ML20024G721

LER 91-012-00:on 910326,potential Gas Binding of Centrifugal Charging Pumps Due to Voids in Boric Acid Gravity Feed Line Identified.Caused by Hydrogen Coming Out of Solution in Lower Pressure Ccp Suction header.W/910425 Ltr

ML20024G721
Person / Time
Site:	Comanche Peak
Issue date:	04/25/1991
From:	Guldemond W, Hope T TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-012, TXX-91145, NUDOCS 9104260240
Download: ML20024G721 (7)

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Log # TXX-91145 File # 10200 Ref. # 50.73(a)(2)(v) nlELEC7RIC April 25, 1991

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U. S. Nuclear Regulatory Comission Attn Document Control Desk Washington, D. C. 20555

$UBJECT: COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)

DOCKET NO. 50-445 EVENT OR CONDITION THAT COULD HAVE PREVENTED FULFILLMENT OF THE SAFETY FUNCTION OF STRUCTURES OR SYSTEMS LICENSEE EVENT REPORT 91-012-00 Gentlemen:

Enclosed is Licensee Event Report 91-012-00 for Comanche Peak Steam Electric Station Unit 1. " Potential Gas Binding of Centrifugal Charging Pumps due to Voids its the Boric Acid Gravity Feed Line."

Sincerely.

William J. Cahill Jr.

By: _[

Manager. Site Lit'nsing JAA/bm c - Mr. R. D. Martin, Region IV ResidentInspectors.CPSES(2)

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Ultrasonic examination of the Chemical and Volume Control System (CVCS) suction piping was performed on March 4, through March 15,1991. These examinations revealed volds in the alternate boration line and the gravity feed line from the Boric Acid Storage Tank (BAT) Engineering evaluation shows that volds in the alternate boration line would not affect operability of the Centrifugal Charging Pumps (CCPs). However, engineering evaluation indicates that the vold in the gravity feed line from the BAT could cause damage to or gas binding of the CCPs.

The potential root cause was identified as hydrogen coming out of solution, in the lower

pressure CCP suction header. Corrective actions include daily venting of the gravity feed line and further monitoring for hydrogen accumulation. Based on the results of this monitoring, venting requirements will be established.

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1. DESCRIPTION OF THE REPORTABLE EVENT ,

y A. REPORTABLE EVENT CL ASSIFICATION Any event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to shutdown the reactor and maintain it in a safe condition, or mitigate the consequences of an accident.

B. PL ANT OPERATING CONDITIONS PRIOR TO THE EVENT On March 26,1991, Comancho Peak Steam Electric Station (CPSES) Unit 1 was in Mode 5, Cold Shutdown, with the Reactor Coolant System (RCS) (Ells:(AB)) at a temperature of 130 Jegrees Fahrenholt and pressure of approximately 300 pounds per square Inch-gage.

C. STATUS OF STRUCTURES. SYSTEMS OR COMPONENTS THAT WERE INOPERABLE AT THE START OF THE EVENT AND TH AT CONTRIBUTED TO THE EVENT There were no inoperable structures, systems or components that contributed directly to the event.

D. N ARR ATIVE

SUMMARY

OF THE EVENT. I'ACLUDING DATES AND APPROXIM ATE TIMES On October 29,1990, Westinghouse sont a Is'ter to CPSES regarding the formation and venting of hydrogen in the Chemical and Volume Control System (CVCS)

(Ells:(CB)) in response to Nuclear Regulatory Commission (NRC) Information Notice (lN) 90 64," Potential for Common Mode Failure of High Pressure Safety injection Pumps or Release of Reactor Coolant Outside Containment During a Loss of-Coolant Accident." In this letter Westinghouse, identified locations in the CVCS suction piping where gases would tend to accumulate. Westinghouse recommended ultrasonic examination to monitor the rate at which gas accumulates in these locations.

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0'1l2- 010 013 OF 0lB From March 4,1991, through March 15,1991, ultrasonic examination of various locations of the CVCS suction piping was performed. Locations examined included the 8 inch diameter suction header; the Positive Displacement Charging Pump (PDP) (Ells:(P)(CB)) suction line; the Centrifugal Charging Pump (CCP) 02 (Ells:(P)(CB)) mlniflow line; and all of the vertical piping connected to the 8 inch diameter suction header, including alternate boration, boric acid filter, chemical feed, and the gravity feed line from the Boric Acid Storage Tank (BAT) (Ells:(TK)(CB)).

The ultrasonic examinations revealed volds in two locations, the 2 inch diameter alternate boration line and the 3 inch diameter gravity feed line from the DAT. The size of the vold Identified in the alternate boration line was determined to bo relatively small. Engineering evaluation shows that a void in this line would not cause any significant degradation in CCP or PDP performance, or affect operability of the Emergency Core Cooling System (ECCS)(Ells:(BO)). The size of the vold.

found in the BAT gravity feed line was much larger. Engineering evaluation indicates that this void could potentially cause damage to or gas binding of the CCPs when the BAT gravity feed line is used for boration, forcing the gas bubble into the suction header, or when pr_ essure conditions change causing expansion of the bubble into the suction header.

On March 26,1991, this event was recorded via the appropriate administrative procedure. The reportability of this event was uncertain at first, however, after further evaluation it was determined to be reportable at 1645 on March 28,1991. At 1840 t on March 28,1991, the NRC Operations Center was notified via the Event Notification System.

E.

i THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE OR PROCEDURAL ERROR

- Ultrasonic examination of various locations of the CVCS suction piping was performed due to cocerns expressed by Westinghouse in their October 29,1990,  !

letter. As a result of the examinations, conducted from March 4,1991, through March 15,1991, volds in two locations of CVCS suction piping were identified.

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B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE Not applicable there were no component failures associated with this event, C. S_YSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS Not applicable there were no component failures associated with this event.

D. FAILED COMPONENT INFORM ATION Not applicable there were no component failures associated with this event, Ill. AN ALYSIS OF THE EVENT A. SAFETY SYSTEM RESPONSES THAT OCCURRED Not applicable - there were no component failures associated with this event, B. DUR ATION OF SAFETY SYSTEM TRAIN INOPER ABILITY Not applicable there were no safety systems which were rendered inoperable due to a failure,

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C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT The operability of two independent ECCS subsystems, as required by Technical Specifications 3/4.5.2, ensures that sufficient emergency core cooling capability will be available in the event of a Loss of Coolant Accident assuming the loss of one subsystem through any single failure consideration. Either subsystem operating in conjunction with the accumulators (Ells:(ACC)(BP)) is capable of supplying sufficient core cooling to limit the peak cladding temperatures within acceptable limits.

During this event the potential for gas binding of the CCPs existed due to void accumulation in the CVCS suction piping. This increased the probability of a common mode failure of both independent ECCS subsystems.

IV. CAUSE OF THE EVENT ROOT C AUSf, Evaluation of this event has identified the potential root cause to be hydrogen coming out of solution in the lower pressure CCP suction header and collecting in the vertical piping.

This phenomenon is not present under current plant conditions (Mode 5), and therefore cannot be verified until normal RCS hydrogen concentration is re established.

V. CORRECTIVE ACTIONS A. Ifg1EDIATE The gravity feed line from the BAT was vented. Administrative controls were established to vent this line daily.

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B. CORRECTIVE ACTIONS TAKEN TO PREVENT RECURRENCE ROOT CAUSE Evaluation of this event has identified the potential root cause to be hydrogen coming out of solution in the lower pressure CCP suction header and collecting in the vertical piping.

CORRECTIVE ACTION The gravity feed line from the BAT will be monitored for hydrogen accumulation upon return to normal hydrogen concentration in the RCS Based on the results of this

' monitoring, venting requirements will be established.

VI. PREVIOUS SIMILAR EVENTS On October 4,1990, NRC IN 90 64 was issued. During evaluation of IN 90 64 it was concluded that a design error existed that could result in the common mode failure of the CCPs due to gas binding (the CCP suction piping, high point, solenold opereted isolation vent va!ves (SOLV) (Ells:(FSV)(CB)) were oriented in the wrong direction). This condition wae addressed in Licensee Event Report (LER) 90 035.

As a result of tha October 29,1990, letter from Westinghouse addressing the SOLV orientation, various locations in the CVCS suction piping were identified as having the pntential for gas to accumulate. The subsequent ultrasonic examinations are the subject of this LER (91012).

Vll. ADDITIONAL INFORMATION The times listed in the report are approximate and Central Standard Time.

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