ML17263A315

Forwards Description of Activities Re Control Rod Sys Malfunction on 930629.Caused by Minor Misalignment Between Control Rods in Group 1 & Group 2 of Bank D.Control Rods Will Be Maintained in Manual Control

ML17263A315
Person / Time
Site:	Ginna
Issue date:	07/02/1993
From:	Widay J PACIFIC GAS & ELECTRIC CO.
To:	Linville J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
NUDOCS 9307210099
Download: ML17263A315 (6)

Text

ACCELERATED DOCUMENT DISTRIBUTIONSYSTEM REGULAR Y INFORMATION DISTRIBUTIO YSTEM (RIDS)

ACCESSION NBR:9307210099 DOC.DATE: 93/07/02 NOTARIZED: NO DOCKET ¹ FACIL:50-.244 Robert Emmet Ginna Nuclear Plant, Unit 1, Rochester G

05000244 AUTP..NAME AUTHOR AFFILIATION WIDAY,J.A.

Pacific Gas S Electric Co.

RECIP.NAME RECIPIENT AFFILIATION LINVILLE,J.C.

Region 1 (Post 820201)

SUBJECT:

Forwards description of activities re control rod sys malfunction on 930629.Caused by minor misalignment between control rods in Group 1

& Group 2 of bank D.Control rods will be maintained in manual control.

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TITLE: General (50 Dkt)-Insp Rept/Notice of Violation Response NOTES:License Exp date in accordance with 10CFR2,2.109(9/19/72).

05000244 RECIPIENT ID CODE/NAME PD1-3 PD 1NTERNAL: AEOD/DEIB AEOD/DSP/TPAB DEDRO NRR/DRCH/HHFB NRR/DRSS/PEPB NRR/PMAS/ILPB2 OE D~

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ROCHESTER GAS AND ELECTRIC CORPORATION

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TONK

$1>N 89 EAST AVENUE, ROCHESTER, N.Y. 14649-0001 U.S. Nuclear Regulatory Commission Region I

Attn:

James C. Linville Chief, Projects Branch No. 3 Division of Reactor Projects 475 Allendale Road King of Prussia, PA 19406 TfLfPHOhf AllfA COOf 7la 546.2700 July 2, 1993

Subject:

Rod Control System Malfunction R.E. Ginna Nuclear Power Plant Docket No. 50-244

Dear Mr. Linville:

As requested, Rochester Gas and Electric is transmitting a description of the activities related to the rod control system malfunction which occurred on 6/29/93. A description of the event and the troubleshooting efforts, an analysis of the impact on safety, and the interim actions to be implemented are included below.

Event

Description:

On 6/29/93, a malfunction in the rod control system caused a minor misalignment between the control rods in group 1 and group 2 of bank D. Bank D group 1 was indicating 212 steps on its step counter and 216 steps on the Microprocessor Rod Position Indication system (MRPI). Bank D group 2 was indicating 209 steps on its step counter and 204 on MRPI. This caused a Rod Control Urgent Failure alarm which stopped all automatic and manual rod motion.

(Bank D contains 4 rods, 2 in each group.

The rods in each group are located symmetrically across the core.

Group 1 contains rods C7 and K7, group 2 contains rods G3 and G11.)

The troubleshooting efforts are described in Attachment 1.

Efforts to determine the root cause are continuing.

Impact on Safety:

T hni I S e ifi I n Ii bili Tech Spec 3.10.4.1 requires the rods to be "operable and positioned within a12 steps of their group step counter demand position".

The safety function of the control rods is to shutdown the reactor upon initiation of a reactor trip signal.

Control rod movement via the rod control system is a control function and is not required for the rods to be considered operable.

Standard Tech Specs defines operability for a control rod as being tripable.

Therefore, as long as the rods are tripable they are operable.

Both flux map traces and MRPI indicated that the rods were moving when a demand signal was present.

This proves that the 1 Gin~

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rods were not "immovable as a result of excessive friction or mechanically untripable" and therefore were operable.

Since the alignment specification was also met, Tech Spec 3.10.4.1 was fullysatisfied.

Tech Spec 3.10.1.1 specifies the shutdown margin that must be maintained.

Tech Spec 3.10.1.3 specifies that the control rods must be maintained above the Rod Insertion Limits (RIL). The RIL for 100% power is 184 steps on Bank D. The maximum rod insertion was Bank D at 205 steps.

Therefore, Tech Spec 3.10.1.3 was satisfied.

Since Tavg was on program, and the rods were maintained above the RIL, the shutdown margin requirement was also met.

Based on this evaluation, the control rods were operable at all times and all Tech Specs were satisfied.

P I

dMalf n in ne unc The Bank D rods are maintained near the fully withdrawn position in order to maintain axial offset within its target band as required by Tech Specs.

Even if uncontrolled rod withdrawal were to occur (ie. urgent failure alarm did not stop rod motion), there would be a very small positive reactivity addition since Bank D rods are in a low worth region.

In addition, since the malfunction resulted in movement of a group of rods rather than a single rod, core symmetry would be maintained and the peaking factors would be less severe, This is consistent with the licensing basis for Ginna as described in UFSAR section 15.4.2, Uncontrolled RCCA Withdrawal at Power.

Interim Actions:

Until there is reasonable assurance that the cause of the rod control problem has been corrected, the following actions will be taken. The control rods will be maintained in manual control.

The Bank D rods will be exercised daily to ensure the rod control system is functioning properly.

The temperature, in the area of the rod control cabinets, at which ventilation will be increased has been reduced-from 92 'F to 85'F in an attempt to mitigate potential temperature related effects. This direction has been provided to Operations through the daily operations plan.

Very truly yours,

~i~d.M Josep A. Widay JPW/001 attachment xc:

Mr. Allen R. Johnson (Mail Stop 14D1)

Project Directorate l-3 Washington, D.C. 20555 U.S. Nuclear Regulatory Commission Region I

475 Allendale Road King of Prussia, PA 19406 Ginna Senior Resident Inspector

Attachment 1

Sub-~e Bank D Group 1 Rod Control Problem On June 29, 1993 at 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br /> with the plant operating at 97.54 power and normal steady state condition a

Rod Control urgent failure Rod Stop (C30) alarm was received when Control Bank "D" stepped in response to an Automatic Zn demand signal.

Rod Control System indication prior to and after receipt of the Rod Control Urgent Failure Alarm was as follows:

Prior:

Bank D Group 1 counter at 211 steps Group 2 counter at 210 steps

~Afte Bank D Group 1 counter at 212 steps Group 2 counter at 209 steps Urgent Alarm in Logic Cabinet DS1 light lit on 1BD Slave Cycler printed circuit card location A-414 in Logic Cabinet.

Light indicates a slave cycler fault.

Bank Overlap counter at 601 steps MRPI indication for Bank D Group 1

Rods (K7 and C7) was 216 steps.

MPRI Indication for Bank D

Group 2 Rods (G3 and G11) was 204 steps.

Ambient temperature in the vicinity of the Rod Control Cabinets was approximately 87 degrees F. at the time the problem occurred.

Troub o

s and Resu ts:

Setup a Visicorder to monitor Bank D Group 1 "Lift",

"Moveable",

and "Stationary" Coil voltages.

Requested Operations reset Rod

. Control Urgent Failure Alarm.

Requested Operations to step Bank D "IN" one step while monitoring coil voltages with visicorder.

Both Groups moved one step in and Visicorder traces of coil voltages showed proper signal sequencing.

Requested Operations to step Bank D "IN" a few steps and "OUT" a few steps.

This was repeated three times with both groups responding properly.

Visicorder traces of coil voltages showed proper signal sequencing for both "IN" and "OUT" motion.

Temperature in the vicinity of the Rod Control Cabinets at time of testing was 73 degrees F.

Reduction in temperature caused by increased ventilation.

Rod Control Indication at the completion of the above Rod testing. was:

0 Bank D Group 1 Counter at 212 steps Group 2 Counter at 209 steps 0

.Bank D P/A converter at,212 steps Per procedure guidance 0'perations realigned Bank D Group 1

rods'ith Bank D Group 2 rods at 209 steps, verified P/A converter Bank D indication was at 209 steps, and had I&C position Bank overlap counter at 599 steps.

Operations satisfactorily performed procedure PT-1 (Rod Control System) which verified operability of all control rods.

On June 30, 1993, analysis of the problem continued.

Contact was made with Westinghouse to inform them of our problem and to also obtain their assistance.

After several conversations and a lot of research the final consensus was that the supervisory Logic II printed circuit 'was the most probable cause of the problem.

The supervisory Logic II card provides (1)

A Buffer Memory Control Circuit which accepts input commands, (2)

Feeds the Master Cycler which generates the "Go" pulses for rod movement, (3)

Feeds the Bank Overlap Circuit for data logging and (4)

Outputs to the Slave Cycler which generates current orders for Rod Movement.

Operations performed procedure PT-1 (Rod Control System) procedure'o verify operability of all control rods.

During the performance of procedure PT-1, ISC personnel obtained recordings of the voltages for Group Counter Coils while stepping the Group Counters for "IN" and "OUT" movements to ensure that high voltage spikes were not being fed back into the Logic Cabinet (as was experienced at Salem).

All voltages were normal which proved the diodes across the Group Counter coils were performing their intended function.

RG&E and Westinghouse were satisfied that Ginna does not have the same problem as Salem; because (1) Salem's problem affected only one Rod Cluster where Ginna's affected the whole group, (2)

Salem didn't receive an urgent failure

alarm, (3)

Salem's problem persisted while Ginna's Problem occurred only

once, and (4)

Salem's problem was the Slave Cycler Decoder Card where Ginna's problem is upstream in that.logic.

On July 1, 1993, the supervisory Logic II printed Circuit Card was replaced and Operations successfully completed procedure PT-1 (Rod Control System) for proving operability of all control rods.