ML17305B361

LER 91-001-00:on 910110.determined That Postulated Break in Reactor Coolant Pump High Pressure Seal Cooler Could Result in RCS Leak Outside Containment.Caused by Tube Rupture in Seal Cooler.Rcs Activity monitored.W/910211 Ltr

ML17305B361
Person / Time
Site:	Palo Verde
Issue date:	02/11/1991
From:	Bradish T, James M. Levine ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
192-00713-JML-T, 192-713-JML-T, LER-91-001, LER-91-1, NUDOCS 9102200280
Download: ML17305B361 (20)

Text

ACCELERATED DI TRIBUTION DEMONST ATION SYSTEM REGULATORY XNFORMATION DISTRXBUTION SYSTEM (RIDS)

ACCESSION NBR:9102200280 DOC-DATE- 91/02/11 NOTARIZED:'NO DOCKET I FACIL:STN-50-528 Palo Verde Nuclear Station, Unit 1, Arizona Publi 05000528 AUTHOR AFFILIATION AUTH. NAME BRADISH,.T.R.

LEVINE,J.M.

'rizona Arizona Public Service Public Service Co.

Co.

(formerly Arizona Nuclear Power (formerly Arizona Nuclear Power RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 91-001-00:on 910110.determined that postulated break in reactor coolant pump high pressure seal cooler could result D in RCS leak outside containment. Caused by tube rupture in seal cooler.RCS activity monitored.W/910211 ltr.

DISTRIBUTION CODE: XE22T COPIES RECEIVED:LTR ENCL SIZE:

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

NOTES:STANDARDIZED PLANT 05000528 A D

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL D PD5 LA 1 1 PD5 PD 1 1 TRAMMELL,C 1 1 TRAMMELL,C. 1 1 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/LHFB11 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICB 7E 1 1 Ngg/QSZ~B 1 1 NRR/DST/SRXB 8E RES/DSIR/EIB 1

1 1

1 EG G

FILE FILE '1 1 1 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 NOTES 1 1 D

A D

D NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE O'ASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM P 1-37 (EXT. 20079) TO ELli%11NATE YOUR NAivIE FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEEDI FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 35 ENCL 35

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Arizona Public Service Company PALO VERDE NUCLEAR GENERATING STATION P.O, BOX 52034 ~ PHOENIX, ARIZONA85072-2034 192-00713-JML/TRB/RKR JAMES M. LEVINE VICE PRESIDENT February 1.1, 1991 NUCLEAR PRODUCTION U. S. Nuclear Regulatory Commission Attention: Document Control Desk Mail Station Pl-37 Washington, DC 20555

Dear Sirs:

Sub) ect: Palo Verde Nuclear Generating Station (PVNGS)

Unit 1 Docket No. STN 50-528 (License No. NPF-41)

Licensee Event Report 91-001-00 File: 91-020-404 Attached please find Licensee Event Report (LER) No. 91-001-00 prepared and submitted pursuant to 10CFR50.73. In accordance with 10CFR50.73(d), we are 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, Compliance Manager at (602) 393-2521.

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

J. B. Martin D. H. Coe A. C. Gehr A. H. Gutterman INPO Records Center 9102200280 910 '1 l PETER ADOCK 05000528 S PbR

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NRC FOAM 366 U.S. NUCLEAR REGULATORY COMMISSION (609) APPROVED OMB NO. 31504)104 EXPIRES: 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS INFORMATION COLLECTION AEOUESTr 50/) HRS. FORWARD LICENSEE EVENT REPORT {LER) COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (Pe)30). V.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON. DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31500104). OFFICE OF MANAGEMENTAND BUDGET,WASHINGTON, DC 20503.

FACILITY NAME (I) DOCKET NUMBER l2) PA E Palo Verde Unit 1 0 5 0 0 0 1 OFp 8 TITLE (4)

EVENT DATE I5)

Postulated Reactor'Coolant LER NUMBER (6)

S stem Leak Not Included REPOAT DATE (7)

In Desi n OTHER FACILITIES INVOLVED (6) i MONTH DAY YEAR YEp R ITS sEQUENTIAL ver IIEvrcrQN MONTH DAY YEAR FACI LITY NAMES DOCKET NUMBER(SI NUMBER rebec NUMBER Palo V 0 5 0 0 0 5 0 1 1 0 0 1' 0 0 2 9 1 Palo Verde Unit 3 o 5 o o o 5 3. 0 OPERATING THIS REPORT IS SUBMITTED PURSUANT T0 THE RLOU)REMENTS OF 10 CFR (It /Check one or more of rne foiiowinP/ ill)

MODE (9) 20.402(b) 20.405(c) 50.73(el(2)(iv) 73.71(b)

POWER 20A05(el(i)(i) ill(lv) 50.36(el)1) 50.73(el(2) lr) 73.71(cl LEVEL 1 p p 20A05(sill)(ill S0.36 lc) (2) 50.73(e) l2) (vBI OTHER ISpecifyin Abrrrsct below end in TEL HRC Form 20.405( ~ )ill(ill) 50.73le) (2) li) 60.73(e 1 (2 l(rill)lA) 366A/

20A05(e) 50.73(e) (2)(ID 50.73(el(2) lrliil(BI

~,".~N ., ~ed%'rr;i 20A05( ~ )ll)(v) 50.73( ~ ) (2 1 Bit) 50.73(e) (2) (el LICENSEE CONTACT FOR THIS LER (12I NAME TELFPHONE NUMBER AREA CODE Thomas R. Bradish Com liance Mana er 3 3 2 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPOAT 113)

MANVFAC REPORTABLE MANUFAC EPORTABLE CAUSE SYSTEM COMPONENT CAUSE SYSTEM COMPONENT TVRER TURER TO NPADS W>@%PNk jr MoQ> v(c

~'

vc Ya w4:cA SUPPLEMENTAL REPORT EXPECTED 114) MONTH DAY YEAR EXP EClED SUBMISSION DATE I'ISI YES Iffyet, compiere EXPECTED SV64//SSIOH DATE/

ABSTRACT ILimit to ter/0 rpeceL I e, epproeimereiy fifteen rfnpre.specs typewritren lined (16)

At approximately 1500 MST on January 10, 1991, Palo Verde Units 1, 2, and 3 were in MODE 1 (POWER OPERATION) at approximately 100 percent power when PVNGS Engineering determined that a postulated break in a Reactor Coolant Pump (RCP) high pressure seal cooler could result 'in a reactor coolant system (RCS) leak outside containment. A conservative evaluation of this postulated event based on assumptions used in the Standard Review Plan (NUREG 0800) determined that the Exclusion Area Boundary cumulative thyroid dose could exceed 10CFR100 limits. An evaluation based on existing RCS activity showed that doses would be a small fract:ion of 10CFR100 limits.

The cause was that a tube rupt:ure in the seal cooler and its effect was not considered in the original plant design.

Immediate corrective actions were taken to: 1) monitor RCS act'ivity to ensure 10CFR100 limits would not be exceeded as a result .of this postulated event and.

2) monitor the Nuclear Cooling Water System to provide early detection of a seal cooler leak. A design change is being developed to mitigate the postulated event described in this LER. The design change is expected to be completed in Units 1, 2, and 3 by July 1993.

No previous similar events have been reported in accordance with 10CFR50.73.

NAC Form 366 (649)

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NRC FORM368A US. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 31500108 (SS9)

EXPIRES! 8/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT ILER) INFORMATION COLLECTION REOUESTI 50J> 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 (31504108>, OFFICE OF MANAGEMENTAND BUDGET,WASHINGTON, DC 20503.

FACILITYNAME (11 DOCKET NUMBER (21 LER NUMBER (8) PAGE (3)

YEAR SEOUSNTIAL REVISION rgp NUM88R NUM SII Palo Verde Unit 1 0 5 0 0 0 5 OF TEXT IIImoro oporo II mordrod, Ir(o odds/onoIHRC Form 35643/ ((7)

I. DESCRIPTION OF WHAT OCCURRED:

A. Initial Conditions:

At approximately 1500 MST on January 10, 1991, Palo Verde Units 1, 2, and 3 were in MODE 1 (POWER OPERATION) at approximately 100 percent power.

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

Event Classification: A condition that was outside the design basis of the plant.

At approximately 1500 MST on January 10, 1991, PVNGS Engineering determined that a postulated break in the Reactor Coolant Pump (RCP)(P)(AB) high pressure seal cooler (SEAL)(CLR)(AB) could result in a reactor coolant system (RCS)(AB) leak outside the Containment building (NH). A conservative evaluation of this postulated event based on the assumptions used in NUREG 0800, Standard Review Plan (SRP) determined that the Exclusion Area Boundary (EAB) cumulative thyroid dose could exceed 10CFR100 limits. An evaluation of this postulated event based on existing RCS activity showed that doses would be a small fraction of 10CFR100 limits. The evaluation also showed that this postulated event would not result in any fuel damage.

During an evaluation based on the recommendations in NRC Information Notice 89-54, "Potential Overpressurization of the Component Cooling Water System," PVNGS Engineering identified a postulated scenario in which a double ended guillotine break of a RCP seal cooler tube could result in overpressurization of the Nuclear Cooling Water System (NCWS) (CC) and therefore, the potential existed for a leakage path outside of Containment. This failure could result in high pressure, high temperature RCS fluid entering the low pressure, low temperature NCWS piping, Most of the RCS leakage would flow from the RCP body through clearances between the impeller hub and bearing sleeve, through a clearance between the bearing sleeve and stop seal, into a flow passage in the bearing sleeve, and through drilled clearances in the RCP seal housing. This leakage would then proceed to the RCP seal cooler via the seal cooler inlet valve (ISV)(AB), A parallel flowpath would also be established past the journal bearing and the RCP seal cooler outlet valve (ISV)(AB).

NRC Form 368A (SJ>9)

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NRC FORM 355A US. NUCLEAR REGULATORY COMMISSION (SZ9) APPROVED 0M B NO. 31500)oi EXP IR ES: 0/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LERI INfORMATION COLLECTION REQUEST: 60A) 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 (3150OIOE). OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC 20503.

FACILITYNAME (I I DOCKET NUMBER (2) LER NUMBER (Sl PAGE (3)

YEAR

'> SEQUENTIAL 'PISI REVISION

,.W NUMBER %4 NUMSER Palo Verde Unit 1 o s o o o 528 91 001 0 0 030" 0 8 TEXT /// moro spoco tr roEII/rod, IrJo odd/I/ono/HRC form 3SSAS/ OT)

Calculations using two-phase choked flow models, assuming only the hydraulic resistance of the limiting restriction in the flow path, indicate the initial leakage flow rate through a doubled ended guillotine break of the tube would be approximately 58 pounds mass per second (ibm/sec). Since NCWS containment .isolation valves (ISV)(CC) are not designed to isolate or remain isolated against pressures that could result from this RCS leakage, RCS fluid from the tube failure 'is postulated to flow into the NCWS providing a potential release path outside Containment through the NCWS surge tank pressure relief valve (TK)(RV)(CC) on the Auxiliary Building (NF) roof. This relief valve [set at 10 pounds per square inch gauge (psig)j discharges to an open atmospheric scupper on the Auxiliary Building roof. Since the magnitude of the break exceeds the capacity of the pressure relief valve, the design pressure of the surge tank (15 psig) could be exceeded.

In addition to the above, a postulated catastrophic high pressure cooler tube rupture may simultaneously initiate degradation of the RCP seals of the affected pump because cooling and lubricating flow would be diverted to the break and any residual fluid remaining in the seal housing would be evacuated via t'e auxiliary impeller in the RCP seal housing. However, this degradation does not increase the radiological consequences of this postulated event since the leakage would be confined to Containment.

The NCWS is a closed loop cooling system which provides cooling water to numerous heat exchangers that contain radioactive water.

The NCWS is constantly monitored by an on-line radiation monitor (MON)(IL) which alarms in the Control Room (NA) when the cooling water activity reaches a maximum preset level. The radiation monitor is capable of detecting RCS in-leakage of 0.08 gallons per minute (gpm) within one hour after the leak begins.

An evaluation of the radiological consequences of this scenario using postulated design basis conditions fi.e, constant, continuous reactor coolant leakage rate and accident dose parameters (iodine spiking factors, reactor coolant activities corresponding to one-percent failed fuel and no operator actions) as specified in the SRP for Chapter 15 FSAR analysis] indicates that EAB cumulative thyroid dose could exceed 10CFR100 limits within 30 minutes. An evaluation using existing conditions at PVNGS showed that EAB dose will be limited to a small fraction of 10CFR100 limits.

Evaluations of limiting design basis events also show that this postulated event would not result in fuel failure.

NRC Form 355A (SS9)

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NRC FORM 388A U S. NUCLEAR REGULATORY COMMISSION (689) APPROVED 0MB NO. 31500108 EXPIRES: 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT ILER) INFORMATION COLLECTION REQUEST. 50.0 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 (31504108), OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC 20503.

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

YEAR SEQUENTIAL ~>> O II8 V IS KIN g@ NUM 8 II NVM SII Palo. Verde Unit 1 o e o o o OF 0 8 TEXT /Ifmore e/reoe /e r))or/red, oee edd)r)rne/PORC Form 3//84'e/(17)

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 at the start of the event which contributed to this event.

D. Cause of each component or syst: em 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.

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

Not applicable - no component failures were involved.

G. For a failure 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 - no failures were involved which rendered a train of a safety system inoperable.

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

Not applicable - there have been no component or system failures or procedural errors identified.

Cause of event The postulated event discussed in Section I.B was not considered in t:he original design of t:he plant (SALP Cause Code B: Design, Manufacturing, Installation Error). The design basis of the RCP seal coolers described in the Combustion Engineering Standard Safety Analysis Report (CESSAR) and the NRC Safety Evaluation Report for Palo Verde was that any leakage from the RCS would be detected by a combination of the NCWS radiation monitors and the high surge tank level switches which alarm in the Control Room.

Once leakage is detected it would be isolated using the RCP seal cooler isolation valves. The possibility of a tube rupture in the seal cooler and its subsequent effect on the NCWS was not considered in the original plant design.

NRC Form 368A (8 89)

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NRC FORM SSSA U.S. NUCLEAR REGULATORY COMMISSION (54)9) APPROVED 0MB NO. 31504)104 EXPIRES: 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT ILER) INFORMATION COLLECTION REOUEST: 50A) HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (P4)30). U.S, NUCLEAR REGULATORY COMMISSION, WASHINGTON, OC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31504)104). OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON. DC 20503.

FACILI1'Y NAME (1) DOCKET NUMBER LT) LER NUMBER (S) PAGE (3)

'ix, saavarrTIAL i~" rravrsiorr g2<

NUM Err r/UM 44 Palo Verde Unit 1 0 5 0 0 0 0 0 0 50F 0 8 TEXT ///moro 4/roro /4 ror/rrood, oro oddr)/ooo/NRC Form 36S43/ (17)

No unusual characteristics of the work location (e.g., noise, heat, poor lighting) contributed to this postulated'event. The postulated event was not a result of personnel errors nor procedural errors.

J. Safety System Response:

Not applicable - there were no safety system responses and none were necessary.

K. Failed Component Information:

Not applicable - no component failures were involved.

II. ASSESSMENT OF THE SAFETY CONSEQUENCES AND IMPLICATIONS OF THIS EVENT The postulated event discussed in Section I.B would be a small break loss of coolant accident (LOCA) based on the criteria specified in operating procedures. Control Room personnel would respond by entering and executing the actions for a small break LOCA...RCP alarm response procedures would direct the operators to close the seal cooler isolation valves to terminate the event. The valves are designed to operate against full differential RCS pressure, however they do not receive emergency power. If the affected seal cooler could not be isolated,,the RCS would be depressurized to allow the NCWS containment isolation valves to be closed to isolate the leak.

A conservative evaluation of the radiological consequences of a postulated guillotine break of the RCP seal cooler tubing was performed.

This evaluation used a constant, continuous reactor coolant leakage rate to the atmosphere of 58 ibm/sec and accident dose parameters (i.e.,

iodine spiking factors, reactor coolant activities corresponding to one percent failed fuel, no operator action to isolate the break, etc.)

assumed in the SRP for Chapter 15 accident analyses. The evaluation assumed all of the leakage was released to atmosphere and took no credit for iodine partitioning factors. This evaluation indicates the EAB cumulative dose would exceed 10CFR100 limits for dose to the thyroid within 30 minutes of the 'postulated event. If iodine partitioning factors, flashing and time dependent leakage were considered in this analysis, the results would be less than 10CFR100 limits.

An evaluation of the consequences of the postulated guillotine break of the seal cooler tubing was also performed using existing conditions at PVNGS rather than the conservative parameters specified in the SRP. The evaluation used an iodine spiking factor of 40, iodine 131 dose equivalent concentration of S.OE-2 microcuries per milliliter (uci/ml) and eight failed fuel pins, all based on actual worst case data for NRC Form 368A (54)9)

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NRC FORM 365A U.S. NUCLEAR REGULATORY COMMISSION (669) APPROVED OMB NO,31504104 E XP I R ES: O/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT ILER) INFORMATION COLLECTION REOUEST: 50.0 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(6041(M), OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC 20503.

FACILITYNAME (I) DOCKET NUMBER (2) LER NUMBER (5) PAGE (3)

SEOVSNTIAL AovrsroN NUMsorl N v M 8 o rr Palo Verde Unit 1 0 5 0 0 0 OF p TEXT ///moro o/roco /J ror/ckat, ooo oddr)/orro/HRC Forrrr 366AS/(Il)

PVNGS Units 1, 2, and 3. An initial, continuous reactor coolant leak rate to the atmosphere of 58 ibm/sec (i.e., no credit taken for reduced leak rate due to system depressurization), no operator action, no partition factor, and accident (SRP specified) Chi/Q values were conservatively used. This evaluation resulted in radiological consequences which are a small fraction of 10CFR100 limits. The EAB 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> cumulative thyroid dose would be 10.2 Rem and the Low Population Zone (LPZ) 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, cumulative thyroid dose would be less than 13 Rem.

The 30 day Control Room thyroid dose was calculated to be 1.9 Rem.

The potential leak was also evaluated based on 'leak before break criteria, If a leak were to develop by some preexisting flaw or unidentified mechanism, the low stresses in the piping would result in a stable crack up to a. leak rate of approximately 1.3 gpm. This stable crack size was determined using the methodology of NUREG/CR-4572 HNRC Leak Before Break (LBB.NRC) Analysis Method for Circumferential Through-Wall Cracked Pipes Under Axial Plus Bending Loads," which includes loads during normal operation and a safe shutdown earthquake. NUREG 1061 "Evaluation of Potential for Pipe Breaks " requires the application of a factor of safety of two to the critical crack size to arrive at a leakage crack size. The resulting leak rate including this safety factor is 0.8 gpm. Recognizing that the tubing would leak before breaking, NUREG 1061 requires that the leak detection system used be capable of detecting a leak equivalent to one tenth of the leak rate expected from the leakage crack size. In this case that value would be 0.08 gpm. On-line radiation monitoring and chemical sampling are capable of detecting leakage at this level.

An evaluation of the radiological consequences of small leakage through the high pressure seal cooler tubing was performed based on leak before break criteria. This evaluation was based on a constant leak rate of 1.3 gpm to conservatively bound the maximum stable crack size leak rate analyses. The evaluation assumed reactor coolant activity corresponding to one percent failed fuel, a partition factor coefficient for iodine species of 0.01, and accident Chi/Q values. The results show that for this scenario, the radiological consequences are well below 10CFR100 limits. 'The EAB 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> cumulative thyroid dose would be approximately 1.7E-5 Rem and the LPZ 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thyroid dose would be approximately 4.1E- '

Rem.

Due to uncertainties in the failed fuel predictions and the spiking factor, PVNGS will monitor RCS I-131 dose equivalent concentration levels. If these values exceed a level of 2E-1 uci/cc RCS I-131 dose equivalent, EAB doses will be reevaluated and additional actions will be taken if required. With the activity at or below this level, offsite doses will be limited to a small fraction of 10CFR100 limits.

The double ended guillotine break of RCP seal cooler tubing was NRC Form 366A (649)

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NRC FORM SSSA UA. NUCLEAR REGULATORY COMMISSION APPROVEO 0MB NO. 31500)0O (SJIS)

EXPIRES OI30(IJ2 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT ILER) INFORMATION COLLECTION REOUESTI 50.0 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 (31500104). OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, 00 20503.

FACILITYNAME ('I) DOCKET NUMBER (2) LER NUMBER IS) PAGE (3)

SEQUENTIAL REVISION NVM TR NVMSOR Palo Verde Unit 1 0 5 0 0 0 5 2 8 9 0 1 0 0 0 7 oFO 8 TEXT Illmoro opooo lo roOrdrod. VTO oddldorrol lVRC Form 3()r)A BI (17) evaluated to assess the potential for causing fuel failure by examining the spectrum of break sizes for a small break LOCA.' failure of the RCP seal cooler would correspond to a break size of 0.0043 square feet.

The smallest. break size evaluated for small break LOCA analysis is 0.02 square feet, and does not result in fuel failure. This break size bounds all break sizes less than 0.02 square feet, and is considered .

bounding for this postulated event. Based on this analysis, the RCP seal cooler tube failure postulated event would not result in fuel failure.

The capability of the Refueling Water Tank (RWT)(TK)(BP) to provide makeup water for this postulated event was evaluated and the RWT inventory demand was determined to be approximately 487,600 gallons.

Technical Specification 3.1.2.6 specifies a minimum RWT inventory of 600,000 gallons, based on an RCS average temperature of 565 degrees Fahrenheit. Therefore, the RWT inventory is adequate for this postulated event.

Based on these evaluations, it is concluded that although the consequences =of a postulated guillotine break of the seal cooler tubing using SRP specified parameters exceeds regulatory limits, an evaluation of this postulated event using existing PVNGS data demonstrates radiological consequences below 10CFR100 limits. An evaluation of the small leakage that might occur before identification and isolation based on the application of leak before break criteria also demonstrates radiological consequences below 10CFR100 limits.

III'ORRECTIVE ACTION:

A. Immediate:

'he consequences of this postulated event were, evaluated and a Justification for Continued Operations (JCO) was developed and submitted to the NRC (161-03709-WSC/JST, dated January 18, 1991).

To ensure that any leak of the RCP seal cooler will be detected in a timely fashion the following compensatory measures (only applicable in Modes 1 through 4, POWER OPERATION through HOT SHUTDOWN). have been put in place:

Chemistry sampling and abnormal occurrence procedures have been changed to provide for backup grab samples to be taken at least every 14 hours with the NCWS radiation monitor (RU-

6) operable'his method will detect in-leakage lower than 0.08 gpm and also provide a confirmation of RU-6 operation.

If RU-6 is out of service the Chemistry samples will be taken at least every 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, NRC Form 35SA (BJIB)

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NRC FORM366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 31600)04 (669)

E xp I 8 E s: 6/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT ILER) INFORMATION COLL'ECTION REQUEST: SOA) HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (P430), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20655, AND TO THE PAPERWORK REDUCTION PROJECT (31600)Be). OFFICE OF MANAGEMENTAND BUDG ET, WASHINGTON, DC 20603.

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

YEAR N::.I SEQUENTIAL

'oi NVMeeII m~1 Reve)IQN gpS NUMeeo Palo Verde Unit I 0 5 0 0 0 5 8 9 0 0 I 0 0 QF 0 8 TEXT ///moro <<reoe /e rer/v/red. Iree eddie'aoe/HRC farm 3664'e/((7)

2. The radiation monitor RU-6 alarm response procedure and chemistry sampling procedure have been revised to require specific actions be taken quickly to identify the source of any in-leakage to the NCWS.

3. In the event manual sampling detects short lived fission product activity (indicative of Reactor Coolant Leakage into the NCWS) or a radiation monitor alarm is received and manual sampling detects short lived fission product activity, an orderly plant shutdown to Mode 5 (COLD SHUTDOWN) will commence. Sampling will continue during shutdown to monitor the leakage and to determine the source of the leakage.

If RCS in-leakage through the seal cooler is determined not to be the source, the plant will not be shutdown and sampling shall continue. Manual samples will be taken at least every 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> to ensure that no RCS leakage in the NCWS would go undetected by the radiation monitor due to higher background activity.

4, RCS I-131 dose equivalent concentration levels will be monitored. If these values exceed a level of 2E-1 uci/cc, RCS I-131 dose equivalent, offsite doses will be reevaluated and additional actions will be taken if required.

B. Action to Prevent Recurrence:

A design change is being developed to mitigate the postulated event described in this LER. Implementation of this design change is expected to be completed in Units 1, 2, and 3 by July 1993.

IV. PREVIOUS SIMILAR EVENTS:

No previous similar events have been reported in accordance with 10CFR50,73.

NRC Form 366A (669)

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