05000346/LER-1980-033-01, /01T-0:on 800425,determined from Bechtel Study That Bleed Rate for 12 Hydraulic Snubbers Would Be Insufficient to Permit Thermal Growth of Piping During Transient Concurrent W/Locked Snubber

/01T-0:on 800425,determined from Bechtel Study That Bleed Rate for 12 Hydraulic Snubbers Would Be Insufficient to Permit Thermal Growth of Piping During Transient Concurrent W/Locked Snubber

ML19309H584
Person / Time
Site:	Davis Besse
Issue date:	05/06/1980
From:	Quennoz S TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19309H579	List: 05000346/LER-1980-033, Forwards LER 80-033/01T-0 05000346/LER-1980-033-01, /01T-0:on 800425,determined from Bechtel Study That Bleed Rate for 12 Hydraulic Snubbers Would Be Insufficient to Permit Thermal Growth of Piping During Transient Concurrent W/Locked Snubber
References
LER-80-033-01T, LER-80-33-1T, NUDOCS 8005130534
Download: ML19309H584 (3)

LER-1980-033, /01T-0:on 800425,determined from Bechtel Study That Bleed Rate for 12 Hydraulic Snubbers Would Be Insufficient to Permit Thermal Growth of Piping During Transient Concurrent W/Locked Snubber

Event date:
Report date:
3461980033R01 - NRC Website

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60 61 OOCKET NUY8ER 68 63 EVENT DATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h fiiTTl l(NP-32-80-07) on 4/25/80 Toledo Edison determined it had an immediately reportabic l

g l finding based on a study conducted by Bechtel Associates in response to LER NP-32-79-07 j o l4 l lwhich concerned hydraulic snubber deficiencies. The study showed that for 12 snubbersl g o l s j lthe bleed rate would be insuf ficient to permit thermal growth of the piping during a l

l o is l ltransient concurrent with a locked snubber. There was no danger to the public or sta-l lo l 71 [ tion personnel.

Only under extremely improbable conditions would the snubbers have l

l o l R I l been called upon to function as described.

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l A lg l I l 2 l 0 l 7 lg 33 J4 35 36 37 40 41 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h li l 0 l lThe original acceptance value for a bleed rate of 4 1"/ minute was from the manufacturi-ler's recommendations. The architect / engineer math model requires the bleed rate to be l i i

between 6-10" per minute. The bleed rates for all the remaining snubbers have l

,, lbeen reviewed and found to be conservative.

The 12 snubbers will be reset during the l l current refueling outage under Maintenance Work Order 80-2110.

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419-259-5000, Ext. 239 g DVR 80-075 Stephen M. QuennoZ PHONE:

NAME OF PREPARER

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONC SUPPLEMENTAL INFORMATION FOR LER NP-32-80-07 DATE OF EVENT: April 25, 1980 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Hydraulic Snubber Deficiency Conditions Prior to Occurrence: The unit was in Mode 6, with Power (MRT) = 0 and Load (Gross MWE) = 0.

Description of Occurrence: As a part of the corrective action described in Licensee Event Report NP-32-79-07 concerning hydraulic snubber deficiencies, the architect /

engineer conducted a study to determine realistic requirements for hot and cold pis-ton settings, and lockup and bleed rates. As expected, it was determined that for most snubbers the original tolerances were unnecessarily restrictive, and could be relaxed without impairing clant safety.

However, during this review, some uncertainties appeared regarding snubber bleed rates.

Subsequent investigation, including discussions with the snubber uanufacturer, showed that for 12 snubbers the as-installed bleed rate would be insufficient to permit ade-quate thermal growth of the piping during a transient concurrent with a locked snubber.

If the snubber were to lock up due to a seismic event which would cause or result in a l.':

concurrent event where a pressurizer relief valve lif ted (either code safety or elec-tromatic) or where auxiliary feedwater turbine 1-1 was started, the affected snubbers i

would have impeded the thermal expansion resulting from the steam flow in the associated piping.

of the stresses involved. Resultant failure of the piping system was thus assumed without further ana Designation of Apparent Cause of Occurrence: As a result of combining a seismic event with either of the upset conditions described above, the bleed rates previously set were not adequate to allow unrestricted growth of the piping.

The setting for bleed rate of 4 i 1 inches per minute was from the manufacturer's recommendations.

The architect /

engineer math model requires the bleed rate to be between 6-10 inches per minute.

The bleed rates for all the remaining snubbers have been reviewed and found to be conserva-tive.

Analysis of Occurrence:

There was no danger to the health and safety of the public or I

to station personnel.

The insufficient bleed rate of the hydraulic snubbers could have prevented the fulfillment of the functional requirements of systems required to i

ecpe with accidents analyzed in the Final Safety Analysis Report and therefore is a rsportable occurrence per Technical Specification 6.9.1.8.f.

Only under extremely improbable conditions would the snubbers have been called upon to function as des'cribed.

LER 680-033 w

• TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORE\\ TION FOR LER NP-32-80-07 PAGE 2

Corrective Action

The 12 snubbers of concern will be reset during the current refueling shutdown and prior to restart of the unit.

Failure Data: There have been no known previous occurrences of non-conservative snuhbor settings.

LER #80-033 e