ML20012B854

Special Rept:On 900312,ESF Actuation Signal Occurred Which Resulted in Initiation of Train a Safety Injection & RCS Pressure Transient.Caused by Failed Blocking Diode Due to Short.Plant Restored to Stabilized Condition

ML20012B854
Person / Time
Site:	Comanche Peak
Issue date:	03/13/1990
From:	William Cahill TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TXX-90107, NUDOCS 9003160493
Download: ML20012B854 (3)

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.e . n Log # TXX-90107 F

""" File # 10013, 10125'

- C Ref.#10CFR50.72(a)(1) nlELECTRIC i March 13, 1990 Wmism J. Cahill, Jr.

Execut6ve Vke hesident

.U.' S. Nuclear Regulatory Commission

Attn: . Document-Control Desk .

Washington,-DC 20555 i

SUBJECT:

COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)  ;

DOCKET NO. 50-445 TRANSMITTAL 0F REPORT FOLLOWING A NOTIFICATION -

0FUNUSUALEVENT(NUREG-0654):

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Dear Sir:

As specifie'd 'in the CPSES Emergency Plan, TU Electric hereby transmits the - '

attached report which summarizes the incident which occurred on March 12,-

1990. ' As stated in the corrective action, an evaluation'is'in process and a Licensee Event Report (LER) will be submitted in accordance with 10CFR50.73 by April 12, 1990. '

Sincerely, o

William J. Cahill, Jr.

DEN /GLB/daj Attachment c - Mr. R. D. Martin, Region IV Mr. J. H. Wilson, NRR-0SP.

' Resident-Inspectors, CPSES (3)

Mr. Robert Lansford, Division of Emergency Management 1

t COO 3160493 900313.

PDR- ADOCK 05000445 S PDC  ;

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. 400 North Olive Street LB. 81 Dallas, Texas 75201

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Enclosure TXX-90107 Page 1 of 2 TU Electric Comanche Peak Steam Electric Station, Unit 1 Docket No. 50-445 Notification of an Unusual Event as a Result of Safety Injection Actuation Report Requirement This_ report is being submitted as recommended by NUREG-0654,

" Criteria for Preparation and Evaluation of Radiological Emergency Response Plans and Preparedness in Support of Nuclear Power Plants" and in accordance with Comanche Peak Steam Electric Station (CPSES) Emergency Plan Procedures. The CPSES Emergency Plan procedures require that a written summary be submitted within 24. hours of the closeout of the Notification of an Unusual

- Event (NOUE).

Event Description On March 12, 1990 at 1401 CST with the plant in Hot Shutdown and the Reactor Coolant System (RCS) temperature at 250 degrees F and pressure at_370 psig, an Engineered Safety Features Actuation-

- Signal (ESFAS) occurred which resulted in the initiation of a Train ~A Safety Injection (SI). The plant staff response to the transient.was in accordance with' Emergency Operating Procedures

-(EOPs). Activation-of the Emergency Plan with the_ Notification of an Unusual Event occurred at 1420. Notification.of the-following offsite agencies was-accomplished in accordance with procedural-requirements: Hood County; Somervell County; Texas Department of Public Safety -- Waco; Nuclear Regulatory Commission, Bethesda; Texas Division of Emergency Management -

Austin; Texas Bureau of Radiation Control - Austin.

Injection flow was terminated in accordance with the EOPs, and the plant was restored _to a stable condition with RCS temperature at 180 degrees F and pressure at 350 psig. During plant recovery, Reactor Coolant flow was reinitiated-resulting in a

-RCS pressure transient; the Pressurizar Power Operated Relief Valve (PORV) actuated to mitigate the transient. The NOUE was terminated at 1625. The initial review conducted subsequent to the event indicates that all components and systems functioned as designed following the SI actuations. At no time was there a threat to the health and safety of the public as a result of-the event.

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Enclosure TXX-90107 Page 2 of 2 ,

Cause Determination At the time of the event, routine maintenance was being performed on the containment Particulate Iodine Gas (PIG) monitor.

Procedural guidance requires that the Containment PIG monitor be de-energized prior to checking / replacing the filter elements.

De-energization of the containment PIG initiates an ESFAS, causing a Containment Ventilation ILolation (CVI) Signal. A blocking diode normally prevents the CVI signal from reaching the SI relays. However, because the blocking diode failed in a shorted condition, the signal was not blocked, resulting in actuation of the SI relays.

Corrective Actions Immediate corrective actions were focused on restoring the plant to a stable condition. Actions to prevent recurrence will be determined based on the results of the Evaluation Team findings associated with-the Plant Incident investigation of this event.

, The details of the event and the subsequent recovery, including root cause determination and recommendations for. corrective actions, will be included in the Licensee Event Report to be submitted to the Commission in accordance with 10CFR50.73.

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