Regulatory Guide 1.97

Instrumentation for Light-Water-Cooled Nuclear Power Plants to Assess Plant Conditions During and Following an Accident

ML13350A295
Person / Time
Issue date:	12/31/1975
From:	NRC/OSD
To:
References
RG-1.097
Download: ML13350A295 (4)

U.S. NUCLEAR REGULATORY COMMISSIONDecember 1975(REGULATORY GUIDEOFfICE OF STANDARDS DEVELOPMENTREGULATORY GUIDE 1.97INSTRUMENTATION FOR LIGHT-WATER-COOLEDNUCLEAR POWER PLANTS TO ASSESS PLANT CONDITIONSDURING AND FOLLOWING AN ACCIDENT

A. INTRODUCTION

possible situations that were not completely anticipatedin the design of the plant; (2) to help predict the courseCriterion 13, "Instrumentation and Control," of that an accident will take: (3) to determine whether theAppendix A, "General Design Criteria for Nuclear Power reactor trip and engineered safety-featui'e systems arePlants." to 10 CFR Part 50, "Licensing of Production functioning properly- (4) to determincwhcther the plantand Utilization Facilities," includes a requirement that is responding properly to the safet, inehies in opera-instrumentation be provided to monitor variables and tion; (5) to allow for early initiati rn of actiki to protectsystems for accident zonditions as appropriate to ensure the public safety (if necescry);- (6) to furnish dataadequate safety. needed to take manual actioni-f (a) an engineered safetyfeature malfunctions,4b) unanticipated conditions re-Criterion 19. "Control Room." of Appendix A to 10 quire operator intervention, or"(c) the plant is notCFR Part 50 includes a requirement that a control room responding effectively to,.:the safety systems in opera.be provided from which actions can be taken to tion; (7) to provideiinforniation to the operator that willmaintain the nuclear power unit in a safe condition enable himn -to ýdeterrnine whether there has beenunder accident conditions, including loss-of-coolant acci. significant *fuel ox system damage: and (8) to providedents. Criterion 19 also requires that equipment at mateiial evidence fdr post-accident investigation into theappropriate locations outside the control room be ,ausess.and consequences of the event.provided, including instrumentation and controls to ' ' "maintain the unit in a safe condition dunng hot sr f ac n t o ar nshutdown. , At %he start of an accident, the operator cannottit ".-;,'.always immediately determine what accident hasCriterion 64, "Monitoring Radioactivity Releases'"! of .ccurred or is occurring and therefore cannot determineAppendix A to 10 CFR Part 50 includes a-requirement "the appropriate response. For this reason, the reactorthat means shall be provided for monitoring the reactor trip and certain safety actions (e.g., emergency corecontainment atmosphere, space cooling actuation, containment isolation, or depressuri-for recirculation of loss.of-coolant accident fluids;*efflu- zation) are designed to be performed automaticallyent discharge paths, and the plant environs for radio- during the initial stages of an accident. Instrumentationactivity that may be released 1iom postulated accidents. is also provided to indicate plant parameters that arerequired to enable the operation of manually initiatedThis guide describes a rrii h6 iac ptable to the NRC safety-related systems and other appropriate actions.staff for requirementsto provide instruý.entatir', to 'monitor plant variables If normal power plant instrumentation remains func-and systems.'-.auribg and following an accident in a tional for all accident conditions, it can provide indica-hight-water-coole. bc'lc p'power plant. tion, records, and (with certain types of instruments)wte.-w pntime-history response for many parameters important to\

B. DISCUSSION

following the course of the accident. However, sincesome accidents impose severe operating requirements onMonitored variables and systems should be used by instrumentation components, it may be necessary tothe operator in accident surveillance (1) to help deter- upgrade some instrumentation components to withstandmine the nature of an accident, with emphasis on more severe accident conditions and to measure a greaterUSNRC REGULATORY GUIDES Comments should bs Sent to the Secretary of the Commission. U.S. Nuclearegulators, Guide% are issued to describe and make available to the public SRegulatorvy Commistion. Washington. D.C. 2056. Attention Docieting andmeillods acceptable to the NRC stallf of mplemelting specific parts of theComnmmis sion's regulations. to delineate techniques used by the &felt Iilu. hle guides ate iSsued in the following Itn broad divisions:11ing specific problems or postulated accidents. or to provide guidatce to appli.cents Regulatory Guides ate not substitutes lot regulaliors. and compliance I, Pow*r Reactors 6 Productswith them is not requited Methods and solutions different from tho-e set out in 2 Research and Toil Reactors 7. Transportationthe guides will be acceptable if they pi~ide a basis rlo the tindings requisie to 3 Fuels and Materials facilities 8 Occupational 1Helt0hthe issuance ar continruanice ol ae rriit or license by the Commission 4 Environmsenlal and Siting 9. Antitrust RevoiewComments and suggestion& tfo in these guides are encoutoged 5 Materials and Plant Protection 10 Generalat all times, and guides will be ftvised. as Appropt-ate. to accommodate cornmmints and so releI new rfnormaltoint oe apietrnce However. comments on Copies of published guides mey be obtained by written request Indicating thethis ,guide. it r1c11¥ed within about twO months alter its issuance. will be pet. divisions desired to the U.S Nuclear Commission. Washington. 0 Cticulatly useful in evaluating the need for an tealy revision 20%6. Attention Director. Otlices of Standards Development range of monitored variables than might normally beexpected.Examples of' serious events that threaten safety areloss-of-coolant accidents (LOCAs). ,iticipated transientswithout scram (ATWSs), reactivity excursions, andradioactivity releases that initiate containment isolation.5,ich events require the operator to understand, in ashort time period, the state of readiness of engineeredsafety features and their potential for being challengedby an accident in progress. Instrumentation provided forthis purpose should simplify the accident assessmentprocess and the determination of the status of engi-neered safety features.To determine the important variables and systemswhose values or status should be displayed to theoperator and therefore the monitoring instrumentationthat should be installed, a study (Ref. I) was made of arange of postulated accidents. The study concluded thatthe following capabilities are most important to main-taining the integrity of the power plant after anaccident: reactor shutdown, core cooling, contaiimentisolation, containment pressure control, primary systempressure control, and a heat transfer path from tie coreto a heat sink. These vital capabilities are designed topreser-'.e the integrity of the barriers to radioactivityrelease (i.e., the fuel cladding, primary coolant bound-ary, and containment).In selecting parameters for accident surveillance,attention should be given to providing information thatwill aid the operator in achieving and maintaining a safeshutdown condition, with emphasis on controlling reac-tivity and establishing a heat transfer path from the coreto the heat sink. Particular attention should be given toparameters that indicate that the barriers to radioactivityrelease are being challenged and that public safety maybe in jeopardy. Thus, instrumentation that shows theabsence or presence of significant fuel damage ormetal-water reaction is of special importance.Information concerning the integrity of the primarycoolant boundary and the containment is also of vitalinterest. For example, the character of a postulatedLOCA during the first two or three minutes of theaccident can best be determined by monitoring thereactor coolant pressure transient. An analog recorderwith a response and sensitivity consistent with theanticipated pressure transient would be the type ofinstrument needed for this purpose. Comparable recordsof the pressure transients and temperature gradient inthe containment could also be very useful.Because both short- and long-term operational effec.tivencss of the emergency core cooling system (ECCS)are important, sufficient information concerning theECCS status should be proided to permit post-accidentsurveillance. Similarly, the status of the emergencypower system should be displayed at all times to theoperator in the main control room.The effectiveness of containment atmosphere cleanupsystems in removing airborne activity from the contain-ment atmosphere should be monitored (i.e.. measured).The temperatures and humidity of iodine traps shouldalso be monitored to dterrniinc whether the traps areoverheating and thus potentially in danger of losing theirradionuclide inventory or failing to remove the radio-nuclides from the containment atmosphere.The required instrumentation should be capable ofsurviving the accident environment that it must monitor.It therefore should either be designed to withstand theaccident .environment or be protected by a local.artificial environment. If the environment surroundingan instrument component is the same for accident andnormal operating conditions (e.g., the instrumentationcomponents in the main control room), the instrumen-tation components need no special environmental capa-bility.The required instrumentation should also be capableof functioning after, but not necessarily during, a safeshutdown earthouake.Instrumentation selected for accident monitoringshould permit relatively few devices to provide theessential information needed by the operator to satisfythe general objectives. Where practical, the same instru-ments should be used for normal and accident operationto obtain the advantage of normal inservice surveillance.However, the instruments should be specifically identi-fied on control panels so that the operator can easilydetermine that they are intended for use under accident,as well as normal, conditions.

C. REGULATORY POSITION

1. For each postulated accident that threaten- publicsafety (for example, a LOCA or ATWS event, ieactivityexcursion, or radioactivity release that initiates contain-ment isolation), the applicant should perform detailedsafety analyses to determine (a) the parameters to bemeasured and (b) ihe instrument ranges, responses, andaccuracies required to provide the operator with theinformation necessary to assess the nature of dieaccident, the course the accident will take, the responseof the safety features, the potential for breaching thebarriers to radioactivity release, the need for manualaction, and the operating status of significant equipmentduring and following the accident. The guidelines inReferences I and 2 should be used to make suchanalyses, along with the guidelines in Reference 3dealing with monitoring inside the power plant.2. The essential instrumentation required by theoperator to diagnose and monitor significant accidentI1.97-2 Iconditiuns should be specified for each system requiredto be operable during and after the accident. Atabulation of such instrumentation should be provided,along with a documented justification to show that theinstrumentation is adeqtate to provide the operator withthe necessary information. The table should include theinstruments' major operational parameters and indicatethe manner in which the instrument outputs will berecorded.3. The accident monitoring instrumentation compo-nents and modules should be of a quality that isconsistent with minimum maintenance requirements andlow failure rates. Quality levels should be achievedthrough the specification of requirements known topromote high quality.4. The accident-nionitoring instrumentation shouldbe designed with sufficient margin to maintain necessaryfunctional capability under extreme conditions (as appli-cable) relating to environment, energy supply, malfunc.tions, and accidents. Thie instrumentation should eitherbe qualified to survive the appropriate operating condi-tions or be suitably protected from the environment. Itsqualifications should be in accordance with RegulatoryGuide 1.89, "'Qualification of Class I E Equipment forNuclear Power Plants." and it should continue tofunction within the required accuracy subsequent to.but not necessarily during, a safe shutdown earthquake.5. The accident-monitoring instrumentation shouldbe designed with redundant channels so that a singlefailure does not prevent the operator front determiningthe nature of an accident, the functioning of theengineered safety features, the need for operator action,and the response of the plant to the safety measures inoperation. One channel of each redundant se; ofchannels should be recorded and energized from thestation Class I E instrumentation a.c. system.NOTE: "Single failure" includes such events as theshorting or open-circuiting of interconnecting signal orpower cables. It also includes single credible malfunc.tions or events that cause a number of consequentialcomponent, module, or channel failures. For example,the overheating of an amplifier module would be a"single failure" even though several transistor failuresmight result. Mechanical damage to a mode switchwould be a "single failure" although several channelsmight become involved.6. Channels that provide signals for redundant chan-nels should be independent and physically separated toaccomplish decoupling of the effects of unsafe environ-mental factors, electric transients, and physical accidentconsequences documented in the design basis and toreduce the likelihood of interactions between channelsduring maintenance operations or in the event ofchannel malfunction.7. To the extent practical. accident-monitoring in-strumentation inputs should be from sensors thatdirectly measure the desired variables,8. To the exztent practical. the same indicators shouldbe Lsed for accident novilorhig as are used in thenormal operations of the plant.9. The accident-monitoring instrumentation shouldbe specifically identified on control panels so that theoperator can easily discern that they are intended for useunder accident conditions. The displays should bearranged to simplify the operator's surveillance, interpre.tation, and response determination following an accidentsignal.10. Any equipment that is used for both accidentmonitoring and control functions should be classified aspart of accident-monitoring instrumentation. The trails-mission of signals from accident-monitoring equipmentfor control system use should be through isolationdevices that are classified as part of the accident.monitoring instrumentation and that meet all recont-mendations of this document.II, Means should be provided for checking. with ahigh degree of confidence. the operational availability ofeacht input sensor during reactor operation. This may beaccomplished in various ways: for example:a. By perturbing the monitored variable;b. By introducing and varying, as appropriate, asubstitute input to the sensor of the same natureas the measured variable. orc. By cross-checking between channels that bear aknown relationship to each other and that havereadouts available.12. Capability should be provided for servicing,testing, and calibrating the accident-monitoring instru-mentation. For those parts of the instrumentation wherethe required interval between testing will be less than thenormal time interval between generating station shut-downs, a capability for testing during power operationshould be provided. Servicing, testing, and calibrationprograms should be specified to ensure proper perfor-mance at all times.13. The design should permit administrative controlof the means for manually bypassing channels.14. The design should permit administrative controlof the access to all setpoint adjustments, modulecalibration adjustments, and test points.15. The accident-monitoring instrumentation shouldbe designed to provide the operator with accurate,1.97-3 I ---complete, and timely information regarding its ownstatus. The design should minimize the development ofconditions that would cause meters, annunciators.recorders, alarms, etc., to gve anomalous indicationsconfusing to the operator.16. The instrumentation should be desigred to facili-tate the recognition, location, replacement, repair, oradjustment of malfunctioning components or modules.

D. IMPLEMENTATION

The purpose of this section is to provide informationto applicants and licensees regarding the NRC staff'splans for using this regulatory guide.Except in those cases in which the applicant proposesan acceptable alternative method for complying withspecified portions of the Commission's regulations, thisguide will be used by tie staff in evaluating allconstruction permit applications submitted after August1, 1976.UNITEO STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON. 0. C. 20555.OFFICIAL BUSINESSPENALTY FOR PRIVATE USE. $300)1. Battelle-Columbus Laboratoir.,s. "Monitoring Post.Accident Conditions in Power Reactors," BMI-X.647,Apr. 9, 1973.2. U.S. Nuclear Regulatory Commission, "StandardFormat and Content of Safety Analysis Reports forNuclear Power Plants," NUREG-75/094, RegulatoryGuide 1.70, Rev. 2, Sept. 1975.3. BNWL-1635, "Technological Considerations inEmergency Instrumentation Preparedness," May 1972.Copies of the above documents are available from theNational Technical Information Service, Springfield, Va.2216).POSI'TAGE AND) FEErS PAID U.S. NUCLEAR IREGULATORYCOMMISSIONREFERENCES1.97-4