ML18153C507

Special Rept:On 901224,quadrant to Average Power Tilt Exceeded 2.0% for Greater than 24 H.Caused by Xenon Transient & Change in Tave Coupled w/pre-existing Core Asymmetry.Isophase Bus Duct Shunts Repaired

ML18153C507
Person / Time
Site:	Surry
Issue date:	01/23/1991
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
91-026, 91-26, NUDOCS 9101300212
Download: ML18153C507 (3)

Text

ACC'ELERATED DjOOBUTION DEMONS'jATION. SYSTEM REGULATORY INFORMATION-DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9101300212 DOC.DATE: 91/01/23 NOTARIZED: NO DOCKET.#*

• FACIL:50-281 Surry Power Station,. Unit 2,-Virginia Electric & Powe 05000281 AUTH. NAME AUTHOR AFFILIATION* . ..

STEWART, W. L.* Virginia Power (Virginia Electric &* Power. Co.)

RECIP. NAME * . RECIPIENT AFFILIATION . . . . .

Document .Control Branch (Document Control Desk) R

SUBJECT:

Special rept:on 901224,quadrant to average power tilt* I exceeded 2. 0%. for greater than 24 h. caused by xenon.

• transient & change in Tave coupled w/pre-existing core *D asymmetry. Isophase bus duct shunts repaired ..

s DISTRIBUTION CODE: IE22D. COP_IES ~ECEIVED:LTR _I ENCL l_

• SIZE: p_

TITLE: 50. 73/50. 9 Licensee Event Report (LER), Incident Rpt, et-c-.-~-- I

• NOTES: lcy NMSS/IMSB/PM. 05000281 A RECIPIENT COPIES RECIPIENT COPIES D ID CODE/NAME LTTR ENCL ID CODE/NAME .LTTR.ENCL PD2-2 LA 1 1 PD2-2 PD 1 1 D BUCKLEY,B 1 1 s

INTERNAL: ACNW 2 2 ACRS 2 2*

AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DET/ECMB 9H .1 1 NRR/DET/EMEB 7E 1 1 NRR/DLPQ/LHFBll 1 *1 NRR/DLPQ/LPEBlO 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPBl 1 2 2 .. .* NRR/DST/SELB 80 1 1 NRR/DST/SICB 7E* 1 1 d'~PLB8g~ 1 1 NRR/DST/SRXB BE 1 .1 1 1 RES/DSIR/EIB 1 1 RGN2 .. FILE 01 1 ~ 1 EXTERNAL: EG&G BRYCE,J.H 3 3 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MAYS,G 1 1 NSIC MURPHY ,G.A. 1 1 NUDOCS FULL TXT 1 1 R NOTES: 1 1 I D

s I

A D

D NOTE TO ALL "RIDS" RECIPIENTS:

. .* . - - . . . . s PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROO!'v1 Pl-37 (EXT. 20079) TO ELIMINATE YOUR NM1E FROM D1STRIBU1:f0N LISTS FOR DOCUMENTS_ YOU DON'T NEErn TOTAL NUMBER OF COPIES REQUIRED: LTTR. 34 ENCL 34 1~~--

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VIRGINIA ELECTR;C AN~ POWER Co~PANY RICHMOND, VIRGINIA 23261 I

January 23, *1991 United States Nuclear Regulatory Commission . Serial No. 9-1-026 Attention: Document Control Desk NO/RJS Washington, D. C.

• 20555

• Docket No. . 50-281 License. No. . DPR-37 Gentlemen: *

• VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION. UNIT 2 SPECIAL REPORT

• QUADRANT TO AVERAGE POWER TILT EXCEEDS 2.0% FOR GREATER THAN 24 HOURS Surry Technical Specific.ation 3.12.B.7.a requires an evaluation be performed and a special report issued to the Nuclear Regulatory Commission un.der certain conditions when the quadrant to average power tilt .exceeds 2.0% for greater tha11 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.. On December 24, 1990, the Surry Unit 2 quadrant to average -power tilt exceeded 2.0%

for greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. A description of the circumstance$ surrounding this event

• and an evaluation of the cause* of the event is provided in the Attachment to this letter.

Should you have ariy further qu_estions, please contact us.

Attachment cc: U. s: Nuclear. Regulatory Commission*.

Region 11 * *

• 101 Marietta Street, N. W. -

Suite 2900 Atlanta, Georgia 30323 -

Mr. W. E. Holland NRC Senior Resident Inspector Surry Power Station

~101300212 910123 P**D*R** A[1r_1c.¥ b5000281 PDF:

• ATTACHMENT.

SPECIAL REPORT QUADRANT TO AVERA"GE POWER TILT EXCEEDS 2.0%

FOR GREATER IJ1AN 24

• H04RS on December 23, 1990, a Unit 2 controlled rampdown was exe.cuted from 90% power.

to 54% power in an attempt to reduce the temperature on three isolated phase bus duct structural supports. The supports were being heated by the circumferential degradation of a section of bus duct shunt straps. Prior to the controlled rampdown, Surry Unit 2 had been operating at 90% reactor power with the control rod in position M-12 inoperable and withdrawn two steps. The Hi Flux Trip Setpoint was reduced to 97% to allow power operation with control rod M-12 inoperable and withdrawn to the two step position. A manual radial tilt calculation performed subsequent to the ramp at 201 O hours, indicated an excore quadrant power tilt (QPT) of 4.4%.

Following the determination that OPT was greater than 2.0%, the Hi Flux Trip Setpoint was verified to. be reduced by at least 2% for every* 1% of quadrant power tilt as required by the Technical Specification 3.12.B:6.b. Hourly manual QPT calculations were initiated to monitor and trend the tilt. These calculations showed QPT to be trending downward and it was anticipated that it would fall below 2.0% prior to exceeding the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> limit. As a precautionary measure, preparations were initiated to reduce Overpower Delta-Temperature and Overtemperature Delta-Temperature trip setpoints should the excore tilt exceed 2.0% for more than the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> limit as required by the Technical Specifications.

At 201 O hours on December 24, QPT exceeded 2.0% for greater than a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period and an NRC Resident Inspector was notified. The reduction in Overpower Delta-Temperature and Overtemperature Delta-Temperature trip setpoints and incore flux maps were completed on December 25, 1990. The nuclear engineering staff concluded that the limits placed on core peaking factors by TS 3.12.B.1 were not exceeded during this event. This conclusion was based upon: 1) incore maps taken on December 21 at 90% power, 2) the subsequent reduction in power on December 23, 1990, and 3) the incore maps taken on December 25 at 54% power. Furthermore, the safety analysis performed to justify power operation with control rod M-12 inoperable evaluated the impact of a stuck rod on QPT and provided an analyzed envelope for operation of up to 5.0% QPT with the Hi Flux Trip Setpoint at 97%.

The xenon transient and change in Tave associated .with the rampdown, coupled with the preexisting core asymmetry due to operation with control rod M-12 inserted, resulted in the observed excore tilt. Since the core peaking factors were within limits, this event did not constitute an unreviewed safety question nor were the health and safety of the public affected. Following repairs to the isophase bus duct shunts, the reactor was ramped to 90% power and the QPT returned to less than 2.0%

The company's nuclear engineering staff is on call to assess indicated asymmetries and to determine bot channel factors for their impact on the M-12 safety analysis as soon as practical following QPT exceeding 2.0%. *