05000346/LER-1979-064-01, /01T-0 on 790621:impact Points of Eight Main Steam Line Seismic Restraint Locations May Deform If Sufficient Seismic Event Occurs.Caused by Design Deficiency.Web Reinforcing Plates Installed at Impact Points

/01T-0 on 790621:impact Points of Eight Main Steam Line Seismic Restraint Locations May Deform If Sufficient Seismic Event Occurs.Caused by Design Deficiency.Web Reinforcing Plates Installed at Impact Points

ML19224C997
Person / Time
Site:	Davis Besse
Issue date:	07/03/1979
From:	Batch S TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19224C994	List: 05000346/LER-1979-064, Forwards LER 79-064/01T-0 05000346/LER-1979-064-01, /01T-0 on 790621:impact Points of Eight Main Steam Line Seismic Restraint Locations May Deform If Sufficient Seismic Event Occurs.Caused by Design Deficiency.Web Reinforcing Plates Installed at Impact Points
References
LER-79-064-01T, LER-79-64-1T, NUDOCS 7907100444
Download: ML19224C997 (3)

LER-1979-064, /01T-0 on 790621:impact Points of Eight Main Steam Line Seismic Restraint Locations May Deform If Sufficient Seismic Event Occurs.Caused by Design Deficiency.Web Reinforcing Plates Installed at Impact Points

Event date:
Report date:
3461979064R01 - NRC Website

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U. S. NUCL E AR REGUL A10RY COM*.11SSION NRC F ORM 366 (7 77)

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40 41 47 43 44 47 33 cAUSE DESCf'.lPTION AND CORRECTI'/E AC TIONS oj l The c'ause of the occurrence is a design deficiency in that the initial desinn detail i

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Installat ion of web reinforcing plates l was completed under Facility Change Request 79-257 on June 25, 1979.

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NAME OF PREPARER ce

TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-32-79-08 DATE OF EVENT:

June 21, 1979 FACILITY:

Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Main steam line seismic restraints design deficiency Conditions Prior to occurrence: The unit was in Mode 5, with Power (MWT) = 0, and Load (Gross MWE) = 0.

Description of Occurrence: A review of the snubber and seismic restraint design on main steam seismic restraints SR4 and SR7 performed by the architect / engineer, Bechtel Corporat ion, led to a question of the need for web reinforcing plates at the impact point on the seismic restraints. The original calculations were examined and found to indicate that overstressing of the restraint could occur at the impact point if a suffi-cient seismic event occurred.

However, the requirement for reinforcing was not included in the restraint detail.

Further revieu of the stress at the impact point on 148 maia steam line and main feed-water seismic restraints discovered that seismic restraints SR2 and SR6 also needed the reinf orcing plat;;. - Cic.:: :izzi

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C"'., CR?, S".2 and SR6 are locate:'

on both main steam lines, a total of eight seismic restraint locations were affected.

Although it was determined the impact points of ttese eight scismic restraint locations could have de fo rmed, it has not yet been ascertained if main steam line damage could have been inflicted from a design basis earthquake loading.

Since the potentiality existed that the performance of the main steam line restraints could be less conservative than assumed in the accident analysis, this report is being submitted in accordance with Technical Specification section 6.9.1.8.1.

Designation of Anparent Cause of Occurrence:

The cause of this occurrence is a design deficiency in that the initial design detail did not require the placement of web re-inforcing plates at the impact point on the eight af fected seismic restraints. The restraints were initially designed by the architect / engineer of Davis-Besse Unit 1, Bechtel Corporation.

Anal-sis of Occurrence:

There was no danger to the health and safety of the public or to station perssanel.

The seismic restraints are only required for protection from a seismic event and do not af fect normal unit operation.

The architect / engineer is in the process of performing an analysis to determine if any damage could have been in-flicted on the main steam line if a seismic event had occurred.

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TOLEDO EDISO:4 CO:!PA!;Y DAVIS-BESSL 1;UCLEAR PGId STATIO:' l':;1T 0 :E SlTPPLE'!E:;TAL I ;FOR'MTIO:: FOR LER ':P-32-79-08 PAGE 2

Corrective Action

The design calculations for 140 main steam and main feedwater seismic restraint locations were reviewed and found to be adequate.

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plates were designed to reduce the stress and prevent deformation at the impact point for the eight deficient locations.

Facility Change Request 79-257 and the associated Maintenance ',Tork Order :0:0 79-257 were prepared to install web reinforcing plates en the eight deficient main steam linc seimic restraint locations.

Installation of these web reinforcing plates was completed on June 25, 1979.

Failure Data: There have been no previously reported similar occurrences.

LER #79-064 A

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