ML20012D953

Special Rept 1-SR-90-002:on 900221,RCS Pressure Transient Resulted in Automatic Actuation of Pressurizer Porv.Caused by Failure of Procedure to Consider Variation in Plant Response for Stated Sys.Operating Procedure Will Be Revised

ML20012D953
Person / Time
Site:	Comanche Peak
Issue date:	03/21/1990
From:	William Cahill, Woodland D TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	Martin R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
1-SR-90-002, 1-SR-90-2, TXX-90114, NUDOCS 9003290141
Download: ML20012D953 (3)

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ll'E:ll:- Log- # TXX-90114

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- - -File # 10250-905.4 nlELECTRIC March 21, l990

- Wmiasm J. CahiR. Jr.

Emunvr nt brMrM Mr.:R.:D. Martin,-'RegioniIV i

U. S. Nuclear Regulatory Commission l611 Ryan. Plaza, Suite 1000,

' Arlington. Texas 76011

SUBJECT:

COMANCHE' PEAK STEAM-ELECTRIC' STATION (CPSES)

DOCKET NO. 50 445 AUTOMATIC OPERATION OF PRESSURIZER PORV IN RESPONSE TO A LTOP SIGNAL SPECIAL REPORT NO.'l-SR-90-002 Gentlemen:-

. Enclosed:is- a 30 day special report submitted in accordance with CPSES Unit 1 Technica11 Specification 3.4.8.3, " Reactor Coolant System Overpressure

_ Protection Systems."

Sincerely.

William J. Cahill; Jr.

By: W

'D.~R. Woodlan Docket Licensing Manager JLR/vid Enclosure-c Document Control Desk

U. S. Nuclear Regulatory Commission Washington D. C. 20555-Resident Inspectors. CPSES (3) 900321  %

j900329014j DR ADOCK 05000445 Ed

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400 North Olive Street L.B. 81 Dallas. Texas 75201 2

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(. IEnclosura TXX 90114 fpagt 1 of 23 .

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. . TU Electric Comanche Peak Steam Electric Station, Unit 1 Docket No. 50-445 q

Automatic Operation of Pressurizer Power Operated Relief Valve in Response to -

a Low Temperature Overpressure Protection Signal Special Report No.1-SR 90-002-00  ;

1.0' REPORT REQUIREMENT On February 21,1990, 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 Unit 1 Technical Specification 3.4.8.3, REACTOR -

COOLANT SYSTEM OVERPRESSURE PROTECTION SYSTEMS LIMITING

' CONDITION FOR OPERATION. Specification 3.4.8.3 requires that a Special y Report be submitted to the Nuclear Regulatory Commission pursuant to ',

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 a RCS pressure transient.

E i 2.0 ' EVENT DESCRIPTION On February 21,1990, at approximately 1317 CST, with the plant in cold '

ll shutdown and RCS temperature at 140 degrees F, a Pressurizer PORV L automatically opened in response to a Low Temperature Overpressure .

l Protection (LTOP) signal Just prior to the event the RCS fill and vent procedure had been completed up to the vent of the RCS following the fourth Reactor Lr Coolant Pump (RCP) one minute run. At the time of the event, the RCS was in a lf water solid condition and was being pressurized to 325 psig in preparation for L the RCP ten minute runs. Letdown flow had been reduced to a flowrate less than the charging flowrate, resulting in an increasing RCS pressure. The solid plant l pressure response to the reduced letdown flowrate was quicker than anticipated by the Reactor Operator (RO) and resulted in RCS pressure exceeding the target L: - value. The RCS reached a maximum pressure of 436 psig. The system functioned as designed, causing a Pressurizer PORV to open for approximately 4 seconds, preventing the RCS pressure from exceeding the applicable limits. The  ;

n RO. reduced charging flow and increased letdown flow, stabilizing RCS pressure E at 260 psig within two minutes. A review of recorded data subsequent to the event verified that the open PORV resulted in a drop in RCS pressure to 350 psig and a corresponding rise in the Pressurizer Relief Tank level.

E: , 4 E5 closure TXX-90114 r

• page 2 of 2 .;

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.I 3.0 CAUSE OF EVENT' I

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The following have been identified as causes for the event:

-+ The procedure for filling and venting the RCS requires that the operator perform an iterative process, but does not consider the variation in plant _ i

. response to identical instructions in going from a system containing air to a -

water solid system. The procedure does not adequately caution the RO of '

the change in expected plant response.-

-The process for pressurizing the RCS following' a vent had been to  :

completely isolate letdown flow resulting in a loss of-letdown flow alarm  ;

for the failed fuel monitor. The alarm, which should have alerted the RO to insufficient letdown flow, had become an expected alarm.

4.0 CORRECTIVE ACTION' The pressure transient was discussed with the RO, and the need for increased board awareness during solid plant operations was reinforced. A Lessons ,

Learned summary was reviewed by all crews, and increased sensitivity of the ,

' plant to changes in letdown and charging was discussed

~

' T_he operating procedure will be revised as follows to incorporate lessons learned from this event:

• Eliminate repetitive steps for which differing plant responses are expected, a Instruct the operator to avoid completely securing letdown flow, ensuring normal operation of the failed fuel monitor, and adequate operator response to a loss-of-flow alarm,

. Cautions will be added to alert the operator of expected plant responses in transitioning from a system with air to a water solid system,-

- Incorporate instructions for establishing a pressurizer bubble using decay-heat and pressurizer heaters prior to starting an RCP in order to reduce the number of evolutions occurring during solid plant opertations.

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