor vessel will be operated in accordance
'with 10 CFR Part 50, Appendix G requirements.
This provides acceptable margins of safety to prevent brittle f'-ecture of the vessel during any conditions of normal operation, including anticipated operational occurrences and system,
hydrostatic tests, to which it may be subjected during the remaining service life.
6 Other methods of volumetric examination with the existing limitations which I
will produce meaningful results have not been fully developed at this time.
However, acoustic emission, which is considered to be in the developmental stage, is being studied by the licensee as an examination technique for these welds.
Tne licensee has committed to adopt alternative inspection methods and include them in the inservice inspection program for surveillance of these welds when an alternate technique is demonstrated to be practical and1 endorsed by t,he NRC.
We conclude that the vessel design and ongoing surveillance program of the reactor vessel materials in the beltline region are adequate for providing an acceptable. level 'of safety and assurance that the vessel structural integrity will not be compromised during the inspection period.
B.
Reactor Vessel Bottom Head and Shell Course Weld Examination (Relief Request C-2), Examination Category B-8, Item 81.2.
Code-Requirement:
Volumetric examination of shell longitudinal and circumf *ential welds.
Examination shall cover at least 10% of the length of each longitudinal weld and 5% of the length of each circumferential weld during the inspection interval.
1 Code Deviation Request:
Request relief from volumetric examination of welds in bottom head and some welds in vessel shell course.
Reason for Request
i Accessibility for inspection of these welds was not provided for in the plant design.
Inspection from outside the vessel is precluded due to the vessel insulatfon and the close proximity of the biological shield wall.
This mirror-type insulation on the vessel wall is made up of interlocking panels, making removal difficult. The annular dimension between the shield wall and the insulation is only four inches which is not sufficient to allow direct access
.to personnel.
Inspection of these welds from-inside the vessel is hampered by the vessel internal design.
The core shroud, jet pumps, and other brackets are not designed to be removed.
However, longitudinal welds in the uppermost f
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4 shell course are above the biological shield wall making them accessible for ultrasonic examination. Also, a complete volumetric examination can be conducted on the vessel-to-flange, head-to-flange, and all other closure head welds.
Relief is therefore required for all longitudinal and circumferential welds in the vessel shell below the top shell course including the bottom head welds.
No viable alternative for inspection of these welds currently exists.
Staff Evaluation:
Imposition of code requirements to the full extent would subject the licen' ee '
s to' extreme hardships in necessitating removal of portions of the concrete biological shield to perform the required examinations for the outside surface.
These limitations of design and geometry make the code inspections impractical.
Other vessel welds of the same examination category which are higher stressed and thus more susceptible to inservice flaw growth will be examined in accordance with the requirements of Section XI.
In examining these welds, it is recommended that the licensee follow the augmented program outlined below:
(a) Examine volumetrically at least 100% of accessible length of each longi-tudinal weld and at least 100% of the accessible length of each circum-ferential weld, from either inside or outside the vessel.
(b) Visually inspect to the extent practical, and from the vessel inside surface, the areas of the welds required to be examined.
(c) In the, event that a Code unacceptable flaw is detected,100% volumetric examination shall be performed on the welds listed.
We conclude that the vessel design, ongoing surveillance program of the reactor vessel materials in the beltline region, and the augmented examination require-ments are adequate for providing an acceptable level of safety and assurance that the. vessel structural integrity will not be compromised during the inspection interval.
C.
Reactor Vessel and Piping Integral Support Weld Examinations (Relief Request C-13) Examination Category B-H, Item Bl.12 and B-K-1, Item B4.9.
Code Requirement:
In the case of reactor vessel support skirts, volumetric examination performed during each inspection interval shall cover at least 10% of the circumference of the weld to the vessel.
In the case of support lug attachments, 100% of welding to the vessel shall be examined.
For piping, the weld and base metal
'of 25% of the supports shall be examined each interval.
Code Deviation Request:
Perform surface examinations in nieu of volumetric examinations.
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Reason for Request
The attachment welds at Dresden station which connnect the support members to t
the' piping (vessel) are fillet welds.
Since these welds are not full penetra-1:
tion welds, the heat-affected zone of the attachment weld is confined to the outer diameter surface of the pipe.
Because of this location of. the heat-affected zone, any cracking expected due to.the preser.ce of the attachment weld would initiate from the 00 surface.
Therefore, performing a dye penetrant
' examination would detect crack initiation in this area with more reliability than an ultrasonic examination which is required by Section XI, 1975 Addenda of the 1974 Edition of the ASME Code.
This argument is further justified by the Summer 1978 Addanda of the 1977 Edition of Section XI which requires a dye penetrant examination of this weld.
Dresden Station believes that adequate safety margins will remain by performing a dye penetrant examination of this weld and that the health and safety of the public will not be affected.
If it is determined ti..n there are other types of support attachment welds in the 2
station, the required examination will be performed.
Staff Evaluation Because of the weld design, ultrasonic examination of the welds is an impractical
-inspection technique.
Based on loading conditions of these welds flaws would most likely occur at the weld surface and thus be detectable by surface examina-tion. The licensee i.as committed to perform a surface examination of these welds.
The staff concludes that' due to weld design, volumetric examination of the fillet weld is not practical and that the alternate examination proposed by the licensee is acceptable.' Therefore, the staff grants relief from the volumetrie ' examination requirements for the support skirt weld.
D.
Main Recirculation Pump Integral Support Weld Examination (Relief Request C-5) Examination Category B-K-1, Item B5.4.
Code Requirement:
Volumetric examination of 25% of the integrally welded pipe supports.
Code Deviation Request:
Perform a surface examination in lieu of a volumetric examination.
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Reason for Request===
Each of the two recirculation pump casings. has two welded lugs which are used in supporting the pump.
The pump casing itself is cast stainless stee! and the lugs are made from stainless plate and fillet welded to the casing.
The combination of high u.Itras nic beam attenuation in the cast material and the geometry of the fillet welds makes a meaningful ultrasonic examination i
impossible.
A surface examination of these fillet welds and the surrounding base material will provide a more sensitive and reliable means of detecting defects in these welds.
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o Staff Evaluation:
The pumps and the. welded supports are made of cast austenitic steel which makes an ultrasonic examination inspection impractical beca.use of high ultra-sound attenuation.
Based on weld geometry and loading conditions, the most probable inservice defect would occur at the surface of the weld or base metal and would be detected by surface examination.
The licensee has proposed surface examination of the weld and base metal as an alternative examination.
We conclude that the proposed surface examination is acceptable and grant relief from the volumetric examination requirements.
E.
Main Recirculation Pump Casing Examinations (Relief Request C-10) Examina-tion Category B-L-2, Item B5.7.
Code Requirement:
One pump in each group of pumps performing similar functions in the system shall be examined during each inspection interval.
The examinations may be performed at or near the end of the inspection interval.
Code Deviation Request:
Delete visual examination of pump casings.
Reason for Request
The recirculation pump casing material is a cast stainless steel (ASTM A351-CF8).
This material has performed very well in nuclear service and has demonstrated substantial resistance to such chemical processes as pitting corrosion and stress corrosion cracking which would decrease the structural integrity of the pump.
To do the required visual inspection of this pump's internal surfaces, large amounts of radiation exposure and time would be required.
This was demonstrated at a similar nuclear station, where an expenditure of approximately 1000 man-hours and 50 man-rem was required to complete the visusl inspection of one pump which has the same design as the pumps in Dresden Units 2 and 3.
Since the pump is a casting which will normally have rough i iternal surfaces, making even a direct visual inspection for surface irregularities is extremely difficult.
The large expenditure of man-rem and man-hours to complete the visual inspection is not commensurate to the increased safety achieved by the inspection.
Dresden Station believes that adequate safety margins are inherent in the basic pump design and that the health and safety of the public will not be adversely affected by not performing the visual examination of the pump casing internal surfaces.
Staff Evaluation:
The disassembly of the main recirculation pumps to the degree necessary to inspect the' internal pressure retaining surfaces (casing) is a major effort in 6
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i terms of exposure of personnel and manpower. The visual examination is specified
.to determine whether unanticipated severe degradation, of the casing is occurring i
due to phenomena such as erosion, corrosion, or cavitation.
Pressure and flow are monitored to assess performance and could detect degradation of the pump casings.
In addition, any degradation of the pumps would normally be detected during primary system hydrostatic tests prior to startup from refueling outages.
If a crack were to develop after hydrotesting, the drywell leak detection system would provide warning of any degradation at an early stage.
We conclude that the initial design of the pumps which prevents disassembly with a minimum of manpower and personnel exposure and prohibits a _msaningful visual examination of the interior surfaces makes the code required examinations impractical.
The alternate testing to be performed by the licensee will provide an acceptable' alternative to these examinations.
F.
Recirculation Pump Discharge Valve Support Weld Examinations (Relief Request C-7) Examination Category B-K-1, Item 86.4.
Code Requirement:
Volumetric examination of 25% of the integrally welded pipe supports.
Code Deviation Request:
Substitute a surface examination for the volumetric examination.
Reason for Request
Each of the two recirculation pump discharge valves has four welded lugs attached by fillet welds to the cast stainless body.
These lugs are attached to I-beams which support the valve.
The combination of high ultrasonic beam attenuation in th'e cast material and the geometry of the fillet welds makes a meaningful ultrasonic examination impossible.
A surface examination of these fillet welds and the surrounding base material will provide a more sensitive and reliable means of detecting defects in these welds.
Staff Evaluation:
The valves and welded supports ~ are made of cast austenitic steel which makes an ultrasonic examination impractical because of the high attenuation of ultrasound.
Based on the weld geometry and loading conditions the most probable inservice defects would occur at the surface of weld or base metal and would be detected by a surface examination.
The licensee has proposed surface examination of the weld and base metal as an alternative examination.
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The staff concludes that the proposed surface examination is acceptable and granta relief from the volumetric examination requirements.
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Valve Interna'l Surface Examination (Relief Request C-17) Examination Category B-M-2, Item B6.7.
Code Requirement:
Visual examination of one valve in each group of valves (as specified in category B-M-2) each 10 year interval.
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Code Deviation Request:
Conduct visual examinations only if valve is disassembled for maintenance.
Reason for Request
In the class 1 system, there are 61 valves which are greater than four inches nominal pipe size.
These valves vary in size, design, and manufacturer, but are all manufactured from either cast stainless steel or carbon steel and contain no welds in the valve body casings. The performance of these valve bodies has been excellent in BWR applications and based on this performance as well as industry and regulatory acceptance of these valve bodies, continued excellent performance is anticipated. To do the required visual inspection of the valves' internal surfaces, large amounts of radiation exposure and time would be required since many of these valves are located in areas where radiation is high and. space for disassembly limited.
Completing the visual examination has only a very small potential for increasing plant safety margins and a very disproportionate impact on expenditures of plant manpower and radiation exposure.
Furthermore, the valve bodies are castings which will normally have rough internal surfaces.
This makes even a direct visual examination for surface irregularities extremely difficult.
The large expenditure of man-rem and man-hours to complete the visual inspection is not commensurate to the increased safety achieved by the inspection.
Dresden Station believes that adequate safety margins are inherent in the valve desian and construction and that the health and safety of the public will not be adversely affected by not performing the visual examination of the valve body internal surfaces.
Staff Evaluation:
Disassembly of these valves for the sole purpose of a visual examination, in
, absence of other required maintenance, represents an unnecessary exposure to radiation and contamination.
Contamination levels in the valves associated with the recirculation loops are particularly high due to the physical location of these valves at the bottom of the system.
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Class 1 valves are subject to system hydrostatic examination and containment isolai. ion valves are leak-tested periodically.
The licensee has agreed t'o visually examine any valves that are disassembled for routine maintenance.
In addition, the staff recommends that the licensee conduct a valve wall thickness examination on any valves that are not. visually examined for routine maintenance.
We conclude that the inspection program outlined above will provide adequate assurance of valve integrity.
Therefore, reifef is granted from the visual examination requirements for Category B-M-2 valves.
H.
Primary Containment Penetration Welds (Relief Request C-8) Examination Category B-J, Item 84.5.
Code Requirement:
Volumetric examinations performed during each inspection interval shall cover all of the area of 25% of the circumferential joints including the adjoining one foot sections of longitudinal joints and 25% of the pipe branch connections.
Code Deviation Request:
Perform visual examinations of one welt in each penetration.
Reason for Request
Each primary containment penetration assembly, due to its design, leaves one pressure retaining piping weld inaccessible for examination by either surface or volumetric means.
The welds can only be examined by inspecting for evidence of leakage during system hydrotests.
Staff Evaluation:
Augmented examination of containment penetration welds is described in Standard Review Plan 3.6.1 and consists of volumetric examination of all welds during each inspection interval.
These requirements exceed those of Section XI.
The licensee has provided sketches illustrating the inaccessibility of these welds.
The initial design of the assemblies did not provide for accessibility for inservice examinations.
To maintain the sample size of examination and to assure that the integrity of the containment pressure boundary is maintained in the event that the inner inaccessible weld fails, we require that the outer out-of-containment weld'p'ressure boundary weld be volumetrically examined,
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where practical, over 100% of its length during each inspection interval.
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addition, the licensee will conduct visual examinations of the containment penetration assemblies for leaking during hydrostatic testing.
We conclude that the augmented examinations to be performed by the licensee, where practical, will assure that the integrity of the containment pressure boundary will be maintained.
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Branch Pipe Connection Weld Examination (Relief Request C-9) Examination Category B-J, Items 84.6 an.d 84.7.
Code Requirement:
Volumetric examinations performed curing each inspection interval shall cover all of the area of 25% of the circumferential joints including the adjoin,ing one foot sections of longitudinal joints and 25% of the pipe branch connections greater than six inches in diameter.
For piping six inches in diameter or smaller, a surface examination shall be conducted.
Code Deviation Request:
Conduct visual examin' tions in lieu of volumetric or surface examinations.
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Reason for Request
Many of the branch pipe connections on carben steel piping are constructed with reinforcement saddles. These saddles are fillet welded over the actual branch pipe connection weld.
A volumetric examination cannot be done on e ther the branch pipe connection weld or the two saddle welds. A visual i
examination will be conducted during the system hydrotest on the two saddle welds.
Staff Evaluation:
The design of the saddle reinforcement used at Dresden prevents a volumetric examination from being performed on some pipe branch welds.. The licensee will conduct visual examinations of these welds during hydrostatic testing to assure that their integrity is maintained. We conclude that these supplemental visual examinations are an acceptable alternative to the code required volumetric examinations.
J.
LPCI Heat Exchanger Nozzle to Vessel Weld Examination (Relief Request C-4)
Examination Category C-8, Item C1.2.
Code Requirement:
Volumetric examination covering 100% of the nozzle to vessel attachment weld.
Code Deviation Request:
Perform visual examination in lieu of volumetric examination.
Reason for Request
There are four Class 2 nozzles on each of the two LPCI heat exchangers.
Two of the nozzles are 18-inches in diameter and two are one-inch diameter drain connections.
The 18-inch nozzle-to-shell welds are covered by reinforcement saddles making the welds inaccess' ble for volumetric examination.
The geometry
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l of the saddle and the fact that it is fillet welded to the nozzle and to the heat exchanger do not permit a meaningful ultrasonic test of the two accessible saddle welds. A visual examination will be conducted on the two exposed saddle welds during the system hydrotest.
Staff Evaluation:
Eecause the LPCI Heat Exchangers are covered with a reinforcement saddle that is fillet welded to the nozzle and to the heat exchanger, the nozzle-to-vessel welds are physically inaccessible fcr inspection.
The licensee has agreed to performing visual examinations of the saddle welds for evidence of leakage
.during system hydrostatic tests. We conclude that this supplemental examination will provide assurance that system integrity will be maintained.
K.
Ultrasonic Testing Calibration Standards (Relief Request C-15)
Code Requirements:
Anpendix I of the 1974 Edition of Section XI through the Summer 1975 Addenda applies to Class 1 and 2 ferritic vessels 2-1/2 inches and greater in wall thickness and has the following relevant requirements:
I-3121 Block Selection
" Material from which the block is fabricated shall be from one of the following:
(1) the component nozzle dropout; (2) the component prolongation; or (3) when it is not possible to fabricate the block from material taken from the component, it may be fdbricated from a material of a specification included in the applicable examination volumes of the component.
The acoustic velocity and attenuation of such a block shall be demonstrated to fall within the range of straight beam longitudinal wave velocity and attenuation found in the unciad cc -ponent."
I-3122 Cladding "Where the component material is clad, the block shall be clad to nominal thickness 1/8 in.
Deposition of clad shall be by the automatic method used on the inside of the component. Where the automatic method is impractical, deposition of clad shall be by the manual mett od used to cover the circumferen-tial welds of the component."
I-3123 Heat Treatment "The calibration block shall receive at least the minimum tempering treatment required by the material specification for the type and grade, and a postweld heat treatment of at least 2 hr.
The heat treatment shall generally conform to NS-2210."
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I-3124 -Surface Finish
~"The finish on the surfaces of the block representing the interior and exterior surfaces of the component shall be representative of the surface finishes of the component."
.For welds where Appendix I is not applicable,Section XI of the Code specifies that the provisions of Article 5 of Section V shall apply.
The relevant requirements in Section V are given in paragraph T-533 which states:
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" Drilled holes shall serve as basic calibration reflectors to establish a t
primary reference response of the equipment and to. construct a distance-amplitude correction curve.
These holes shall be located either in the finished component or_in a basic calibration block of similar metal'.urgical structure and the same or an equivalent P-number grouping as the finished component.
For the purposes of this paragraph, P-numbers 1, 3, 4, and 5 materials are considered equivalent."
Code Deviation Request:
Use existing calibration standards purchased to the requirements of the 1971 Edition of the ASME Code, which specify that blocks be the same or equivalent P-number grouping.
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Reason for Request
The UT cali,bration-standards currently being used at Dresden were purchased to the requirements of the 1971 edition of the ASME code which was in effect it i
the time.
This edition required the calibration blocks to be of the same or 2
equivalent P-number grouping.
Consequently, this is the only certification presently existing for each standard.
The requirements of the 1975 Summer i
Addenda to the 1974 Edition of the ASME Code require a much stricter selection i
of material and metallurgical properties for each standard.
The calibration standards presently in use at Dresden Station do not have these properties and certifications. They have been used in the inservice inspections since 1972
.and further use would provide continuity to the Inservice Inspection Program.
Therefore, relief is requested for' continued use of the existing standards and certifications.
Staff Evaluation:
1 The licensee has not demonstrated that use of the ferritic vessel calibration blocks specified in the 1974 Edition of the cnde is impractical and therefore i
relief cannot be granted at this time.
For some welds, (where Article 5 of
'Section V ~ applies), the material requirements may be met by the existing calibration blocks.
If the licensee can demonstrate to the staff that the existing blocks meet all of the requirements of Article 5 of Section V, such I
as thickness, reflector geometry, and curvature, these blocks may be used for 1
examinations.of welds _in other than _ Class 1 and 2 ferrinic vessels of greater l
than 2-1/2 inches thickness.
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Ultrasonic Examination Recording Levels for Piping Welds (Relief Request C-16).
Code Requirement:
'ASME Code Section XI (1974 Edition), Paragraph IWA-2232, Ultrasonic Examination:
" Ultrasonic examination shall be conducted in accordance with the provisions of Appendix I.
Where Appendix I (I-1200) is not applicable, the provisions of Article 5 of Section V shall apply."
ASME Code Section V (1974 Edition), Paragraph T-537, Evaluation of Indications:
"All indications which produce a response greater than 20% of the reference level shall be investigated to the extent that the operator can evaluate the shape, identity, and ' location of all such reflectors in terms of the ac,ceptance-rejection standards of the referencing Code Section."
Code Deviation Request:
Use ultrasonic recording sensitivity of 50% DAC.
Reason for Request
The techniques for performing the ultrasonic examinations required by the Summer, 1975, Addenda of Section XI are detailed in Appendix I of Section XI and Article 5 of Section V.
Neither of these sections specifically addresses the ultrasonic examination of welds in piping.
For guidance concerning these welds, later editions of the code were reviewed and found to specify 50% DAC as the minimum level of recording for welds in piping.
Since Appendix I of the Summer,1975, Addenda of Section XI also specifies 50% DAC as the minimum level for recording (but for welds in vessels 2-1/2 inches thick and greater),
using this recording' level for piping welds would provide continuity to the recording levels of all ultrasonic examination data produced during an inservice inspection.
Staff Evaluation:
Recording and evaluating indications at 20% DAC is impractical for the following reasons:
1.
The welded joints in nuclea" piping frequently contain Code allowable wall thickness differences (12% of nominal thickness) as well as some weld drop-through, counterbore taper, crown height, etc.
These conditions generate an extremely large number of geometric reflectors which produce UT indications greater than 20% OAC.
2.
Weld metal in stainless steel piping contains reflectors due to the metallurgical structure which produce a large number of UT indications.
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All examination personnel experience radiation exposure during inservice examinations.
The Section.V requirement to record and evaluate UT indications at the 20% DAC places an unnecessary burden on the limited number of experienced and qualified examiners available to the owner.
As an alternate examination the staff requires the following:
A.
Indications 50% of DAC or greater shall be recorded.
B.
An indication 100% of DAC or greater shall be investigated by a Level II or Level III examiner to the extent necessary to determine the shape, identity, and location of the reflector.
C.
Indications 20% of DAC or greater which are interpreted to be a crack must be identified and evaluated to the rules of Section XI.
D.
The owner shall evaluate and take corrective action for the disposition of any indication investigated and found to be other than geometric in nature.
II.
Augmented Examinations The licensee is not conducting volumetric or surface examinations on certain Class 1 and 2 welds based on ASME Code exemption criteria in Subarticles IWB-1220 and IWC-1220 respectively.
It is our position that a representative sample of welds in the emergency core cooling system, the residual heat removal system, and,the containment heat removal system must be examined.
Therefore, an augmented ISI program should be developed for welds in the these systems and submitted to the staff for review prior to the sta-t of the next inspection period.
The " chemistry control" provision contained in IWC-12?0(c) is not an acceptable basis for exempting components frr> examini. tion because practical evaluation, review, and acceptance standards cannot be defined.
One basis for selecting a representative sample of welds in these systems should be components in similar plants which have experienced generic failures as identified in I&E Bulletins, including lines of less than 4 inch diametar or low pressure /
temperature conditions.
The calculations and assumptions made in determining line sizes exempted under the provisions of IWB-1220(b)(1) should be providad to the staff for review prior to the start of the next inspection peric;.
Additional weld examinations may be required based on the results of the r2 view.
III. Additional Relief Requests in addition to the relief requests evaluated in Section I, the licensee submitted five other requests for relief which involved updating exa ' nation requirements to the 1977 Edition through Summer 1978 Addenda of Section XI of the ASME Code.
Updating to the requirements 01' later NRC approved Editions and Addenda is permitted by 50.55a(g)(4)(iv), provided all of the related requirements of the respective editions or addenda are met.
We have evaluated the following 14
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relief requests submitted by the licensee and have determined that the alternate examinations proposed are acceptable and in accordance with 50.55(g)(4)(iv):
' Relief Request Examination Component Identification Category 1.
C-11 B-G-1, Items 84.7, 2 inch bolts and 84.3, B5.1, B5.7, studs B6.1, B6.2 2.
C-12 B-I-1, Items Bl.13, Cladding Bl.14 3.
C-13 B-K-1, Item B4.9 Welded support B-H, Item Bl.12 4.
C-14 C-D, Items '1.4, Class 2 Bolting C
C2.4, C3.2, C4.2 5.
C-18 N/A Class 2 & 3 Pressure Tests 3.0
SUMMARY
Based on the evaluations of the requested relief from the code requirements, we concluded that the Dresden Nuclear Station Unit Numbers 2 and 3 Inservice Inspection Program meets the requirements of.the 1974 Edition through Summer 1975 Addenda of the ASME Section XI Code to the extent practical and thus is in compliance with 10 CFR 50.55a(g).
4.0 ENVIRONMENTAL CONSIDERATION
S We have determined that these amendments and granting of certain requests for relief do not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that these actions are insignificant from the standpoint of environmental impact and pursuant to 10 CFR 551.5(d)(4) that an environmental impact statement, or negative declaration and environmental impact aopraisal need not be prepared in connection with the issuance of these amendments a,w granting of the requests for relief.
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5.0 CONCLUSION
We have concluded:
(1) because the amendments di 70t involve a significant increase in the probability of consequences of accidents previously considered and do not involve a significant decrease in a safety margin, the amendments do not-involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of these amendments will not be inimical to the.ommon defense and security or to the health and safety of the public.
Date:
December 31, 1980
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