ML19319D176
| ML19319D176 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 06/08/1978 |
| From: | Ormston A FLORIDA POWER CORP. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8003130742 | |
| Download: ML19319D176 (8) | |
Text
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rs o4/<s/n REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
DISTRIBUTION FOR INCOMING MATERIAL 50-302 REC: REID R W ORG: ORMSTON A J DOCDATE: 06/08/78 NRC FL PWR DATE RCVD: 06/12/79 DOCTYPE: LETTER NOTARI ZED: YES COPIES RECEIVED SUDJECT:
LTR 3 ENCL 40 FORWARDING REVISED RESPONSE TO QUESTIONS 6, 7.
& G ORIGINALL SUBMITTED ON 06/02/78 CONCERNING LONG TERM REPAIR SCHEt1E THAT WOULD DE IMPLEMENTED ON THE "B" OTSG UURING THE REFUELING OUTAGE FOLLOWING COMPLETION OF THE FIRST FUEL CYCLE.
NOTARIZED 06/03/78 PLANT NAME: CRYSTAL RIVER #3 REVIEWER INITIAL:
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DISTRIBUTOR INITIAL: M6 oco************** DISTRIBUTION OF THIS MATERIAL IS AS FOLLOWS
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GENERAL DISTRIBUTION FOR AF'(ER ISSUANCE OF OPERATING LICENSE.
(DISTRIBUTION CODE AOO1)
FOR ACTION:
DR CHTer ORB #4 BC**W/7 ENCL INTERNAL:
PG CT
_**W/ ENCL NRC PDR**W/ ENCL 1 & E**W/2 ENCL OELD**LTR ONLY HANAUER**W/ ENCL CORE PERFORMANCE BR**W/ ENCL AD FOR OPER TECH **W/ ENCL ENGINEERING BR**W/ ENCL REACTOR SAFETY BR**W/ ENCL PLANT SYSTEMS BR**W/ ENCL EEB**W/ ENCL EFFLUENT TREAT SYS**W/ ENCL J.
MCGOUGH**W/ ENCL EXTERNAL:
LPDR'S CRYSTAL RIVER, FL**W/ ENCL TIC **W/ ENCL NSIC**W/ ENCL ACRS CAT B**W/16 ENCL i
9 DISTRIBUTION:
LTR 40 ENCL 39 CONTPOL NBR: -75A w.""._.I
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SIZE: 3P+4P 000********************************
THE END 8003130 g
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_o.e.. e.._r June 8,1978 Mr. Robert W. Reid, Chief Operating Reactors Branch #4 Division of Operating Reactors U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Subject:
Crystal River Unit #3 Docket No. 50-302 Operating License #DPR-72
Dear Sir:
On June 2,1978 we submitted responses to questions contained in of your letter of May 2,1978.
Since submitting this information, we have had further internal discussions pertaining to our response to questions 6, 7 and 8 and believe that clari-fication to our response to these questions is necessary.
Attached is a revised response to questions 6, 7, and 8 collectively. We request that this information be used in lieu of the response contained in our June 2, 1978 letter to questions 6, 7 and 8.
This revision is required to correctly relay our position to you. Our June 2 submittal contained information which indicated that the "long term repair scheme" would be implemented on the "B" 0TSG during the refueling outage following completion of the first fuel cycle. We have made no decision yet to implement the long term repair and feel that it would be imprudent to make that decision at this time. We are confident that there are no safety implications involved with continued operation of CR-3 due to OTSG concerns at this time and prefer to delay a decision as to the long term repair implementation until a later date.
In addition, our June 2 submittal contained a paragraph with the heading Calculations as part of the response to questions 6, 7 and 8.
This information is not relevant and has been deleted from the attached, corrected response.
.We request that this information in our June 2 submittal be disregarded.
We believe there is no reason to assume tube-to-tubesheet leakage paths at this time as the OTSG has been leak tested and there is no mechanism to induce weld failures for the remainder of the first fuel cycle.
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General Othee 3201 Tniny-founn street soutn. P O Box 14042. St Petersourg F'orica 33733 813-866-5151
Mr. Robert W. Reid Page Two June 8, 1978.
We apologize for any inconvenience thir may cause you or your staff and appreciate your consideration of our request.
Very truly yours, FLORIDA POWER CORPORATION Dbb A. J. Ormston Vice President AJ0/hw 3/9a Attachments - 1 File: 3-0-3-a-3 y
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STATE OF FLORIDA COUNTY OF PINELLAS A. J. Ormston, Vice President for Florida Power Corporation, states that he is authorized on the part of said company to sign and file with the Nuclear Regulatory Commission the information attached hereto; and that all such statements made and matters set forth therein are true and correct to the best of his knowledge, information and belief.
}r w A j/J.Ormston' Subscribed and sworn to before me, a Notary Public in and for the State and County above-named, this 8th ' day of June,1978.
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, i Notary Public Notary Public, State of Florida at Large,
, My Commission Expires: July 25,1980 m
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Revised response to Questions 6, 7 and 8 of Enclosure 2 of May 2, 1978 lette..
Questions 6, 7, 8 are answered in unison as they all pertain to Once-through-Steam Generators (OTSG's). The answer takes the form of an updated status of the OTSG test and repair program.
Question 6 -
Describe the damage to the steam generator tubesheets and steam generator tubes.
Question 7 -
Describe your plans to repair the damaged components of the steam generators includinq the procedures for rewelding grinding or milling, testing, and inspection.
Question 8 -
Provide the results of the inspections, tests, and repairs discussed above.
Answer:
B&W has concluded that continued operation of CR III "B" OTSG for a short period (1 year or less) does not represent a safety problem.
The damace has been limited to tube ends and weld deposited Inconel.
The strength of the tube-to-tubesheet joint to resist an accident event has not been reduced since the "hard" tube roll strength capacity has been determined indeperdent of the seal weld. The seal weld minimum leak path has not been decreased below minimum ASME code requirements for a seal weld, the seal capabilities of the weld for the short term have only been effected in the areas of low cycle fatigue and stress corrosion cracking.
Low cycle fatigue is not considered a safety problem since only ' plant heat-ups and cooldowns affect this property.
Failures of this nature will only cause plant shutdowns for repair when the leakage exceeds plant i
limitations.
Stress corrosion cracking is a long term phenomenom requiring incubation periods longer than the anticipated time to the next refueling. Again failures of this nature result only in plant shutdowns for weld repairs when leakage exceeds plant limitations.
Backoround:
The structural attachment of the tube to the tubesheet is at the primary side of the tubesheet. The 56 foot long, 5/8" 0.D. tubes extend from the primary sides of the upper and lower tubecheets, through the two foot. thick tubesh,eets, and through 15 support plates spaced thrae to four feet apart.
The attachment to the tubesheet consists of a "hard" roll expansion approximateiy 1 inch into the tubesheet measured from the tube-to-tubesheet fillet seal weld on the tubesheet primary face.
A high quality automatic machine fillet weld at the tubesheet primary face provides the primary-to-secondary side seal. This is an Inconel weld between the Inconel tube and Inconel clad (5/16" thick) tubesheet.
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h are imposed on the tube-to-tubesheet joint are primarily k!i!i koabs due to thermal differentials and pressure fluctuations (pulses). Lateral loads and their resulting moments applied by secor.dary side conditions are attenuated within the 23 inches of tubesheet before reaching the 1 inch "hard" tube roll.
Damage Damage to the tube and extending above the tube-to-tubesheet weld, the weld itself, and clad has been varied.
The tube-to-tubesheet damage has been classified into the following categories:
Class I (55% of the tubes)
Impact or roll over of tube ends may exist on the 0.D. or I.D.
Deformed material does not include weld metal.
Class II (6% of the tubes)
Part411y separated chip (sliver); may exist with Class 1, III, or IV damage..
Class III (26% of the tubes)
Minor weld damage extending into the upper 1/3 of weld metal.
Class IV (17% of the tubes)
Damage to the tubs ends and weld metal is excess of Class III.
(Above percentages exceed 100% since Class II can exist with Cless I, III, & IV).
Tests A ten tube mock-up of the damage was prepared at B&W fabrication facilities. 'The mock-up damage was made by beating the tubes with a ballpeen hammer. The damage mock-up includes the worst damage observed at the site. Hardness traverses across the damaged tube ends, welds, and into the clad showed the effects of significant cold working. The highest of the 250 readings were mostly in the high 300's (Knoop hardness scale) with three readings exceeding 400. Normal readings for Inconel weld metal may range as high as 200.
The high hardness readings indicate increased yield and ultimate strengths, potentially increased resistance to high cycle fa'igue failure, decreased resistance to low cycle fatigue failure, and decreased resistance to stress corrosion cracking.
The minimum leak path (normally the weld throat of the tube-to-sheet fillet weld) of the mock-up damage was measured. Measurements were made per procedures used to inspect daily product quality control samples of shop production welds (stage micrometer at approximately 15 x power). The minimum measured leak path was.051 inches compared to minimum tube wall thickness of 0.032 inches.
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Tests of the roll joint showed a minimum strength of 2500 pounds axial tube load to initiate relative motion with the tubesheet.
The h..11 mum load to completely free the tube from the tubesheet was 4520 'ibs.
The minimum tube yield strength based on the specified minimum yield stress of 35,000 pst is 2200 lbs. The tests were performed on samples that were expanded, welded, and stress relieved per standard B&W fabrication procedures. The welds were removed in their entirety prior to performing the tube pulling tests.
Repair Repair of the steani generator has been separated into two phases:
a short term repair and a long term repair.
The short term is presently underway and consists of:
Video Inspection & Cat. Tubes Locate Leaks & Identify
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Install Dome Shielding & J Leg Screens Repair Leaks, NDE Repairs, & Dress Tubes Remove Shielding 100% Free Path Check Clean Obstructed Tubes & E/C Explosive Plug & Leak Test 100% Free Path Check OTSG-A Remove Screens & Close Up OTLGs The video inspections and cataloging of damage has been completed and the results reported above. All tube-to-tubesheet welds have been inspected and no leaks have been found.
Leak testing was performed by p essurizing the partially filled secondary side with helium and inspecting each weld individually wita a mass spectrometer capable of detecting a 10-8 cc/sec leak.
The dome shielding has been installed and the tube ends dressed with hand held tools. The remaining items of the short term repair have yet to be completed.
The following long term repair may be performed at a future date:
Dome Decon Prep.
Install Decon Equip. Bladders Decontaminate Dome Setup Machine Carriage Machine / Spot Face Tubes (57%/43%)
Deburr Tube Ends & Vacuum Clean Spot Face as Necessary Roll Expand as Necessary Remove Mach. Carriage Setup & Preheat Tubesheet Install / Setup Weld Carriage Weld Spot Face Tubes (2800)
Video Inspect Welds Clean for Pt Inspection i
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Remote machines to support the long term repair are presently being designed and fabricated.
Prior to installation at the site, all remotely controlled machinery will be proven in mock-ups.
Conclusion Based on the above assessment the structural capacity of the tube-to-sheet joint has not been degraded because of the "hard" roll capacity to continue to carry axial tube loads greater than the tube yield strength and the attenuation of lateral tube loads up through the 2 foot thick tubesheet. Therefore, the damage sustained by the OTSG will not have a detrimental effect on its safe operation over the time remaining on this fuel cycle.
Further analyses will be performed and operating experience gained during the remainder of the first fuel cycle. The need for implementation of the long term repair scheme is not clear at the present time. This decision will be made and justified prior to startup following the first refueling outage.
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