NRC Generic Letter 1981-14
| ML031210309 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 02/10/1981 |
| From: | Eisenhut D G Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| GL-81-014, NUDOCS 8103130222 | |
| Download: ML031210309 (14) | |
FEB 1 0 1981TO ALL OPERATING PRESSURIZED WATER REACTOR LICENSEES
SUBJECT: SEISMIC QUALIFICATION OF AUXILIARY FEEDWATER SYSTEMSOAenertc Letter No, 81,'141Our letter to you dated October 21, 1980, identified concerns regardingthe seismic qualification of Auxiliary Feedwater (AFW) systems. Thatletter outlined the continuing evaluation program being conducted bythe staff with regard to this issue to assure conformance of each plantwith General Desin Criteria 2 and 34, of Appendix A to Part 50. As aresult of the NRC s continuing review of this issue, including thecompletion of site visits described in our previous letter, we havedetermined that it is necessary to request certain information fromPWR licensees and to request that certain actions be performed by PWRlicensees, as described below. The purpose of our information requestis to obtain sufficient information that identifies the extent to whichAFW systems are seismically qualified. We are also requesting that PWR1icensees perform a walk-down of the non-seismically qualified portionsof their AFW systems to identify apparent and practically correctabledeficiencies that may exist.For plants with AFW systems that are not seismically qualified eitherin whole or in part, our plan involves Increasing the seismic resistanceof the systems In a timely, systematic manner to ultimately providereasonable assurance, where necessary, that they are able to functionfollowing the occurrence of earthquakes up to and including the design SafeShutdown Earthquake (SSE) for the plant. This plan is a result of astudy of the seismic requirements which should be applied to AFW systemsfor those not presently seismically qualified, as discussed in NUR£E-0667, Transient Response of Babcock and Wilcox-pesigned Reactors."Enclosure 1 to this letter contains a request for information from alloperating PWRs concerning AFW system seismic design. We have determinedN that docketed information from licensees is not sufficient to allow usto conduct a detailed review of this aspect of AFW systems. In addition,for a number of older plants, this Information is likely not to beO current. Furthermore, since the safety significance of the system maynot have been defined for all plants, the AFW system may not have beenadequately maintained and considered to be included within the scopeof IE Bulletins 79-02, 79-04, 79-07, 79-14, and 80-11, and XE InformationGO Notice 80-21. Therefore, the existing AFW systems, either in total ora in part, may have as-built characteristics which result in uncertainseismic design characteristics. For plants with AFW systems, or portionsq thereof, which are not seismically qualified, Enclosure I also requestsinformation concerning systems which provide an alternate decay heat -Vremoval pat A,1k4. 1We are also requesting that you conduct a walk-down by personnel experiencedin the analysis, design and evaluation of such structures, systems andcomponents, of the non-seismically qualified portions of the AFW systemfor the purpose of identifying more readily recognized deficiencies inseismic resistance. These walk-downs are requested for only thoseportions of the AFW system which have not been designed, constructed,and maintained as seismically qualified systems in accordance with thecriteria for safety-grade systems at the facility. The scope of thewalk-down should include the types of equipment, components, and pipingdescribed in Enclosure 2. Enclosure 1 describes what we consider tocomprise the bounds of the AN system, and any alternate decay heatremoval paths.For plants with AFW systems that are not seismically qualified, we consi-der that actions should be taken soon to ensure a reasonable level ofearthquake resistance. This applies to both the AFW system and thealternate system used for decay heat removal if portions of it are notseismically qualified. Based upon the consideration of the past perfor-mance of nuclear and fossil power plants, and other non-nuclear facilitiessubject to large earthquakes, we note that well engineered structures,equipment, components and piping possess a substantial amount of inherentseismic resistance, even without the rigorous seismic qualificationperformed for safety-grade portions of nuclear facilities. Of thefailures of structures, piping, equipment and components noted inthese past earthquakes, a large fraction have been due to brittlefailure, lack of restraint, large displacements, or some other obviousdeficiency which would have been easily identified before the failurecaused by the seismic event. Such identified deficiencies could havebeen corrected to significantly enhance reliability without detailedseismic analyses but by exercising careful engineering Judgement. Theseconsiderations were factored into the development of Enclosure 2. Inaddition, certain of these deficiencies were noted as existing at theseveral facilities for which we conducted AFW system walk-downs (seeEnclosure 3 for details of the visits). Accordingly, your walk-downof the non-seismically qualified portions of the AFW system and otheralternate decay heat removal systems should identify any appropriatemodifications in the context of the above discussion.Enclosure 2 identifies in more detail the actions we consider appropriatefor plants with AFW systems, or portions thereof, that are not seismicallyqualified. Although we are not at this time requesting that the AFWsystem be modified to be in conformance with the facility design seismicrequirements, we have stated that our plan Is to increase the seismicresistance, where necessary, to ultimately provide reasonable assurancethat the system will function after the occurrence of earthquakes up toand including the SS *w: w-----? ---e-3 -Accordingly, the following actions are requested by this letter:1. In accordance with 10 CFR 50.64(f) of the Commission's regulations.all PWR licensees are requested to provide the information containedin Enclosure 1 within lM days of receipt of this letter; and2. The results of any walk-downs are requested within M) days ofreceipt of this letter. These results should include all identi-fied deficiencies and all corrective actions taken, or plannedalong with the schedules for such. Such modifications, if any,shall be handled in the customary manner consistent with theprovisions of your license and the Commission's regulations.Responses should be submitted to enable us to determine whether or notyour licensefthould be modified, suspended, or revoked.rDarrell GX4fsenhut, DirectorDivision of Licensing
Enclosures:
As stated"This request for information was approved byclearance number R0072 which expires Novemberburden and duplication may be directed to theOffice, Regulatory Reports Review, Room 5106,Washington, D. C. 20648.sGAO under a blanket30, 1983. Comments onU.S. General Accounting441 6 Street, N.W.,4R scoIzz-V -:.,ORAB: DL ?5017jp:dn;OFFICESURNAMEODATE iC/SEPB:DL41Wiss .....1W.0"nW~sself~................................76 M -' ..... ,,....~ i .................................Y..w .~ X v........Rpfer.1 /..1 /81.. T...............D:DSI hIDRoss......................................I1 /8iN." W ........ --- .......I........... ..... ........ .............-),.................. *. .........NRC FORM 318 410/80) NRCM 0240OFFICIAL RECORD COPY* USGPO: 1980-329-82
° 9UNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, D. C. 20555* 0 FEB 1 0 1981TO ALL OPERATING PRESSURIZED WATER REACTOR LICENSEES
SUBJECT: SEISMIC QUALIFICATION OF AUXILIARY FEEDWATER SYSTEMS(Generic Letter No. 81-14)Our letter to you dated October 21, 1980, identified concerns regardingthe seismic qualification of Auxiliary Feedwater (AFW) systems. Thatletter outlined the continuing evaluation program being conducted bythe staff with regard to this issue to assure conformance of each plantwith General Design Criteria 2 and 34, of Appendix A to Part 50. As aresult of the NRC's continuing review of this issue, including thecompletion of site visits described in our previous letter, we havedetermined that it is necessary to request certain information fromPWR licensees and to request that certain actions be performed by PWRlicensees, as described below. The purpose of our information requestis to obtain sufficient information that identifies the extent to whichAFW systems are seismically qualified. We are also requesting that PWRlicensees perform a walk-down of the non-seismically qualified portionsof their AFW systems to identify apparent and practically correctabledeficiencies that may exist.For plants with AFW systems that are not seismically qualified eitherin whole or in part, our plan involves increasing the seismic resistanceof the systems in a timely, systematic manner to ultimately providereasonable assurance, where necessary, that they are able to functionfollowing the occurrence of earthquakes up to and including the design SafeShutdown Earthquake (SSE) for the plant. This plan is a result of astudy of the seismic requirements which should be applied to AFW systemsfor those not presently seismically qualified, as discussed in NUREG-0667, "Transient Response of Babcock and Wilcox-Designed Reactors."Enclosure 1 to this letter contains a request for information from alloperating PWRs concerning AFW system seismic design. We have determinedthat docketed information from licensees is not sufficient to allow usto conduct a detailed review of this aspect of AFW systems. In addition,for a number of older plants, this information is likely not to becurrent. Furthermore, since the safety significance of the system maynot have been defined for all plants, the AFW system may not have beenadequately maintained and considered to be included within the scopeof IE Bulletins 79-02, 79-04, 79-07, 79-14, and 80-11, and IE InformationNotice 80-21. Therefore, the existing AFW systems, either in total orin part, may have as-built characteristics which result in uncertainseismic design characteristics. For plants with AFW systems, or portionsthereof, which are not seismically qualified, Enclosure 1 also requestsinformation concerning systems which provide an alternate decay heatremoval pat FEB 1 0 1981We are also requesting that you conduct a walk-down by personnel experiencedin the analysis, design and evaluation of such structures, systems andcomponents, of the non-seismically qualified portions of the AFW systemfor the purpose of identifying more readily recognized deficiencies inseismic resistance. These walk-downs are requested for only thoseportions of the AFW system which have not been designed, constructed,and maintained as seismically qualified systems in accordance with thecriteria for safety-grade systems at the facility. The scope of thewalk-down should include the types of equipment, components, and pipingdescribed in Enclosure 2. Enclosure 1 describes what we consider tocomprise the bounds of the AFW system, and any alternate decay heatremoval paths.For plants with AFW systems that are not seismically qualified, we consi-der that actions should be taken soon to ensure a reasonable level ofearthquake resistance. This applies to both the AFW system and thealternate system used for decay heat removal if portions of it are notseismically qualified. Based upon the consideration of the past perfor-mance of nuclear and fossil power plants, and other non-nuclear facilitiessubject to large earthquakes, we note that well engineered structures,equipment, components and piping possess a substantial amount of inherentseismic resistance, even without the rigorous seismic qualificationperformed for safety-grade portions of nuclear facilities. Of thefailures of structures, piping, equipment and components noted inthese past earthquakes, a large fraction have been due to brittlefailure, lack of restraint, large displacements, or some other obviousdeficiency which would have been easily identified before the failurecausedby the seismic event. Such identified deficiencies could havebeen corrected to significantly enhance reliability without detailedseismic analyses but by exercising careful engineering judgement. Theseconsiderations were factored into the development of Enclosure 2. Inaddition, certain of these deficiencies were noted as existing at theseveral facilities for which we conducted AFW system walk-downs (seeEnclosure 3 for details of the visits). Accordingly, your walk-downof the non-seismically qualified portions of the AFW system and otheralternate decay heat removal systems should identify any appropriatemodifications in the context of the above discussion.Enclosure 2 identifies in more detail the actions we consider appropriatefor plants with AFW systems, or portions thereof, that are not seismicallyqualified. Although we are not at this time requesting that the AFWsystem be modified to be in conformance with the facility design seismicrequirements, we have stated that our plan is to increase the seismicresistance, where necessary, to ultimately provide reasonable assurancethat the system will function after the occurrence of earthquakes up toand including the SS '-J FEB I 0 1981-3-Accordingly, the following actions are requested by this letter:1. In accordance with 10 CFR 50.54(f) of the Commission's regulations,all PWR licensees are requested to provide the information containedin.Enclosure 1 within 120days of receipt of this letter; and2. The results of any walk-downs are requested within 120 days ofreceipt of this letter. These results should include all identi-fied deficiencies and all corrective actions taken, or plannedalong with the schedules for such. Such modifications, if any,shall be handled in the customary manner consistent with theprovisions of your license and the Commission's regulations.Responses should be submitted to enable us to determine whether or notyour license should be modified, s spended, or revoked.arre G. isenhut, DirectorDivision o Licensing
Enclosures:
As stated"This request for information was approved by GAO under a blanketclearance number R0072 which expires November 30, 1983. Comments onburden and duplication may be directed to the U.S. General AccountingOffice, Regulatory Reports Review, Room 5106, 441 G Street, N.W.,Washington, D. C. 20548."
Enclosure 1REQUEST FOR INFORMATIONAUXILIARY FEEDWATER SEISMIC DESIGNIn responding to this letter, the AFW system boundary from suction to discharge(including the water source and heat sink) shall include those portions of thesystem required to accomplish the AFW system function and connected branchpiping up to and including the second valve which is normally closed orcapable of automatic closure when the safety function is required. TheAFW system boundary shall also include any portion of branch piping thatis structurally coupled to the AFW system boundary such that the seismicresponse of the branch piping transmits loads to the AFW system. As aminimum, this includes the branch lines outside the AFW system boundary toa point of three orthogonal restraints. All mechanical and electrical equip-ment,piping (e.g., instrument air), conduits and cable trays, which arenecessary or contain items which are necessary, for the operation of theAFW system shall also be considered. In addition, the structures housingthese systems and components shall be included. Similar considerationsshall be applied when considering alternate means of decay heat removal.A. Specify whether your AFW system is (a) designed, constructed,and maintained (and included within the scope of seismic relatedBulletins 79-02, 79-04, 79-07, 79-14, and 80-11, and IE Informa-tion Notice 80-21), in accordance with Seismic Category I require-ments (e.g., conformance to Regulatory Guides 1.29 and theapplicable portions of the Standard Review Plan or comparablecriteria) or (b) designed, constructed and maintained (andincluded within the scope of seismic related Bulletins 79-02,79-04, 79-07, 79-14, and 80-11, and IE Information Notice 80-21)to withstand a Safe Shutdown Earthquake (SSE) utilizing theanalytical, testing, evaluation methods and acceptable criteriaconsistent with other safety-grade systems in your plant. Toassist the staff in an expedious assessment of your plant, ifyour AFW system, or portions thereof, is not qualified to with-stand an SSE utilizing the analytical, testing and evaluationcriteria consistent with other safety-grade systems in yourplant, we request that you identify those components andstructures not seismically qualified in the appropriate rowof the attached Table 1.B. Where seismic qualification is indicated by leaving Table 1 blank,provide a description of the methodologies and acceptance criteriaused to support your conclusion of seismic qualification, including:Seismic analyses methods employed, seismic input, load combinationswhich include the SSE, allowable stresses, qualification testingand engineering evaluations performed.In addition, where seismic qualification of a secondary watersupply or path is relied upon, provide a summary of the proce-dures which would be followed to enable you to switch from theprimary to secondary sourc Enclosure 1REQUEST FOR INFORMATIONAUXILIARY FEEDWATER SEISMIC DESIGNIn responding to this letter, the AFW system boundary from suction to discharge(including the water source and heat sink) shall include those portions of thesystem required to accomplish the AFW system function and connected branchpiping up to and including the second valve which is normally closed orcapable of automatic closure when the safety function is required. TheAFW system boundary shall also include any portion of branch piping thatis structurally coupled to the AFW system boundary such that the seismicresponse of the branch piping transmits loads to the AFW system. As aminimum, this includes the branch lines outside the AFW system boundary toa point of three orthogonal restraints. All mechanical and electrical equip-ment,piping (e.g., instrument air), conduits and cable trays, which arenecessary or contain items which are necessary, for the operation of theAFW system shall also be considered. In addition, the structures housingthese systems and components shall be included. Similar considerationsshall be applied when considering alternate means of decay heat removal.A. Specify whether your AFW system is (a) designed, constructed,and maintained (and included within the scope of seismic relatedBulletins 79-02, 79-04, 79-07, 79-14, and 80-11, and IE Informa-tion Notice 80-21), in accordance with Seismic Category I require-ments (e.g., conformance to Regulatory Guides 1.29 and theapplicable portions of the Standard Review Plan or comparablecriteria) or (b) designed, constructed and maintained (andincluded within the scope of seismic related Bulletins 79-02,79-04, 79-07, 79-14, and 80-11, and IE Information Notice 80-21)to withstand a Safe Shutdown Earthquake (SSE) utilizing theanalytical, testing, evaluation methods and acceptable criteriaconsistent with other safety-grade systems in your plant. Toassist the staff in an expedious assessment of your plant, ifyour AFW system, or portions thereof, is not qualified to with-stand an SSE utilizing the analytical, testing and evaluationcriteria consistent with other safety-grade systems in yourplant, we request that you identify those components andstructures not seismically qualified in the appropriate rowof the attached Table 1.B. Where seismic qualification is indicated by leaving Table 1 blank,provide a description of the methodologies and acceptance criteriaused to support your conclusion of seismic qualification, including:Seismic analyses methods employed, seismic input, load combinationswhich include the SSE, allowable stresses, qualification testingand engineering evaluations performed.In addition, where seismic qualification of a secondary watersupply or path is relied upon, provide a summary of the proce-dures which would be followed to enable you to switch from theprimary to secondary sourc C. If a lack of seismic qualification is indicated foritems 1, 2, 3, 4, 5 and 6, 7, or 8 in Table 1, provide additionalinformation which specifies the level of seismic qualificationafforded in the original design for each of these areas.D. If substantial lack of seismic qualification is indicated foritems 1, 2, 3, 4, 5 and 6, 7, or 8 in Table 1, provide thesame information requested in A through C for any alternatedecay heat removal system. The bounds of these systems shallbe considered to a similar extent as that described for theAFW system. Provide a summary of the procedures by whichoperation of these alternate heat removal systems will beaccomplishe TABLE 1AUXILIARY FEEDWATER SEISMIC QUALIFICATIONkl) Pumps/Motors(2) Piping(3) Valves/Actuators(4) Power Supplies(5) Primary Water and SupplyPath(6) Secondary Water and SupplyPath*(7) Initiation and Control System(8) Structures Supporting or Housingthese AFW System Items*Applicable only to those plants where the primary water supplyor path is not provided, however, a seismically qualified alternatepath exist ENCLOSURE 2ACTIONS REQUESTED OF PRESSURIZEDWATER REACTOR LICENSEES WITHOUTA SEISMICALLY QUALIFIEDAUXILIARY FEEDWATER SYSTEM1. For all mechanical and electrical equipment and components includingbattery racks, controls, instruments, motors, compressors, tankselectrical supplies and the cabinets containing such items, noteall items which are not securely attached to their supportingstructures such that there is substantial resistance to movementcaused by seismically induced forces.2. For piping, note cases where relatively large deflections cannotbe accommodated without impairing system function. Where suchdisplacements will lead to loss of system function, note wheresufficient amounts of restraint could be afforded, thus signifi-cantly reducing stresses that would be imparted to such items aspump nozzles and branch connections, as appropriate. Further,note eccentric valve operators that are not sufficiently supportedand act to severly overload the pipe. Where such support islacking, you should note where substantial restraints could beadded to the extent practical. Also, where pipes are restingon existing supports, note where substantial resistance to thepipe moving off these supports could be added where it does notalready exist.3. For cable trays and conduits, assure that relatively largedisplacements can be accommodated without impairing systemfunction where seismic restraint is substantially less thanrequired for these which are seismically qualified. Focusparticular attention on preventing the breakage of the electricaland control cables they contain at such places as points ofattachment of the cables to equipment or other relativelyfixed points. Note where any deficiencies exist.Given the time frame we are recommending for the completion of theseactions, no explicit analyses are requested to demonstrate system qualifi-cation unless deemed necessary by you. However, sound engineering judgementshould be applied considering the level of seismicity specified foryour site and the design requirements for other seismically qualifiedsystems in the facility when judging the necessity for and adequacy ofany modifications (e.g., piping, cable trays, conduit, equipment andcomponent restraints,and estimations of displacement levels). Further,these actions shall be accomplished using personnel who are experiencedin the analysis, design and evaluation of such structures, systems andcomponent Where you have determined that it is prudent to institute modifications,no modifications should be instituted which will detrimentally affectthe function of the piping, equipment and components of the system,considering all other loads in addition to seismic. For example, whenproviding additional restraints to piping systems, assure that they donot have a detrimental impact on the system considering all loads, inaddition to seismic, including thermal loads and support displacementinduced loads.Similar considerations as described above should be given to othernon-seismically qualified piping, equipment and components in thevicinity of the non-seismically qualified portions of the AFW and thealternate decay heat removal systems to provide for a substantialdecrease in their susceptibility to failure if such failure couldimpact the function of the AFW and alternate decay heat removal system ENCLOSURE 3RESULTS OF NRC STAFFWALK-DOWNS OF AFW SYSTEMSPlant 1 -Seismically Qualified AFW System (Operating License issuedin 1975)Several locations were found in which the supports for the control-airfor the auxiliary feedwater pumps or for the auxiliary feedwater controlvalve were disconnected from their intended mounting locations. Thesewere examples of important, but non-essential systems (i.e., localmanual control of the pumps and valves could be used if the air-systemwere damaged) which could be easily upgraded to increase the plantsability to remove decay heat following an SSE.Plant 2 -Non-Seismically Qualified AFW System (Operating Licenseissued in 1963)At least two supports to the auxiliary feedwater piping were eithernot connected to piping or not connected at the mounting location.The bolts securing the auxiliary feedwater water supply tank (deminer-alized water tank) to its pad were rusted and not tightened down (i.e.,3/4 inch space between the support and nut intended to hold it down).Also, a long span of 2-inch piping was found having vertical supportonly to which lateral support could easily be provided.Plant 3 -Non-Seismically Qualified AFW System (Operating Licenseissued in 1967)Three areas were identified for which remedial actions could be implementedin a reasonably short time. The first of these was one of the station'sbattery racks. While the existing racks provided for some degree oflateral seismic and resistance, the configuration did not appear to havea level of integrity commensurate with the important of the batteriesto plant safety. These racks appeared flimsy in comparison to thosewhich were installed to current seismic design criteria prescribed bythe licensee for safety related systems.The second area was the suction side of the Auxiliary Feedwater pumpswhich consists of a single header from the condensate storage tank.The header has some lateral support, however, the condensate storagetank was not qualified. The tank is not anchored at its base and thepermanent alternate supply is through the tank. There is a capabilityto install a hose from a qualified water source to the pump suctionand bypass the condensate storage tank. Keeping such a hose in placewould enhance system reliability.The third area was the main instrumentation and control panels in thecontrol room. These are supported at the bottom by a concrete channeland at the top by steel knee braces anchored to the concrete ceilingwith expansion anchors. The requirements of IE Bulletin 79-02 had not
-2-been applied to these anchor bolts and base plates. Conformance withthe IE Bulletin requirements for the factors of safety and consideringbase plate flexibility for the original seismic loads would increasereliability. Also, some loose and missing screws were noted in thesepanels which could be easily tightened and replaced.