05000237/LER-2013-002

LER-2013-002,

Event date:	07-20-2013
Report date:	09-27-2013
2372013002R00 - NRC Website

DOCKET

2013 00

PLANT AND SYSTEM IDENTIFICATION

Dresden Nuclear Power Station (IMPS) Unit 2 is General Electric Company Soiling Water Reactors with a licensed maximum power level of 2957 megawatts thermal. The Energy Industry Identification System codes used in the text are identified as (XX].

A. flutamdlismiltizistinct Unit 02 Event Date: 07-20-2013 Event Time: 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> CDT Reactor Mode: 1 Mods None: Power Operation Power Level: 100 percent B. peacriadoe of pier On July 20, 2013, at approximately 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> CDT, Operations personnel were performing Dresden Operating SASIVINHIMICID (DOS) 0700-07, Rod Block Monitor Functkinal Test, for Rod Block Monitor 8. The procedure instructed personnel to lower the Rod Block Monitor (ROM) (Its] indicated power using the PVVR knob until the associated downer** indicating light illuminates which indicates a downscale trip of the monitor. However while lowering the potentiometer, the lower stop was reached before tie downscale trip was received. The lowest power that was achieved was approximately seven (7) percent The performance of the survaillence was suspended. The malfunction was discussed and it was concluded that the inability to echieve the downscale was due to a malfunction in the testing CarCUitry. Therefore ROM 3 was considered operable, returned to service and troubleshooting was planned.

Prior to troubleshooting being completed, three controls rods (CRD) (AA) were withdrawn. CRD F6 was moved from position 20 to position 22 on July 23, 2013. On July 27, 2013, CRDs D8 and M8 were moved from position 00 to posaion 08.

Subsequent to the movement of the control rods, engineering performed an extensive evaluation of the RBM 8 symptoms that we observed during the performance DOS 0700-07. On July 29, 2013, based on englneerirp's evaluation, it was recognized that the symptoms observed during the testing of RBM 8 on July 20, 2013, had been misdiagnosed and the RBM should have been declared inoperable following the inability to complete the procedural steps.

Plant technical specificabons LCO 3.3.2.1, "Conbol Rod Block Instrumentation," require that an inoperable RBM channel be restored to the operable status within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> tf the channel is not restored to the operable status within this tinieframe, then one RNA channel must be placed in the tripped condition within one hour which would prevent control rod withdrawal. Since it was unrecognized that RBM 8 was inoperable, these actions were not completed, The selection of a non-peripheral control rod with reactor thermal power grater than or equal to 30 percent power during a time that the RBM is inoperable constitutes an entry into a Technical Specification specified condition that is prohibited by LCO Applicability 3.0.4.

This event is being reported in accordance with 10 CFR 50.73(*X2)(iXEI), "Any operation or condition which was prohibited by the plants Technical Specifications.

NRC FORM MfM (10-2010) C Cause of Event - Engineering personnel commenced a review of the symptoms that had been observed by Operations personnel during the performance of DOS 0700.07. Following an extensive review of the REM circuitry, Engineering determined that ROM 8 Downscale Rod Block Function was not capable of performing it intended function in all postulated conditions.

Troubleshooting and repair, as directed by Work Order 01659122-01, revealed that the symptoms observed during the July 20 testing we the results of a failure of quad trip card 2 (Z28), circuit C or 3, such that contact K7 on averaging card Z30 was always energized. Nth contact K7 energized, the contact would be in the dosed position. When the RBM circuit is normal end Operations is performing DOS 0700.07, averaging card Z30 contacts K1 through 101 are open. As a result of remaining energized the contact for K7 was dosed on July 20, 2013. This affected the PWR TEST signal that Operations personnel adjusted while performing DOS 0700-07, Step 1.24.

The evaluation completed by Engineering personnel revealed that there were multiple symptoms within the circuitry that would indicate that the RBM was not operating properly. Although the indications existed, the significance of these anomalies was outside the knowledge base of the licensed operators. Even though procedure DOS 0700-07 Step1.24 tested the downscale function, it was not annotated as acceptance criteria. Therefore this tad the licensed operators to make a knowledge-based performance mode decision.

An additional contributor to this event was the fact that the symptoms observed during the July 20 testing were believed to be exclusive to the RBM testing cktuity. This thought process was further reinforced by information that had been previously provided to the operating staff by maintenance personnel. The lack of a more rigorous rev** to ensure channel operability following the anomalous symptoms allowed the REM inoperability to go undetected.

D.

The purpose of the RBM is to limit control rod withdrawal if localized neutron flux exceeds a predetermined setpolnt during control rod manipulations. Even though not credited in the Control Rod Withdrawal Error analysis, the RBM is designed to block control rod withdrawal to preclude a Minimum Critical Power Ratio Safety Limit violation. The ROM supplies a trip signal to the Reactor Manual Control System [JD) to appropriately inhibit control rod withdrawal during power operation above the 30 percent RATED THERMAL. POWER setpoint when a non-peripheral control rod is selected.

The three control rods that we withdrawn between July 20, 2013 and July 29, 2013, F-8, D-8 and M-8 were interior rods. RBM 8 would have used all 8 Local Power Range Monitor (LPRM) signals, and none of the 8 LPRM signals were downscale. With these conditions, K7 being continuously energized would have no adverse effects. Additionally, ROM 7 was operable during this event and was capable of providing the control rod block function if the monitor settings were exceeded.

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Plant personnel replaced the failed card.

WC FORM 380A (10-2010) 1. FACILITY AA* Ma* ulk plu)smit 3. PAIN NM FORM 314A cio-2eim LICENSEE EVENT REPORT ((ER) BAR RSOULATORY cc sNa+

NARPIATIVII

A Training Request is being generated to evaluate the need for personnel training associated with issues identified in the casual evaluation.

Plant Operations procedure DOS 0700-07 and Maintenance procedure DIS 0700-08 are being revised to ensure that the testing of the downscale function is recognized as acceptance criteria.

Additionally, the results of the event investigation are being presented to appropriate plant Operations and Maintenance personnel.

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G. Contwowat Foamy Dds:

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