ML20199J855

Special Rept 2-SR-97-001:on 971025,RCS Pressure Transient Resulted in Automatic Actuation of Pressurizer Porv.Caused by Operator Misconception Over Actual Arming Setpoint of LTOP Sys.Alarm Procedures Will Be Revised

ML20199J855
Person / Time
Site:	Comanche Peak
Issue date:	11/24/1997
From:	Terry C TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2-SR-97-001, 2-SR-97-1, TXX-97250, NUDOCS 9711280250
Download: ML20199J855 (4)

Text

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Log # TXX 97250

.. 9 File # 10200

. .; 905.4 Ref. # 10CFR50.36(c)(2) nlELECTRIC' November 24, 1997 ,

C. I. awe Terry cw o he,+,

Mr. E. W. Herschoff. Regional Administrator U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive Suite 400 Arlington TX 76011

SUBJECT:

COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)

DOCKET NO. 50 446 AUTOMATIC OPERATION OF PRESSURIZER PORV IN RESPONSE TO A LOW TEMPER $TURE OVERPRESSURIZATION SIGNAL (LTOP)

SPECIAL REPORT NO. 2 SR 97 001 Gentlemen:

Enclosed is a 30 day special report submitted in accordance with CPSES Unit 2 Technical Specification 3.4.8.3. " Reactor Coolant System Overpressure Protection System."

-' This communication contains new commitments regarding CPSES Units 1 and 2 as identified in the Attachment.

Pleasc contact Mr. Randy Blankenship at 254 897 5890, should you have questions concerning the material contained in this report.

Sincer y, hi&

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C. L. Ter i

i RTB/rb Attachment Enclosure -[-@)3 ,

c- NRC Document Control Desk J. I. Tapia Region IV T. J. Polich. NRR Resident Inspectors. CPSES 9711200250 971124 PDR ADocK050004g llIllNIjll,R,555 P. O. Don 1002 Glen Rme Tcsas 7 tot 3

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Attachment to TXX 97250 Page 1 of 1 .-

- Attachment  :

-. l This communication contains the following new commitments:

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-; CDF Number. ComaitBent .

27114 CPSES will assess if the misconception of the LTOP- i arming temperature is a general knowledge deficiency ar.d  :

conduct appropriate training if deemed necessary. l Alarm procedures ALM 0064A and B will be revised to i 27115 include the LTOP arming setpoint.

27116 - Integrated plant operating procedures. IPO 005A and B i will be revised to add appropriate provisions to  ;

establish temperature and-pressure conditions during <

cooldown which will not unnecessarily challenge LTOP - l actuation.

- The CDF number is used by TV Electric for the internal tracking of CPSES  ;

commitments.  !

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t Enclosure to TXX 97250  ;

Page 1 of 2  ;

TU Electric Cceanche Peak Steam Electric Station. Unit 2 Docket No. 50 446 Automatic Opera. tion of Pressurizer Power Operated Relief Valve in Response 2 to a low Temperature Overpresture Protection (LTOP) Signal Special Report No. 2 SR 97 001 1.0 REPORT REQUIREMENT  ;

Cn October 25. 1997, a Reactor Coolant System (RCS) pressure transient resulted in the automatic actuation of a Pressurizer Power Operated Relief Valve (PORV). This Special Report is being submitted in accordance with Comanche Peak Steam Electric Station (CPSES) Unit 2 Technical Specification 3.4.8.3. REACTOR COOLANT SYSTEM OVERPRESSURF PROTECTION SYSTEMS LIMITING CONDITION FOR OPERATION. Technical Specification 3.4.8.3 requires that a Special Report be submitted to the Nuclear Regulatory Commission pursuant to Technical Specification 6.9.2 describing any event in which a Pressurizer PORV. or the Residual Heat Removal suction relief valves, or the RCS vents are used to mitigate an RCS pressure transient.

The FORVs automatically opened for RCS pressure relief when the LTOP system actuated during a RCS cooldown and dcpressurization.

Actuation occurred when the RCS temperature decreased to the 6rming J' setpoint for the LTOP system. RCS pressure was not increasing at t'ae time of actuation.

1 2.0 EVENT DESCRIPTION Initiatina Circumstancn On October 25. 1997 CPSES Unit 2 was ccnducting a normal cooldown from H0DE 3. HOT STANDBY to MODE 5. COLD SHUTDOWN at the 1 commencement of the third refueling outage for the unit (2RF03).

Prior to pressurizer pressure decreasing below 800 psig isolation of the safety injection accumulators was to occur per normal plant cperating procedures. Delays were experienced during the accumulator isolation )rocess which maintained reactor coolant system ,'RCS) pressure ligher than was anticipated for the corresponding RCS temperature as cooldown continued. The control ,

room operators were awat e of the approaching arming of the LTOP actuation setpoint and that the RCS pressure was above the setpoint for the corresponding temperature. The operators believed that the pressure / temperature relationship would be acceptable for the LTOP logic prior to reaching the LTOP- arming temperature. This operational philosophy was acce) table with the exception that the operators were mistaken as to t1e arming temperature of L10P.

Alarms were also received indicating that the RCS .

pressure / temperature relationship would exceed the LTOP setpoint if

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Enclosure to TXX 97250 l Page 2 of 2 t LTOP were armed. The operators responded to these alarms with the belief that the RCS pressure would be below the setpoint prior to 1 reaching the LTOP arming temperature which they believed to be 320'F , As such, when the RCS temperature decreased to approximately 350'F, LTOP actuated as the RCS pressure was still above the system -

setpoint.

PORV Mitiaation Effects At approximately 2105 CST, PORV 2 PCV 456 lifted when the RCS t temperature decreased to 352'F, The PORV remained open with the  ;

operator monitoring the situation. Although decreasing, RCS 1 aressure remained above the setpoint for automatic actuation of the 20RV with the lower setpoint, 2 PCV 455A. Therefore at . i approximately 2108 CST, 2 PCV 455A armed and automatically opened further depressurizing the RCS. Once RCS pressure was below the -

corresponding pressure setpoint for the LT09 PORVs, the operator took manbal control and closed the valves terminating the RCS depressurization. The operator closed the valves to limit the discharge of RCS inventory to the pressurizer relief tank and over '

concern for personnel within the containment building. RCS parameters were stabilized at 340'F and 500 psig. The PORVs performed all required actions.

3.0 CORRECTIVE ACTIONS The root cause analysis performed by CPSES, concluded that the i primary cause was that of the operators' misconception over the actual arming setpoint of the LTOP system. The alarm procedures for system alarms did not serve as an effective barrier for this event as they did not contain the arming temperature for LTOP.

CPSES will assess if the misconception of the LTOP arming temperature is a general knowledge deficiency and conduct appropriate training if deemed necessary.

Alarm procedures ALM 0064A and D will be revised to include the LTOP arming setpoint.

Integrated plant operating procedures, IPO 005A and B will be ,

revised to add appropriate provisions to establish temperature and pressure conditions during cooldown which will not unnecessarily challenge LTOP actuation. ,

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