05000346/LER-1984-001, Revised LER 84-001-01:on 840108,core Imbalanced Positively & Axial Power Shaping Rods Automatically Inserted.Caused by Large Difference in Amount of Xenon in Top of Core & Failed Integrated Circuit Gate,Respectively

Revised LER 84-001-01:on 840108,core Imbalanced Positively & Axial Power Shaping Rods Automatically Inserted.Caused by Large Difference in Amount of Xenon in Top of Core & Failed Integrated Circuit Gate,Respectively

ML20088A620
Person / Time
Site:	Davis Besse
Issue date:	03/29/1984
From:	Murray T, Swartz J TOLEDO EDISON CO.
To:	NRC OFFICE OF ADMINISTRATION (ADM)
References
K84-355, LER-84-001, LER-84-1, NUDOCS 8404120304
Download: ML20088A620 (4)

LER-2084-001, Revised LER 84-001-01:on 840108,core Imbalanced Positively & Axial Power Shaping Rods Automatically Inserted.Caused by Large Difference in Amount of Xenon in Top of Core & Failed Integrated Circuit Gate,Respectively

Event date:
Report date:
3462084001R00 - NRC Website

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i MNIC Foren 384 U S. NELEAR KEGULATORY COMMES$60N

"" APPROVED Oue NO 3150-4104 5""* 5 84' '85 LICENSEE EVENT REFORT (LER)

FACILITY NAME (Il DOCKET NUMBER (28 PAGE43)

Davis-Besse Unit 1 o 15 l 0 l0 l 0 l 3l4 16 1 l0Fl O! 3 14 fliNeactor trip caused by autcmatic insertion of Axial Power Shaping Rods AYENT DATE (51 LE R NUMBE R 161 REPORT DATE 17) OTHER F ACILITIES INVOLVED (4#

MONTH DAY YEAR YEAR IE '

• 8 MONTH DAY YEAR F ACILIT V N AwfS DOCKET NUMeERis) 0 15101010 1 1 I 0 lt 0l8 8 4 8 l4 0l0l1 0l1 0 l3 2l9 8 l4 o isto l0 tol l l OPE R ATING TH18 REPORT IS SUSMITTED PURSUANT TO THE REOUIREMENTS OP 10 CPR {. (Chere one or more of rae renewest 1118 MOOE m 1 20 402M 20 406(el SX 00.73'eH2Het 73 71141 POWER 20 406teH111d 60 3eleH1) 50.738eH2Het 73.7118)

SEOP O 14 i 6 20 0steH1H., so3si. m s0.73.H2H,ei

_ guEgsggAg 20 406falt1H6hl 50 73tel(2ibt 50.73taH2HendHAl JudA1 20 406teH1Hivl 50.734s H2 H W) 80 731sH2Hvii6H01 20 4064eH1Het 60.73teH2 Heel to.73(all2Hal LICENSEE CONTACT FOR TMit LER (12)

NAME TELEPHONE NUMBER ARE A CODE John D. Swartz 4 ;1,9 2i 5i 9l g5l0g0l0 COMPLETE ONii LINE FOR EACH COMPONENT F AILURE DESCR' SED IN TH18 REPORT (13i i

"A "A% E CAUSE SYSTEM COMPONENT R' O NPROg CAUSE $YSTEM COMPONENT .

f TU g 'h'O NPR X RlB 16 l9 Ml4 i5 i 5 Y i t i l i t l I I I I I I I I I I I I I SUPPLEMENTAL REPORT E RPECTED (148 MONTM DAY YEAR

$U8 MISSION

\ ES {!r yn como.re EXPTCTEn SUBVI55 TON DA TEI NC l l l AanR ACT ,t.m., ,,1ax roa. . . ..m.r.o.,r . .a. n , a. i o e, Due to a condenser tube leak, reactor power was reduced to 46%. Operators borated the Reactor Coolant System to minimize the normal negative imbalance caused by the rod insertion during the power reduction. When core imbalance turned around and became positive due to rod withdrawal and Xeron, operators added deminerclized water i to the RCS to allow rods to insert. Due to a failure in the Control Rod Drive Control System, the operators could not operate the Axial Power Shaping Rods to help reduce the positive core imbalance, and the Axial Power Shaping Rods inserted without command. The imbalance as read by the out-of-core detectors was much greater tha 1 the imbalance as read by the incore detectors. The apparent reason for g the out-of-core detectors reading rusch greater than the more accurate incore detectors is because the out-of-corcs are calibrated to irnbalance caused by an Axial Power Shaping Rod movement. The positive core irrbalance increased to the Reactor Protec-tion System flux /de lta flux / flow setpoint, and the reactor tripped about 3.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after reducing power to 46%. The Control Rod Drive Control System problem was due to a faulty logic card which was later repaired.

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' NRC Fem 3640 0 S. NUCLEOR REGULOTORY COMMISSION LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPROVEO Ove NO 3150-0104 E APtRES 8'31 BS E U3 DOCKET NUM8ER L21 g gg YEA" w [a v, a Davis-Besse Unit 1 015101010l3l4l6 8I4 --

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011 0l2 oF 0 13 "Te~TcEf*p"tTE"of"ffEcIfrEEnTe?"On January 8 , 1984, the unit was operating at approxi-mately 100% power. At 1640 hours0.019 days <br />0.456 hours <br />0.00271 weeks <br />6.2402e-4 months <br />, high c.nductivity alarms of the condensate discharging from the polishers were received by Control Room operators, and a i reduction in power to 50% was commenced at a rate of 1/3% per minute, eventually reaching 46%.

As the Integrated Control System (ICS) reduced reactor power, regulating Group 7 rods inserted into the core, and the core imbalance went from -2% to a maximum negative imbalance of -10% as measured by the out-of-core detectors. The more accurate incore detector system read -8%. The imbalance remained at approximately

-8% for approximately one hour.

I

In response to the Xenon buildup, the control rods withdrew to a maximum value of 91% withdrawn at 2115 hours0.0245 days <br />0.588 hours <br />0.0035 weeks <br />8.047575e-4 months <br />. During the 1.5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> period of rod withdrawal, the core imbalance increased to +20% by out-of-cores (+10% by incores) due to both rod withdrawal and the relative burnout of Xenon in the top of the core as compared to the bottom. To limit rod withdrawal, the operator began adding demineralized water at 1955 hours0.0226 days <br />0.543 hours <br />0.00323 weeks <br />7.438775e-4 months <br />. The control rod insertion (due to the water added) was not enough to completely stop the increase on imbalance.

1 Approximately eight minutes prior to the trip, the Axial Power Shaping Rods (APSR) were selected to be withdrawn, however, the rods automatically started inserting.

The Reactor Operator stopped the insertion by selecting a different group of regulat-ing rods.

The reactor tripped at 2318 hours0.0268 days <br />0.644 hours <br />0.00383 weeks <br />8.81999e-4 months <br /> on Reactor Protection System (RPS) flux / delta flux / flow. At this time, the out-of-core detectors, which the RPS looks at, were indicating an imbalance of approximately +24%. The incore detectors were indicating an imbalance of approximately +12%. This event is reportable under 10CFR50.73(a)(2)

(iv), Automatic Actuation of RPS.

Designation of Apparent Cause of Occurrence: The cause of the positive imbalance was due to the large difference in the amount of Xenon in the top of the core as compartd to the bottom. The apparent reason for the out-of-core detectors reading much greater than the more accurate incore detectors is because the out-of-cores are calibrated to imbalance caused by an APSR movement. The imbalance caused by APSR movement is more conservative than any combination of Xenon, Group 7, or APSRs.

Therefore, the reactor trip imbalance setpoint is always conservative.

The cause of the APSR in motion, without a manual command, was found to be a failed integrated circuit gate on system logic module C6 (IC2). The fault caused a con-stant manual "in" command, which when Group 8 was selected, resulted in the APSR group run in.

Analysis of Occurrence: The RPS acted as designed, tripping the reactor when the flux / delta flux / flow setpoint was reached on the out-of-core detectors. A reactor g trip would have occurred earlier in the event if the plant would have been at a higher power during the imbalance swing due to a tighter RPS operating envelope on flux / delta flux / flow.

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MRC Form 3000 U S NUCLEGR REGULOTORY COMMISSION LICENSEE EVENT REPORT (LER) TEXT CONTINUATION arraoveo ove No. siso-cio.

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"EEclTiEratToTTY$756Ei"of-core detector imbalance to an imbalance caused by APSR I movement is more conservative than any combination of Xenon, Group 7, or APSRs.

Therefore, the reactor trip imbalance setpoint is always conservative.

Corrective Action: On January 9, 1984 at 0830 hours0.00961 days <br />0.231 hours <br />0.00137 weeks <br />3.15815e-4 months <br />, Instrument and Control Mechan-ics repaired the faulty system logic card under Maintenance Work Order 1-84-0102-00.

The group was tested satisfactorily and declared operable at 1245 hours0.0144 days <br />0.346 hours <br />0.00206 weeks <br />4.737225e-4 months <br /> on January 9, 1984. Toledo Edison personnel will work with Babcock & Wilcox to investigate the

, possibility of reducing some of the excess conservatism in out-of-core imbalance 1

indication.

I Failure Data: This is the first failure of this type system logic module.

1 Report No: NP-33-84-01 DVR No(s): 84-001 1

i geo.wa..

d TOLEOO

%m EDISON March 29, 1984 Log No. K84-355 File: RR 2 (NP-33-84-01)

Docket No. 50-346 License No. NPF-3 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555 Gentlemen:

Enclosed is Revision 1 to Licensee Event Report 84-001, which is being submitted in accordance with 10CFR50.73. The revisions to the report are indicated by a "1" in the left margin of each page.

The system code for component failures was taken from the old LER instruc-tion book since the new IEEE-805 is not yet available.

Yours truly, 4h Terry D. Murray Station Superintendent Davis-Besse Nuclear Power Station TDM/lj k Enclosure cc: Mr. James G. Keppler, Regional Administrator, USNRC Region III Mr. Walt Rogers DB-1 NRC Renident Inspector JCS/001  %

THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENL'E TOLEDO, OHIO 43052 i