05000368/LER-1986-006, Corrected LER 86-006-00:on 860421,reactor Protective Sys Actuated on Two of Four Core Protection Circulator Channels. Caused by Electrical Noise from Starting Reactor Coolant Pump.Channel C Circuit Card Replaced

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Corrected LER 86-006-00:on 860421,reactor Protective Sys Actuated on Two of Four Core Protection Circulator Channels. Caused by Electrical Noise from Starting Reactor Coolant Pump.Channel C Circuit Card Replaced
ML20205S139
Person / Time
Site: Arkansas Nuclear Entergy icon.png
Issue date: 05/30/1986
From: Dante Johnson
ARKANSAS POWER & LIGHT CO.
To:
Shared Package
ML20205S137 List:
References
LER-86-006-01, LER-86-6-1, NUDOCS 8606120001
Download: ML20205S139 (3)
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LER-2086-006, Corrected LER 86-006-00:on 860421,reactor Protective Sys Actuated on Two of Four Core Protection Circulator Channels. Caused by Electrical Noise from Starting Reactor Coolant Pump.Channel C Circuit Card Replaced
Event date:
Report date:
3682086006R00 - NRC Website
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NRC Form 366 U.S. Nuclear Regulatory Commission (9-83) Approved OMB No. 3150-0104 Expires: 8/31/85 LICENSEE EVENT REPORT (L E R)

TACRITTRAME (1) Arkansas Nuclear One, Unit Two IDOCKET NUMBER (2) lPAGE (3) l0l5l010101 31 61 8til0Fl013 TITLE (4) Inadvertent Reactor Protective System Actuation During Surveillance Testing EVENI DXTE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (8) l l l 15equential l Revision l l l Month l Day l Year Year l Number l Number l Month l Day lYear l Facility Names Docket Number (s) l l 1 l l l l l N/A 0 5 0 0 0 Oi41211l8l61816' --l Ol 01 6l--) 0 1 0 1015l310l8161 N/A 0 5 0 0 0 UPERATING l ITHIS REPORT 15 5UBMITIED PUR5UANT TO THE REQUIREMENTS OF 10 CFR b:

MODE (9) l 31 (Check one or more of the following) (11)

POWERI l l 20.402(b) l l 20.405(c) l Xl 50.73(a)(2)(iv) l 1 73.71(b)

LEVEll 1 l[l50.36(c)(1) l l 50.73(a)(2)(v) l[I73.71(c)

(10)101010l[I20.405(a)(1)(1) l 20.405(a)(1)(ii) l l 50.36(c)(2) l _lI 50.73(a)(2)(vii) l 50.73(a)(2)(viii)(A)l _l Other (Specify in l_l 20.405(a)(1)(iii) l I 50.73(a)(2)(i) [ Abstract below and l _ l 20.405(a)(1)(iv) l[l50.73(a)(2)(ii) l[I50.73(a)(2)(viii)(B)] in Text, NRC Form l ,_l 20 405(a)(1)(v) I_i 50.73(a)(2)(iii) l_1 50.73(a)(2)(x) i 366A)

LICENSEE CONTACT FOR THIS LER (12)

Name  ! Ielephone Number l Area l Dwight J. Johnson, Plant Licensing Engineer ICode l 15l0l1191614l-13111010 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13) l l l lReportablel l l l l lReportablel CausetSysteml Component Manufacturerl to NPRDS CauselSysteml Component Manufacturer to NPRDS l l l l l l 1 Bl Jl Cl l Al Ml Pl GI 01 6l 3l Y l l l l l l l l l l l l l 1 l l 1 l l 1 i i I l l l 1 l l l l l l l l l 1 I l 1 l 1 i l i l l SUPPLEMENT REPORT EXPECTED (14) l EXPECTED 1 Month Day Year l SUBMISSION l l~l Yes (If yes, complete Expected Submission Date) lWl No l OATE (15) ! l l 1 l l ABSTRACT (Limit to 1400 spaces, i.,e., approximately fifteen single-space typewritten lines) (16)

At 1123 hours0.013 days <br />0.312 hours <br />0.00186 weeks <br />4.273015e-4 months <br /> on 4/21/86 with the unit in mode 3 operations, an inadvertent actuation of the reactor protective system (RPS) occurred. The RPS actuation resulted in the insertion of the ' A' shutdown group of control element assemblies (CEA) that were withdrawn per procedure. Normal mode 3 subcritical operations continued without incident. The RPS actuation occurred during functional testing of the channel 'C' logarithmic excore power nuclear instrumentation. During this test a component failure in a circuit card prevented the bypassing of channel 'C # RPS low departure from nucleate boiling ratio (DNOR) and high local power density (LPD) trip functions. To perform the functional test, the bypasses for DNBR and LPD in channel ' A' of the RPS (required due to electrical noise) were removed to allow bypassing of the channel C RPS trip functions, as required by procedure. When the test was initiated, concurrent trips on LPD and DNBR existed in channels 'A' and 'C' of the RPS with no actual bypasses in place. This created a 2 out of 4 channel trip logic. The malfunctioning circuit card in channel 'C' was replaced and the test was completed successfully. The corrective action for the noise problems associated with channel 'A' is planned for the upcoming refueling outage. The unit was returned to full power operations on 4/22/86. This event posed no threat to the health and safety of the general public. Similar occurrences were reported in LERs 50-368/86-005, 50-368/85-020, 50-368/84-001, and 50-368/84-00/.

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8606120001 860530 PDR ADOCK 05000368 -

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Form 1062.018 U.S. Nuclear Regulatory Commission

'NRC Form 366A (9-83) Approved OMB No. 3150-0104 Expires: 8/31/85 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION TACILIIY NAME (1) lDOCKLI NUMBER (2) l LLR NUMBER (6) l PAGE (3) l l l lSequentiall 1 Revision l Arhansas Nuclear One, Unit Two l l Year Number Number l 10151010101 31 61 81 8l 6 --

01 01 6 --

0l Ol012l0F[013 lEXI (if more space is required, use additional NRC Form 366A's) (17)

I. Description of Event A. Unit Status Arkansas Nuclear One, Unit Two (ANO-2) was operating in hot standby (Mode 3) operations with reactor coolant system (RCS) average temperature 545 degrees Fahrenheit and pressurizer pressure of 2250 psia. ANO-2 had shut down on an automatic reactor trip due to a reactor coolant pump trip on 4/21/86 at 0532 hours0.00616 days <br />0.148 hours <br />8.796296e-4 weeks <br />2.02426e-4 months <br /> (reference LER 50-368/86-004).

B. Component identification Printed circuit card containing a linear amplifier / relay assembly; EIIS Identifier = JC-AMP.

The printed circuit card involved in this event is located in the reactor protective system (RPS). This card is utilized whenever a particular RPS trip function bypass is manually inserted in a particular RPS channel. The printed circuit card assembly is manufactured by General Atomic Company.

C. Sequence of Events At 0532 hours0.00616 days <br />0.148 hours <br />8.796296e-4 weeks <br />2.02426e-4 months <br /> on 4/21/86, ANO-2 tripped from 100% power due to the tripping of a reactor coolant pump (RCP) breaker. Hot shutdown (mode 3) conditions were being maintained in anticipation of a return to power operations. The 'A' shutdown bank of control element assemblies (CEAs) were withdrawn per procedure. At 1123 hours0.013 days <br />0.312 hours <br />0.00186 weeks <br />4.273015e-4 months <br /> on 4/21/86, a licensed control room operator was performing a functional test of the channel 'C' logarithmic excore nuclear instrumentation as required for preparation for an approach to criticality and power operations later in the day. During the performance of this functional test, a malfunction of the bypass feature for the RPS trip functions of departure from nucleate boiling ratio (DNBR) and local power density (LPD) in channel 'C' occurred. To facilitate the bypass of the channel

'C' RPS trip functions as required by procedure, the channel 'A' RPS DNBR and LPD trip functions were unbypassed. Due to continuous electrical noise, trip signals were present in channel 'A'. Upon malfunction of the bypass circuit in channel 'C', an RPS actuation occurred.

This actuation resulted in the insertion o'f the withdrawn bank of CEAs but had no other effect on unit operations and resulted in no actuation of any additional safety features equipment. Maintenance activities were directed toward correcting the bypass malfunction of channel 'C' RPS. This activity was completed 4/21/86 at 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br />. The unit was returned to full power operations 4/22/86.

II. Event Cause A. Event Analysis The channel 'A' RPS DNBR and LPD trip functions were bypassed during shutdown operations due to a cabling problem associated with the channel 'A' logarithmic excore nuclear instrumentation (NI) which allows electrical noise to propagate through this channel. This noise causes the logarithmic NI signal to be elevated such that the interlock in the excore NI circuit for core protection calculator (CPC) ' A' is not satisfied and the CPC trips cannot be bypassed.

Since the CPC 'A' cannot be bypassed, the channel 'A' RPS trip functions generated by CPC 'A' (i.e., DNBR and LPD) were bypassed during shutdown operating modes. The electrical noise problem in channel 'A' excore NI was detailed in LER 50-368/85-020. Because of the requirement that a functional test of the channel 'C' excore NI be performed prior to criticality, the RPS channel A DNBR and LPD trip functions were unbypassed to allow bypassing the channel 'C' trip functions (as required by procedure). This left the channel 'A' DNBR and LPD functions in the tripped conditions. Due to a failure of a printed circuit card the bypass utilized in the channel 'C' RPS did not actuate and upon initiation of the functional test concurrent DNBR and LPD trips existed in channels ' A' and 'C' of the RPS. This condition satisfied the 2 out of 4 trip logic and resulted in an RPS actuation which inserted the 'A' shutdown bank of CEAs.

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Form 1062.018 NRC Form 366A U.S. Nuclear Regulatory Commission (9-83) Approved OMB No. 3150-0104 Expires: 8/31/85 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION l

FACILITY NAME (1) l0OCKET NUMBER (2) l LER NUMBER (6) l PAGE (3) l l l l lSequentiall l Revision!

Arkansas Nuclear One, Unit Two l l Year Number Number l  ;

10l51010101 3l 61 81 81 6 --

Oi 01 6 --

01 Ol01310Fl013 '

TEXT (If more space is required, use additional NRC Form 366A's) (17) l B. Root Cause Root cause of the RPS actuation was the existence of simultaneous DNBR and LPD trips in channels ' A' and 'C' of the RPS. This actuation was the result of cabling noise in channel

' A' excore NI not allowing CPC ' A' to be bypassed and the failure of the bypass function in channel 'C' RPS due to a malfunction in a printed circuit card.

C. Basis for Reportability This event is being reported under the provisions of 10CFR50.73(a)(2)(iv) as an unanticipated actuation of the RPS. Since this event resulted in the insertion of control rods into a subcritical core and hot shutdown (mode 3) operations continued unimpaired, the event posed no threat to the health and safety of the general public.

III. Corrective Actions A. Immediate immediate corrective actions consisted of verifying all the reactor trip safety functions.

Since stable mode 3 conditions existed and were unperturbed as a result of the RPS actuallon, required operator response to this event was minimal.

8. Subsequent Actions Subsequent actions, focused on evaluating the cause of the bypass faulure in the channel 'C' RPS. Once the problem was identified as a failed printed circuit card component, that card was removed and replaced. The channel 'C' excore NI functional test was then completed and the applicable sections verifying bypass functions of the channel 'C' plant protective system (PPS) monthly test was performed. Both tests were completed satisfactorily and the plant was restarted.

C. Future .

No future action is planned for the channel 'C' RPS bypass failure as this failure was the result of a relay malfunction on the printed circuit card that was replaced. The channel 'A' excore NI cabling is planned to be replaced during the next refueling outage (June 1986) as an extended outage will be required for the corrective maintenance. No other actions are planned.

IV. Additional Information A. Similar Events Similar occurrences of RPS actuation during sub-critical operations were reported in LERs 50-368/86-005, 50-368/85-020, 50-368/84-007 and 50-368/84-001.

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