ML20064F018
| ML20064F018 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 07/31/1978 |
| From: | Leslie Liu IES UTILITIES INC., (FORMERLY IOWA ELECTRIC LIGHT |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7811270202 | |
| Download: ML20064F018 (9) | |
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IOWA EtscTaic IIGHT AND Powsn CoupyE flLE COP General Qffice Cenan Ramos. IOWA
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Mr. Harold Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Ccmission Washington, D.C.
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Dear Mr. Denton:
During the meeting with the NRC staff concerning the recirculation inlet nozzle safe-end July 7,1978, we stated that we would provide a repair report. Enclosed is a report titled "Duane Arnold Energy Center Recirculaticn Inlet Safe-End Repair Program." A copy of this report is also being provided to Mr. J. G. Keppler. The initial cut on the N2A safe-end is presently expected to occur approximately August 8, 1978.
If you have any questions, please feel free to con-tact us.
l Very truly yours, v'
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Lee Liu Senior Vice Fresident - Engineering LL/XAfi/jo cc: K. Meyer D. Arnold R. Lcwenstein H. Rehrauer File B-31C 781127OSO.L F
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g Duane Arnold Energy Center Recirculaticn Inlet Safe-End Repair Program On June 17, 1978, during weekly control valve testing an automatic reactor scram occurred due to pro-blems in reactor protection system relays associated i
with the testing.
The resulting plant shutdown provi-dad an opportunity to perform a drywell inspection to determine the source of 3 GPM of unidentified leakage.
The plant technical specifications limit unidentified leakage into the primary containment to 5 GPM.
Water was found leaking from the shield blocks around the "B"
recirculation system N2A inlet nozzle.
The reactor was placed in a cold shutdown condition and the shield blocks' removed for further inspection of the nozzle crea.
The
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leakage was found to be the result of a cirrumferential through wall crack 4 to 6" in length in the nozzle safe-end.
The details of this event were reported in DAEC License Event Report 78-030 and in subsequent meetings with NRC staff personnel.
Ultrasonic testing and radiographic examinations were perfomed to determine the full extent of the cracking in the N2A safe-end and to check for similar problems in 4
the other 7 safe-ends.
The visible portion of the through 4
wall crack in the N2A safe-end appears to be located along
.the fusion line of the weld repair of a fabrication machi-nining error as shown in Figure 1.
The geometry of the t
crack through the safe-end. wall could not be determined exactly; however, it is possible that the crack initiated in the crevice at the mating surface of the thermal sleeve b
on the inside of the safe-end.
The' examinations revealed linear indications in,4 other safe-ends, none of which were through wall cracks.
Another safe-end showed some non-linear indications, but meets the NDP. acceptance require-ments.
The remaining 2 nozzle safe-ends had no indications.
Representatives of the NRC Regicn III Of:! ice of Inspection and Enforcement have reviewed these preliminary NDE results.
A su= mary of these preliminary findings were presented to the NRC at a meeting in Bethesda on June 27.
Further de-tails and prelim:. nary plans for the replacement program we're presented to the NRC at another meeting on July 7.
The cracking mechanism is likely to be either fa-tigue or crevice corrosion cracking.
Poasille contributing factors include the crevice geometry, stress levels, the plant cperating history, and the weld repair.
Checks are being conducted en the recirculatien Icop pipe whip restraints to verify that these did not contribute to abnormal stresses.
The records of the weld repairs indicate that they were performed in accordance with MPE code requirements.
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7/31/78
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A more definitive determination of the cracking mechanism will be made through chemical and metallurgical analyses on the safe-end after it has been removed.
The analyses will be performed in the laboratiories of a quali-fled independent contractor employed by Iowa Electric.
It is expected that specialists at General Electric will also participatu.
Although the scope of the analyses cannot be finalized before further examination of the safe-end, it is expected t. hat the following elements will be included in the investigative program.
e Ultrasonic inspection of the outside of the sample to establish location and exts it of cracking.
e Meta 11cgraphic examination of representative ~
sections through the crack to establish rela-(
tionship between crack path and micro-struc-ture of safe-end material.
Identification of the mode of cracking, either intergranular or transgranular.
Establishment of the micro-structure of safe-end h se metal, thermal sleeve attachment weld and repair weld zone.
e visual, low magnification and scanning electron microscope ex'.mination of crack surfaces to assist in establishihg the mechanism and mode of fracture and to identify other pertinent fractographic features, ie.:
point (s) of initiation, direction of propagation, extent of surface deposits, etc.
e Chemical analysis of safe-end material to b
verify conformance with applicable specifications.
e Preparati~on of detailed report and findings.
The analysis program is being organized te provide for early determinauien of the principal metallurgical fac.?crs and to maintain the safe-end in a condition suitable for such additional examination as may be necessary.
The NRC staff l
will be consulted as the program is developed.
A copy of the analysis report will be transmitted to the NRC for their review.
The N2C has been consulted in the development of the safe-end re placement program and NEC meeting cer=lents have been addressed.
Review of the tiroposed replacement program and the proposed cutting sequence was conducted by the I&E office on July 17.
The entire N2A safe-end will be removed and replaced with a newly fabricated safe-end in accordance with the requirements of ASME Section XI, 1974 Edi-tion, Summer 1975 Addenda, Repair Procedure No.
3, IWB-4410.
Modifications have been incorporated in the replacement safe-v.-
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//31/.78 Sage,3 end which will reduce the susceptibility of the safe-end to cracking.
Iowa Electric has employed NUTECH corporation to perform a second party verification of,these modifica-tions.
As shown in Figure 2, the replacement safe-end in-corporates a tuning fork configuration to eliminate the contact crevice and has an increased cross-section thick-ness.
These modifications also reduce stress concentra-tions and allcw access for liquid penetrant, radiographic,.
i and ultrasonic examinations.
A portion of the existing thermal sleeve will also be replaced with an adaptar ccm-patible with the new safe-end.
The replacement safe-end will be analyzed in accordance with the original stress report requirements under ASME Section III, 1965 Edition Summer 1967 Addenda.
An amendment to the original stress-report will be prepared for the replacement safe-end.
As shown in Figure 3 the cracked safe-end will
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be removed by cutting the safe-end and thermal sleeve at a point approximately 2 inches inboard of the crack.
A second cut will be made near the elbow in the recirculation line allcwing.the safe-end with its attached stainless steel transition piece and attached section of recirculation line to be removed as a unit.
This will provide access for the repairs and minimizes the number of cutting opera-tions required to be performed in the radiation area.
The transitien piece and'section of recirculation line will be cut from the cracked safe-end (approximately 2 inches from the crack) to be reinstalled later along with the re-placement safe-end.
This also avoids the need for any bimetallic welds during the repair process.
The cutting se-quence has been reviewed by Region III I&E personnel.
Iowa Electric will notify the Region III office at least 2 days prior to com=encement of cutting operations.
(i The welding. sequence for installing the replace-l ment safe-end as:sembly is shown in Figure 4.
The replace-ment safe-end will be installed using welding materials meeting the requirements of ASME Section III, 1974 Edition, Summer 1975 Addeada, NB-2400, or a later edition of the Code, depending on material availability.
All welds will be examined by radiography and liquid penetrant within the limits afforded by the access and structure.
These non-destructive examinations will be in accordance with ASME Section III, 1971 Edition, Summer 1975 Addenda, NB-5000.
An ultrasonic inservice " baseline" examination will be per-formed on all new butt welde in accordance with ASME Section XI, 1974 Editien, Gu=mer 1975 Addenda, in accordance with the present DAEC insarvice inspection progrut.
A hydrostatic test of the primary system including all welds l
made during this repair will be perfer=ed in accordance
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with ASME Section XI, 1974 Idition, Su=mer 1975 Addenda, Sectitn IW3-5222.
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v 7/31/78 Pagb 4-Repairs will be conducted with all fdel removed from the vessel, the recirculation line riser drained and the jet pump annulus level lowered.
DAEC has emnloyed a radiation consultant to assist in the design of shielding and to assist in developing special procedures for con-trolling exposure to personnel.
Shiciding will be construc-ted from lead b:.ocks and the reactor vessel head replaced to provide additional shielding.
A radiation survey was conducted with the annulus level lowered to verify the adequacy of the shielding provisions.
Repair procedures including erection of shielding will be tested on mock-ups to further reduce personnel exposure.
It is currently planned that the remaining 7 inlet nozzle safe-ends will be replaced in a manner iden-tical to the N2A safe-end.
Iowa Electric Will provide a' safe-end to the NRC to allow performance of an indepen-
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dent metallurgical analysis.
r The safe-end replacement program is being con-ducted by DAEC plant personnel under established plant procedures.
A repair task force has been organized'under the head of the DAEC maintenance group'and has overall responsibility for accomplishing the replacement program.
Consultants and contractors are being employed for certain I
tasks such as fabrication of the replacement safe-end, metallurgical analyses, shielding design, and manpower support.
Special written precedures are being developed as necessary for accomplishing the repairs, with special emphasis on QA/QC and on maintaining worker exposure as low as reasonably achievable.
These procedures are being prepared, reviewed, and approved in accordance with the DAEC Quality Assurance program and plant technical speci-C fications. Proeddures are also being reviewed by Region III 7
I&E office personnel.
In addition, at least 2 working i
f days notice will be provided to the Region III I&E office prior to irreversible operations.
Written procedures'are i
being provided for the cutting sequence, installation se-quence, and reltted operations such as shielding installa-tion and reactor vessel draining.
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It is noted that on July 21, examinations per-formed under the DAEC QA program determined that the materials which had been obtained for use in the manufacture of the replaceme'nt saf 2-ends were not acceptable due to improper grhin size.
New materials meeting necessary requirements are being fabri:ated.
Preparations are underway so that cutting operations to rencve the cracked safe-end may begin about August 1.
The core has been off-loaded and shielding and temporary piping supports are under construction.
Shielding, temporary sup-ports, and instrumentation will be installed and work enclosures erected prior to the start of cutting work.
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WELD SEQUENCE FOR REPLACEMENT SAFE END ASSEMBLY Figuro 4
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