ML17305A627

LER 90-001-00:on 900223,manual Reactor Trip Occurred During Planned Shutdown.Caused by Axial Shape Index Approaching Limit at End of Core Life Shutdown.Reactor Manually Tripped So That Channel Trip Setpoint Not exceeded.W/900326 Ltr

ML17305A627
Person / Time
Site:	Palo Verde
Issue date:	03/26/1990
From:	Bradish T, James M. Levine ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
192-00640-JML-T, 192-640-JML-T, LER-90-001-02, LER-90-1-2, NUDOCS 9004040165
Download: ML17305A627 (18)

Text

ACCELERATED DISHUBUTION DEMONSHRATION SYSIKM

~ ~

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9004040165 DOC.DATE:,90/03/26 NOTARIZED: NO 'DOCKET,.C FACIL:STN-50-529 Palo Verde Nuclear Station, Unit 2, Arizona Publi 05000529 AUTH. NAME AUTHOR AFFILIATION BRADISH,T.R. Arizona Public Service Co. (formerly Arizona Nuclear Power LEVINE,J.M. Arizona Public Service Co. (formerly Arizona Nuclear Power RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 90-001-00:on 900223,manual reactor shutdown.

trip during planned W/9 'ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED: LTR TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

J ENCL g SIZE:

NOTES:Standardized plant. 05000529 RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA .1'1 1- PD5 PD 1 1 PETERSON,S. 1 INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB'EDRO 1 1 AEOD/ROAB/DS P 2 2 1 1 NRR/DET/ECMB 9H 1 .1 NRR/DET/EMEB9H3 1 1 NRR/DET/ESGB 8D 1 1 NRR/DLPQ/LHFB1'1 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB11 1 .1 NRR/DREP/PRPBll 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICB. 7E 1 1 SZ LB8Dl 1 1 NRR/DST/SRXB 8E 1 1 REG F 02 1 "1 RES/DSIR/EIB 1 1 F1LE 01 1 1 EXTERNAL EGGG STUART g V A 1 1 L ST LOBBY WARD 1 1 LPDR 1 1 NRC PDR 1 1 NSIC MAYS,G 1 1 NSIC MURPHYgG ~ A 1' NUDOCS FULL TXT 1 1 NOTES NOTE TO ALL "RIDS" RECIPIENIS:

PLEASE HELP US TO REDUCE, WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES -REQUIRED: LTTR 35 ENCL 35

,I

~ I

Arizona Public Service Company PALO VERDE NUCLEAR GENERATING STATION P.O. BOX 52034 ~ PHOENIX. ARIZONA85072-2034 JAMES M. LEVINE 19 2-"006'4 0- JML/TRB/RKR VICE PRESIDENT March 26, 1990 NUCLEAR PRODUCTIDN U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unit 2 Docket No. STN 50-529 (License No. NPF-51'),

Licensee Event Report 90-001-00 File'0-020-404 Attached please find Licensee Event Report (LER) No. 90-001-00 prepared and submitted pursuant to 10CFR50.73. In accordance with 10CFR50.73(d), we are herewith forwarding a copy of the LER to the Regional Administrator of the Region V office.

If you have any questions, please contact T. R. Bradish, (Acting) Compliance Manager at (602) 393-2521.

Very truly yours, JML/TRB/RKR/tlg Attachment cc: W. F. Conway (all with attachment)

E. E. Van Brunt J. B. Martin D..H. Coe

. T. L. Chan A. C. Gehr J. R. Newman INFO Records Center 90o-'2 90LI 'og.

AD O~~0LI052'r'DFl

. poc

0 NRC Forrrr 355 V <L NUCLEAR REOULATORY COMMISSION (94)3 I APPROVED OMS NO. $ 1500104 LICENSEE EVENT REPORT {LER) EXPIRES: 5/31/SS FACILITY NAME (I) DOCKET NUMBER (1) PA Palo Verde Unit 2 0 5 0 0 0 5 2 9 1 OFO TITLE 141

'Mannual Reactor Tri Durin Planned Shutdown EVENT DATE(5I 7'ONTH LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (5)

DAY YEAR YEAR SSOVSNTI*L NUMSEII 4 NUMBER MONTH DAY YEAR FACILITYNAMES DOCKET NUMBERIS) 0 5 0 0 0 02 23 9 090 0 0 1 p p 0 3 2 6 9 0 0 5 0 0 0 OPERATINO THIS REPORT IS SUBMITTED PURSUANT 7 0 THE REOUIREMENTS OF 10 cF R ()I ICnrck onr or mort ol tnr Iollowlntl (I'I MODE (Sl 20.402(4) 1 20.405(cl 50.7$ (el(1)(lr) 7$ .7((SI tOWER 20.405( ~ ) (I 1(il SOM(cl(II 50.734) (2l(el 7$ .71(cl LEVEL p 20.405 (e) II I (4) 50.35(c) (1) 50.7$ (e) (2)(rS I OTHER ISprcily in At<et<oct S~

o g'+~+' : 4 20.405 (el(1)(4l) 50,73(el(2)(ll 50,734) (2)(r41) (Al orlow re<I in Fret, iVRC Form

$ 5((AI 20.405( ~ l(1)(lr) 50.73(el(2) (4( 50.734) (2) (rl4) (5) 20.405( ~ ) (I ) (rl 50.734) (2) (Sl) 50.73(e) (2)(el LICENSEE CONTACT FOR THIS LER (12I NAME TELEPHONE NUMBER AREA CODE Thomas R. Bradish (Acting) Compliance Manager 6 023 93 2 521 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAVSE SYSTEM COMPONENT MANUFAC.

TVRER TO NPRDS '4 .~~<4' REPORTABLE .8;.<PS<o

. ~

' CAUSE SYSTEM COMPONENT MANUFAG TURER EPORTABLE TO NPRDS

ÃL%%I SUPPLEMENTAL REPORT EXPECTED (Ill MONTH DAY YEAR EXPECTED SUBMISSION DATE (151 YES IIIyrL comPlrtr EXPECTED SVSMISSIOII DATE/ NO ABSTRACT ILlmlt to tr00 u>>crt, ir., rpproeimrtely Iiltrrn tintfr tl>>cr typewrinrn linN/ (15)

At approximately 2301 MST on February 23, 1990, Palo Verde 'Unit 2 was in Mode 1 (Power Operation) at. approximately 24 percent power during a planned shutdown for a refueling outage when the reactor was manually, tripped by a reactor operator because the Axial Shape Index was,approaching its trip setpoint on the Core Protection Calculator. The reactor trip was di'agnosed as an uncomplicated reactor trip. No other safety system responses occurred and none were required. At approximately 2311 MST on February 23, 1990 the plant was stabilized in Mode 3 (Hot Standby) at normal temperature and pressure.

The cause of the manual reactor trip was that the Axial Shape Index was approaching its trip setpoint during an end of core life shutdown. The corrective action was to trip the reactor and ensure the Axial Shape Index remained within limits.

A previous similar event was reported in LER 528I/'87-018-01.

NRC eorm 3el

ig ll l

NRC FORM 355A U.S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 31604)04 (SJIQ)

EXPIRES: 1/30/Q2 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT ILER) INFORMATION COLLECTION REOUEST: 60A) HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (P430). U.S. NUCLEAR REGULATORY COMMISSION. WASHINGTON. DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31604)(M), OFFICE OF MANAGEMENTAND BUDGET. WASHINGTON, DC 20503.

FACILITYkAME (1) DOCKET NUMBER (2) LER NUMBER (5) PAGE (3)

YEAR SEOVENTIAL 4EV0 ION NVMSER NVM 54 Palo Verde Unit 2 0 5 0 0 0 52 990 0 0 1 0 002 oF 0 7 TEXT llfmO>> NNce /T nocked, u>> afdidoAAIHRC Form 35543/ ()7)

DESCRIPTION OF WHAT OCCURRED:

A. Initial Conditions:

At approximately 2301 MST on February 23, 1990, Palo Verde Unit 2 was in Mode 1 (Power Operation) at approximately 24 percent power during a planned shutdown for refueling.

B. Reportable Event Description (Including Dates and Approximate Times of Major Occurrences):

Event Classification: Any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature (ESF)(JE),

including the Reactor Protection System (RPS)(JC).

At approximately 2301 MST on February 23, 1990, while shutting down for a planned refueling outage, the Unit 2 reactor (RCT)(AC) was manually tripped by a reactor operator (utility, licensed) due to the Axial Shape Index approaching its trip setpoint on the Core Protection Calculator (CPU)(JC). The reactor trip was diagnosed as an uncomplicated reactor trip. No safety system responses occurred and none were required. At approximately 2311 MST on February 23, 1990, the plant was stabilized in Mode 3 (Hot Standby) at normal temperature and pressure.

The Axial Shape Index is defined as "the power generated in the lower half of the core less the power generated in the upper half of the core divided by the sum of these powers" (Technical Specification Definition 1.2). Axial Shape Index is calculated in each of the four Core Protection Calculator Channels. When a Core Protection Calculator Channel calculates an Axial Shape Index greater than .50 or less than minus .50, it generates a trip signal to the Plant Protection System (JC). The Plant Protection System has a two-out-of-four logic thus requiring Axial Shape Index trip signals from two Core Protection Calculator Channels to initiate a reactor trip.

Prior to the event, at approximately 1700 MST on February 23, 1990, Unit 2 was at approximately 97 percent power when boration was started to shutdown the reactor for the scheduled refueling outage. During the reactor shutdown, Axial Shape Index increased in the negative direction. The Group 4, Group 5, and Part Length Control Element Assemblies (CEAs)(ROD)(AA) were inserted in NRC Form 355A (58Q)

iJ IO

'4

NRC FORM 366A UA. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3)504)104 (64)9) EXP I R ES.'/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LER) INFORMATION COLLECTION REOUEST: 50Al HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (F430). U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (3)504)104), OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (ll DOCKET NUMBER 121 LER NUMBER (6) PAGE (3)

YEAR Q~ EEQVENTIAI NVM E4 Pk 4EVISK)N

>6> NVMEE4 Palo Verde Unit 2, 0 s o 0 0 529 9 0 001 00 03 QF 0 7 TEXT /// more 4/rece /4 tJJr/rerL cree er/r/iaorre/HRC Form 36649/ (I2) accordance with an approved procedure to dampen the negative shift in Axial Shape Index. During the CEA insertion, Axial Shape Index initially became less negative, but then the trend continued in the negative direction. At approximately 2023 MST, insertion of Group 4 CEAs was stopped in accordance with an approved procedure due to indication of a potential ground. Manipulation of the Group 5 and Part Length CEAs continued to optimize Axial Shape Index control.

At approximately 2130 MST with the reactor at approximately 40 percent power and decreasing due to increasing Xenon concentration, a maximum dilution (120 gpm) was started to slow the power decrease and stabilize Axial Shape Index. At approximately 2149 MST,, with Axial Shape Index approaching the limit (minus .28) of Technical Specification 3.2.7.a, the Group 4 CEAs insertion was continued in accordance with an approved procedure. No grounds were detected .during this insertion.

At approximately 2218 MST on February 23, 1990, the Axial Shape Index decreased below the limit (minus .28) of Technical Specification Limiting Condition for Operation 3.2.7.a and the associated ACTION statement was entered. The Group 4, Group 5, and Part Length CEAs were again manipulated in accordance with an approved procedure in an attempt to control Axial Shape Index without success.= The Reactor Engineer (utility, non-licensed) and Control Room Shift Supervisor (utility, licensed) discussed the situation and determined that any further power reduction would increase the negative shift in Axial Shape Index. At approximately 2256 MST, the Shift Supervisor and Operations Supervisor (utility, licensed) were discussing the potential for Axial Shape Index approaching the trip setpoint on the Core Protection Calculator. At this time the Channel D Core Protection Calculator generated a trip signal to the Plant Protection System based on Axial Shape Index exceeding its trip setpoint (minus 0.50). The Shift Supervisor and Operations Supervisor decided to manually trip the reactor if any of the untripped Core Protection Calculator channels Axial Shape Index reached minus 0.49.

Axial Shape Index continued to approach the trip setpoint for the Core Protection Calculators non-tripped channels and at approximately 2301 MST on February 23, 1990, the reactor was manually tripped when Channels A and B Core Protection Calculators Axial Shape Index reached minus 0.49. The reactor trip was uncomplicated and at approximately 2311 MST on February 23, 1990, the plant was stabilized in Mode 3 at normal temperature and NRC Ferro 366A (669)

i

~ 0 f.

NRC FORM 366A ILS. NUCLEAR REGULATORY COIAMISSION APPROVEO 0MB NO. 31500104 (64)9)

E XP IR ES: 4/30/92 ESTIMATED BURDEN PEA RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LER) INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWAAO COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH IP430), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31500104). OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON,OC 20503.

FACILITY NAME (1) DOCKET NUNIBER (2) LER NUMBER (6) PAGE (3)

SEQUENTIAL REVISION YEAR NUMSER NUMSER Palo Verde Unit 2 0 s 0 0 o,529 9 0 '001 00 04 OF 0 7 TEXT /I/msve SFSCs /4 NqukwL s44 SI/I/e'an4/H/IC Foml 36643/ (17) pressure. There were no Engineered Safety Features responses or actuations and none were necessary.

C. Status of structures, systems, or components that were inoperable at the start of the event that contributed to the event:

Not applicable - no structures, systems or components were inoperable which contributed to this event. The Group 4 CEAs were not inoperable. Their use was restricted based on past experience and justification for continued operation.

D. Cause of each component or system failure, if known:

Not applicable - no component or system failures were involved.

E. Failure mode, mechanism, and effect of each failed component, if known:

Not applicable - no component failures were involved.

F. For failures of components with multiple functions, list of systems or secondary functions that were, also affected:

Not applicable - no component failures were involved For failures that rendered a train of a safety system inoperable, estimated time elapsed from the discovery of the failure until the train was returned to service:

Not applicable - there were no failures that rendered a train of a safety system inoperable.

H. Method of discovery of each component or system failure or procedural error:

Not applicable - there were no component or system failures or procedural errors.

Cause of Event:

The cause of the manual reactor trip was that the Axial Shape Index was approaching its limits during an end of core life shutdown (SALP cause code'). Past industry experience shows it is difficult to maintain operating limits, especially Axial Shape Index, during an end of cor'e life shutdown, particularly with NRC Foml 366A (689)

IO IO l

~~

NRC FORM 366A US. NUCLEAR REGULATORY COMMISSION APPROVEO 0MB NO. 31500(04 (609)

E XPIR ES; 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LER) INFORMATION COLLECTION REQUEST: 500 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (P430). U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON. DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (3)504)104), OFFICE OF MANAGEMENTAND BUDGET. WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR I: L1 SEQUENTIAL 4~% NVMoerl jg rrU>>

~

AEVISrON ell Palo Verde Unit 2 0 5 0 0 0 5 2 9 0 001 00 05 oF 0 7 TEXT llfmore 4r>>ce Jrr nrRrked, rree Arr Ike>>l NRC Arrrr 3664 BJ (Ill large (height) cores. The shutdown plan, based on an evaluation of core parameters during a normal shutdown, predicted Axial Shape Index would approach its limit at the end of the shutdown. As described in Section I.B, the shutdown plan did not maintain Axial Shape Index within its limits. There were no personnel errors or procedural errors that contributed to this event. There were no unusual characteristics of the work location that contributed to the event.

The restriction to movement of Group 4 CEAs from approximately 2023 MST to approximately 2149 MST due to the indicated ground as described in Section I.B, may have contributed to the event.

However, due to operator actions to control Axial Shape Index as a result of the restriction on movement of Group 4 CEAs, the exact effect cannot be accurately determined. The CEA grounding problem had been identified prior to this event. Justification for continued operation had previously been prepared. A procedure had been approved for CEA operation when there are indicated grounds on CEAs,.

Safety System Response.:

A manual reactor trip occurred due to the Axial Shape Index approaching its trip setpoints on the Core Protection Calculators as described in Section I.B. No other safety systems responses occurred and none were required during this event.

Failed Component Information:

Not applicable - no failed components were involved.

II. ASSESSMENT OF THE SAFETY CONSEQUENCES AND IMPLICATIONS OF THIS EVENT:

The reactor trip was manually initiated prior to the reactor exceeding a Core Protection Calculator trip setpoint and was diagnosed as an uncomplicated reactor trip. No safety systems response was required.

The event did not result in any challenges to fission product barriers or result in any releases of radioactive materials. Therefore, there were no safety consequences or implications as a result of this event.

This event did not adversely affect the health and'afety of the public.

NRC Forrrr 366A (64)9l

O. i~

l'

NRC FORMSSSA US. NUCLEAR AEGULATORY COI4MISSION APPROVEO DMS NO. 3(504))04 (5SQ) ~

EXPHI ES: 4/30t02 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LER) INFORMATION COLLECTION AEQUEST: 500 HRS. FORWARD COMMENTS REGARDING SUROEN ESTIMATE TO THE RECOADS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (P4)30), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON. DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31504104), OFFICE OF MANAGEMENTAND SUDGET, WASHINGTON, OC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMSER LS) PAGE (3)

REVISION YEAR NUMSER NUM ER Palo Verde Unit 2 0 5 0 0 0 5 2, 9 9 0 P P=l 0 0 0 OF p TEXT tlt moro Spore ts orN)rorL Irro eArko'arel ttRC Form SSSAS) (IT)

III. CORRECTIVE ACTIONS:

A. Immediate:

1 The reactor was manually tripped to ensure the Axial Shape Index Core Protection Channel trip setpoint was not exceeded.

B. Action to Prevent Recurrence:

Because of the reactor core physical characteristics there is a potential for a reactor trip during an end of core life shutdown. However, APS is enhancing the procedures listed below to reduce the chance of a reactor trip during a planned shutdown.

Procedure 4XOP-XZZ05 "Power Operation", is being enhanced to include a requirement to obtain Reactor Engineering's prediction of important parameters prior to starting a shutdown (when time permits). This requirement is expected to be implemented by October 31, 1990.

B. Procedure 72PR-9ZZ01 "Reactor Engineering Program", is being enhanced to provide more formal control of the information provided to Operations by Reactor Engineering. This is expected to be implemented by October 31, 1990.

The Unit 2 Control Element Drive Mechanism coils are being inspected and re-worked during the current refueling outage to correct CEA grounding indications.

IV. PREVIOUS SIMILAR EVENTS:

LER 528/87-018-01 described an event where the reactor tripped during an end of core life shutdown. The reactor was shutting down to evaluate a possible Reactor Coolant System leak. The reactor trip was automatically initiated when the Core Protection Calculator generated a trip signal to the Plant Protection System due to Axial Shape Index deficient exceeding limits. The root cause of the event was a procedure. The procedure did not contain sufficient strategies for controlling Axial Shape Index at the end of core life. The procedure was updated to include strategies for controlling Axial Shape Index during an end of core life shutdown. Although these were similar events, the corrective action could not have prevented the event NRC Form 36SA (54)9)

NRC FORM 355A US. NUCLEAR REGULATORY CON)MISSION APPROVED OMB NO. 31500104 (589)

EXPIRES: 4/30/92 ESTIMATED'URDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT {LER) INFORMATION COLLECTION REQUEST: 60J) HRS.

REGARDING BURDEN ESTIMATE TO THE RECORDS FORWARD'OMMENTS TEXT CONTINUATION, AND REPORTS MANAGEMENT BRANCH (P430). U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (3(50410(). OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON. DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER IS) PAGE (3)

YEAR NUM Srl '4 N'll. SEQUENTIAL .WA rrEVrSIOrr rrvMFErr Palo Verde Unit 2 o s o o o 5 2 9 90 0 01 0 0 70F 0 7 TEXT /llrrroro Jlro>> /o rooted,'v>> afdio'orro/HRC Frnrr 35/AB) (17) described in this report, even though strategies for controlling Axial Shape Index were used in accordance with the approved procedure.

NRC Form 355A (589)

~1+

j'