05000298/LER-1982-013, Forwards LER 82-013/03L-0.Detailed Event Analysis Submitted

Forwards LER 82-013/03L-0.Detailed Event Analysis Submitted

ML20054L011
Person / Time
Site:	Cooper
Issue date:	06/28/1982
From:	Lessor L NEBRASKA PUBLIC POWER DISTRICT
To:	Jay Collins NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20054L012	List: 05000298/LER-1982-013, Forwards LER 82-013/03L-0.Detailed Event Analysis Submitted
References
CNSS820686, NUDOCS 8207070066
Download: ML20054L011 (3)

LER-2082-013, Forwards LER 82-013/03L-0.Detailed Event Analysis Submitted

Event date:
Report date:
2982082013R00 - NRC Website

text

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• COOPER NUCLE AR ST ATioN Nebraska Public Power District " " * "A"E" *"MM; Usi.*>'f^ "

CNSS820386 June 28, 1982 ff$I%

Mr. John T. Collins, Regional Administrator N I l98*9 , i-U.S. Nuclear Regulatory Commission 'y #

Region IV 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76011

Dear Sir:

This report is submitted in accordance with Section 6.7.2.B.2 of the Technical Specifications for Cooper Nuclear Station and discusses a reportable occurrence that was discovered on June 7, 1982. A licensee event report form is also enclosed.

Report No.: 50-298-82-13 Report Date: June 28, 1982 Occorrence Date: June 7, 1982 Facility: Cooper Nuclear Station Brownville, Nebraska 68321 Identification of Occurrence:

A condition which resulted in operation in a degraded mode per-mitted by the limiting condition for operation established in Section 3.6.H.1 of the Technical Specifications.

Conditions Prior to Occurrence:

1 The reactor was in cold shutdown for refueling.

Description of Occurrence:

During performance of Surveillance Procedure 6.3.10.9.1, Snubber i

Operability Test, two mechanical shock suppressors, RR-SNB-SS7Al l

and RR-SNUB-SS7B1, were found inoperable.

1 Designation of Apparent Cause of Occurrence: ,

The apparent cause of this occurrence is attributed to a single high load cycle resulting in cracked thrust bearings on both PSA-10 snubbers.

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Mr. John T. Collins June 28, 1982 Page 2.

Analysis of Occurrence:

The two subject shock suppressors are Pacific Scientific Company Model PSA-10. They were installed on the Reactor Recirculation (RR) piping inside primary containment. The mechanical snubbers are installed to protect the piping during seismic events. No known seismic events have occurred at CNS since the last inspection of these snubbers in the fall of 1981.

A previous failure of snubber RR-SNUB-SS7Al was discovered during inspections of snubbers for IEB 81-01. The NRC was notified of this event by LER 50-298-81-09 and a failure analysis was presented to the NRC in a letter to J. T. Collins dated 1-19-82 in response to IEB 81-01. The failed snubbers in that occurrence were in-spected and found to contain a broken thrust bearing. The recent failures of snubbers RR-SNUB-SS7Al and RR-SNUB-SS7B1 are apparently identical to the previous failure of snubber RR-SNUB-SS7A1.

It is felt that the broken thrust bearings were caused by an over-load of the snubbers due to a water hammer event from the operation of the RHR shutdown cooling system or movement of this piping during RR pump trip or start. General Electric has identified in SIL 175 that under certain operating conditions the RHR System can produce water hammer events and specifically identifies the RHR/RR pipe tee as a problem area. RR-SNUB-SS7Al and RR-SNUB-SS7B1 are located on the RR discharge lines at the RHR/RR pipe tee. We have observed the RHR/RR tee during shutdown cooling starts and no particular movement occurs. Both recirculation pumps were tripped at power and restarted during the time these snubbers were in-stalled.

. This event presented no adverse consequences from the standpoint of public health and safety.

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Corrective Action:

The failed snubbers will be repaired, if possible, and returned to spare parts inventory. To preclude recurrence of this event, the snubbers, RR-SNUB-SS7Al and RR-SNUB-SS7B1, have been replaced with Bergen Patterson, B-P-10 Model, hydraulic snubbert. Additionally, the companion snubbers RR-SNUB-SS7A2 and RR-SNUB-SS7B2 have been replaced with B-P-10 model hydraulic snubbers to ensure a matqhtd response of the seismic structure. These B-P-10 model snubbers are the original snubbers designed and installed by General Electric l during construction of the plant. The B-P-10 snubbers operated satisfactorily from 1974 to 1976, however, they were replaced with l

> PSA-10 model snubbers as a part of the hydraulic snubber replace-ment program in 1976. The B-P-10 snubbers have been refurbished with new ethylene propylene compound seals and have satisfactorily demonstrated proper lockup and bleed rates.

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Mr. John T. Collins June 28, 1982 Page 3. ,

Additional snubbers on the RR lines were inspected and were found satisfactory. Further evaluation of these RR line snubbers is t.nder review. Our operating procedures were reviewed to ensure they address the recommendations of SIL 175.

Sincerely, 1; ,

L. C. Lessor Station Superintendent Cooper Nuclear Station l- LCL:cg Attach.

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