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 COMMISSION December 1975 (REGULATORY GUIDE

OFfICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 1.97 INSTRUMENTATION FOR LIGHT-WATER-COOLED

NUCLEAR POWER PLANTS TO ASSESS PLANT CONDITIONS

DURING AND FOLLOWING AN ACCIDENT

A. INTRODUCTION

possible situations that were not completely anticipated in the design of the plant; (2) to help predict the course Criterion 13, "Instrumentation and Control," of that an accident will take: (3) to determine whether the Appendix A, "General Design Criteria for Nuclear Power reactor trip and engineered safety-featui'e systems are Plants." to 10 CFR Part 50, "Licensing of Production functioning properly- (4) to determincwhcther the plant and 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 protect systems for accident zonditions as appropriate to ensure the public safety (if necescry);- (6) to furnish data adequate safety. needed to take manual actioni-f (a) an engineered safety feature malfunctions,4b) unanticipated conditions re- Criterion 19. "Control Room." of Appendix A to 10 quire operator intervention, or"(c) the plant is not CFR 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 will maintain the nuclear power unit in a safe condition enable himn -to ýdeterrnine whether there has been under accident conditions, including loss-of-coolant acci. significant *fuel ox system damage: and (8) to provide dents. Criterion 19 also requires that equipment at mateiial evidence fdr post-accident investigation into the appropriate 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 n shutdown. , At %he start of an accident, the operator cannot tit ".-;,'.always immediately determine what accident has Criterion 64, "Monitoring Radioactivity Releases'"! of .ccurred or is occurring and therefore cannot determine Appendix A to 10 CFR Part 50 includes a-requirement "the appropriate response. For this reason, the reactor that means shall be provided for monitoring the reactor trip and certain safety actions (e.g., emergency core containment atmosphere, space containing-*;ompronents cooling actuation, containment isolation, or depressuri- for recirculation of loss.of-coolant accident fluids;*efflu- zation) are designed to be performed automatically ent discharge paths, and the plant environs for radio- during the initial stages of an accident. Instrumentation activity that may be released 1iom postulated accidents. is also provided to indicate plant parameters that are required to enable the operation of manually initiated This guide describes a rrii h6 iacptable to the NRC safety-related systems and other appropriate actions.

staff for complyinW4ikther*..,mission's requirements to 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

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B. DISCUSSION

following the course of the accident. However, since some accidents impose severe operating requirements on Monitored variables and systems should be used by instrumentation components, it may be necessary to the operator in accident surveillance (1) to help deter- upgrade some instrumentation components to withstand mine the nature of an accident, with emphasis on more severe accident conditions and to measure a greater USNRC REGULATORY GUIDES Comments should bs Sent to the Secretary of the Commission. U.S. Nuclear egulators, Guide% are issued to describe and make available to the public SRegulatorvy Commistion. Washington. D.C. 2056. Attention Docieting and meillods acceptable to the NRC stallf of mplemelting specific parts of the Comnmmission's regulations. to delineate techniques used by the &felt *rn Iilu. hle guides ate iSsued in the following Itn broad divisions:

11ingspecific 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 Products with them is not requited Methods and solutions differentfrom tho-e set out in 2 Research and Toil Reactors 7. Transportation the guides will be acceptable if they pi~ide a basis rlothetindings requisie to 3 Fuels and Materials facilities 8 Occupational 1Helt0h the issuance ar continruanice ol ae rriit or license by the Commission 4 Environmsenlal and Siting 9. Antitrust Revoiew Comments and suggestion& tfo imp*ovements in these guides are encoutoged 5 Materials and Plant Protection 10 General at all times, and guides will be ftvised. as Appropt-ate. to accommodate cornm mints and so releI new rfnormaltointoe apietrnce However. comments on Copies of published guides mey be obtained by written request Indicating the this

,guide. it r1c11¥ed within about twO months alter its issuance. will be pet. divisions desired to the U.S Nuclear R*gulatol*t Commission. Washington. 0 C

ticulatly useful in evaluating the need for an tealy revision 20%6. Attention Director. Otlices of Standards Development

range of monitored variables than might normally be power system should be displayed at all times to the expected. operator in the main control room.

Examples of' serious events that threaten safety are The effectiveness of containment atmosphere cleanup loss-of-coolant accidents (LOCAs). ,iticipated transients systems in removing airborne activity from the contain- without scram (ATWSs), reactivity excursions, and ment atmosphere should be monitored (i.e.. measured).

radioactivity releases that initiate containment isolation. The temperatures and humidity of iodine traps should

5,ich events require the operator to understand, in a also be monitored to dterrniinc whether the traps are short time period, the state of readiness of engineered overheating and thus potentially in danger of losing their safety features and their potential for being challenged radionuclide inventory or failing to remove the radio- by an accident in progress. Instrumentation provided for nuclides from the containment atmosphere.

this purpose should simplify the accident assessment process and the determination of the status of engi- The required instrumentation should be capable of neered safety features. surviving the accident environment that it must monitor.

It therefore should either be designed to withstand the To determine the important variables and systems accident .environment or be protected by a local.

whose values or status should be displayed to the artificial environment. If the environment surrounding operator and therefore the monitoring instrumentation an instrument component is the same for accident and that should be installed, a study (Ref. I) was made of a normal operating conditions (e.g., the instrumentation range of postulated accidents. The study concluded that components in the main control room), the instrumen- the following capabilities are most important to main- tation components need no special environmental capa- taining the integrity of the power plant after an bility.

accident: reactor shutdown, core cooling, contaiiment isolation, containment pressure control, primary system The required instrumentation should also be capable pressure control, and a heat transfer path from tie core of functioning after, but not necessarily during, a safe to a heat sink. These vital capabilities are designed to shutdown earthouake.

preser-'.e the integrity of the barriers to radioactivity release (i.e., the fuel cladding, primary coolant bound- Instrumentation selected for accident monitoring ary, and containment). should permit relatively few devices to provide the essential information needed by the operator to satisfy In selecting parameters for accident surveillance, the general objectives. Where practical, the same instru- attention should be given to providing information that ments should be used for normal and accident operation I

will aid the operator in achieving and maintaining a safe to obtain the advantage of normal inservice surveillance.

shutdown condition, with emphasis on controlling reac- However, the instruments should be specifically identi- tivity and establishing a heat transfer path from the core fied on control panels so that the operator can easily to the heat sink. Particular attention should be given to determine that they are intended for use under accident, parameters that indicate that the barriers to radioactivity as well as normal, conditions.

release are being challenged and that public safety may be in jeopardy. Thus, instrumentation that shows the

C. REGULATORY POSITION

absence or presence of significant fuel damage or metal-water reaction is of special importance. 1. For each postulated accident that threaten- public safety (for example, a LOCA or ATWS event, ieactivity Information concerning the integrity of the primary excursion, or radioactivity release that initiates contain- coolant boundary and the containment is also of vital ment isolation), the applicant should perform detailed interest. For example, the character of a postulated safety analyses to determine (a) the parameters to be LOCA during the first two or three minutes of the measured and (b) ihe instrument ranges, responses, and accident can best be determined by monitoring the accuracies required to provide the operator with the reactor coolant pressure transient. An analog recorder information necessary to assess the nature of die with a response and sensitivity consistent with the accident, the course the accident will take, the response anticipated pressure transient would be the type of of the safety features, the potential for breaching the instrument needed for this purpose. Comparable records barriers to radioactivity release, the need for manual of the pressure transients and temperature gradient in action, and the operating status of significant equipment the containment could also be very useful. during and following the accident. The guidelines in References I and 2 should be used to make such Because both short- and long-term operational effec. analyses, along with the guidelines in Reference 3 tivencss of the emergency core cooling system (ECCS) dealing with monitoring inside the power plant.

are important, sufficient information concerning the ECCS status should be proided to permit post-accident 2. The essential instrumentation required by the surveillance. Similarly, the status of the emergency operator to diagnose and monitor significant accident

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conditiuns should be specified for each system required 7. To the extent practical. accident-monitoring in- to be operable during and after the accident. A strumentation inputs should be from sensors that tabulation of such instrumentation should be provided, directly measure the desired variables, along with a documented justification to show that the instrumentation is adeqtate to provide the operator with 8. To the exztent practical. the same indicators should the necessary information. The table should include the be Lsed for accident novilorhig as are used in the instruments' major operational parameters and indicate normal operations of the plant.

the manner in which the instrument outputs will be recorded. 9. The accident-monitoring instrumentation should be specifically identified on control panels so that the

3. The accident monitoring instrumentation compo- operator can easily discern that they are intended for use nents and modules should be of a quality that is under accident conditions. The displays should be consistent with minimum maintenance requirements and arranged to simplify the operator's surveillance, interpre.

low failure rates. Quality levels should be achieved tation, and response determination following an accident through the specification of requirements known to signal.

promote high quality.

I

10. Any equipment that is used for both accident

4. The accident-nionitoring instrumentation should monitoring and control functions should be classified as be designed with sufficient margin to maintain necessary part of accident-monitoring instrumentation. The trails- functional capability under extreme conditions (as appli- mission of signals from accident-monitoring equipment cable) relating to environment, energy supply, malfunc. for control system use should be through isolation tions, and accidents. Thie instrumentation should either devices that are classified as part of the accident.

be qualified to survive the appropriate operating condi- monitoring instrumentation and that meet all recont- tions or be suitably protected from the environment. Its mendations of this document.

qualifications should be in accordance with Regulatory Guide 1.89, "'Qualification of Class I E Equipment for II, Means should be provided for checking. with a Nuclear Power Plants." and it should continue to high degree of confidence. the operational availability of function within the required accuracy subsequent to. eacht input sensor during reactor operation. This may be but not necessarily during, a safe shutdown earthquake. accomplished in various ways: for example:

5. The accident-monitoring instrumentation should a. By perturbing the monitored variable;

be designed with redundant channels so that a single failure does not prevent the operator front determining b. By introducing and varying, as appropriate, a the nature of an accident, the functioning of the substitute input to the sensor of the same nature engineered safety features, the need for operator action, as the measured variable. or and the response of the plant to the safety measures in operation. One channel of each redundant se; of c. By cross-checking between channels that bear a channels should be recorded and energized from the known relationship to each other and that have station Class I E instrumentation a.c. system. readouts available.

NOTE: "Single failure" includes such events as the 12. Capability should be provided for servicing, shorting or open-circuiting of interconnecting signal or testing, and calibrating the accident-monitoring instru- power cables. It also includes single credible malfunc. mentation. For those parts of the instrumentation where tions or events that cause a number of consequential the required interval between testing will be less than the component, module, or channel failures. For example, normal time interval between generating station shut- the overheating of an amplifier module would be a downs, a capability for testing during power operation

"single failure" even though several transistor failures should be provided. Servicing, testing, and calibration might result. Mechanical damage to a mode switch programs should be specified to ensure proper perfor- would be a "single failure" although several channels mance at all times.

might become involved.

13. The design should permit administrative control

6. Channels that provide signals for redundant chan- of the means for manually bypassing channels.

nels should be independent and physically separated to accomplish decoupling of the effects of unsafe environ- 14. The design should permit administrative control mental factors, electric transients, and physical accident of the access to all setpoint adjustments, module consequences documented in the design basis and to calibration adjustments, and test points.

reduce the likelihood of interactions between channels during maintenance operations or in the event of 15. The accident-monitoring instrumentation should channel malfunction. be designed to provide the operator with accurate,

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complete, and timely information regarding its own REFERENCES

status. The design should minimize the development of conditions that would cause meters, annunciators.

recorders, alarms, etc., to gve anomalous indications

)

1. Battelle-Columbus Laboratoir.,s. "Monitoring Post.

confusing to the operator.

Accident Conditions in Power Reactors," BMI-X.647, Apr. 9, 1973.

16. The instrumentation should be desigred to facili- tate the recognition, location, replacement, repair, or adjustment of malfunctioning components or modules.

2. U.S. Nuclear Regulatory Commission, "Standard

D. IMPLEMENTATION

Format and Content of Safety Analysis Reports for Nuclear Power Plants," NUREG-75/094, Regulatory The purpose of this section is to provide information Guide 1.70, Rev. 2, Sept. 1975.

to applicants and licensees regarding the NRC staff's plans for using this regulatory guide.

3. BNWL-1635, "Technological Considerations in Except in those cases in which the applicant proposes Emergency Instrumentation Preparedness," May 1972.

an acceptable alternative method for complying with specified portions of the Commission's regulations, this guide will be used by tie staff in evaluating all Copies of the above documents are available from the construction permit applications submitted after August National Technical Information Service, Springfield, Va.

1, 1976. 2216).

UNITEO STATES

POSI'TAGE AND) FEErS PAID **

NUCLEAR REGULATORY COMMISSION

WASHINGTON. 0. C. 20555 U.S. NUCLEAR IREGULATORY

. OFFICIAL BUSINESS COMMISSION

PENALTY FOR PRIVATE USE. $300

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