ML20237H295
| ML20237H295 | |
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| Site: | Browns Ferry  |
| Issue date: | 07/20/1986 |
| From: | AMERICAN SOCIETY OF MECHANICAL ENGINEERS |
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| NUDOCS 8709030200 | |
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Text
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c010603 MPC-Vol. 26 ATTACl&ENT B l
Improved Technology i
L For Critical
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l Bolting Applications s
presented at THE 1986 PRESSURE VESSELS AND PIPING CONFERENCE AND EXHIBITION CHICAGO, ILLINOIS JULY 20 - 24,1986
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sponsored by
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THE METAL PROPERTIES COUNCIL. INC.
3r jointly with THE ELECTRIC POWER RESEARCH INSTITUTE THE PVP MATERIALS AND FABRICATION COMMITTEE, ASME edited by E. A. MERRICK TENNESSEE VALLEY AUTHORITY M.PRAGER THE METAL PROPERTIES COUNCIL, INC.
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8709030200 870825 DR ADOCK 050 9
THE AME RIC AN SOCIETY OF MECH ANIC AL E N GIN E E R S United Engineering Center 345 East 47th Street New York, N.Y.10017 f
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' OVERVIEW OF ISSUES RELATED TO NUCLEAR BOLTING APPLICATIONS
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E. A. Merriek fJ Tennessee Valley Authority
-l Knouvdle Tennessee T. U. Mereton Electric Power Research Wtitute j
Palo Alto, California I
L t.. McElhaney.
Tennesue Vaney Autnerity Knosed6e, Tennessee E
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b ABSTRACT The service history of bolting is good:.however, during the past several years, the U.S. Nuclear This paper will furnish information on the failure.
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.. industry has experienced an increase in the number of experience, an overview of the AIF program, summarize reported bolt failures. Failure or degradation has some of the results of the' work performed, and provide-recommendations on the issues,
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been reported in several generic areas which may impact plant safety or reliability. The generic bolting BOLTING EXPERIENCE IN U.S. NUCLEAR PLANTS:
g applications where failures or degradation have been
. experienced by the: industry include pressure boundary
.There are millions of bolts used in commercial.
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manways and flanges, component supports, and rtuelear plants. In each unit, two or three thousand of
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embedments, as well as bolting used in component these are used in the primary reactor coolant pressure 3=
internals, An aggressive program to assure the.
boundary comoonents, their internals, and supports continued integrity of bolted joints is nearing While the number of reported bolting failures has completion.
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. increased over recent years, there is some evidence
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INTRODUCTION-which indicates that the increase is a function of the.
increased number of installed bolts. It appears also that as plant maintenance personnel gain experience This paper updates refe*ence [1], previously during early plant operation, the incidents of leaking presented at the 8th Internat?onal Conference on joints and reported failures. decrease. The success k' '
Structural Mechanics in Reacter Technology, in history of fasteners is excellent wnen comoared to the Brussels., Belgium, NovemDer, 1985. The Atomic number of failures.
Industrial Forum (AIF), in conjunction with the 4
' Electric Power Research Institute (EPRI), The Materials The U.S. Nuclear Regulatory Comission (NRC), in Properties Council, Inc. (MPC), the utilities and other 4
. industry organizations, responded to the bolting need NUREG-0933, designated the Generic Safety Issue 29 as a high priority issue " Bolting Degradation or Failure in by formulating.a comprehensive program to address the Nuclear Power plants" [2), and indicated its concern:
issues. The goals of this program are to provide "There are numerous bolting applications in nuclear cefinition of the critical issues involved and to power plants.,,."
. consolidate industry resources in order to supply an appropriate response to the bolt integrity question.
"The number of bolting-related incidents has j
Work includes corrosion and fracture mechanics studies, increased... therefore, there is increased concern 4
. non-destructive examination (NDE) development, codes regarding the integrity of the primary pressure and standards activities, and maintenance and training boundary in operating nuclear power plants and the tasks.' Technology exchange has been effective in reliability of the component suoport structures as u ring increased attention to the behavior of bolting following a LOCA (loss of coolant accioent) or in E S. nuclear plants. Nothing has been discovered t1 earthquake."
raise concern regarding bolting integrity, primarily due to the redundant nature of bolting in critical There are four distinct bolting issues groused by closere joints, application and apparent cause as described below; i
Group I
- Degradation or failure of pressure program and examines both pressure boundary and structural support bolted connections to assess the boundary bolting Ne to general borated water corrosion (n stage or erosion / corrosion). The degradation of the overall bolted connection. The
.cause of failure is attributed to high rates of consequences of joint degradation in terms of leakage corrosion of low alloy steels in the presence of and leak-before-break margin for pressure boundary borated water. This is primarily a maintenance joints, and support, stiffness and faulted load condition margin for structural support joints, is
- problem, being examined. This approach is an alternative to Group II - Degradation or failure of pressure individual fastener integrity assessment. Since one of boundary bolting due to stress corrosion cracking the principal design features of a bolted connection is (SCC). The cause of these failures can be its stru,ctural redundancy, this alternative seems more attributed to an undesirable combination of realistic, provided that acceptance criteria for both stress, environment, and material condition.
safety and reliability can be mot.
Generally., these types of failures are associated with leaking gaskets or the use of certain The ultimate goal is to use the generic analytical l
lubricants and/or sealants. Failures can be methodologies developed by EPRI for bolted joint eliminated through proper use of tensioning integrity assessment, supplemented by industry technioues, lubricants and sealants.
experience and data - both nuclear and non-nuclear - to demonstrate the. safety margins in both pressure Group 111 - Degradation or failure of internals
.Soundary and structural joints, and to recommend bolting due to fatigue and stress corrosion realistic inspection or maintenance programs for l
cracking. Failures are generally related to utilities.
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materials, heat treatment, forming technioue, high
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steady-state stresses, or cyclic service.
CURRENT ACCOMPLISHMENTS f
Failures can be eliminated by. alternate materials selection and design modifications.
The integrated colting program is sciieduled for completion in May 1986. Currently, most of the Group IV - Degradation or failure of supports and identified deliverables are available. The most embedment bolting due to SCC. Failure can be notable are: overall bolting failure and success I
attributed to a combination of high stress, rates, fracture mechanics (FH) assessment, generalized 3
susceptible material condition, and a wet closure integrity (leak-before-break) model, bolt-up environment. They can be eliminated by attention procedure guidelines, thread lubricants evaluation, and I
to pretension and materials.
mechanical maintenance training taces.
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Failure groups 1, II, and IV above have been Overall Bolts Failure probabilities addressed generically under the auspices of a joint AIF/MPC Task Group on Bolting. Pressure boundary An experience base of bolt failures and/or bolting (Groups I and !!) has a greater influence on problems has been generated and analyzed. Of the five j
system integrity and the highest priority in the types of pressure boundary closures studied,
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industry program. Internals boltiny, (Group III) is specifically pressurizer, steam generators, reactor being effectively addressed by component vendors and coolant pumps, and valves, steam generator manway owners' groups and is not being considered generically.
bolting exhibited the highest total reject rate. The Supports /embedment bolting (Group IV) presently has a reject rate Gr manway bolting attributed to wastage i
secondary priority in the industry program. The wa
.2 x 10 and the rate for cracking was 2.3 x remainder of this paper will focus on the pressure 10 boundary and sucports/emcedment generic program.
Fracture Mechanics Assessment GENERIC INDUSTRY PROGRAM ON PRESSURE BOUNDARY AND The initial technological thrust regarding bolted SUPPORTS BOLTING joint integrity was directed toward the evaluation of j
- The ouestion of fastener integrity is very complex individual fasteners using probabilistic fractuie
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ond involves many disciplines (e.g., metallurgy, mechanics analysis. As with any FM evaluation, loads,
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fracture mechanics, mechanical and corrosion properties, and crack sizes had to be known. The NDE j
engineering) and activities such as bolt tension requirements for the FM based approach exceeded the control, NDE, design, specifications and standards, state-of-the-art capabilities. It soon became evident manufacturing, and osality assurance / control. Research that a more prudent and simpler approach to bolted cctivities have focused on understanding, identifying joint integrity assessment was possible and desirable, and implementing solutions to the issues. The research Nevertheless, the fracture mechanics research has work on bolting is in three key areas - structural greatly improved the state of information regarding integrity analysis (including nondestructive bolts and W er threaded f asteners. Cipolla [3] has studied the application of fracture mechanics to e'xamination) corrosion studies, and maintenance fasteners, and has presented a simplified analysis improvements, method for approximating the Stress intensification factor for an elliptical surface crack at the root c i
EPRI is completing a " Generic Bolted Joint thread. This approach will be integrated into cesign Integrity" project which integrates the industry 2
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9 life and failure prevention analyses.
Leak 7tchtness Generalized Joint integrity Model The most desirable attribute of a bolted joint is its leak tightness. A recent NRC survey (5]
Probably the most.significant contribution of the demonstrated that over 90% of all bolted connections in integrated bolting program is the development of the the primary pressure boundary are leak tight. The key generalized joint integrity model, wherein the closure elements that contribute to leak tightness are:
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is modeled accurately, incorporating the load shedding adeouate joint design, proper cleanliness, proper and redundancy. inherent to bolted connections. With gasketing, uniform and sufficient preload. It should the evaluation based upon the> erall closure, the be noted that all but the first element are controlled details of individual fastener degradation are not by station maintenance. The integrated bolted joint
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required. As a result, the complexity of the program addresses two aspects; the uniformity of calculations and data burdens are substantially reduced preload and an evaluation of thread lubricants. The and many of the areas of greatest uncertainty are findings indicate that a joint can be prepared with
'i avoided. Either wastage or stress corrosion cracking uniform preload in the bolts even with simple toroue b'
can be accommodated in the model. Ecually important is wrenches, if particular attention is paid to bolt-up, the fact that the NOE requirements of the generalized Recommendations include stepped torque values with joint integrity model are well within the multiple passes and ver#fication of proper preload by i
state-of-the-art capabilities, ultrasonic or other methoO Studs are preferred over i
bolts for many applications. Leak tightness can be L
The philos phy behind the n.odel is analogous with assured with proper care.
the leak-before-break philosophy used in FM evaluations of other pressure boundary components. The steps A second task evaluates thriad lubricants. The l
required to achieve the desired result, i.e.,
work includes laboratory and fie)J tests and indicates demonstrate that a degraded joint (due to wastagt, that the nickel based lubricants can %e substituted for cracking, etc.) has ample margin against catastrophic those using molybdenum disulphides (MoS ) without 2
failure when the leakage from the joint reaches levels modifying the nut factor and, thus, the torque values, that have a very hign probability of detection, A recommendation is made to not usa these MoS -based l
2 include: knowledge of the degree of load shedding to lubricants when dissociation is even suspecteo, i.e.,
'I adjacent fasteners due to fastener degradation, when the joint will be exposed to water and high knowledge of the joint opening profile accounting for temperatures. Reviews by Rungta and Majumdar (2) also gasket spring back and flange distortion, realistic included work in this area. The Materials Properties calculation of leak rates through the degraded-joints, Council has done extensive studies on various thread margin demonstration in load-carrying capability of lubricants and their contribution to SCC (5),
degraded joint and margin definition.
This philosophy was initially successfully applied
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to a steam generator manway cover to show its load Industry resolution of the generic issues is j
carrying capability. Example calculations indicate scheduled for 1986, and is planned to be accomplished p
that for a typical sixteen bolt joint, about three utilizing AIF and EPRI guidelines, and American Society I
bolts must fail before a " detectable" leak (10 gom) is for Testing and Materials (ASTM) and American Society i
generated. The stresses.in tne adjacent bolts increase of Mechanical Engineers ( ASME) standards activities.
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by less tnan 30% (well below the yield strengtn of the bolts).
On September 20, 1984, the Institute of Nuclear Power Operations (INp0) issued SOER No. 84-5 entitled, b
Cipolla and Proctor (4) continued this work and "Solting Degradation or Failures in Nuclear Power j
have proposed a method to establish leak rate margins Plants." INPO conducted an independent review of the and nondestructive examination limits for bolting issues and arrived at conclusions which reinforced materials comonly used in primary pressure boundary previous AIF recommendations. The SOER serves to closures. Analysis methods for determining the highlight and provide a " road map through the. issues to structural behavior and leakage of a bolted closure for utilities." The INPO SOER depends heavily on AIF/MPC various amounts of bolt degradation were refined and and EPRI programs.
calculations completed for several additional essential 7
components (check valve flanges, reactor coolant pump ASTM committees, having responsibility over f
main flange, and pressurizer manway flange). Initial bolting material specifications, have reviewed results indicated that leak rates between 1 gpm and 10 specifications under their jurisdiction to determine 4
gpm are possible without compromising the closure need for modifications based on commercial nuclear j
fntegrity. These analyses should provide sufficient industry experience and input from the industry
' basis for recommending revisions to present Code NDE program. Several specifications have already been j
requirements. Use of leak-before-break criterion is modified. At the Novemoer 1985 meeting of the ASTM considered an effective method of assuring closure Subcommittee F16.02 (on structural bolting), it was
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integrity while reducing demands on NDE. These recomended that a new Subcommittee be formed within calculations clearly demonstrate the degradation ASTM to rationalize ASTM structural bolting QA tolerance of bolted connections.
requirements. This recommendation is under consideration by Committee F 16.
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EPRI is developing two reference manuals to industries expected to benefit from BTC technology address how to identify safety-related joints, includes the f astener, enemical, petroleum, aerospace,
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selection of appropriate procedures, assembly and nuclear power, automotive and manufacturing industries.
dissembly procedures using various methods, inspection and verification of previous procedures to solve Problems which have occurred in the past. Thess CONCLUSION manuals will serve as a repository of useful information learned from EPRI analytical and The purpose of the AIF/MPC Task Group was to experimental programs and, whan published, they will develop and execute the AIF program for resolution of give the utility industry guidelines for bolted joints.
generic bolting issues. Since this has been Several utilities are already using drafts of these accomplished and all work is nearing completion, the guidelines in their efforts to enhance their bolting Task Group was disbanded in November 1985. The AIF program. It is believed that the bolting reference Subcommittee on Materials Requirements will be manuals will satisfy the industry's need for guidance available to handle any residual problems.
in this area.
Plans are to develop two comprehensive documents EpAI is developing an interpretive paper on pressure boundary bolts and structural bolts for use explaining the current ASME Boiler and Pressure Vessel by utilities. These would be considered the final Coda Rules for Bolting. ANSI /ASME Section III, Nuclear products from the program. They will be approved by Power Plant Components, has been reviewed and the AIF Subcommittee on Materials Requirements and recommendations have been developed for clarification distributed to utilities and the NRC for their use and and amplification of existing requirements. ANSI /ASME information in resolution of the issues.
Section XI, Rules for Inservice Inspection of Nuclear l
Power Plant Components, is considering recommendations The bolting issue is an example of a cooperative to rationalize bolting inspection requirements to focus effort between the utilities, the vendors, and the NRC on "at-risk" applications in service sensitive lines, to resolve a problem with poten+1cl saf n y
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Results from the_ EPRI generic joint integrity program significance. Shortcomings in design, material will be used as input to develop empirical rules for specification, procurement, and maintenance were
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inspection frequency and acceptance reoutrements. NOE identified. Fixes to alleviate concerns regarding rules will be modified to accomodate recent pressure boundary bolt integrity were formulated and
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develo nents in NDE technology.
are being implemented. The implementation of the recommendations will result in improved plant
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An EPRI/MEAC workshop was held in November 1985 availability and reliability, with reduced maintenance,
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in Charlotte, NC to enhance technology transfer. This man-rem exposure, and inspection costs.
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workshop was aimed primarily at informing maintenance personnel of the issues and alerting them to the REFEMNCES practical tools being developed in this program to aid them in achieving leak free joints. Tne workshop was a 1.
Merrick, E. A. and Marston, T. U., " Industry tremendous success with participants agreeing that Response to the issue of Bolting Degradation or additional workshops would be useful.
Failure," Paper No. 06/1, Presented at SMIRT/8, 6
Brussels, Belgium, August 1985.
i The Bolting Technology Council was formed to h
provide opportunities for threaded fastener and tool 2.
NUREG-0933, "A prioritization of Generic Safety users to engage in cooperative activities. As stated Issues," Safety Program Evaluation Branch, i
in their Bylaws, the purpose of the Council is "to Division of Safety Technology, U.S. NRC, December sponsor research; to recomend practicest to act as a 1983, New Generic Issue 29, " Bolting Degradation 3
clearinghouse for information; and to provide education or Failure in Nuclear Power Plants."
concerning the art and science of the lastallation and behavior of mechanical fasteners and their interaction 3.
Cipolla, R.
C., " Stress Intensity Factor with the joints they are used in."
Approximations for Semi-Elliptical Cracks at the Thread Root of Fasteners, Imoroved Technoloov for Although a large number of engineering and Critical Boltino Applications, ASME prusure industrial societies have been organized to deal with Vessel and Piping Conference, Chicago, July 1986, i
O various aspects of fasteners and joints, very little attention is paid to the important job of installing 4.
Cipolla, R. C. and Proctor, R.
R., " Application of 3
fasteners correctly. It is therefore the intent of the Leak-Before-Break Analysis Methods to Primary Council to cotolement rather than duplicate the work of System Bolted Closures," Imoroved Technology for others.
Critical Bolting Applications, ASME pressure Vessel anc Piping Conference, Chicago, July 1986 lho Bolting Technology Council is affiliated with The Materials Properties Council, Inc. (MPC), formerly 5.
U.S. Nuclear Regulatory Comission, NUREG 1095, The Metal Properties Council. Specific areas of "Evaluatiot. of Response to IE Bulletin 82-02, interest include achieving, maintaining and post-Published May 1985, assembly changes in preload, behavior of the joint 6.
The Metal Properties Council, Inc., " Progress under load, and joint failure modes. A partial list of Reports and Backgrounc Techni:al Information on MPC Bolting Task Group Study of Lucricants and 4
Sealants." December, 1985.
p i
APPLICATION OF LEAK BEFORE BREAK ANALYSIS METHODS TO PRIMARY i
SYSTEM BOLTED %OSURES R, C. Cipeda, Prmcipal Engmeer and R. R. Proctor. Engmeer Aptech Engmeerms Servss, Inc, Palo Alto, Cahfornia
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ABSTRACT basis for integrating appropriate mitigating measures, such as preload control, nondestructive examination l
A strategy is proposed that will establish leak (NDE), 6nd leak detection capabilities, in order to rate margins and nondestructive examination limits for assure the integrity of the primary pressure boundary.
bolting materials cocraonly used in primary pressure A Bolted Joint Integrity Program has been boundary closures. In the application of leak-before-sponsored by the Electric Power Research Institute 3
break analysis methods to closures, an analogy is (EPRI) w.th the main objective of obtaining a better drawn between a welded joint and a bolted joint with understanding of the behavior of bolted closures.
regard to structural redundancy, load shedding Primary emphasis is placed on the safety acceptance of a
h behavior, and early warning detection created bys the the degraded bolted closure, but it is expected that presence of a leak. Analysis methods for determining improvements in closure reliability will occur as the structural behavior and leakage of a bolted well. The purpose of this paper is to present a leak-3 closure for various amounts of bolt degradation are before-break strategy for resolving bolted closure p resented. Calculations have been completed for two integrity issues as the continuation of past work (5) steam generator / pressurizer manway cover designs, two and to show how this approach could be implemented k
check valve flanges, and a reactor coolant pump main through the ASME Boiler and Pressure Vessel Code (6).
h flange. Results indicate that leak rates in excess of a
f 1 GPM (0.042 kg/s) and as high as 10 GPM (0.42 kg/s)
LEAK-BEFORE-BREAK EVALUATIONS FOR CLOSURES are possible without compromising the closure integrity Hgnificantly.
The leak-before-break criterion was originally proposed in the late 1960s as a means of estimating P
INTRODUCTION the necessary toughness of pressure vessel steels so that a surface crack could grow through the wall, Recent service experience with primary pressure causing leakage of vessel contents to oetectable y
I boundary bolting in pressurized water reactors (PWR) levels before f racturing. As a result, this philo-indicates carbon steel fasteners can become degraded sophy has been effectively used in the assessment of as the result of prolonged contact with primary intefrity issues for weloed pressure vessels and coolant water at elevated temperatures Q,
.2_, 3.).
The pipirg comoonents fabricated from ductile materials.
closures that have expertenet.d bolting degradation If a component exhibits a leakage failure mode prior include primary side manway covers of steam generators to the point where the actual integrity becomes and pressurizer, coolant pump main flanges, and some questionable, then the demands on ICE methods other primary valve flanges. Of the closures listed, the than leak detection can be reduced. Hence, the steam generator manway covers have been the most objective of any leak-before-break analysis is to show troublesome (4)l fasteners have been observed to suffer that leakage will always precede failure by a suitably Individua safe margin.
from general corresten (wastage) at the shank or The basic similarities between a bolted closure c
threaded sections or f rom stress corrosion cracking and a welded joint with respect to material selection,
, (SCC) at the thread root. Although degradation of design requirements, control of fabrication processes, indivi6ual fasteners has raised some questions with and preservice inspection suggest that an assessment regard to closure integrity, operating experience also plan for closures could make use of a leak-before-suggests that only a small numoer of closures have break philosophy in tauch the same fashion as with actually degraded while in service. By focussing on welded ploes or vessels. Since one of the principal these
- service sensitive" closures, a Deneric plan for design features of a bolted connection is its addressing the integrity of a joint could be deve-structural redundancy it seems plausible that a loped. Such a plan would also provice a rational bolted closure, even w,ith some degraced or failed 5
fasteners, could meet acceptance criteria consistent The parameters that govern bolt degradation and with current industry practice provided that ample ultinately the integrity of a closure would naturally include the material condition, the closure loads, safety margins and closure reliability could be demonstrated. As an alternative to :urrent emphasis and the environment being contained. Because the SCC within the ASME Code on individu.1 f astener integrity, susceptibility of low alloy steels increases with increasing streng'th, those parameters that aff ect an assessment strategy is proposed that will establish variability in strength are the most important:
j the acceptance of a closure provided that the specifically, material specification, heat treatment, f ollowing conditions are met:
and nominal strength level. The stress-related j
e Leak-before-break of the closure is assured variables include preloading method, preload level, under the design basis conditions for the plant anticipated service loadings, and the joint faiffness
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and load redistribution characteristics of the 0
e The safety consequences of closure leakage are closure. Given suitable numerical cethods, the closure displacements and bolt stresses can be acceptable computed for a wide range of degraded bolt C U ditions.
e The margin against break at the point when the Finally, the environment variables include tempera-leakage becomes detectable exceeds an ture. humidity, and the presence of corrosive agents.
These environmental eff ects are used to estimate the acceptance level range of possible initial degraded bolting conditions A proposed assessment strategy for bolted clo-prior to.the application of service loadings. Based -
y sures that exploits the leak-before-break philosophy on these postulated conditions, requirements for 6
is depicted in Figure 1.
The suitability of this alternative NDE measures can be proposed once the resulting leak rates and available safety margins are strategy to closure evaluations will depend on established for a given closure design.
a available margins as dictated by the conditions required for closure f ailure, the amount of externri leakage from the cloture, and the availability of ' eak SERVICE SEftSITIVE CLOSURES a
detection instrumentation. Clearly, the character-The focusing of inspection and maintenance i
.istics characteristics of joint behavior in terms of activities on service sensitive closures will allow 3
load redistribution and gasket unloading followed by for more effective resolution of equipment leakage flange separation must be quantified for a valid and accurate determination of safety margins. Load problems. During the investigation of primary changes witnin the joint are due to postulated bolt pressure boundary bolting problems, the AIF/MPC Task degradation (wastage or cracking due to corrosion)
Group on Bolting and EPRI developed a Bolt f ailures y
that will cause the degraded region of the closure to Data Base with a specific objective of identifying unload at the expense of neighboring regions which now troublesome closures. The failure data were compiled must carry a greater portion of the pressure loadings.
primarily from utility responses to IE Bulletin 82-02 and Licensee Event Reports up to September 1984. It j
q was the intention of the AIF/MPC Task Group that this field infomation, along with historical data on plart clew.
specific closure perfomance from preservice and hydrotesting, will nelp define the service sensitive l
b closu res.
The Bolt Failure Data Base was used to estimate T
rejection rates for f asteners used in five closures N
( d.) : steam generator manways, pressurizer manways, M
- m. t.< m valves, reactor coolant pump (RCP) seals, and RCP p.,r
.)
D'9rmt
- um,s m
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flanges. A sumary of bolt rejection rates for all s,
reported causes including boric acid corrosion, r echanical damage, cracking, etc., is given in Table 1.
The rejection rates were computed on two
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j-first on the total numoer of bolts at risk and
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bases:
again on the total service years for the bolts at
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i toad risk. On either basis, the ranking of closure type is
*['Z" the same with the steam generator manways exhibiting the highest frequency of f astener replacements. The j
RCP main flange, pressurizer manway, and valves
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greater than six inches (15 cm) in diameter were also
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i troublesome but all exhibited rejection rates less o
than half that f or the steam generator manway.
o a
The cause for rejection of generator manway studs c y,,
was principally due to boric acid corrosion as shown
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s a mre in Table 2.
Galling and mechanical damage to threads j
1 were also major contributors to stud rejection suggesting thread lubrication problems. It is important to note that SCC was only a small percentage of the causes for rejection.
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Although one can argue on the overall conclusions j
that can be reached from these limitec data, the l
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infomation does help to focus the types of components reautring utility attention f or improved mainter.ance mem practice as well as identifying candicate closum designs f or evalt.ation by leak-bef ore-break analys ts metnocs.
Figure 1 - Closure Integrity Assessment Strategy.
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Q Table !
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the gasket. The finite element mesh for the 16-stud REJECTION RATES FOR BOLTING IN PRIMARY cover is shown in perspective view sn Figure 2.
The studs were modelled by beam elen2nts which were M,
PRESSURE BOUNDARY CLOSURES (ALL CAUSES) connected directly to the solid elements. Orthogonal rigid links were connected to the beam element end-M t
nodes to, induce stud bending when cover and flange I
Total Bolts Total Bolt surf aces d'o not remain perpendicular to the stud -
I Closure Yype -
At Risk Service years during loading. To simplify the analysis, the gasket was modelled as an clastic foundation represented by Steam Generator Manways 5.81 3.98:
discrete uniaxial clastic springs. The elastic loading and unloading behavior of a spiral wound
't -
Reactor Coolant Pump 2.85t 2.a3:
Main Flange asbestos filled gasket was inferred from experimental cyclic stress deflection curves (8) and used to Pressurizer Manways 2.281-1.20%
define the spring element stiffnesses. The Valves (>6 Inches 2.10i*;
deflections from the tests were matched to the actual 3
(15.2 cm) Diameter) manway by relating the gasket properties through ratios involving stress area and gasket thickness.
Reactor Coolant Pump 0.82%
0.85%
Because of the massiveness of the vessel flanges, the Seal Flange.
flange surface was assumed to be rigid. Stud preload was established in the model by imposing a
- Estimated For All Primary Valves By Statistical An'alysis (4) differential temperature between the studs and the b'NoteiBoltsatriskisthetotalpopulationofboltsinser-cover. A nominal preload of approximately 30 ksi ce for the given closure during the reporting period)
(207 MPa) and internal pressure of 2235 psi (15.4 MPa) were used in the study. Stud degradation was Table 2 modelled by changing the area of individual bolt elements to simulate partial wastage or by removing.
STEAM GENERATOR MANWAY bolt elements to model complete fastener failure.
STUD REJECTIONS BY CAUSE Cover separation was predicted in the 20-stud model when approximately two studs were assumed to i'
Bolts
% Of have failed; whereas, in the 16-stud manway, the i
Cause For Rejection Rejected Total cover first lif ted away from the gasket when one stud was assumed to have failed. When increased amounts 1
Boric acdd corrosion 116 37.1 of degradation were pemitted, including multiple h
Galled /msebanical damage /
65 21.3 stud failures, a redistribution in both gasket and threat damage / removal damage stud loads was observed. The change in gisket load -
Pitting /recoval damage 65*
21.0 in a 20-stud manway from the "preload only" case
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Stress cor-osion cracking 32
].3 throtr.n to various degrees of stud failures under unear indications 16
.5 internal pressure of 2235 psig (15.4 MPa) is shown in i
Cracks 5
1.6 figure 3.
The uniform gasket load becomes nonlinear.
Corrosion / erosion / steam cut 4
1.2 as the studs degrade and eccentric pressure loading Corrosion / mechanical damage 3
1.0 causes gasket compression to shift. The angular Other
__,a, 1.0 position at zero gasket load indicates the extent of cover separation.
TOTAL 310 100.0 Stud load redistribution was most significant for
. the five studs nearest to the degraded region.
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'61 at one facility for one event Figure 4 illustrates the load shedding and redistri-bution characteristics of the 20-stud manway for a ANALYSIS OF TYPICAL CLOSURES Primary Manway Cover Altnougn' there are more than 300 primary nanway covers in use ir steam generators and pressuriters of
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f
' United States Ilants, the basic design is very similar im.u
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in all applications. Most covers are typically
/
27-inch (69 cm)-diameter circular plates covering a 16-inch (40.6 s:m) opening. The cover is 5.75 inches (14.6 tm) thip. and held to the vessel by 16 studs.
i i
The 16 studs are fabric.stec from AIST 4340 steel
/
s I
according to either ASTM A193-B7 or A320-L43 speci.
/
fications and are 1.875 inches (4.76 cm) in diameter.
3-A 20-stud manway cover of similar geometry is also
/
used by ane PWR vendor. The 20 studs are smaller in
///h
%.0"""
)
size, typically 1.3 inches (3.3 cm) in diameter and
/
/
f abricated from similar materials.
=
b vvom A three-dimensional finite element model was developed to study the deformation behavior of bcth I
g cover designs as a function of stud preload and I
f u.s.i=.u different degrees of stud degradation. A general l
purpose finite element computer program called AN5YS 1
Q) was used to solve for cover displacements as a f unction of circumferential position, and the l
j conditions unoer which the cover would separate from Figure 2 - Sixteen-Stvo fianway Cover Mocel, j
7 i
m
e r
i I
8 0
4 I
i 6
L t
20 stes siea-ey Covet gg
\\
n.,
it P
tr Preload one prentu,
r 1
, g, (sil Steet entact) h p
if y' 10 3
g
}
\\
t a oae u.o re= oves five stedt Sevea studs e
three Stues 1
b 2
I f
I l
f f
{
p 0
30 W
90 tM iW 480 Aaquise Polipon, 4 (Oegrees) 5 Figure 3 - Gasket Load Redistribution for Different Stud failure Conditions.
(NOTE: 1 KIP = 4.45 KN)'
The finite element model representing 180' i
range of conditions including a worst case of seven segment of the pump casing, flange, and cover is shown adjacent or contiguous studs completely faileti (100%
F d egraded). It is observed that the two studs nearest to the f ailed region receives the greatest increase in 204tud asa er co er f
load, while the second end third nearest neighbors
" ~
u,,,,,,,,,i,,,
receive a smaller fraction. The load in the fourtte and fifth closest stud decreases with the unloading p,. 223s ni us.4 me )
g caused by the reduced stiffness of the cover / flange M "
y joint. The applied pressure loading performs a greater amount of work in deforming the more flexible 2.6 -
2 (degraded) portions of the closure, while slightly 3
less work is done on the greater stiffnesses of the 2.4 3
undergraded portions of the closure.
A similar trend in load change is observed in the 2.2 16-stud design except that the load increase in the nearest stud is greater due to the fewer number of 2.0 studs and greater angular distance between the faste-ners. Here, load redistribution was most significant i.
for the three nearest Stuos to the degraded region,, as f
shown in Figure 5.
Only the first two studs share an
". 'a 5'"'"""
increased load whereas the third nearest is observed 3,,,,
aee res t to unload. Percent age-wise the stud stress increases a
e g,
f aster in the 16-stud manway for a given amount of 5
fore a eren closure damage, but larger amounts of leakage would
' g 'g also be expected.
Reettor Coolant Purno Hain Flance
\\r -_
eo ta acernt r
Ine main flange ano cover of a Type E RCP was
~
- ""'"'/
evaluated in the same manner as the manway closure.
The pump cover is composed of an insert plate and 3
botting ring with a bolt circle dianeter of approxi-cately 58 inches (147 cm). The insert and ring is 0*
beld to the pump casing by 16 studs. 4.75 inches (12 cm) in diameter and approximately 36 inches (91 cm) long. The opening of the pump casing is 48 inches (122 cm) in diameter and the outside diameter of the rtng is approximately 80 inches (203 cm). The studs "O,
l l
l l
l are f abricated f rom A1514340 steel. Because the
%,,, c,, n o,,,,,,, %,,
mating flange on the casing is et comparable site to the cover, the pump casing was al:0 modelled so that figure 4 - Load Redistribution in Five f;earest the compliance of the mating flange is well repre-5tuos to Degraced Region in a 20-stud Man =ay.
sented.
8
r6 studs (beams) and the co..-! body tt -Ive an approxi.
mate streten of 25 mils (u.64 mm) translating to a e
st d ** 'e stud stress of about 25 ksi (172 MPa). Internal pump 000 o
pressure was assumed to be 2250 psi (15.5 MPa).
0 O
The unloading o' Se flange as studs were removed i.
... o,...u i s t en.
t a,<.u t ie. )
was similar to that ooserved for the manway Cover a e
'm except that gasket unincdtng was more uniform with o
i e,. trn eu, O ta ***)
little or no increase in gasket compressive load.
i
/
/
~
Ring / insert plate is expected to separate when only g
L' one stud is assumen *.o have f ailed. The increase in
.e,.,
s h-
- L8 stud stress for various degrees of stud degradation is I
shown in Figure 7.
lhe four closest studs to the degraded region are observed to carry increased i
L' amounts of load above f. heir original level of approxi-3 j
snead merest mately 35 ksi (240 f"6).
As with the manway cover, c Li f
the two studs adjacent to the degraded region receive e
.J the largest increan in load. The load ratios are Lo
r greater than the manways because the pressure load is about nine times greater for the pump cover.
o.s 1
Turd nearest 3.2
- 0. 6 M
oc pump tlenge 16 studt waiform prelodd 2.8 ei. 2250 on ot s **ei c.!
=
2.6 f
f f
f f
g o
i t
3 4
s 2.4 u,,,,,,,,,
lauseer of contiguous failed $tves f ailed region 1.2 f
Figure 5 - Load Redistribution in the Three i
3 Nearest Studs Due to Stud Degradation 2.0 su..d,,,n t 1
in a 16-Stud Manway.
g i.s 1
9 in Figure 6.
The model is comprised of 1200 sQid
. elements with the studs being represented by beam a Le elements and attached to the solid body in the same
- L in,4.e.rnt 4
manner as the aanway model. Two pressure retaining La gaskets are used in the actual assembly of this pump; 2
however, a single line of gasket (spring) elements of i L2 equivalent area and location is employed in the model j
room warnt to simplify the model geometry. The studs are no preloaded by a differential temperature between the 2
o.s i
citroser "e* asuatr o.6 S end 186,71 S 4le)
I
,g n, l
. 3 k
t u
o i
2 3
4 aumer et coatiguous f aneo st as k
% j[ A y.
,V. '
t
\\
Figure 7 - Load Redistribution in Reactor
[
^ - -
Coolant Pump Main Flange.
\\'
' \\
a
/-
'/'
Two Dotted flange check valves, one small six-1 Zi7
@f inch (15 cm) swing check and another larger ten-inch (25 cm) check, were analyzed in similar manner as the l
m ih (Q
previous closures. The valve flanges complied with g
- 4 p
ANSI 016.5 steel pipe flange cesign, 1500 lb class.
s N
Check valves were selected for evaluation because they
""*' /
mented in the Bolts Data Base.
exhibited the most flange leakage problems as docu-The six-inch (15 cm) valve has a 14.25 inch (36.2 cm) diameter cover with a neck diameter of 7.825 Figure 6 - Reactor Coolant Pump Model, inches (19.9 cm). Twelve 1.25 inch (3.2 cm) diameter l
9 i
I
._-_-_______-____D
studs hold the cover to the bndy with a specified The unloading of the flange due to stud degrada-preload torque of 500 f t-lbs (680 J). The ten-inch tion was similar to the manway cover analysis except (25 cm) valve has a 19.875-inch (50.5 cm) bonnet that the ten-inch (25 cm) valve was less uniform, cocering a 11-inch (28 cm) diameter opening. Sixteen probably because of the nonsymetric valve flance body s
studs,1.625 inches (4.1 cm) in diameter, are used in geometry. The redistribution of the original 37 ksi this design. The stud material is the same for both (255 MPa) bolt stress is shown in Figures 10 and 11.
j calves, specifically ASTM A193-87.
Cover sept. ration is expected to occur at some point A three-dimensional finite element model of each af ter two contiguous studs have f ailed although the calve is shown in Figures 8 and 9.
Both models are specific analysis to shcn conditions for bonnet lif t-l 180* symetric representations containing approxi-off was not performed. The load redistribution in the 3
mately 700 elements in each. Because of the impor-ten-inch (25 cm) valve was relatively uneven between tance of flange stiffness on stud load, the valve two and four contiguous stud failures 1 however, bodies were also modelled. The basic modelling of the because of the greater density of studs, significant L
studs and gasket follow that of the previous analyses, load is carried by the two studs nearest the degraded A unifom preload of approximately 35 ksi (240 HPa) region of the closure as compared to the smaller was applied to the studs and the internal pressure was valve.
i 2250 psi (15.5 MPa).
3.2 f
2.0 -
si..sca en.o uw,
-e, l.a -
N UNNNNf l
l.s an. n.
2.i q
t.t 2.0
)
,~s
/
he a res t.s.tud
/
n.s
,ee., \\
- t. e.o 3
r e 1.s
)
j w
e t.4 j
j secons nee est en mua i m.
g v
3 1.2 Figure 8 - Six-Inch (15 cm) Check Valve liedel.
- l0 s
~
0.s
/
)
Third nearest o.s C.4 i
e i
a
<ee coat us renee stvas
,--m
'/ / / / ljl; Q,
Figure 10 - Load Redistribution in Three Nearest
i;j Studs to Degraded Region in a 6-lach (15 cm) Check valve.
.f f-_f-LEAK RATE PREDICTIONS l
7-xl I. -
\\
h_,
4 Model Description i
t Seiection of an appropriate model for predicting i
flow through a slit will depend on the fluid conditions I
I I
O and geometric characteristics of the crack (Figure 12). In this case, the slit is represented by the gap between the unloaced portion of the gasket and 8**7 the previously mating flange surf ace. The ratio of flow path length to characteristic dimension (i.e..
hydraulic diameter) defined as L/D, is used to specify the degree of thermal noneoutlibrium of the escaping fluid. A leak rate model following this approach F1gure 9 - Ten-Inch (25 cm) Check valve Model.
based on Henry's homogeneous nonequilibrium crit 1 cal 10
Flow fills
- 3 ' '.
slit i
e 6
4 6
s i
l choaing u
v e.. ie c s.m...i.e 4, _,,,
4 16 st.4s aiform eccle.d 2'8 si
- 2750 ott {tt.6 s*el
~
=
76 Q.
. m,% -
wm, ww w o ww%mwg %
l
~
~
l Jet Two onase
,,,subcooled gl,,
2.2 llouia jet m ature g
t.o (a) Two-Phase Flow Through a Long, Narrow st..
.,e
, te
,,g we4 re9'*
Slit.
l.4
=
e
. 1. 4 Length
~
_[
E snea.
.,eu
/a Iait plane g
At (ares at L/o a 12) gg Ned ae. rest 0.6 Fourth *e L'
/
.A inlet flane n
e 0.4 0.2 Otrection of flow I
I 0'0 (b) Critical Flow Model For Leakage Through o
a a
4 s
e i
s
%.eer of coat i,.
r.t ied st"*'
a Slit.
l
?
Figure 11 - Load Redistribution in a Ten-Inch Figure 12 - Critical Flow Model For Leakage Through a Slit.
d (25 cm) Check Valve.
m i
flow model (9) has been developed by Collier (10) and where o' is the momentum density equal to mixture subsequently modified by Abdollahian and ChexaI~( H).
density (p.) for the homogeneous flow assumption.
4 The general features of the discharge of initially Equation (2) can be integrated along the flow path to 4-subcooled or saturated liquid through a slit is shown evaluate the overall pressure drop across the slit as j
in Figure 12. In the region 0 < L/D < 3, a liquid jet the sum of individual drop components to give:
surrounded by a vapor annulus is fomed. For lengths AP + AP
+ AP
+ AP (3) f between L/0 = 3 and L/D = 12, the liquid jet breaks up 6P
=
total e
ae aa f
E into droplets at the surf ace and small bubbles are entrained within the jet. It is assumed that no mass p
p p
or heat transfer takes place between entrance and g
g g
E "
change and area change, respectively, and APf is the re ion s gi b f rict on s
s h
The flow is assumed to be isenthalpic and homo-P geneous, and all nonequilibrium effects are Introcuced iterative process f or a 9tven set of sta9 nation l
througn a single parameter which is a function of conditions and slit geometry. The details of the equilibrium quality and flow path length to diameter numerical procedure are given elsewhere (J.J,12. For situations where.the flow is not choked, the Te'a)k.' ate ratio. L/D. The one-dimensional mixture mass and momentum conservation equations are used to evaluate is calculated from single phase relations with the pressure drop components. The continuity equaticn f riction included:
gg 0
8 h+fh0 2g (4)
(1)
G
=
g where 6 is the mass flux, A is the slit opening area, 4
when g, is gravitational acceleration, P and y a re J
and 2 is the direction of flow coordinate. The pressure and specific volume at stagnatio8. and E is g
momentum equation is:
the back pressure. Calculated leak rates by the above methods have agreed well with experimental studies 2 -
2 (2)
U*
h = f h hf
+
h C
Ccx, outed Closure teakaoes ine lean rate for each closure was calculated by PICEP (g) which was modified to accomodate the 11 t
t.
' expected slot openings for the bolted flange connections as determined from the finite element relatively high margins at the 1 GPti (0.042 kg/s) leak
- rate, results. - The subcooled fluid conditions for a pressure of 2235 psi (15 4 HPa) and 2250 psi (15.5 MPa) of a temperature of 600*F (316*C) were assumed.
IMPACT OF CLOSURE INTEGRITY ASSESSMENTS ON Leak rate estimates for all the closures analyzed NONDESTRUCTIVE EXArt! NATION 3
previously are presented in. Figure 13. The pump main flange showed the greatest capacity for producing With reference to the requirements under large leak rates owing to the large diameter of the Section X1'of the ASME Code, two areas where closure sealing surface and smaller number of studs per are integrity assessments would affect NDE are the extent,
i length.. The manway covers and valve bonnets exhibit of examinations (!WB-2000) and the flaw acceptance "1
similar leak rates and trends. Being a smaller standards (IWB-3000). The extc* sf examination for e
t closure, the six-inch (15 cm) valve is predicted to peessure retaining bolting is divided into two
'2 produce smaller leak rates at lesser levels of stud categories as dictated by bolt size. Category 6-G-1 degradation; however, significant leakages are covers principally volumetric examination of boltin possible once degradation has extended to a larger whose diameter is greater than two inches (5.1 cm).g percentage of the bolting.
Category B-G-2 is for bolting two inches'(5.1 cm) in diameter or less with visual surface examination
',y specified only. These NOE requirements were developed from conventional bolted joint fabrication 1
1 i
6 4
applications; however, nuclear power plant field experience presented earlier suggests that the 5-.
volumetric / visual examination cutoff at two inches (5.1 cm) may revire reassessment. If these field.
c =o.. i..
N 06sMO 7
data provide a statistically representative measure of :
8 8
primary pressure boundary closure performance, service a
N (P e flue' -
sensitive closures could be identified and,
(
lo U'""*"
appropriately ranked and NDE requirements established '
~
based on known closure performance and on likely ro.u m,,
f ailure modes. The NDE requirements developed from k
Q such an approach would not necessarily be the same es a
- /
those in the present 1983 edition of the Code, it 1P 3,,
would be expected that any alternative approach would
/-
/
' '/
/
emphasite volumetric examination with supplemental
~
f.
E'
/
/
5 visual / volumetric NDE for those situations when f
- -/
/-
leakage from the closure has occurred during service.
s 1
- /
Category B-G-1 acceptance standards for nonaxial 2
/
g flaws are 0.250 inch (0.64 cm) and one inch (2 5 cm) f
_1
/
mi for axially oriented flaws. Closure assessment based on leak-before-break will provide a relationship
- I
/
j
/
between leak rate and closure integrity as measured in 5'
/((
f ut u.ess
- wr3 temrof bolt degradation. By selecting a minimum su. wen cwo..i.,
i required safety margin, which may vary for different
- o. i._
3 service loading levels, the results from a closure assessment would give the basis for establishing NDE
[
requirements. The logic of integrating a leak-before.
break philosophy into a determination of. requirements
,7
/
and criteria for NDE is shown in Figure 14. From an f
f established set of safety margins, a range of degraded
/
8g conditions would be postulated that mt.intains a f
1 l,
constant level of closure safety. Leak rates are computed for the range of postulated conditions and the minimum leak rate used to establish detecta-a bility limits.
Likewise, the type and extent of n
,etcen,.ovirmessu,
degradation used in the analysis for leak rates provices the basis for selecting NDE requirements and levels of acceptance. Clearly, the example analyses Figure 13 - Leak Rate Predictions For Otfferent Primary System (losures, presented herein provide sufficient bases for initiating Code revisions.
For the closures analyzed, a leak rate of one gallon per minute or 1 GPH (0.042 kg/s) is achieved St#fiARY AND CONCLUSIONS when approximately one to three stuos have failed.
The available margins at 1 GPM (0.042 kg/s) are shown Closure integrity assessments will provide A in Table 3 where the safety factor is based on load rational basis for recocnending revisions to present Code NDE requirements. Satisfying a leak before-break required to f ail the stud nearest the degraded region by net section tensile overload. In *his determina-criterion is an effective strategy for assuring I
. tion, the direct (o
- conservatively adde 3)and compared with specifiedand bending (o ) stresses were closure integrity while at the same time reducing I
demands on NDE. Preliminary analysis of various s
minimum strength properties.
The six-inch (15 cm) primary pressure boundar valve exhibits the smallest margin for the condition and pressurizer manways,y closures (steam generator RCP main flanges, and check where 28*. of the studs are gone, but because of the valves) suggests that integrity can be assured by smaller pressure load. a safety factor of 2.2 still monitoring closure leakage in excess of operational The pump and manway covers all exhibit limits.
exists.
Large leak rates are predicted when a few fasteners are assumed to have failed.
Aoequate 12 ve
Table 3 9
ASSESSMENT OF MARGINS AT ONE GPM (0.042 kg/s) LEAKAGE Percentage Computed Assumed Failed Studs Factor Of g
>La Closure Type Bolting For One GPM 16 Stud Manway Cover
' t 'e8 k Safety At One GPM Material Leakane
[.
20 Stud Manway Cover SA320.L43 15.9%
3 RC Pump Flange AS40.B24 14.5%
3.2 3.0 6 Inch (15 cm) Check Valve A193.B7 7.8%
3.3 A193 87 27.5%
10 Inch (25 cm) Check Valve 2.2 A193 87 17.8%
2.6 o
W.
safety margins can be demonstrated provided that closure damage is local and that bolting materials are Hall, J. F., "A Survey of the Literature on Low-3.
suf ficiently ductile as to tolerate. heavy damage Allow Steel Fastener Corrosion in PWR Po g
induced by corrosion.
Plants,"
Topical Report NP-3784 (December 1 j
h,-
- 4. -Capener, E. L., and R. C. Cipolla, " Evaluation o i
.ll,"*'."l,,,7ll'l,,
Bolting Service Experiences in Primary Pressure Boundary Closures " Aptech Engineering Serv Inc., Report AES 6111290-3 EPR] RP2055-5 (December 1984).
~
'4 5.
"The Use of leak-Before-Break Crite a.u.i.i. o.va.e C**""
Assessment of Eargins in Addressing Closure y
Inte'rity issues," Paner 06/3, SMIRT-8 D
Con rence, Brussels, Belgium (August 1985).
,,g,,,,,,,,,
a,ui 6.
Arnerican Society of Mechanical Engineers, Boiler and Pressure Vessel Code,Section XI, " Rales for Components," 1983 Edition.tne Inservice Insp h
7.
DeSalvo, G. J., and J. A. Swanson, "ANSYS -
L n iu n 3,,. t.,,gn. a.wrau cuaina nac Engineering Analysis Systems User's Manual,"
- emais tualisa aneeuac, I
PA (itarch 1,1983). Revision 4.1, Swanson A Figure 14 - Flowchart Showing the Determination Barergui, A., "Short Tem Creep and Relaxation 8.
of NDE Perfomance Requirements and Behavior of Gaskets,"' Welding Research Council Acceptance Criterion.
Bulletin 294 (1985).
ACKNOWLEDGEMENTS 9.
of Initially Saturated or Subcooled L "The Two-Phase Critical Discharge the Electric Power Research Institute, Palo Alto,This work was perfomed und Nuclear Science and Enoineerino, Vol. 41 (1970)
California (USA), Research Project 2055-5.
10.
Collier, R.
P., et al., "Two-Phase Flow Through 1
The authors also wish to acknowledge the assistance Intergranular Stress Corrosion Cracks and provided by the AIF/MPC Task Group on Bolting with Resulting Acoustic Emission," Electric Power Babcock and Wilcox Company, itr. Edgar Lanceman ofspecial thanks extended Research Insitute, Report (in publication).
Westinghouse Electric Corporation, and tir. Walter Bak 11.
of Combustion Engineering, Inc.
Abdollahian, D., and B. Chexal, " Calculation of i
Leak Rates Through Cracks in Pipes and Tubes,"
Electric Power Researcn Institute, Report NP-3395 REFERENCES (December 1983).
I 1.
Merr-t ck, E. A., and T. U. Marston, " Background 12.
Norris, 0, A. Okamoto, B. Chexal, and '.
and Industry Response to the lssue of Bolting Griesbach "PICEP: Pipe track Evaluatitn Degradation or Failure in U.S. Cornercial Nuclear Program,", Electric Power Research insitute, Brussels, Belgium (August 1985). Power Plants," Paper 06/1, StilRT-8 Conference Special Report NP-3595-SR ( August 1984).
2.
Anderson W., and P. Sterner, " Evaluation of Responses, to IE Bulletin 82-02," NUREG-1095 (May 1985).
l 4
13 o
p@haMT-.
\\
ATTACHMENT C Issue 1.2.1 - Material Compatibility Concern Number IN-85-021-X04
?
IN-85-824-001 5
IN-86-184-001
'.d p
Issue 1.2.2 - Material Adequacy r,
Concern Number PR-85-042-001 Issue 1.2.3 - Inadequately Supported Flange.
Concern Number BNP-QCP 10.35-8-22
)
)
~
1
_ _--- _ _