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Home       > Electronic Reading       Room       > Document       Collections       > Generic       Communications >       Generic       Letters >       1996       > Gl96001 
				UNITED STATES                         NUCLEAR REGULATORY COMMISSION                     OFFICE OF NUCLEAR REACTOR REGULATION                            WASHINGTON, D.C.  20555                               January 10, 1996NRC GENERIC LETTER NO. 96-01:  TESTING OF SAFETY-RELATED LOGIC CIRCUITSAddressees All holders of operating licenses or construction permits for nuclear powerreactors.PurposeThe U.S. Nuclear Regulatory Commission (NRC) is issuing this generic letterto:  (1) notify addressees about problems with testing of safety-related logiccircuits, (2) request that all addressees implement the actions describedherein, and (3) require that all addressees submit a written response to thisgeneric letter regarding implementation of the requested actions.  BackgroundThe NRC staff had previously issued the following information notices (Ins)regarding problems with testing of safety-related logic circuits:IN 88-83, "Inadequate Testing of Relay Contacts in Safety-Related LogicCircuits," dated October 19, 1988; IN 91-13, "Inadequate Testing of EmergencyDiesel Generators (EDGs)," dated March 4, 1991; IN 92-40, "Inadequate Testingof Emergency Bus Undervoltage Logic Circuitry," dated May 27, 1992; IN 93-15,"Failure to Verify the Continuity of Shunt Trip Attachment Contacts in ManualSafety Injection and Reactor Trip Switches," dated February 18, 1993; and     IN 93-38, "Inadequate Testing of Engineered Safety Features ActuationSystems," dated May 24, 1993.  Despite these notices, recent events haveoccurred similar to those described in the INs which indicate that licenseeshave not taken sufficient action to correct previously identified problems inlogic circuit surveillance testing.  On March 7, 1995, NRC issued IN 95-15,"Inadequate Logic Testing of Safety-Related Circuits," which informedlicensees about these recent events at Cooper Nuclear Station, Fermi 2,Waterford 3, Grand Gulf Nuclear Station, and Arkansas Nuclear One, Unit 1 andUnit 2.Description of CircumstancesThe NRC has documented a significant number of instances involving problemswith logic testing of safety-related circuits in the information noticesdescribed above.  These information notices discuss events at variouspressurized water and boiling water reactors.  The examples of problems withlogic testing cover a wide range of systems including safety injection system 9601050193.                                                            GL 96-01                                                            January 10, 1996                                                            Page 2 of 7actuation, containment spray system actuation, residual heat removal system actuation, diesel generator load sequencing, and reactor protection systemactuation.  In most cases, the affected logic circuits functioned properlywhen testing in accordance with technical specification (TS) requirements wasperformed.  The NRC has taken enforcement action in many of these cases sincethey resulted in TS violations.  The details of these instances are includedin the information notices cited above.  An example of the details associatedwith this issue at Fermi Station is repeated here.On July 15, 1994, during a routine review of surveillance procedures requiredby the Fermi Unit 2 TS, the licensee (Detroit Edison Company) discovered thatneither the procedures used for testing the load shedding of the 4160 voltResidual Heat Removal (RHR) pumps nor the related instrumentation and control(I&C) logic functional test procedure provided for the full testing of the RHRpump start logic.  The conductors which connect the I&C and electricalportions of the circuit were not tested.  Also, the test procedures did notinclude verification that the switchgear breaker would not close with anundervoltage signal present at the bus.After investigating further, the licensee discovered additional deficienciesin the undervoltage functional test surveillance procedures including thelogic functional test surveillance procedures for the three other engineeredsafety buses.  Also, the surveillance test overlap did not include sufficientoverlap of the logic circuit to cover the degraded voltage trip input to thenon-interruptible air supply system isolation logic, the degraded voltage tripinput to the bus feeder breaker position, and the alternate automatic closurecircuits for the EDG output breakers.  The licensee further determined thatthe 480 volt load shed logic had not been fully tested.On September 9, 1994, the licensee identified additional surveillancedeficiencies and expanded the investigation of its surveillance procedures forEDGs and I&C overlap testing.  During this investigation, the licenseedetermined that (1) multiple pathways for starting an EDG through theemergency core cooling system (ECCS) logic were not being tested separately,(2) emergency equipment cooling water (EECW) actuation from the load sequencerwas not being differentiated from EECW actuation on reactor building closedcooling water low pressure, and (3) test acceptance criteria permittedperformance outside of the TS limits.In October and November 1994, the licensee identified several other testdeficiencies in its surveillance procedures.  These deficiencies were relatedto the core spray system, RHR system, reactor protection system, safety reliefvalves, alternate rod insertion and main steam isolation valve leakage controlsystem logic, remote shutdown panel, primary containment manual isolationvalves, and alternate shutdown panel transfer switches.To address the above deficiencies, the licensee has taken the followingcorrective actions:  (1) reviewed deficient procedures and performed requiredsurveillance to establish operability, (2) reviewed similar procedures to .                                                            GL 96-01                                                            January 10, 1996                                                            Page 3 of 7identify other deficiencies, (3) is creating electrical overlap drawings, and (4) is training authors and technical reviewers of procedures to be fullyaware of logic surveillance requirements.  The NRC staff issued a notice ofviolation to Detroit Edison Company concerning the above issue (NRC InspectionReport No. 50-341/94-12).Discussion A number of NRC regulations document the requirements to test safety-relatedsystems to ensure that they will function as designed when called upon.  Forexample, Title 10 of the Code of Federal Regulations (10 CFR), Section 50.36,"Technical Specifications," paragraph (c)(3) states that, "surveillancerequirements are requirements relating to test, calibration or inspection toassure that the necessary quality of systems and components is maintained,that facility operation will be within the safety limits, and that thelimiting conditions of operation will be met."  Surveillance requirements toassure continued operability of safety-related logic circuits have beenincluded in the plant-specific technical specifications for all operatingnuclear power plants.Other documents that provide a basis for these requirements include:      þ     10 CFR 50.55a, "Codes and Standards," paragraph (h) which includes            reference to Institute of Electrical and Electronic Engineers            (IEEE) Standard 279, "Criteria for Protection Systems for Nuclear            Power Generating Stations"      þ     Appendix A to 10 CFR 50, General Design Criterion (GDC) 21,            "Protection System for Reliability and Testability"      þ     Appendix A to 10 CFR 50, General Design Criterion (GDC) 18,            "Inspection and Testing of Electric Power Systems"      þ     Appendix B to 10 CFR 50, Criterion XI, "Test Control"      þ     Regulatory Guide (RG) 1.118, "Periodic Testing of Electric Power            and Protection Systems"      þ     RG 1.32, "Criteria for Safety-Related Electric Power Systems for            Nuclear Power Plants"As noted above, the NRC staff has issued a number of information notices(identified in the "Background" section) that document identified deficienciesin actuation logic surveillance test programs.  However, because of the numberof more recently identified similar deficiencies, the NRC staff has determinedthat licensees may not have yet adequately addressed this issue and furtheraction is necessary. .                                                            GL 96-01                                                            January 10, 1996                                                            Page 4 of 7The NRC staff finds that the failure to adequately test safety-relatedactuation logic circuitry is safety significant in that inoperable essentialelectric components required for automatic actuation of post-accidentmitigation systems may be undetected for extended periods.  This isparticularly true for the reactor protection system, whose unavailability isshown in probabilistic risk assessments to be a dominant contributor topotential core damage scenarios.  Undetected reactor protection systemavailability/reliability degradation is also a potentially significantcontributor to overall risk.  Unavailability of those circuits associated withautomatic emergency core cooling system (ECCS) actuation, especially in aloss-of-offsite-power situation, is a lesser contributor to overall risk butis important in ensuring post-accident recovery in accordance with licensingbases.  Failure to automatically actuate safety systems also places theadditional burden on the operators of having to manually actuate requiredfunctions and thus increases the chance for operator error.The NRC staff notes that even in cases where surveillance testing of the logiccircuits has not been complete, it is likely that only very small portions ofthe circuit have been omitted from the test.  Further, the NRC staff is notaware of instances of specifically identified surveillance inadequacies thatresulted in the unavailability of the safety system when called on during anevent.  Nevertheless, as indicated above, the NRC staff finds that compliancewith the plant-specific technical specifications is essential in order tomaintain the validity of the assumptions in the licensing basis accidentanalyses.  On the basis of the recent events, previously issued INs,complexity of the logic, and contribution to the core damage frequency, theNRC staff has further determined that licensees should review theirsurveillance procedures for the reactor protection system, EDG load sheddingand sequencing, and actuation logic for the engineered safety features systemsto ensure that complete testing is being performed as required by the technical specifications.Requested ActionsThe NRC staff requests that all addressees take the following actions:(1)   Compare electrical schematic drawings and logic diagrams for the reactor      protection system, EDG load shedding and sequencing, and actuation logic      for the engineered safety features systems against plant surveillance      test procedures to ensure that all portions of the logic circuitry,      including the parallel logic, interlocks, bypasses and inhibit circuits,      are adequately covered in the surveillance procedures to fulfill the TS      requirements.  This review should also include relay contacts, control      switches, and other relevant electrical components within these systems,      utilized in the logic circuits performing a safety function..                                                            GL 96-01                                                            January 10, 1996                                                            Page 5 of 7(2)   Modify the surveillance procedures as necessary for complete testing to      comply with the technical specifications.  Additionally, the licensee       may request an amendment to the technical specifications if relief from      certain testing requirements can be justified. It is requested the completion of these actions be accomplished prior tostartup from the first refueling outage commencing one year after the issuanceof this generic letter. Note:  Some licensees may have already performed the requested reviews andtaken appropriate corrective actions.  These licensees do not need to performany additional review unless modifications have been made to the logiccircuits for these systems.  In these cases the modifications should bereviewed.  Licensees are reminded that following modifications to safety-related logic circuits, full functional testing of the modification should beconducted.  Licensees should not rely on routine surveillance testing toconfirm proper performance of logic circuits following modifications.Required ResponseAll addressees, including those who have already completed the requestedactions, are required to submit a written response to this generic letter asfollows:(1)   Within 60 days of the date of this generic letter, a written response      indicating whether or not the addressee will implement the actions      requested above.  If the addressee intends to implement the requested      actions, submit a schedule for completing implementation.  If an      addressee chooses not to take the requested actions, submit a      description of any proposed alternative course of action, the schedule      for completing the alternative course of action (if applicable), and the      safety basis for determining the acceptability of the planned      alternative course of action.(2)   Within 30 days of completion of the requested actions, a response      confirming completion.  Address the required written report(s) to the U.S. Nuclear RegulatoryCommission, ATTN:  Document Control Desk, Washington, D.C. 20555-0001, underoath or affirmation under the provisions of Section 182a, Atomic Energy Act of1954, as amended, and 10 CFR 50.54(f).  In addition, submit a copy to theappropriate regional administrator. Backfit DiscussionThe actions requested in this generic letter are considered backfits inaccordance with NRC procedures.  Because established regulatory requirementsexist but were not satisfied, these backfits are necessary to bring theaddressees into compliance with existing requirements.  Therefore, on the .                                                            GL 96-01                                                            January 10, 1996                                                            Page 6 of 7basis of 10 CFR 50.109(a)(4)(i), a full backfit analysis was not performed. An evaluation was performed in accordance with NRC procedures, including a statement of the objectives of and reasons for the requested actions and thebasis for invoking the compliance exception.  Response to Question IX in theCRGR review package which is available for inspection in the Commission PublicDocument Room, Gelman Building, 2120 L Street, N.W., Washington, D.C., 20037,contains this evaluation.Federal Register NotificationA notice of opportunity for public comment was published in the FederalRegister (60 FR 27141) on May 22, 1995.  Comments were received from 10licensees, 2 industry organizations, and 1 individual.  Copies of the staff'sevaluation of these comments have been made available in the public documentroom.Paperwork Reduction Act StatementThe information collections contained in this request are covered by theOffice of Management and Budget clearance number 3150-0011, which expiresJuly 31, 1997.  The public reporting burden for this collection of informationis estimated to average 2,000 hours per response, including the time forreviewing instructions, searching existing data sources, gathering andmaintaining the data needed, and completing and reviewing the collection ofinformation.  Send comments regarding this burden estimate or any other aspectof this collection of information, including suggestions for reducing thisburden, to the Information and Records Management Branch (T-6 F33), U.S.Nuclear Regulatory Commission, Washington, D.C. 20555-0001, and to the DeskOfficer, Office of Information and Regulatory Affairs, NEOB-10202,(3150-0011), Office of Management and Budget, Washington, D.C. 20503.Compliance with the following request for information is purely voluntary. The information would assist NRC in evaluating the cost of complying with thisgeneric letter:(1)   the licensee staff time and costs to perform requested evaluation,      corrective actions, and associated testing(2)   the licensee staff time and costs to prepare the requested response and      documentation.                                                            GL 96-01                                                            January 10, 1996                                                            Page 7 of 7If you have any questions about this matter, please contact the technicalcontact(s) listed below or the appropriate Office of Nuclear ReactorRegulation (NRR) project manager.                                          signed by                                    Dennis M. Crutchfield, Director                                    Division of Reactor Program Management                                    Office of Nuclear Reactor RegulationTechnical contact:  Hukam Garg, NRR                    (301) 415-2929                    Internet:hcg@nrc.govLead Project Manager:  Glenn Kelly, NRR                       (301) 415-3028                       Internet:gbk@nrc.gov