Information Notice 1989-68, Evaluation of Instrument Setpoints During Modifications

Evaluation of Instrument Setpoints During Modifications
	ML031190056
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, 05000452, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Crane
Issue date:	09/25/1989
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-89-068, NUDOCS 8909200010
	Download: ML031190056 (10)
	v • d • e

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

.

September 25, 1989

NRC INFORMATION NOTICE NO. 89-68:

EVALUATION OF INSTRUMENT SETPOINTS

-DURING MODIFICATIONS

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

This information notice is being issued to alert addressees to a potential

safety problem resulting from inadequate evaluation of operating and design

characteristics when modifying instrumentation and control (I&C)

systems.

It is expected that recipients will review the information for applicability

to their facilities and consider actions, if applicable, to avoid similar

problems. Suggestions contained in this information notice do not constitute

NRC requirements; therefore, no specific action or written response is required.

Description of Circumstances

Several design inspections of plant modifications in the I&C area by the Nuclear

Regulatory Commission have revealed that calculations relating to the setpoints

of the modified instrument loops were not performed properly to verify that the

original design objectives of the safety systems were still satisfied. Modifi- cations to the instrument system(s) may introduce undesirable operating charac- teristics because of a change in the margin between the nominal setpoint and the

technical specification (TS) limit or a change in the system's response time.

The changed attributes of the I&C components may degrade the safety system's

ability to meet its design requirements. Summarized below are inspection findings

from three recent and two earlier inspections that illustrate these concerns.

Oyster Creek Nuclear Power-Plant (November - December 1988):

The reactor instrumentation system at the Oyster Creek station was modified to

convert certain reactor protection system pressure switches to an analog trip

system. In determining the setpoint values for the modified I&C loops, the

licensee arbitrarily established margin values and was not thorough In accounting

for all potential error contributors to the total uncertainty for I&C measurement

loops.

Because of this, I&C technicians could leave calibrated instrument

channels at the upper limits of their calibration bands and create conditions

that permit setpoints of plant process parameters to deviate beyond their TS

limits without the condition being detected. In this regard, the licensee

identified several instrument loops with a history of exceeding TS limits.

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IN 89-68 September 25, 1989 Zion Nuclear Power Station (March - April 1988):

For modification packages in the I&C area at the Zion station, setpoint calcu- lations for modified instrument loops did not consider head correction changes

caused by changes in instrument tap location.

Also, calculations did not ad- dress compensations for temperature and/or density changes where applicable.

The value of allowance for instrument drift was not related to the interval

between surveillances. The inspection team found that some calculations used

a value equivalent to 12 months drift for instrument loops that had a surveil- lance interval of 18 months.

In addition, calculations used assumed values for

uncertainty in measuring and test equipment (M&TE), assumed values of calibra- tion tolerances, and assumed values of instrument dead-bands.

All these errors

resulted in a nonconservative value of setpoint margin. The failure to account

correctly for drift, head correction, temperature and density correction, ac- curacies of M&TE, and values of calibration tolerances could create an unanalyzed

situation in which the instrument may not be able to initiate the required safety

function even if the process variable is in the non-conservative direction with

respect to the allowable value.

Indian Point, Unit 2 (January - February 1988):

An inspection of the preventive maintenance program at Indian Point Unit 2 revealed that the licensee was not trending for directional changes (positive

or negative) in instrument accuracy occurring between successive calibrations.

The inspection.team-found-that in-several --

loops, -accw'acy-and-drfft-vaTues of,- the instruments were changing only in one direction between successive surveil- lance intervals.

Uncertainty calculations for setpoint margins of these loops

were performed by combining uncertainty attributes using the square root of the

sum of the squares (SRSS) method. This method is acceptable provided uncer- tainty attributes of loop components have random directions.

In a situation

in which uncertainty attributes are known to be changing only in one direction, use of the SRSS method for computing the setpoint margin will result in a non- conservative value. This value, when applied to the setpoint, may compromise

the ability of an instrument to initiate a safety function before the process

variable exceeds its process safety limit.

Furthermore, instrument drift values

occurring in only one direction over several surveillance tests warrant review

by the licensee to determine their cause.

Dresden Nuclear Power Station, Unit 3 (November - December 1985):

The reactor instrumentation system at Dresden Unit 3 was modified by replacing

the old mechanical instruments with new solid-state instruments. The new in- strument loop had increased response time and drift. Also, the accuracy values

of the new instruments were different. The inspection team found that an engi- neering evaluation of the impact of characteristics of new instrument(s) on the

system operation was not performed. Also, an analysis of the impact of the in- creased drift on the existing surveillance frequency was not performed. After

installation, the new instruments were adjusted to the setpoints established for

the original instruments. In this situation, the effectiveness of the modified

system to meet the original design objectives could not be ascertained, creating

a potentially unanalyzed situation.

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IN 89-68 September 25, 1989 Edwin I. Hatch Nuclear Plahnt, Units 1 and 2; Joseph.M.>Farley Nuclear Plant, Units 1 and 2 (May 1986):

Design changes at theWHatch and Farley units included replacement of the existing

mechanical-type instruments with either a single instrument or a string of instru- ments consisting of a'

primary sensor, a signal conditioner, and bistables. An

analysis of the setpoint margin using characteristics of the new instruments was

not performed, and the new instruments were set to either a setpoint established

for the original instruments or to a new setpoint chosen by the instrument vendor.

In the absence of any engineering analysis, the ability of the modified system to

meet the original design objectives could not be ascertained, thus creating a

potentially unanalyzed situation.

Discussion:

'It is important that an engineering analysis be performed to verify that the

static and dynamic characteristics of a system, when modified by the installation

of new instrumentation, continue to meet the design objectives. In modifying I&C

systems, it is important that careful consideration be given to the necessity of

recalculating setpoints, setpoint margins, and values of the TS limits to ensure

that improper operating characteristics have not been introduced by the modifi- cation.

Useful guidance is provided in ISA 67.04-1982, "Setpoints for Nuclear

Safety-Related Instrumentation used in Nuclear Power Plants" which has been

endorsed by Regulatory Guide 1.105 Revision 2-1986,"Instrument Setpoints for

Saftty:-R1lhted Systems".-

-

This information notice requires no specific-action or written response. If you

have any questions about the information in this-notice, please contact one of

the technical contacts listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: S. V. Athavale, NRR

(301)492-0974

V. Mauck, NRR

(301)492-3264

S. C. Guthrie, NRR

(301)492-0991 Attachment: List of Recently Issued'NRC Information Notices

Attachment

I11 89-68

Septembeer 25. 1989 LIST OF RECENTLY ISSUEO

NRC

INFORMATION NOTICES

Jnformatton

o

-of

Yotics No!"

5ubJct

Issuance

Issued to

89-57

89-66

Loss of Residual Heat

Removal Caused by

Accumulator Nitrogen

Injection

Qualification Life of

Solenoid Valves

9/13/89

All holders of OLs

or CPs for PWRs.

9/11/89

All holders of OLs

or CPs for nuclear

power reactors.

9/11/89

All holders of OLs

or CPs for nuclear

power reactors.

9/1/89

All holders of OLs

or Cps for PWRs.

88-46,

Licensee Report of

Supp. 4

Defective Refurbished

Circuit Breakers

89-65

Potential for Stress

Corrosion Cracking in

Steca Generator Tube

Plugs Supplied by

Babcock and Wilcox

89-64

Electrical Bus Bar FailureS

9/7/89

89-63

89-62

89-61 Possible Submergence of

9/5/89

Electrical Circuits Located

Above the Flood Level Because

of water Intrusion and Lack

of Drainage

Malfunction of Borg-Warner

8/31/89 Pressure SeSl

Bonnet Check

Valves Caused By Vertical

Misalignment of Disk

Fanlure of Borg-urner Cate

8/30/89

Valves to Close Against

Differential Pressure

All holders of OLs

or CPs for nuclear

power reactors.

All holders of OLs

or CPs for nuclear

power reactors.

All holders of OLs

or CPs for nuclear

power reactors.

All holders of OLs

or CPs for nuclear

poner reactors. -

83-",

Licensee-Report of Duet-0S2 /B

Af~a s of Us ~

Supp. 2 Refurbished Valves

or Cps for nuclear

power reactors.

OL

Operating License

CP

Construction Permit

UNITED STATES

NUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 2055

OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300

FIRST CLASS MAIL

POSTAGE S FEES PAID

USNRC

PERMIT No. 047

IN 89-68 September 25, 1989 Edwin I. Hatch Nuclear Plant, Units 1 and 2; Joseph M. Parley Nuclear Plant, Units 1 and 2 (May 1986):

Design changes at the Hatch and Farley units included replacement of the existing

mechanical-type instruments with either a single instrument or a string of instru- ments consisting of a primary sensor, a signal conditioner, and bistables. An

analysis of the setpoint margin using characteristics of the new instruments was

not performed, and the new instruments were set to either a setpoint established

for the original instruments or to a new setpoint chosen by the instrument vendor.

In the absence of any engineering analysis, the ability of the modified system to

meet the original design objectives could not be ascertained, thus creating a

potentially unanalyzed situation.

Discussion:

It is important that an engineering analysis be performed to verify that the