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,I WASHINGTON, D. C. 20556 AUGUST 1 6 1982 MEMORANDUM FOR: All Licensing Project. Managers FROM:
T. M. Novak, Assistant Director for Licensing, DL
SUBJECT:
BOARD NOTIFICATION REGARDING CONTROL R0D DRIVE GUIDE TUBE SUPPORT PIN FAILURES AT WESTINGHOUSE PLANTS We are informing the appropriate boards for Diablo Canyon 1 & 2, FNP l-8, Sumer, Callaway 1, and Comanche Peak 1 & 2 of the subject information.-
The issue involves the failures of the support pins.that are attached to the bottom of the control rod drive guide tubes in Westinghouse designed reactors.
The support pins align the bottom of the control rod drive guide tube assembly l
into the top of the upper core plate in a manner that provides lateral support and accommodates thermal expansion of the guide tube relative to the core plate.
Some of the safety concerns to which this information relates are failure to scram, scram system performance during design basis accidents, and potential damage to safety systems and components due to loose parts in the RCS.
For those cases in which this issue is a contention but the hearing has not yet started, you should assure that the substance of this board l
notification is addressed in your SER or SSER.
'T'M. Novak, Assistant Director for Licensing, DL
Enclosure:
As stated cc: L Branch Chiefs J. Kerrigan l
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MEMORANDUM FOR*
' Darrell G. Eisenhut, Director Division of Licensing Office of Nuclear Reactor Regulations FROM:
E. L. Jordan, Director Division of Engineering and Quality Assurance Office of Inspection and Enforcement
SUBJECT:
BOARD NOTIFICATION OF CONTROL ROD DRIVE GUIDE TUBE SUPPORT PIN FAILURES AT WESTINGHOUSE PLANTS The purpose of this memorandum is to infom you of an issue which we believe should be brought to the attention of the Atomic Safety Licensing Board Panel and the Atomic Safety Licensing Appeals Panel. The issue involves the failures of the support pins that are attached to the bottom of the control rod drive guide tubes in Westinghouse designed reactors. The support pins align the bottom of the control rod drive guide tube assembly into the' top of the upper core plate in a manner that provides lateral support and accomodates thermal expansion of the guide tube relative to the core plate (see enclosed notice for details).
. Westinghouse has analyzed the safety implications of a failed pin and cer.cluded that a single pin failure is not a safety concern,' either from the effects of a loose part or the failure of a single control rod assembly to fully insert upon a reactor trip signal.
Since the failures are due to rtress corrosion cracking (SCC), we believe that multiple pin failures are pcssible. Such failures could introduce-several loose parts into the reactor coolant system, and could also inhibit the insertion. of several control rod assemblies upon a reactor trip signal.
For example, one can assume that SCC had progressed to the point where several pins are on the verge of failing.
(Note: Such degradation was detected in a Japanese reactor). With the abeve preconditioning of the pins, we can postulate that a LOCA or other triggering event could induce higher than normal stresses on the pins such that they could fail simultaneously. We, therefore, plan to request additicnal analyses from Westinghouse regarding the potential for multiple pin failures and their effects on plant safety.
In addition, we plan to cetermine which actions are needed to resolve this concern.
Centact:
- 1. Villaiva (301) 492-9635
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that this matter is of sufficient safety significance to warrant board notification.
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M Edward L. Jordan, Director Division of Engineering and Quality Assurance Office of Inspection and Enforcement
Enclosure:
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IE infont.ation Notice No. 82-29 cc:
R. C. DeYoung, IE J. H. Sniezek, IE H. R. Dentor., f;FP.
G. C. Lafris,i;F.R T. A. Ippolite,f;RR J. M. Taylor, IE L. I. Cobb, IE R. L. Baer. IE W. R. Mills, IE T. L. Haroster, IE I. Villaiva, IE R. A. hollanc, IE-A. Pattou, IE l
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SSINS No.:
6835 IN 82-29 1-UNITED STATES
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NUCLEAR REGULATORY COMMISSION 0FFICE OF. INSPECTION AND ENFORCEMENT.
WASNINGTON, D.C. 20555 July 23, 1982 IE INFORMATION NOTICE NO. 82-29:
CONTROL ROD DRIVE (CRO) GUIDE TUBE SUPPORT.
PIN FAILURES AT WESTINGHOUSE PWRS Addressees:
All nuclear power reactor facilities holding an operating license (OL) or construction permit (CP) using a Westinghouse-designed NSSS.
Purpose:
This information notice is provided as notificatin of an event that may have safety significance.
It is expected that recipients will review the-information for applicability to their facilities.
No specific action or response is required.
Descriotion of Circumstances:
Since 1978, several failures of the control' rod drive (CRO) guide tube support pins have occurred.
Westinghouse has notified NRC of these occurrences by the following correspondence:
1.
June 11, 1979, NS-TMA-2099, Letter to 0. Eisenhut from T.'M. Anderson -
concerning support pin and flexure failures in Japan.
2.
March la, 1980, NS-TMA-2214, Letter to Victor Stello from T. M. Anderson; Title 10 CFR Part 21 notification concerning CRD Guide Tube Support Pin Failures at Foreign Plants.
3.
April 23, 1980, NS-TMA-2235, Letter to Stephen S. Pawlicki from T. M. Anderson summarizing Westinghouse /TVA/NRC meeting on May 20, 1980 on Sequoyah guide tube support pins.
4.
June 10, 1980, NS-TMA-2254, Letter to Stephen Pawlicki from T. M. Anderson concerning inspection of support pins.
5.
May 20,1982, NS-EPR-2251, Letter to Victor Stello from E. P. Rahe, Jr.,
concerning a pin failure at Graveline 1 Prior to May of this year, at which time a guide tube pin failed at North Anna 1, these failures had occurred only at foreign reactois (Japan and France).
The pins are used to align the bottom of the CRD guide tube assembly into the top of the ucoer core plate.
Two support pins are bolted into the bottom plate of each lower guide tube, and are inserted into the top of the upoer core plate in a manner that provides lateral support while accommodating thermal expansion of the guide tube relative to the core plate (see attached pin assembly diagram).
Tne pins are about 31 inches long and have a diameter of 0.507 or 0.537 inch (ceoending on reactor design).
The pin assemnly includes (1) a bolt section Nd s N._
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O IN 82-29,.
July 23, 1982 o
Page 2 of 3 to which a nut (sleeve) is threaded to anchor the pin to the guide tube, (2) a collet that rests against the guide tube, and (3) a leaf spring section with the leaf shaped somewhat like a clothespin. The material is Inconel X-750, which, depending on the manufacturer and the fabrication date, has been solution heat treated and age hardened at various temperatures and for various times.
For example, the solution heat' treatment temperatures and times ranged from 1625*F to 2100*F and from hour to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />; age hardening temperatures and times ranged from 1148*F to 1544*F and from 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />, respectively.
The first failures were detected in early 1978 at Mihama Unit 3 in Japan, at which time the top portion of a support pin with the shank and lock nut engaged was found in a steam generator.
Subsequent ultrasonic testing (UT) showed a possibility of cracks in 103 out of 105 pins at the bolt to collet transition region of the pin.
Seven of the Mitsubishi-supplied pins were then removed and inspected, confirming the UT results.
All pins were subsequently replaced and UT inspection was conducted at other Japanese plants.
In all, there have been at least eight support pin failures where a pin has actually broken.
These occurred with both Westinghouse and Mitsubishi-supplied pins.
In a recent f ailure at Fessenheim Unit 1 in France,part of a broken pin caused considerable damage to a steam generator within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of its failure.
It is estimated that the plant will be shutdown for about a year to repair the steam generator.
Although the broken part consists of the bolt section including the nut, only the lock nut of the pin has been found and the bolt portion is still missing.
Previous to the Fessenheim failure, a leaf from a support pin was found in an accumulator check valve at Graveline 1 in France.
It is not known how the leaf traveled to the check valve.
The only domestic pin failure occurred in May 1982 at North Anna 1.
The lock nut of a support pin was found in steam generator "A" and a smaller piece of material, also identified as part of a support pin, was found in steam generator "C."
Damage to the steam generators is considerable, with about 75% of the tube ends sustaining damage.
It is our understanding that the plant was shutdown in less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after detecting the loose parts in the steam generators.
It is also our understanding that the reactor internals will be video inspected to determine the status of the remaining support pins.
nestinghouse's analysis indicated that the failures are caused by stress cor-rosion cracking (SCC) of pins that are solution heat treated at less than 1800 F after which they are age hardened, and then highly stressed (60,000 psi nominal on the shank and 130,000 psi on the leaf spring section of the pin).
The solution heat treatment of the North Anna 1 support pin was 1625*F for 1 nour followed by an age hardening treatment.
The torque on the nut was 210 ft-lb.
Westinghouse now recommends that the pins be solution heat treated at 2000 F for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and age hardened at 1300*F for 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> to minimize the SCC problem.
Westinghouse also recommends that the torque on the lock nut be reduced te 130 to 140 ft-lb.
The consecuences of pin failure for olants with the upper head injection (UHI) design was originally considered to be more acute than those for non-UHI plants.
Tnis concern resulted from the potertial for CRP misalignment in UHI plants on
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IN 82-July 23, 1982 Page 3 of 3
- pin failure.
However, domestic operating UHI plants now have support pins meeting the recommended material process standards and the pin body design has i
been revised to prevent. control rod' misalignment on pin failure.'.
Westinghouse.does not consider CRD misalignment as credible in non-UNI plants..
3 The safety consequence of a support pin as a loose part, however, is still under consideration by NRC.
It is important to. note that, although a single pin failure is of limited safety significance, the' common-mode failure mechanism of stress corrosion cracking could cause several pins to fail.
We are concerned that, if not properly detected, multiple pin failures may occur that could affect redundant safety systems.
1 If you have any questions regarding this matter, please call the appropriate
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regional administrator or this office.
I i
Edward L. Jordan, Director 4
Division of Engineering and Quality Assurance i
1 Technical
Contact:
I. Villaiva IE 301-492-9635 Attachments:
1.
Pin Assembly Diagram 2.
List of Recently Issued IE Information Notices i
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_c h,ie Attachment :
IN 82-29 July 23, 1982 LIST OF RECENTLY ISSUED IE INFORMATION NOTICES Information Date of Notice No.
Subject Issue Issued to 82-28 Hydrogen Explosion While _
7/23/82 All power reactor l=
Grinding in the Vicinity of facilities. holding Drained and Open Reactor an OL or CP Coolant System 82-27 Control of Radiation Levels 7/23/82 All medical in Unrestricted Areas institutions Adjacent to Brachytherapy Patients 7/23/82 All BWR power 82-26 RCIC and HPCI Turbine Exhaust Check Valve Failures reactor facilities holding and OL or CP 82-25 Failures of Hiller Actuators 7/22/82' All power reactor upon Gradual Loss of Air facilities holding Pressure an OL or CP 82-24 Water Leaking from Uranium 7/20/82 All NRC licensed Hexafluoride Overpacks enriched uranium fuel fabrication plants
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81-26, Clarification of Placement 7/20/82 All power reactor Part 3, of Personnel Monitoring facilities holding Sup. No. 1 Devices for External an OL or CP Radiation 82-23 Main Steam Isolation Valve 7/16/82 All BWR power (MSIV) Leakage reactor facilities holding an OL or CP 82-22 Failures in Turbine Exhaust 7/9/82 All power reactor
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Lines facilities holding an OL or CP 32-21 Buildup of Enriched Uranium 6/30/82 All uranium and in Effluent Treatment Tanks plutonium fuel fabrication licensees 4
82-20 Check Valve Problems 6/28/82 All power reactor facilities holding an OL or CP l
OL = Operating License l
CP = Construction Permit l
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