05000498/LER-1993-001, :on 930105,discovered That RCS Loop 3 Outside TS 2.2.1 Range & Loop Declared Inoperable.Caused by Two RCS delta-T Channels Being Inoperable Simultaneously.Loop Restored & Startup Testing Procedure Revised

:on 930105,discovered That RCS Loop 3 Outside TS 2.2.1 Range & Loop Declared Inoperable.Caused by Two RCS delta-T Channels Being Inoperable Simultaneously.Loop Restored & Startup Testing Procedure Revised

ML20128F192
Person / Time
Site:	South Texas
Issue date:	02/03/1993
From:	Ayala C, Kinsey W HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-001, LER-93-1, ST-HL-AE-4321, NUDOCS 9302110289
Download: ML20128F192 (7)

LER-1993-001, on 930105,discovered That RCS Loop 3 Outside TS 2.2.1 Range & Loop Declared Inoperable.Caused by Two RCS delta-T Channels Being Inoperable Simultaneously.Loop Restored & Startup Testing Procedure Revised

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(1)
4981993001R00 - NRC Website

text

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IThe Light company llouston Lighting & Powerfautfesa$ I'fij"8 {c(u@ pen"ating Stajp>n ].p;pos g8f {ap onhgesai]8}

February-3, 1993 ST-HL-AE-4321 File No.:

G26 10CFR50.73 U.

S. Nuclear Regulatory Commission Attention:

Document Control Desk Washington, DC 20555 South Texas Project Unit 1 Docket No. STN 50-498 Licensee Event Report 93-001 Technical Specification 3.0.3 Entry Due to Two Reactor Coolant System Delta-T Channels Beina InoDerable at the same Time Pursuant to 10CFR50.73, Houston Lighting & Power (HL&P) submits the attached Unit 1 Licensee Event Report 93-001 regarding a Technical Specification 3.0.3 entry due to two-Reactor Coolant-System Delta-T channels being inoperable at the same time.

This event did not have any adverse effect on the health and safety of the public.

If you should have any questions on this matter, please contact Mr.

C. A. Ayala at (512) 972-8628 or me at (512) 972-7921.

bk W.

H. Kins Jr.

Vice President, Nuclear Generation JMP/sr

Attachment:

LER 93-001 (South Texas, Unit 1) 100050 t

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- A Subsidiary of flouston Industries incorporated j.

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9302110289 930203 PDR ADOCK 05000498

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HoustonLighting & Power Company ST-HL-AE-4 3 23 South Texas Project Electdc Generating Station File:No.: G26 Page 2 Cc:

i Regional Administrator, Region IV Rufus S.. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 400 Houston Lighting &-Power Company Arlington, TX 76011 P.

O.

Box 61867:

Houston, TX 77208 Project Manager U.S. Nuclear Regulatory Commission INPO Washington, DC 20555 Records Center 1100 Circle 75 Parkway J.

I. Tapia Atlanta, GA 30339-3064 Senior Resident Inspector c/o U..S.

Nuclear Regulatory Dr. Joseph M. Hendrie Commission 50 Bellport Lane P.

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Box 910 Bellport, NY 11713' Bay City, TX 77414 D. K. Lacker J. R. Newman, Esquire Bureau of Radiation Control Newman & Holtzinger,.P.C., STE 1000 Texas Department of Health 1615 L Street, N.W.

1100 West 49th' Street-Washington, DC 20036 Austin, TX-78756-3189 D. E. Ward /T. M.

Puckett U.S. Nuclear Regulatory Comm.

Central Power and Light Company Attn:

Document Control Desk P. O.

Box 2121 Washington, D.C.

20555 Corpus Christi, TX 78403 J.

C. Lanier/M.

B.. Lee City of Austin Electric = Utility Department P.O.

Box-1088 Austin, TX 78767 K. J.-Fiedler/M. T. Hardt City Public Service Board P.

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Box 1771 San Antonio, TX 78296 Revised 02/03/92 4

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South Texas, Unit 1 05000 4 9 8 1 OF 04 piTu m

~Tec~hnical Specification 3.0.3 fREFy Due to Two Reactor Coc,lant

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System Delta-T Channels Being Inoperable at the Same Time EVENT DATE (5) _

LER NUMBER (6 i

REPORT NUMBER (7)

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POWER 20 405ta)(1Hi) 50 36(c)(1) 50 73(a)(2Hv) 73 71(c)

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LICENSEE CONTACT FOR THIS LER (12) v vi.

tLiteatn,E. Noma s pwua. Area coo.i Charles Ayala - Supervising Licensing Engineer (5 1 2) 9 72-8628 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBE 0 IN THIS REPORT (13) nFporTA E

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ABSTRACT (Umit to 1400 spaces, i e, approcrnately 15 single-spaced type'uritteri lines) (16)

On January 5, 1993, at 1033 hours0.012 days <br />0.287 hours <br />0.00171 weeks <br />3.930565e-4 months <br />, Unit 1 was in Mode 1 at 77% power.

While performing a Delta-T evaluation on the Reactor ' Coolant System (RCS), it was discovered that the RCS loop 3 was outside Technical Specification 2.2.1 and was declared inoperable.

Prior to'this event, Excore Power Range channel (N44) had been declared inoperable, with the bistables tripped for RCS loop 4 Overtemperature Delta Temperature (OTDT), to conduct corrective maintenance on the rod stop bistables.

As a

result, Unit 1

entered Technical Specification 3.0.3 when Delta-T loop 3 and loop 4 were both inoperable and compliance with Technical Specification 3.3.1 could not be maintained.

The cause of this event has been attributed to procedure that lacked specific criteria.for declaring a

channel inoperable and for coordinating the Delta-T evaluations with other cross train activities.

Corrective actions

include restoring the RCS loop 4_OTDT bistables and the power range channel (N44),

discussing this event during Licensed Operator Requalification Training, and revising the procedure governing reload startup testing to provide specific guidelines for declaring a loop l

inoperable if it is outside the requirements of Technical Specifications.

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MQUENhAL RCv:SiON NUMBER kJVBER South Texas, Unit 1 05000 4 98 02 04 93

- 001 -

00 e,w..nw an.w wam 3wy 5>c suasu mm o.c.a DESCRIPTION OF EVENT':

On January 5.

1993, at 1033 hours0.012 days <br />0.287 hours <br />0.00171 weeks <br />3.930565e-4 months <br />, Unit 1 was in Mode 1 at 77%

power.

Unit 1 entered Technical Specification 3.0.3 when two out of the four Reactor Coolant System (RCS) Delta-T channels were declared inoperable.

While performing an RCS Loop Delta-T evaluation, it was discovered that the RCS loop 3 extrapolated 100% Delta-T value was 95.69%, and as such was outside Technical Specification 2.2.1, Table 2.2-1, item 7,

note 2 which states that for Overtemperature Delta Temperature (OTDT) trip setpoints, the channel's maximum Trip Setpoint shall not exceed its computed Trip Setpoint by more than-1.7% Delta-T span.

Prior to this event the Excore power range channel (N44) had been declared inoperable, with the bistables tripped for RCS loop 1 OTDT, to conduct corrective maintenance on the rod stop bist ables.

As a result, Unit i entered Technical Specification 3.0.3 when Delta-T loop 3 and loop 4 were both-inoperable and compliance with Technical Specification 3.3.1 could-not be maintained.

At 1058 hours0.0122 days <br />0.294 hours <br />0.00175 weeks <br />4.02569e-4 months <br /> corrective maintenance on Power Range channel N44 was completed and RCS loop 4 OTDT bistables were restored to normal.

At lS hours loop 3 OTDT, Overpressure Delta Temperature (OPDT) and _. ;w Temperature average (Tave) bistables were _ tripped in compliance with Technical Specification 3.3.1 and 3.3.2.

At 1128 hours0.0131 days <br />0.313 hours <br />0.00187 weeks <br />4.29204e-4 months <br />, Delta-T loop 4 was declared operable and Unit 1 exited Technical Specification 3.0.3.

The OTDT trip setting is designed to ensure operation within the Departure from Nucleate Boiling (DNB) design basis and the hot leg boiling limit.

Since both of these limits are functions of coolant temperature and pressure as well as core thermal power, the OTDT trip is correlated with vessel Delta-T, vessel average temperature, and primary system pressure.-

The OTDT protective. function will trip the reactor when the compensated Delta-T in any two'of the four channels exceeds the setpoint.

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DESCRIPTION OF EVENT

(Con't)

During start-up of the Unit, following a refueling outage, Delta-T evaluations are conducted at various power levels to ensure calculated 100% Delta-T's fall within prescribed limits.

Because Technical Specifications dictate that only one channel may be inoperable at a time, the decision to remove any channel from operation for corrective maintenance during Delta-T evaluations places the station at a greater risk of reaching a Limiting Condition of Operation.

The shift supervisor was not awa o that Delta-T evaluations were being performed nor of the potential to declare a RCS channel inoperable as a result of the evaluation.

CAUSE OF EVENT

The cause of this event is an inadequate procedure.

Instructions within the Reload Initial Start-Up Testing procedure involving the Delta-T evaluation stated that any Delta-T loop found outside of tolerance would be declared inoperable prior to increasing reactor-power above 90% Rated Thermal Power (RTP). Additional instructions required that action be taken to recalibrate any loop outside the limit. This procedural guidance left the interpretation that any.

Delta-T Loop found outside of-the acceptance criteria 'could be recalibrated, without being declared inoperable, prior to increasing reactor power above 90% RTP.

The procedure also lacks sufficient direction regarding coordination of the test activities, bNALYSIS OF EVENT:

Failure to maintain the minimum number of channels operable is reportable pursuant to 10CFR50.73 (a) (2) (1) (B). Failure to maintain the -minimum number of channels operable was' a violation-of Technical Specification 3.3.1, table 3. 3-1, item 8 requiring entry into Technical Specification 3.0.3, Limiting Condition For Operation.

Technical Specification 3.0.3 was exited within'one hour when corrective measures were taken to restore one of.the two-inoperable channels.

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PAGE (J) 14QutNT AL FO@oN g-NUMBER NLIMBEM OF South Texas, Unit 1 05000 4 9 8 04 g4 93

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CORRECTIVE ACTIONS

1.

Corrective maintenance to restore the RCS loop 4 OTDT bistables and the power range channel (N44) was completed on January 5, 1993, at 1058 hours0.0122 days <br />0.294 hours <br />0.00175 weeks <br />4.02569e-4 months <br />.

2.

Recalibration of. the RCS Loop 3 Delta-T was completed on January 8, 1993.

3.

This LER will be reviewed by the Unit 2 Operations Crews prior to the end of the upcoming refueling outage. Additionally, this event will be discussed during Licensed Operator Initial Training and Requalification Training by July 16, 1993.

4.

The Reload Initial Start-Up Testing procedure will.be revised to provide specific guidelines for declaring a RCS Loop Delta-T inoperable and for providing guidelines _for _the coordination of test activities. This procedure will be revised and made effective by May 10, 1993.

5.. To minimize the chance of a setpoint exceeding its computed Trip Setpoint by more than the 1.7% delta-T span an evaluation shall be performed to consider the risks and benefits of setting the 100% RCS loop Delta-T's to a conservative value prior to unit

~

start-up following a

refueling.

This evaluation will be completed by May 10, 1993.

6.

To address generic implications, the Reload Initial Start-Up Testing procedure shall be reviewed to determine if' additional-tests include precautionary measures designed to minimize entry into a Limiting Condition of Operation.

.This review will be completed by May 10, 1993.

ADDITIONAL INFORMATION1 An event regarding a Technical Specification violation due to two inoperable nuclear instrumentation was reported to the NRC under Unit 1 LER 90-013 LER\\93029001.01 NRC FOAM 3644 $ 92) t