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 acc

i. significant

• fuel ox system damage: and (8) to provide dent

s. 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 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 iac ptable to the NRC safety-related systems and other appropriate actions.staff for 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\

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 Comnmmis 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 Products with them is not requited Methods and solutions different from tho-e set out in 2 Research and Toil Reactors 7. Transportation the guides will be acceptable if they pi~ide a basis rlo the tindings 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 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 rfnormaltoint oe 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 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 expected.Examples of' serious events that threaten safety are loss-of-coolant accidents (LOCAs). ,iticipated transients without scram (ATWSs), reactivity excursions, and radioactivity releases that initiate containment isolation.

5,ich events require the operator to understand, in a short time period, the state of readiness of engineered safety features and their potential for being challenged by an accident in progress.

Instrumentation provided for this purpose should simplify the accident assessment process and the determination of the status of engi-neered safety features.To determine the important variables and systems whose values or status should be displayed to the operator and therefore the monitoring instrumentation that should be installed, a study (Ref. I) was made of a range of postulated accidents.

The study concluded that the following capabilities are most important to main-taining the integrity of the power plant after an accident:

reactor shutdown, core cooling, contaiiment isolation, containment pressure control, primary system pressure control, and a heat transfer path from tie core to a heat sink. These vital capabilities are designed to preser-'.e the integrity of the barriers to radioactivity release (i.e., the fuel cladding, primary coolant bound-ary, and containment).

In selecting parameters for accident surveillance, attention should be given to providing information that will aid the operator in achieving and maintaining a safe shutdown condition, with emphasis on controlling reac-tivity and establishing a heat transfer path from the core to the heat sink. Particular attention should be given to parameters that indicate that the barriers to radioactivity release are being challenged and that public safety may be in jeopardy.

Thus, instrumentation that shows the absence or presence of significant fuel damage or metal-water reaction is of special importance.

Information concerning the integrity of the primary coolant boundary and the containment is also of vital interest.

For example, the character of a postulated LOCA during the first two or three minutes of the accident can best be determined by monitoring the reactor coolant pressure transient.

An analog recorder with a response and sensitivity consistent with the anticipated pressure transient would be the type of instrument needed for this purpose. Comparable records of the pressure transients and temperature gradient in the 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 the ECCS status should be proided to permit post-accident surveillance.

Similarly, the status of the emergency power system should be displayed at all times to the operator in the main control room.The effectiveness of containment atmosphere cleanup systems in removing airborne activity from the contain-ment atmosphere should be monitored (i.e.. measured).

The temperatures and humidity of iodine traps should also be monitored to dterrniinc whether the traps are overheating and thus potentially in danger of losing their radionuclide inventory or failing to remove the radio-nuclides from the containment atmosphere.

The required instrumentation should be capable of surviving the accident environment that it must monitor.It therefore should either be designed to withstand the accident .environment or be protected by a local.artificial environment.

If the environment surrounding an instrument component is the same for accident and normal operating conditions (e.g., the instrumentation components in the main control room), the instrumen- tation components need no special environmental capa-bility.The required instrumentation should also be capable of functioning after, but not necessarily during, a safe shutdown earthouake.

Instrumentation selected for accident monitoring should permit relatively few devices to provide the essential information needed by the operator to satisfy the general objectives.

Where practical, the same instru-ments should be used for normal and accident operation to obtain the advantage of normal inservice surveillance.

However, the instruments should be specifically identi-fied on control panels so that the operator can easily determine that they are intended for use under accident, as well as normal, conditions.

C. REGULATORY

POSITION 1. For each postulated accident that threaten- public safety (for example, a LOCA or ATWS event, ieactivity excursion, or radioactivity release that initiates contain-ment isolation), the applicant should perform detailed safety analyses to determine (a) the parameters to be measured and (b) ihe instrument ranges, responses, and accuracies required to provide the operator with the information necessary to assess the nature of die accident, the course the accident will take, the response of the safety features, the potential for breaching the barriers to radioactivity release, the need for manual action, and the operating status of significant equipment during and following the accident.

The guidelines in References I and 2 should be used to make such analyses, along with the guidelines in Reference

3 dealing with monitoring inside the power plant.2. The essential instrumentation required by the operator to diagnose and monitor significant accident I 1.97-2 I conditiuns should be specified for each system required to be operable during and after the accident.

A tabulation of such instrumentation should be provided, along with a documented justification to show that the instrumentation is adeqtate to provide the operator with the necessary information.

The table should include the instruments'

major operational parameters and indicate the manner in which the instrument outputs will be recorded.3. The accident monitoring instrumentation compo-nents and modules should be of a quality that is consistent with minimum maintenance requirements and low failure rates. Quality levels should be achieved through the specification of requirements known to promote high quality.4. The accident-nionitoring instrumentation should be designed with sufficient margin to maintain necessary functional capability under extreme conditions (as appli-cable) relating to environment, energy supply, malfunc.tions, and accidents.

Thie instrumentation should either be qualified to survive the appropriate operating condi-tions or be suitably protected from the environment.

Its qualifications should be in accordance with Regulatory Guide 1.89, "'Qualification of Class I E Equipment for Nuclear Power Plants." and it should continue to function within the required accuracy subsequent to.but not necessarily during, a safe shutdown earthquake.

5. The accident-monitoring instrumentation should be designed with redundant channels so that a single failure does not prevent the operator front determining the nature of an accident, the functioning of the engineered safety features, the need for operator action, and the response of the plant to the safety measures in operation.

One channel of each redundant se; of channels should be recorded and energized from the station Class I E instrumentation a.c. system.NOTE: "Single failure" includes such events as the shorting or open-circuiting of interconnecting signal or power cables. It also includes single credible malfunc.tions or events that cause a number of consequential component, module, or channel failures.

For example, the overheating of an amplifier module would be a"single failure" even though several transistor failures might result. Mechanical damage to a mode switch would be a "single failure" although several channels might become involved.6. Channels that provide signals for redundant chan-nels should be independent and physically separated to accomplish decoupling of the effects of unsafe environ-mental factors, electric transients, and physical accident consequences documented in the design basis and to reduce the likelihood of interactions between channels during maintenance operations or in the event of channel malfunction.

7. To the extent practical.

accident-monitoring in-strumentation inputs should be from sensors that directly measure the desired variables, 8. To the exztent practical.

the same indicators should be Lsed for accident novilorhig as are used in the normal operations of the plant.9. The accident-monitoring instrumentation should be specifically identified on control panels so that the operator can easily discern that they are intended for use under accident conditions.

The displays should be arranged to simplify the operator's surveillance, interpre.tation, and response determination following an accident signal.10. Any equipment that is used for both accident monitoring and control functions should be classified as part of accident-monitoring instrumentation.

The trails-mission of signals from accident-monitoring equipment for control system use should be through isolation devices 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 a high degree of confidence.

the operational availability of eacht input sensor during reactor operation.

This may be accomplished in various ways: for example: a. By perturbing the monitored variable;b. By introducing and varying, as appropriate, a substitute input to the sensor of the same nature as the measured variable.

or c. By cross-checking between channels that bear a known relationship to each other and that have readouts available.

12. Capability should be provided for servicing, testing, and calibrating the accident-monitoring instru-mentation.

For those parts of the instrumentation where the required interval between testing will be less than the normal time interval between generating station shut-downs, a capability for testing during power operation should be provided.

Servicing, testing, and calibration programs should be specified to ensure proper perfor-mance at all times.13. The design should permit administrative control of the means for manually bypassing channels.14. The design should permit administrative control of the access to all setpoint adjustments, module calibration adjustments, and test points.15. The accident-monitoring instrumentation should be designed to provide the operator with accurate, 1.97-3 I ---complete, and timely information regarding its own status. The design should minimize the development of conditions that would cause meters, annunciators.

recorders, alarms, etc., to gve anomalous indications confusing to the operator.16. The instrumentation should be desigred to facili-tate the recognition, location, replacement, repair, or adjustment of malfunctioning components or modules.

D. IMPLEMENTATION

The purpose of this section is to provide information to applicants and licensees regarding the NRC staff's plans for using this regulatory guide.Except in those cases in which the applicant proposes 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 construction permit applications submitted after August 1, 1976.UNITEO STATES NUCLEAR REGULATORY

COMMISSION

WASHINGTON.

0. C. 20555.OFFICIAL BUSINESS PENALTY 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, "Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants," NUREG-75/094, Regulatory Guide 1.70, Rev. 2, Sept. 1975.3. BNWL-1635, "Technological Considerations in Emergency Instrumentation Preparedness," May 1972.Copies of the above documents are available from the National Technical Information Service, Springfield, Va.2216).POSI'TAGE

AND) FEErS PAID U.S. NUCLEAR IREGULATORY

COMMISSION

REFERENCES

1.97-4