05000352/LER-1987-001, :on 870105,reactor Encl Secondary Containment Isolation Occurred as Result of Low Differential Pressure. Caused by Events Resulting from Trip of Auxiliary Steam Boiler.Boiler Restarted & Heating Sys Restored

:on 870105,reactor Encl Secondary Containment Isolation Occurred as Result of Low Differential Pressure. Caused by Events Resulting from Trip of Auxiliary Steam Boiler.Boiler Restarted & Heating Sys Restored

ML20210C573
Person / Time
Site:	Limerick
Issue date:	02/04/1987
From:	Logue R, Mengers C PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-#187-2891 LER-87-001, LER-87-1, OL, NUDOCS 8702090419
Download: ML20210C573 (5)

LER-1987-001, on 870105,reactor Encl Secondary Containment Isolation Occurred as Result of Low Differential Pressure. Caused by Events Resulting from Trip of Auxiliary Steam Boiler.Boiler Restarted & Heating Sys Restored

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation
3521987001R00 - NRC Website

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Abstract:

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On January 5, 1987 at 2242 hours0.0259 days <br />0.623 hours <br />0.00371 weeks <br />8.53081e-4 months <br /> with the unit at 100% power, a Reactor Enclosure Secondary Containment Isolation (an Engineered' Safety Feature) occurred resulting from low differential pressure.

Automatic initiation of the Standby Gas Treatment System (SGTS) and the Reactor Enclosure Recirculation System (RERS) followed with the systems operating as designed.

The low differential pressure condition was created when the Reactor Enclosure supply air fans tripped on low supply air temperature following the loss of auxiliary (station heat) steam.

With the loss of supply air, excessive negative pressure was created in the Reactor Enclosure automatically tripping the exhaust air fans resulting in the low differential pressure isolation.

The duxiliary steam was restored, the low differential pressure isolation was reset and normal Reactor Enclosure ventilation was restored at 2245 hours0.026 days <br />0.624 hours <br />0.00371 weeks <br />8.542225e-4 months <br />.

There were no adverse consequences resulting from the event.

Actions to Prevent Recurrence have been reviewed and the Engineering and Research Department has been requested, through EPE 1084, to evaluate possible methods of improving the reliability of the auxiliary boilers.

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Operating Mode 1 (Power Operation)

Reactor Power 100%

Description of the Event:

On January 5, 1987 at 2242 hours0.0259 days <br />0.623 hours <br />0.00371 weeks <br />8.53081e-4 months <br /> with the unit at 100% power, a Reactor Enclosure Secondary Containment Isolation (an Engineered Safety Feature) occurred due to low Reactor Enclosure differential pressure.

Automatic initiation of the Standby Gas Treatment System (SGTS) and the

'A' Reactor Enclosure Recirculation System (RERS) followed with the systems operating as designed.

The low differential pressure condition occurred as a result of a series of events:

1)

The auxiliary steam system was lost which resulted in the automatic trip of the Reactor Enclosure supply air fans due to low supply air temperature.

2)

The loss of supply air caused excessive negative pressure in the Reactor Enclosure which automatically tripped the Reactor Enclosure exhaust air fans.

3)

The tripping of the exhaust air fans resulted in the low differential pressure between the Reactor Enclosure and the outside atmosphere and the subsequent isolation.

The EIIS Codes for the affected systems are BH (SGTS), VA.

(RERS), NG (Reactor Enclosure), and SA (Auxiliary Steam System).

Consequences of the Event:

There were no adverse consequences resulting from this event.

The containment ventilation systems, Standby Gas Treatment (SGTS) and Reactor Enclosure Recirculation (RERS) responded as designed.

If one of the two SGTS trains or one of the two RERS trains had become inoperable, the redundant trains would have operated as designed.

No radioactive release resulted A-2

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Cause of the Event

CAUSE CODE:

Other (X)

This event was the result of a series of events resulting from the trip of an auxiliary steam boiler.

With the

'A' auxiliary boiler out-of-service for maintenance, the

'B' and

'C' boilers were supplying auxiliary steam to the plant at a rate of 20,000 lbs/hr.

When the

'C' auxiliary boiler tripped on high furnace pressure, the

'B' boiler was unable to maintain header pressure and tripped on low atomizing steam pressure.

Loss of the auxiliary steam to the Reactor Enclosure supply air heating coils resulted in an automatic trip of the supply air fans on low supply air temperature (freeze protection).

With the Reactor Enclosure exhaust fans still in operation, excessive negative pressure was created in the Reactor Enclosure resulting from the loss of supply air.

The increasing negative pressure caused the automatic trip of the exhaust air fans.

The Secondary Containment Isolation occurred when Reactor Enclosure to outside atmosphere differential pressure decreased to the trip setpoint of 0.1 inches of water.

The SGTS and RERS then automatically initiated and operated as designed.

Corrective Actions

The outside Assistant Operators (AOs) restarted the auxiliary boilers and restored the plant heating system.

Upon restoration of plant heat, the isolation was reset and reactor building ventilation systems were returned to normal operation.

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Action Taken to Prevent Recurrence:

The Engineering and Research Department has been requested, through EPE 1084, to evaluate possible methods of improving the reliability of the auxiliary boilers or mitigating the effects of the loss of auxiliary steam on the plant.

Previous Similar Occurrences:

Reactor enclosure ventilation isolations were reported in the following LERs: 84-041,84-045, 85-005,85-012, 85-018,85-020, 85-023,85-041, 85-067,85-089.

However, all of these events were of different root causes than this event.

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.A PHILADELPHIA ELECTRIC COMPANY 23O1 M ARKET STREET P.O. BOX 8699 PHILADELPHIA. PA.19101 February 4, 1987 1215)841-4000 Docket No. 50-352 U.S. Nuclear Regulatory Commission ATTN:

Document Control Desk Washington, DC 20555

SUBJECT:

Licensee Event Report Limerick Generating Station - Unit 1 This LER concerns a Reactor Enclosure Secondary Containment Isolation due to low differential pressure resulting from the loss of the Reactor Enclosure Ventilation System.

Reference:

Docket No. 50-352 Report Number:

87-001 Revision Number:

00 Event Date:

January 5, 1987 Report Date:

February 4, 1987 Facility:

Limerick Generating Station P.O. Box A, Sanatoga, PA 19464 This LER is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(iv).

Very truly yours, 4

R.

H. Logue Assistant to the Manager Nuclear Support Department cc:

Dr. Thomas E. Murley, Administrator, Region I, USNRC l

E. M. Kelly, Senior Resident Site Inspector l

See Service List l

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