ML18036B335

LER 93-006-00:on 930525,multiple intermediate-range Monitor Downscales Received While Changing from Range 6 to 7.Caused by Use of Nominal IRM Gain Settings.Setting for Insert Error Reset & Gain adjusted.W/930622 Ltr

ML18036B335
Person / Time
Site:	Browns Ferry
Issue date:	06/22/1993
From:	Kammer D, Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-006-04, LER-93-6-4, NUDOCS 9306290277
Download: ML18036B335 (18)

Text

ACCELERATED DOCUMENT DISTKISUTION SYSTEM REGULA%Z INFORMATION DISTRIBUTIOYSTEM (RIDE)

ACCESSION NBR:9306290277 DOC.DATE: 93/06/22 NOTARIZED: NO DOCKET ¹ FACIL:$0-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 AUTH. NAME AUTHOR AFFILIATION KAMMER,D.ST Tennessee Valley Authority

'ERIGUE,O.J. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 93-006-00:on 930525,initiation of manual scram d'ue to IRMs indication of downscale & blocked control rod movement in both insert & withdraw directions.C/As:RWM setting for insert error was reset.W/930622 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50..73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-4 1 1 PD2-4-PD 1 1 ROSS,T. 1 1 INTERNAL: ACNW 2 ACRS 2 2 AEOD/DOA 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 NRR/DE/EELB 1 1 NRR/DE/EMEB 1 NRR/DORS/OEAB 1 1

'NRR/DRCH/HHFB 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 NRR/DRIL/RPEB 1 1 NRR/DRSS/PRPB 2 ~NE@/DSSA/SPLB 1 1 NRR/DSSA/SRXB 1 REGLE~ 02 1 1 RES/DSIR/EIB 1 RGN2 FILE 01 1 1-EXTERNAL EG&G BRYCEF J H 2 2 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 . 1 NSIC POORE,'W. 1 1 NUDOCS FULL TXT 1 1 NOTE TO ALL"RIDS" RECIPIENTS:

PLBASE HELP US TO REDUCE WASTEI CONTACI'HE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISTIUBUTION LISIS FOR DOCUMENTS YOU DONT'NEEDl FULL TEXT CONVERSION REQUIRED TOTAL NUMBER- OF COPIES REQUIRED: LTTR 32 ENCL 32

Tennessee Valley Authority. Post Office Box 2000, Decatur, Alabama 35609.2000 O. J. "Ike" Zeringue Vice President. Browns Ferry Nuclear Plant

'JUN S 2.>993

.U.S. Nuclear Regulatory. Commission ATTN: Document Control 'Desk Washington, D.C. 20555

Dear Sir:

TVA BROWNS FERRY NUCLEAR PLANT (BFN) UNITS 1, 2~ AND 3 DOCKET NOS. 50-259, 260, AND 296 FACILITY OPERATING LICENSE DPR-33, 52,, AND 68 LICENSEE EVENT REPORT 50-260/93006 P

The enclosed report provides details concerning the manual reactor shutdown resulting from intermediate range monitors indicating downscale .and by control rod movement being blocked. This event occurred during startup from the Unit 2, Cycle 6 refueling outage.

This report is submitted in accordance with 10 CFR 50.73(a)(2)(iv).

C Sincerely,

(

>~i//A'nclosure cc: See page 2

'OC'5 4p 9306290277 930622 PDR ADOCK 05000260 S PDR

Ik 0 2

U.S. Nuclear Regulatory Commission JON 22 1993 cc (Enclosure):

INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, Georgia 30339 Paul Krippner American Nuclear Insurers Town Center, Suite 300S 29 South Main Street West Hartford, Coiinecticut 06107 NRC Resident Inspector Browns Ferry Nuclear Plant

,Route 12, P.'0. Box 637 Athens, Alabama 35609-2000 Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 2900 Atlanta, Georgia 30323 Thierry M. Ross U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852

I~ Ik NRC Form 366 NUCLEAR REGULATORY COWISSION Approved OHB No. 3150-0)04 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

FACILITY NAHE (1) IDOCKET NUHBER (2) I rwn F N r 1 TITLE (4) Hanual Scram After Hultiple Intermediate Range Honitors Downscale Indications.

V 0 V V I I I I I SEQUENTIAL I REVISIONI I I I FACILITY NAHES IDOCKET NUHBER(S Y Y A N Y N I I I I I I I 0622 93 I I I OPERATING I ITHIS REPORT IS SUBHITTED PURSUANT TO THE REQUIREHENTS OF 10 CFR g:

NODE I I 1 w 1 N 120 402(b) l20.405(c) IMI50 73(a)(2)(lv) 173.71(b)

POWER I )20.405(a)( l)(i) l50 36(c)( 1) I l50.73(a)(2)(v) I73 71(c)

LEVEL I I l20 405(a)( l)(ii) )50.36(c)(2) ] )50.73(a)(2)(vii) ]OTHER (Specify in 1 )20.405(a)( l)(iii ) )50.73(a)(2)(i)(B)J )50.73(a)(2)(viii)(A) Abstract below and in

)20.405(a)(l)(iv) )50.73(a)(2)(ii) J

)50.73(a)(2)(viii)(B) Text, NRC Form 366A)

.4 1 v .7 NAHE 0 Krwnr ml'n I AREA CODE I IREPORTABLEI I I IREPORTABLEI I I I NN HNF T P PNN I I I I I I P D 1 EXPECTED i N I SUBHI SSION I I I N 0 ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

On May 25, 1993, at 1926, with the reactor critical during startup and power increasing at a 125 second period, multiple intermediate range monitor (IRM) downscales were received while changing from range six to seven. IRM C was returned to range six resulting in a Reactor Protective System half scram. When the control rod was inserted to lower power, the control rod double notched. With the Rod Worth Minimizer (RWM) set for zero insert errors, thi.s double notching resulted in an insert rod block. Due to the IRMs indicating downscale and control rod movement blocked in both the insert and withdraw directions, a manual scram was initiated at 1936 on May 25, 1993.

The multiple IRM downscale readings were due to the lack of any requirement to ensure the IRM transition gain is correctly adjusted at power'hen changing from the range six to the seven. During the subsequent startup, the RWM setting for insert errors was reset at two and the IRM transition gain was adjusted during the changing from six to seven. TVA will revise the startup procedure and the technical instruction to ensure the IRM transition gain is adjusted to ensure a smoother transition from range 6 to 7. TVA will revise the appropriate startup instructions to ensure the RWM error settings are appropriate.

NRC Form 366(6-89)

II ~

i

NRC Form 366A U.. NUCLEAR REGULATORY COHNISSION Approved OMB No. 3150-0104 (6-B9) Expires LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION 4/30/92'ACILITY NANE (1) IDOCKET. NUNBER (2)

I USE(UENTIAL i tREVISION)

Browns Ferry Unit 2 I A I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

I. PLMT CONDITIONS Units 1 and 3 were defueled. Unit 2 was'n startup mode at zero MWT and zero psigo II. DESCRIPTION OF EVENT A. ~t:

On May 25, 1993, at 1926, with the reactor critical during startup and power'ncreasing at a 125 second period, multiple Intermediate Range Monitor (IRM) [IGI downscales were received while changing from the range six to seven. IRM C was returned to range six resulting in a Reactor Protective System (RPS) [JC] half scram. When a control rod'as inserted to lower power, the control rod double notched. With the RWM set for zero insert errors, this double notching resulted in an insert rod block. Due to the IRMs indicating downscale and control rod movement blocked in both the insert and withdraw directions, a manual scram was initiated at 1936 on May 25, 1993.

This event is being 'reported in accordance with 10 CFR 50.73(a)(2)(iv) as an event or condition that resulted in a manual or automatic actuation of an Engineering Safety Feature.

t t t t B.

~t:

n None.

C. t May 25, 1993 at 1914 CDT Unit' was declared critical.

May 25, 1993 at 1926 CDT IRMs C, D, E, F, and H indicated downscale when ranging from six to seven.

May 25, 1993 at 1928 CDT IRM C switched to range six. A half scram resulted. IRM C returned to range seven and the half scram reset.

NRC Form 366(6-89)

NRC Form 366A (6-89)

U. NUCLEAR REGULATORY COHHISS ION LICENSEE EVENT REPORT (LER) t Approved OHB No. 3150-0104 Expires 4/30/92 TEXT CONTINUATION FACILITY NAHE (1) iDOCKET NUHBER (2) H P I / SEQUENTIAL / i REVISIONS Browns Ferry Uni t 2 I I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

May 25, 1993 at 1933 CDT Control Rod 42-39 double notched with a resulting RWM rod insert block.

May 25, 1993 at 1936 CDT The reactor was manually scramed.

May 25, 1993 at 2230 CDT A four-hour report was made to NRC in accordance with 10 CFR 50.72(b)(2)(ii).

D. th t A None.

E. th The operators recognized the control rod insert block due to a RWM insert error and a rod withdrawal block due to the downscale IRMs and ini.tiated a manual scram.

When control rod movement was blocked in both directions, a manual scram was initiated.

t t When the IRMs indicated downscale readings, rod withdrawal was blocked.

When a control rod was inserted to reduce power,- the control rod double notched. The double notching of control rod appears to be due to the relatively quicker response time of that control rod to an insert signal when compared to the other. With the RWM set for zero insert errors, thi.s double notching resulted in an insert rod block. Thus, the systems responded as designed.

III. -

CAUSE OF THE EVENT With the IRMs indicating downscale and control rod movement blocked in both the insert and withdraw directions, a manual scram was initiated.

NRC Form 366(6-89)

~I 4

NRC Form, 366A U. UCLEAR REGULATORY COHHISSION Approved OHB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAHE (1) IDOCKET NUHBER (2)

I I I I SEqUENTIAL I I REVISION I I I I I Browns Ferry Uni t 2 I Y A I I I l 4

TEXT (If more space is required, use additional NRC Form 366A's) (17)

8. gggtgIIgag-The root cause of this event was determined to be the lack of any requirement to ensure the IRM transition gain is correctly adjusted at power when changing from the range six to the seven.

C. t t A contributing cause of this event was use of the nominal IRM gain settings. These settings were based on calculations instead of real data.

IV. ANALYSIS OF THE EVENT The IRMs monitor neutron flux during the period from the time of initial criticality to run mode. Their purpose is to prevent fuel damage due to operational transients that occur during this intermediate power range. When the IRMs indicated downscale, rod withdrawal was blocked as designed. An attempt to bring, the IRMs back on scale was then made, resulting in an insert rod block when the control rod double notched.

With questionable IRM indications, all control rod movement blocked, and no way to unblock control rod movement without defeating the RWM function and inserting a significant number of additional control rods, Operations personnel discussed the available options and decided to initiate a manual scram.

Although the IRMs had less than desirable indications, all systems worked as designed- Operations personnel responded appropriately and in a conservative manner. There are no nuclear safety implications from this event, therefore, the safety of the plant .personnel and the public was not compromised.

V. CORRECTIVE ACTIONS A. tv t The RWM setting for insert error was reset at two which is allowable per the analysis. The IRM transition gain was adjusted during the ranging from six to seven to,ensure a smooth transition.

NRC Form 366(6-89)

41 NRC Form 366A U.. NUCLEAR REGULATORY COHHISSION Approved OHB No. 3150-0104 (6-89) Expires 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAHE (1) IDOCKET NUHBER (2)

I I. I I SEQUENTIAL I I REVI SION I I I I I Browns Ferry Unit 2 I I I I I TEXT (If more space is required, use additiona1 NRC Form 366A's) (17)

B. tv t t Startup procedure, "Startup Following Refueling Outage," will be revised to caution the operator that the IRM transition gain adjustment may be required when changing from the range six to seven and to perform the necessary calibration to ensure adequate gain setting.

2. Technical Instruction, "Nuclear Instrumentation Initial Gains Adjustment" will be, revised to use values that will result in a smoother transition from range six to range seven for initial IRM gain adjustments.

3. Startup Instructions, "Unit Startup From Cold Shutdown to 'Hot Standby," "Unit Startup From Cold .Shutdown To Power Operation And Return To Full Power From Power Reduction," and "Unit Startup From Hot Standby To Power Operation" will be revised to ensure that the RWM error settings are appropriate.

VI. ADDITIONAL INFORMATION None.

B. v None.

NRC Form i366(6-89)

0 NRC Form 366A (6-89)

U.. UCLEAR REGULATORY COMNISSION LICENSEE EVENT REPORT (LER) t Approved OHB No. 3150-0104 Expires 4/30/92 TEXT CONTINUATION FACILITY NAME (1) (DOCKET NUNBER (2)

I i SE(UENTIAL i iREVISIONt Browns Ferry Uni t 2 I N 8 I I I I TEXT (If more space is required, use additional NRC Form 366A's) (17)

VII. COMMITMENTS

1. Startup Procedure, "Startup Following Refueling Outage" will be revised to warn the operator that the IRM transition gain adjustment may be required when changing from the range six to seven and to perform the necessary calibration to ensure adequate gain setting. This will be completed by July 30', 1993.

2. Technical Instruction, "Nuclear Instrumentation Initial Gains Adjustment" will be revised to use values that will result in a smoother transition from range six to range seven for initial IRN gain adjustments. This will be completed by August 27, 1993.

3. Startup Instructions, "Unit Startup From Cold Shutdown to Hot Standby,"

"Unit Startup From Cold Shutdown To Power Operation And Return To Full Power From Power Reduction," and "Unit Startup From Hot Standby To Power Operation" will be revised to ensure that the RWM error settings are appropriate. This will be completed by July 30, 1993.

Energy Industry Identification System (EIIS) system and component codes are identified in the text with brackets (e.g.,

[ZZ]).'RC Form 366(6-89)

0