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LER 92-013-01:on 920817,scram Setpoint Was Reduced Due to Induced Noise Signal Which Caused Automatic Scram to Occur. C/As:Installed Inductors in Affected Flow Transmitter circuits.W/930618 Ltr
	ML20045D645
Person / Time
Site:	Duane Arnold
Issue date:	06/18/1993
From:	Sueper L, Denise Wilson; IES UTILITIES INC., (FORMERLY IOWA ELECTRIC LIGHT
To:	Martin J; NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
	LER-92-013, LER-92-13, NG-93-2190, NUDOCS 9306290256
	Download: ML20045D645 (7)
	v • d • e

1

Iowa Electric Light and Power Company.

June 18, 1993 NG-93-2190 Mr. John Mar tin Regional Administrator Region III U..S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, IL 60137

Subject:

Duane Arnold Energy Center Docket No: 50-331 '

Op. License DPR-49

Licensee Event Report #92-013 Rev. 01 Gentlemen:

please find attached a copy of the subject revision to Licensee Event' Report '

92-013 Rev. 01. The changes from the original submittal relate to'our-decision to approve the use of light emitting diodes (LEDs) as suitable -

replacements for the incandescent lamps installed in the control rod indications and the establishment of a periodic inspection / replacement !

schedule that is appropriate for the type of indication in use.

3 Very tro y yours, David L. Wilson plant Superintendent - Nuclear DLW/LS/aah cc: Director of Nuclear Reactor Regulation Document Control Desk U.S. Nuclear Regulatory Commisslon Mail Station P1-137 Washington, D. C. 20555 NRC Resident Inspector - DAEC l

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f Aclu!Y NAME (1) DOCKET NUMBER (2) PAGE (3)

Duane Arnold Energy Center 05000 331 10F6 j Tins ta) Reduced 3 cram Setpoint Due to Induced Noise Signa Causes Automatic Reactor Scram EVENT DATE (5) LER NUMBER (6i REPORT NUMBER (7) OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR YEAR MONTH DAY YEAR UBR B 00 F ACluTY NAME DOCKET NUMBER

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08 17 92 92 ~ 013 01 06 18 93 05000 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 6: (Check one or more) (11)

MODE (9) N 20.402(b) 20.405(:) X 50.73(a)(2)(iv) 73.71(b)

POWER 20.405(a)(1)(i) 50.36(c-(1) 50.73(a)(2)(v) 73.71(c)

LEVEL (10) 100 20.405(a)(1)(ii) 50.36(;)(2) 50.73(a)(2)(vii) OTHER 20.405(a)(1)(iii) 50.7?;a)(2)(l) 50.73(a)(2)(viii)(A) '

20.405(a)(1)(iv) 50.7J(a)(2)(ii) 50.73(a)(2)(viii)(B)

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Lenny Sueper, Principal Technical Succort Encineer (3191 851-7365 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIDED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT ^

MANUFACTURER CAUSE SYSTEM COMPONENT MANUFACTUREFI O RD X AD FT I 204 Yes B IG Il G080 No IG 33 G 080 No X IG CNVR 6080 Yes SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MONW DAY YEAR YEs go WWEM pr yes. compiere DFECTED SUBM:SSiON DATO y DATE (15)

ABSJRACT (L;rnr1 to 1400 spaces, i e., approximately 15 single spaced typewritten lines) (16)

P On August 17, 1992, with the plant operating at 100% power, an automatic reactor scram was initiated due to a perceived high average power range neutron flux level. The cause was a noise signal which affected the recirculation flow signals and reduced the flow-biased scram setpoint below the current operating power level.

This revision to the original LER incorporates changes to the corrective actions previously committed to. Specifically, the use of light-emitting diodes (LEDs) has been approved for use in the control rod indication because of their improved reliability over the the incandescent lamps that failed during this event. Therefore, the previous committment to replace the installed indication quarterly has been changed to a committment to periodically inspect or replace the installed indication with a frequency consistent with the expected service life.

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On August 17, 1992, with the plant operating at 100% power, an automatic reactor scram occurred at 0718 hours0.00831 days 0.199 hours 0.00119 weeks 2.73199e-4 months .

An induced noise signal into two ITT Barton model 764 flow transmitters lowered the perceived reactor recirculation flow rate which then lowered the Average Power Range Monitor (APRM) flow-biased scram setpoint below the current operating power level.

Upon receipt of the Reactor Protection System (RPS) actuation due to an f APRM upscale trip, all control rods fully inserted. Initial verification i of 'all rods-in' was hampered by seventeen (of 89) burned out control rod full-in indicating lamps. Additionally, a single, failed control rod Position Indicating Probe (PIP) reed switch for the full-in overtravel position prevented the Safety parameter Display System (SPDS) computer from providing an 'all rods-in' display, which operators use as an alternate way to determine control rod position. Based on this lack of complete control rod position information, the Anticipated Transient Without Scram Emergency Operating Procedure (ATWS-EOP) was entered at 0720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months .

Immediate operator a cions per the ATWS-EOP and its associated Operating Techniques were taken at this time. These include overriding the Automatic Depressurization System (ADS) and preventing injection (locking out/ tripping) of the High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC) systems. Following reset of the scram signal, all control rods settled to the 00 (full-in) position from the overtravel full-in position. When this was accomplished, all rods were verified to be full-in via individual rod 00 positions, available full-in indicating lamps and SPDS computer message of all rods in. The ATWS-EOP was exited at this time (0721 hours0.00834 days 0.2 hours 0.00119 weeks 2.743405e-4 months ) and the ADS, HPCI, and RCIC systems were restored to a standby status.

Following the scram, expected core void collapse caused indicated vessel level to lower below the 170 inch (TAF) low level setpoint to a minimum of 130 inches. All required Primary Containment Isolation System (PCIS) isolations occurred when initiated by the 170 inch low level condition. l Reactor level was prumptly rest ved, utilizing normal feedwater flow. '

Reactor pressure was adequate h maintained throughout the transient by I the Electro-Hydraulic Controls (EHC) system.

When the reactor mode switch was taken out of the 'Run' position as directed by the scram procedure immediate actions, the 'F' APRM generated a >15% (while not in 'Run') upscale trip half-scram. After the trip was verified to be invalid, the 'F' APRM was bypassed and the half-scram was reset.

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This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv),. ,

as actuations of Engineered Safety Features (ESFs). i II. CAUSE OF EVENT A. Induced APRM Upscale Trip:

Immediately following the event, Operations personnel determined the scram had occurred due to upscale trips on each of the six APRMs in the t RPS logic. A review c,f the neutron flux records shortly thereafter found ,

no evidence of a reactor power increase. The APRM reactor neutron flux upscale setpoint logic was then reviewed to ascertain the cause of the signal. '

The APRM neutron flux upscale trip setpoint varies proportionally with reactor recirculation flow by means of a flow-biasing network. The setpoint is automatically adjusted based on recirculation pump flow, with ,

a maximum APRM trip setpoint of 120%. (At 100% recirculation pump output, the trip setpoint is 120%; at lower output levels the setpoint is reduced). A disturbance in the total recirculation flow signal 'provided <

to the APRM flow-biasing network could change the APRM upscale setpoint ;

to a value below actual reactor power, which would result in an APRM ,

upscale trip.

Review of data indicated the output signal of two flow transmitters had spiked downward. The two instruments are located next to each other on an instrument rack. Several spikes were noted over a one minute ,

i timeframe, beginning before and ending after the scram. A detailed investigation was begun to locate the source of the interference. This '

investigation included instrument tubing walkdowns, extensive walkie-talkie radio testing, vibration tests, and several other potential signal sources were checked to determine if a noise spike could be '

induced. Additionally,. electronics contractors were contacted for assistance in determining the source and suggesting potential corrective actions. The only credible source identified was external Radio !

Frequency (RF), although a specific RF emitter was not identified.

Previous plant data was reviewed and no evidence was located to indicate the remaining six recirculation flow transmitters had ever been subjected to spurious noise signals.

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01 4- 0F 6 na en .. . ,,,... ,, awr.s. .. .saa, . nRc F. ,, mn,n B. 'F' APRM Half-scram:

Troubleshooting found the 'F' APRM 15% (while not in 'Run') scram setpoint potentiometer out of adjustment in the conservative direction.

There are many card mounted potentiometers located in.c'ose proximity-to each other in the APRM cabinets. It is likely that thc , correct potentiometer was adjusted during power operation with toe mode switch in 'RUN'. The remaining APRM 15% setpoints were found within l specifications.

C. The ATWS-EOP was entered due to a lack of available control rod position indication 'mmediately following the scram. ADS was locked out as specifically directed by the ATWS-EOP. HPCI and RCIC were locked out as directed by an existing Operator Technique. This technique was based -

on the need to positively control the addition of cold, makeup water to '

the reactor under ATWS conditions.

III. ANALYSIS OF. EVENT: 1 This event had no adverse effect on the safe operation of the facility.

The reactor scram occurred as designed upon receipt of the APRM upscale signals. .All control rods fully inserted. Throughout the transient, i vessel level and pressure were maintained within safe operating limits.

All ESFs functioned as designed. No emergency core cooling systems were initiated in response to the event.

IV. CORRECTIVE ACTIONS:

A. Induced APRM Upscale Trip:

1. Inductors were installed in the affected flow transmitter circuits.

Using a handheld walkie-talkie as a source, testing of these RF ' chokes' showed a reduction from pre-installation spikes of 50 milliamps to post-installation spikes of 2.0 or less milliamps.

2. Additional restrictions have been placed on the allowable presence of handheld radios in the location of the susceptible flow transmitters. ,

Except in emergencies, radios will no longer be permitted in the reactor building corner rooms which contain recirculation flow transmitters.

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3. The recirculation flow transmitters not involved with this l transient will have inductors installed at the next available modification l opportunity. !

B. 'F' APRM Half-scram: r The 15% (while not in 'Run') setpoint potentiometer was properly readjusted.

Additional labeling to aid personnel in identifying the individual :

potentiometer functions will be installed by September 30, 1992.

C. ATWS-EOP Entry:

1. The Operating Technique which directed locking out HPCI and RCIC ;

as an initial action upon entering the ATWS-EOP was revised to allow greater operator flexibility to assess the need for limiting positive reactivity addition from the injection of cold water. ,

2. A preventive maintenance action was initiated to inspect or replace the full-in indication periodically at intervals consistent with the type and expected service life of the lamps in service. '

3. The single, failed overtravel-in PIP input to the SPDS computer has been overridden. This action allows the SPDS to accurately represent the status of the remaining 88 control rods. Analysis shows the reactor will i remain shutdown under all conditions with the control rod with the highest analytical rod worth fully withdrawn. Entry into the ATVS-EOP with 88 of 89 control rods fully inserted would not be required. Prior to an av'ilable a maintenance window to repair the failed PIP, guidance has been t provided to the operators on the necessary steps required to determine the position of the control rod following a scram. -

4. Following several months of evaluation at the site simulator, the plant has approved the use of light emitting diodes (LEDs) as suitable replacements for the incandescent lamps used in the control rod indicators. LEDs offer greater reliability than incandescent lamps.

V. ADDITIONAL INFORMATION:

A. Failed Components The RF susceptible flow transmitters are ITT Barton Model 764.

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YEAR SEOUE NTLAL REVISION ,

. NUMBER - NUMBER Duane Arnold Energy Center 0l5l 0 l0l0 l'3l3 l 1 92 013 -

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The_ failed PIP is GE part number 79E111G001.

The incandescent light bulbs are GE lamp number 327.

The 'F' APRM is GE manufacturer's number 145C3096RSG002.

B. Previous Similar Event:

LER 89-009 details an' event where a transmitting walkie-talkie induced noise into the same flow transmitters involved in this event and caused '

a reactor scram. Following.the 1989 event, general restrictions on the use of radios were. implemented.

C. EIIS Codes:

Component codes:

Flow Transmitters - FT l

System Codes: ,

APRMs - .IG RPS ---- JC PCIS --- JM EHC ---- JG Recirc - AD !

HPCI --- BJ RCIC --- BN ,

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